EKG Dictionary
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The EKG Dictionary

Clear, exam-ready definitions for 158 ECG terms: the waves and intervals, every common rhythm, the blocks, the ischemia patterns, and the syndromes. Every definition cites the guideline, consensus statement or original paper it comes from.

158 terms · last reviewed 2 October 2026

Waves, segments & intervals23

Corrected QT (QTc)QTc · corrected QT interval · rate-corrected QTThe QT interval corrected for heart rate. The most widely used correction is the Bazett formula, which divides the measured QT by the square root of the RR interval in seconds (QTc = QT divided by the square root of RR). Delta wavedelta wave · pre-excitation slur · WPW slurring · slurred QRS upstrokeA slurring of the initial part of the QRS complex caused by ventricular pre-excitation, when an accessory pathway that bypasses the AV node conducts the atrial impulse to the ventricles. Electrical alternansQRS alternans · Beat-to-beat amplitude alternansAlternation of ECG complexes from beat to beat, most classically the QRS complex, which is alternately higher and lower in successive beats; the alternation is cyclic and not related to breathing. Epsilon waveepsilon wave · epsilon potential · postexcitation waveSmall, reproducible, low-amplitude signals between the end of the QRS complex and the onset of the T wave in the right precordial leads (V1 to V3). Isoelectric lineisoelectric baseline · baseline · isoelectric lineThe flat baseline of the ECG, recorded when there are no significant voltage gradients in the ventricles, against which wave amplitudes and ST-segment deviations are measured. J pointJ-point · junction point · QRS-ST junctionThe junction where the QRS complex ends and the ST segment begins, at the transition from ventricular depolarization to repolarization. J wave (Osborn wave)Osborn wave · J deflection · camel-hump sign · hypothermic humpA notch, often of large amplitude, at the J point (the junction of the QRS complex and the ST segment), at the very end of the QRS complex. Low voltageLow QRS voltage · Low-voltage ECG · Diminished QRS amplitudeAbnormally small QRS complexes, defined as a QRS amplitude under 0.5 mV (5 mm) in all limb leads and/or under 1.0 mV (10 mm) in all precordial leads. P waveP-waveThe first deflection of the cardiac cycle, produced by atrial depolarization; activation of the left atrium begins and ends later than that of the right. PR intervalPR · P-R interval · PQ intervalThe time from the onset of the P wave to the onset of the QRS complex, whether the first QRS deflection is a Q or an R wave. PR segmentPR segment · P-R segment · PQ segmentThe normally flat (isoelectric) stretch from the end of the P wave to the onset of the QRS complex, during which the impulse is conducted through the AV node, the His bundle, the bundle branches and the Purkinje fibres. Q waveQ-wave · q waveThe first negative (downward) deflection of the QRS complex, before any R wave. QRS complexQRS · ventricular complexThe combined deflections produced by ventricular depolarization, made up of the Q, R and S waves. QRS durationQRS width · QRS interval · QRS durationThe time from the onset to the end of the QRS complex, the duration of ventricular depolarization. QRS fragmentationfQRS · Fragmented QRS · Notched QRSExtra notches or deflections within a QRS complex of normal duration (under 120 ms): an additional R wave (R'), more than one R', or notching of the R wave or of the nadir of the S wave, present in at least two contiguous leads of one coronary territory (anterior V1 to V5, inferior II, III and aVF, or lateral I, aVL and V6), without a typical bundle branch block. QT intervalQT · Q-T intervalThe time from the onset of the QRS complex to the end of the T wave, spanning ventricular depolarization and repolarization. R waveR-waveA positive (upward) deflection of the QRS complex; when there are two, the second is labeled R prime (R'). R wave progressionR-wave progression · RWP · precordial R-wave progressionThe normal, gradual increase in R-wave amplitude across the precordial leads from V1 toward V6, with a matching decrease in S-wave depth, as the QRS changes from mainly negative in V1 to mainly positive in V6 because left ventricular forces dominate. RR intervalR-R interval · RR · cycle length · R-RThe time between two consecutive R waves (successive QRS complexes), the ventricular cycle length. S waveS-waveA negative (downward) deflection of the QRS complex that follows an R wave. ST segmentST · ST-segment · ST segmentThe portion of the ECG from the end of the QRS complex (the J point) to the beginning of the T wave, corresponding to the plateau phase of the ventricular action potential, when the ventricular cells sit at about the same voltage. T waveT-waveThe deflection following the QRS complex that represents ventricular repolarization (the rapid repolarization phase of the ventricular action potential). U waveU-waveA small, low-amplitude deflection that may follow the T wave, most evident in leads V2 and V3 and often absent in the limb leads.

Rate, rhythm & mechanisms20

Aberrant conductionaberrancy · aberrantly conducted beat · rate-related bundle branch block · functional bundle branch blockAbnormal conduction of a supraventricular impulse through the ventricular conduction system, producing a QRS complex whose shape differs from the baseline QRS (often wide) and may resemble a bundle branch block pattern, a fascicular block pattern, or both, despite the supraventricular origin. Ashman phenomenonAshman beat · Ashman's phenomenonAn aberrantly conducted supraventricular beat, usually with right bundle branch block (RBBB) morphology, that ends a long-short RR sequence (a long cycle immediately followed by a short one). AsystoleCardiac standstill · Flatline · Ventricular asystole · Cardiac arrest (asystolic)Absence of detectable ventricular electrical activity, so no QRS complexes are seen; it is one of the four cardiac-arrest rhythms (with ventricular fibrillation, pulseless ventricular tachycardia and pulseless electrical activity). Automaticityautomatism · pacemaker activity · spontaneous depolarizationThe intrinsic ability of specialized cardiac cells to depolarize spontaneously during phase 4 of the action potential, reach threshold and initiate an impulse without an external stimulus. AV dissociationAVD · atrioventricular dissociationIndependent activation of the atria and ventricles by two separate pacemakers, so P waves and QRS complexes follow their own rates with no consistent relationship between them. Bradycardiabradyarrhythmia · slow heart rate · bradyA ventricular (heart) rate in an adult below 60 bpm by the traditional definition; the 2018 ACC/AHA/HRS bradycardia guideline uses below 50 bpm. Capture beatcaptured beat · sinus capture · capture complexDuring a wide-complex ventricular rhythm with AV dissociation (ventricular tachycardia or an idioventricular rhythm), a beat produced when an atrial impulse gets through the AV junction and depolarizes the ventricles, so its QRS differs from the surrounding wide complexes; if the atrial impulse depolarizes only part of the ventricles, the result is a fusion beat instead. Compensatory pausepostextrasystolic pauseThe pause that follows a premature beat before the next sinus beat, making the R-R interval after the premature beat longer than a normal sinus R-R interval. Ectopic beatectopic · extrasystole · premature beat · premature complexA beat that originates from a focus outside the sinoatrial node (atrial, junctional or ventricular tissue). Escape beatescape complex · subsidiary pacemaker beatA beat from a subsidiary (latent) pacemaker outside the sinus node that fires only after an expected sinus impulse fails to form or fails to reach the ventricles, so it arrives LATE rather than early (the defining contrast with a premature beat, although both are ectopic in origin). Fusion beatfusion complex · summation beat · combination beatA single QRS complex produced when two wavefronts depolarize the ventricles at the same time, typically an impulse conducted from the atria and an impulse arising in the ventricles, giving a hybrid shape between the two pure beats. Heart rateHR · ventricular rate · heart rate (bpm)The number of ventricular depolarizations (QRS complexes) per minute, expressed in beats per minute (bpm). Irregularly irregular rhythmchaotic rhythm · random irregularity · irregularly irregularA rhythm in which the R-R intervals are irregular and vary from beat to beat, so successive beats are unevenly spaced. Normal sinus rhythmNSRThe normal cardiac rhythm, originating in the sinoatrial node and conducted to the ventricles: P waves are upright in leads I and II (and aVF), each P wave is followed by a QRS complex, and the rate is 60 to 100 bpm by the traditional definition (the 2018 ACC/AHA/HRS bradycardia guideline uses below 50 bpm, rather than below 60 bpm, for sinus bradycardia; above 100 bpm is sinus tachycardia). Pulseless electrical activity (PEA)PEA · Electromechanical dissociation · EMDAn organized electrical rhythm on the ECG with no palpable pulse, because the ventricles either do not contract or contract too weakly to produce a detectable pulse (cardiac ultrasound may still show some cardiac motion); it is one of the four cardiac-arrest rhythms. Reentryre-entry · circus movementAn arrhythmia mechanism in which an activation wavefront travels around an anatomic or functional obstacle (or core) and re-excites tissue that has recovered, including its own site of origin, so the arrhythmia sustains itself instead of dying out. Regular rhythmregular · regular R-RA rhythm in which successive R-R intervals are essentially constant, so the QRS complexes are evenly spaced. Regularly irregular rhythmpatterned irregularity · grouped beating · group beatingA rhythm whose R-R intervals are unequal but vary in a repeating pattern rather than randomly, so the irregularity itself recurs. Sinus arrhythmiaA sinus rhythm (normal sinus P waves, upright in leads I, II and aVF) in which the P-P and R-R intervals vary from beat to beat; the 2022 Brazilian ECG guideline characterizes it by a variation in P-P intervals of 160 to 220 ms. Tachycardiatachyarrhythmia · fast heart rate · tachyA heart rate above 100 bpm in an adult. It is a rate descriptor, not a single diagnosis; tachycardias are further classified by QRS width (narrow-complex, QRS under 120 ms, versus wide-complex, described in the 2015 ACC/AHA/HRS SVT guideline as a QRS over 120 ms) and by whether the ventricular rhythm is regular or irregular, to identify the specific mechanism.

Sinus & atrial rhythms15

Atrial fibrillationAFib · AF · A-fib · atrial fibrillationA supraventricular arrhythmia with uncoordinated atrial activation: discrete P waves are absent, the baseline shows irregular fibrillation waves (fine or coarse), and the R-R intervals are irregular when atrioventricular conduction is present. Atrial flutterAFL · A-flutter · aflutter · atrial flutterA macroreentrant atrial tachycardia producing regular flutter waves; in typical cavotricuspid isthmus-dependent flutter they form a sawtooth pattern that is negative in the inferior leads (II, III, aVF) and positive in V1. Atrial tachycardiaAT · atrial tach · atrial tachycardia · ectopic atrial tachycardiaA supraventricular tachycardia arising from a localized atrial site outside the sinus node (by automaticity, triggered activity or microreentry), with regular, organized atrial activity: discrete P waves whose morphology differs from the sinus P wave, typically separated by an isoelectric baseline. AV nodal reentrant tachycardia (AVNRT)AVNRT · AV nodal reentry tachycardia · AV nodal reentrant tachycardia · nodal reentryThe most common regular paroxysmal SVT, caused by reentry within the AV node using functionally distinct slow and fast pathways rather than an accessory pathway. AV reentrant tachycardia (AVRT)AVRT · AV reentry tachycardia · atrioventricular reentrant tachycardia · accessory pathway tachycardiaA regular paroxysmal SVT that uses a reentrant circuit made of the atrium, the AV node, the ventricle and a separate accessory pathway (bypass tract) connecting atrium and ventricle. Multifocal atrial tachycardiaMAT · chaotic atrial tachycardia · multifocal atrial tachycardiaAn irregular atrial tachycardia defined by at least 3 distinct P-wave morphologies with varying PP, PR, and RR intervals and an atrial rate above 100 bpm; the changing P waves are usually attributed to multiple atrial foci, although the mechanism is not firmly established. Paroxysmal SVTPSVT · paroxysmal supraventricular tachycardia · paroxysmal SVTA clinical designation for a regular, rapid supraventricular tachycardia that begins and ends abruptly; these features are characteristic of AVNRT and AVRT and, less often, atrial tachycardia, and the QRS is usually narrow. Premature atrial contraction (PAC)PAC · atrial premature beat · APB · atrial premature complexAn early atrial depolarization from an ectopic focus outside the sinoatrial node, seen as a premature P wave whose morphology differs from the sinus P wave. Sick sinus syndromeSSS · Sinus node dysfunction · SND · Sinoatrial node diseaseA disorder of the sinoatrial node (now usually called sinus node dysfunction) in which its ability to generate and conduct impulses is impaired. Sinoatrial exit blockSA block · SA exit block · sinoatrial block · sinoatrial exit blockA conduction failure between the sinoatrial node and the atrium: the sinus impulse is generated but cannot leave the node, so the atria are not activated and a P wave (with its QRS-T) drops out. Sinus bradycardiasinus brady · SB · sinus bradycardiaA sinus rhythm at a rate below 60 bpm by the traditional definition; the 2018 ACC/AHA/HRS bradycardia guideline uses below 50 bpm. Sinus pausesinus arrest · sinus pause/arrest · sinus pauseA transient failure of sinoatrial node impulse formation (sinus arrest) producing a pause with no P wave, and therefore no QRS-T, until the sinus node or an escape focus fires. Sinus tachycardiasinus tach · sinus tachycardiaA sinus rhythm at a rate above 100 bpm. Impulses arise normally from the sinoatrial node, with a normal P wave (upright in leads I, II and aVF) before each QRS, but at an accelerated rate that is usually a physiologic response to demand, such as exertion, emotion, fever, pain, dehydration or anemia. Supraventricular tachycardia (SVT)SVT · supraventricular tachycardiaAn umbrella term for tachycardias (atrial and/or ventricular rate over 100 bpm at rest) whose mechanism involves tissue from the His bundle or above, that is, atrial or AV junctional tissue. Wandering atrial pacemakerWAP · wandering pacemaker · wandering atrial pacemakerA supraventricular rhythm at a rate below 100 bpm in which the pacemaker site shifts from the sinoatrial node to other atrial sites and/or the AV junction and back, so the P waves change shape from beat to beat (at least 3 different P-wave morphologies), with varying PR and P-P (and thus R-R) intervals and a slightly irregular rhythm.

Junctional & ventricular rhythms19

Accelerated idioventricular rhythm (AIVR)AIVR · accelerated idioventricular rhythm · slow VTA ventricular rhythm at about 40 to 100 bpm (some sources extend the range to 120 or 130 bpm), faster than a ventricular escape rhythm (below about 40 bpm) but usually slower than ventricular tachycardia, produced mainly by abnormal (ectopic) automaticity of a ventricular focus. Accelerated junctional rhythmaccelerated junctional · nonparoxysmal junctional tachycardia · AJRA junctional rhythm faster than the junctional escape rate (about 40 to 60 bpm) but not fast enough to be called junctional tachycardia, conventionally 60 to 100 bpm (the 2015 ACC/AHA/HRS SVT guideline, which calls it nonparoxysmal junctional tachycardia, gives 70 to 130 bpm). Coupling intervalcoupling interval PVC · ectopic coupling interval · CIThe time from a preceding normal (usually sinus) beat to the premature ectopic beat that follows it. Idioventricular rhythmIVR · ventricular escape rhythm · idioventricular escape rhythmA ventricular escape rhythm: a slow rhythm that originates in the ventricles, below the bundle of His, and takes over when higher (sinus or junctional) pacemakers are inhibited or their impulses are blocked. Junctional ectopic tachycardia (JET)JET · junctional ectopic tachycardia · His bundle tachycardiaAn automatic (nonreentrant) tachycardia arising from the AV junction, including the bundle of His (it has also been called His bundle tachycardia). Junctional escape rhythmjunctional escape · nodal escape rhythm · AV junctional escapeA rhythm from the AV junction that takes over as an escape rhythm when the sinus impulse fails or does not reach the ventricles, as in sinoatrial block or high-grade or complete AV block. Junctional rhythmnodal rhythm · AV junctional rhythmA rhythm arising from the AV junction (the AV node region and the bundle of His) rather than the sinus node, with QRS complexes similar to the patient's usual conducted QRS, so they are narrow (under 120 ms) unless a bundle branch block coexists. Junctional tachycardiaJT · focal junctional tachycardiaA junctional rhythm faster than 100 bpm that arises from enhanced (abnormal) automaticity in the AV junction, including the His bundle. Monomorphic VTMMVT · monomorphic ventricular tachycardia · uniform VTVentricular tachycardia (three or more consecutive ventricular complexes at a rate above 100 bpm) in which the QRS complexes have a single, stable morphology from beat to beat within any given lead. Polymorphic VTPMVT · polymorphic ventricular tachycardia · multiform VTVentricular tachycardia (three or more consecutive ventricular complexes at a rate above 100 bpm) in which the QRS morphology changes from beat to beat, with three or more different wide QRS shapes. Premature ventricular contraction (PVC)PVC · ventricular premature complex · VPC · ventricular premature beatAn early beat arising from an ectopic focus in the ventricles, below the bundle of His, rather than from an impulse conducted from the atria. R-on-T phenomenonR on T · RonT · R-on-T PVC · R-on-T PVC phenomenonA premature ventricular complex that falls on the T wave of the preceding beat, that is, during that beat's repolarization. Retrograde P waveretrograde P · retrograde atrial activationA P wave produced by atrial depolarization that travels backward (retrograde) from a junctional or ventricular site up to the atria, usually through the AV node or an accessory pathway, so it is negative (inverted) in the inferior leads II, III, and aVF. Torsades de pointesTdP · torsades · torsade de pointes · twisting of the pointsA form of polymorphic ventricular tachycardia in which the QRS complexes change in amplitude and shape, appearing to twist around the isoelectric baseline ("twisting of the points"), although the twisting may not be seen in every lead or in short episodes. Ventricular bigeminyventricular bigeminy PVC pattern · ventricular bigeminyA repeating pattern in which each normal (usually sinus) beat is followed by a premature ventricular contraction, so that normal beats and PVCs alternate one to one. Ventricular coupletcouplet · paired PVCs · ventricular pair · PVC coupletTwo consecutive premature ventricular complexes (PVCs) occurring back to back with no intervening sinus beat. Ventricular fibrillationVF · V-fib · V fib · VFibRapid, grossly irregular, chaotic ventricular electrical activity, with waves that vary continuously in shape and amplitude, at a ventricular rate usually above 300 per minute. Ventricular tachycardia (VT)VT · V-tach · V tach · VTachThree or more consecutive complexes originating in the ventricles (below the bundle of His) at a rate over 100 bpm, usually producing a wide-QRS tachycardia. Ventricular trigeminyventricular trigeminy PVC pattern · ventricular trigeminyA repeating pattern in which a premature ventricular contraction follows every two normal (usually sinus) beats, so that every third beat is a PVC.

AV & intraventricular conduction18

2:1 AV block2 to 1 AV block · two-to-one block · 2:1 block · 2:1 second-degree AV blockA second-degree AV block in which every other P wave conducts to the ventricles, so conducted and blocked P waves alternate and there are two P waves for each QRS complex. AV blockatrioventricular block · AVB · heart block · AV conduction blockA delay or failure of conduction of atrial impulses to the ventricles, which can occur in the AV node, within the His bundle, or below it. Bifascicular blockbifascicular block · bi-fascicular blockBlock of conduction in two of the three fascicles of the ventricular conduction system (the right bundle branch and the left bundle's anterior and posterior fascicles), classically right bundle branch block combined with left anterior or left posterior fascicular block. Bundle branch blockBBB · bundle-branch blockA conduction delay or block in the right or left bundle branch of the His-Purkinje system, which changes the order in which the ventricles are activated and widens the QRS complex; in left bundle branch block, for example, the left ventricle is activated late by slow conduction across the septum from the right side. First-degree AV block1st degree AV block · first degree heart block · prolonged PR · first-degree AVBA PR interval longer than 200 ms in which every P wave still conducts to the ventricles (1:1 conduction, no dropped beats). High-grade AV blockadvanced AV block · high-degree AV block · advanced second-degree AV block · high-grade second-degree AV blockAn advanced form of second-degree AV block in which two or more consecutive P waves, occurring at a constant physiologic atrial rate, fail to conduct while some P waves still do conduct (for example 3:1 or 4:1 conduction), distinguishing it from complete block, where none conduct. Incomplete bundle branch blockIRBBB · ILBBB · incomplete RBBB · incomplete LBBBA right or left bundle branch block pattern in which the QRS is prolonged but falls short of the complete-block threshold of 120 ms; in adults the QRS duration is 110 to 119 ms. Intraventricular conduction delay (IVCD)IVCD · intraventricular conduction delay · nonspecific intraventricular conduction delay · NSIVCDA widening of the QRS that does not meet the specific criteria for either right or left bundle branch block. Left anterior fascicular block (LAFB)LAFB · left anterior fascicular block · left anterior hemiblock · LAHBConduction delay in the left anterior fascicle of the left bundle branch, which shifts the main direction of left ventricular activation upward and to the left. Left bundle branch block (LBBB)LBBB · left bundle branch block · CLBBB · complete LBBBComplete block of the left bundle branch, so the left ventricle is activated late, by slow conduction across the septum from the right side. Left posterior fascicular block (LPFB)LPFB · left posterior fascicular block · left posterior hemiblock · LPHBConduction delay in the left posterior fascicle of the left bundle branch, which shifts the main direction of left ventricular activation downward and to the right. Mobitz I (Wenckebach)Mobitz type 1 · Wenckebach · second-degree AV block type I · Mobitz 1A form of second-degree AV block in which the PR interval progressively lengthens over successive beats until a single P wave fails to conduct, producing a dropped QRS and a group-beating pattern. Mobitz IIMobitz type 2 · second-degree AV block type II · Mobitz 2 · second-degree AVB type IIA form of second-degree AV block in which, while the sinus (P-P) rate stays stable, single P waves intermittently fail to conduct without any change in the PR interval of the conducted beats (the PR is constant before and after the dropped beat). Pre-excitationventricular pre-excitation · preexcitationEarly activation of part of the ventricular muscle through an accessory pathway (classically a bundle of Kent) that conducts the atrial impulse around the AV node. Right bundle branch block (RBBB)RBBB · right bundle branch block · CRBBB · complete RBBBBlock of conduction in the right bundle branch. The left ventricle still activates normally through the intact left bundle, and the block shows up as a delay at the end of the QRS. Second-degree AV blocksecond degree heart block · 2nd degree AV block · second-degree AVB · 2nd degree heart blockSecond-degree AV block is intermittent failure of atrial impulses to conduct to the ventricles: some P waves are not followed by a QRS, so there are more P waves than QRS complexes. Third-degree (complete) heart blockcomplete heart block · 3rd degree AV block · CHB · complete AV blockA total failure of AV conduction in which no atrial impulses reach the ventricles, so the atria and ventricles beat independently (AV dissociation): the P waves bear no fixed relation to the QRS complexes, and because the atrial rate is faster than the ventricular escape rate there are more P waves than QRS complexes. Wolff-Parkinson-White (WPW)WPW · Wolff-Parkinson-White · Wolff-Parkinson-White syndrome · WPW patternVentricular pre-excitation through an accessory atrioventricular pathway (bundle of Kent) that bypasses the AV node, so part of the ventricle is activated early.

Axis & chamber enlargement14

Cardiac axisQRS axis · mean electrical axis · mean QRS axis · electrical axisThe mean direction of ventricular depolarization in the frontal plane, expressed in degrees on the hexaxial reference system. Cornell criteriaCornell voltage · Cornell index · Cornell voltage criteria · Cornell productThe Cornell criteria are a sex-specific voltage method for diagnosing left ventricular hypertrophy that sums the R wave in aVL and the S wave in V3 (the Cornell voltage). Extreme axis deviationnorthwest axis · extreme axis · extreme right axis deviation · right superior axisA mean frontal-plane QRS axis between -90 and ±180 degrees, in the upper-right ('northwest') quadrant of the hexaxial circle, beyond the adult ranges for marked left axis deviation (-45 to -90 degrees) and marked right axis deviation (+120 to +180 degrees); it is also called extreme right axis deviation. Hexaxial reference systemhexaxial system · hexaxial diagram · hexaxial reference · frontal plane axis systemA frontal-plane diagram of the six limb leads (I, II, III, aVR, aVL and aVF) drawn as axes through a common center, so that the lead directions are spaced 30 degrees apart; it is used to determine the cardiac axis. Left atrial enlargement (LAE)LAE · left atrial abnormality · LAALeft atrial enlargement (also called left atrial abnormality) is an ECG pattern of delayed, prolonged left atrial activation. Left axis deviation (LAD)LAD · left axis deviation · left QRS axis deviationA mean frontal-plane QRS axis of -30 degrees or beyond (that is, -30 to -90 degrees). Left ventricular hypertrophy (LVH)LVH · left ventricular hypertrophy · LV hypertrophyAn electrocardiographic pattern of increased left ventricular mass shown by increased QRS voltage, which may be accompanied by secondary ST-T abnormalities in the left-sided leads (ST depression with asymmetric T-wave inversion; the older label 'strain' is now discouraged). Normal axisnormal QRS axis · normal cardiac axis · normal electrical axisA mean frontal-plane QRS axis lying between -30 degrees and +90 degrees. P mitralenotched P wave · bifid P wave · M-shaped P waveP mitrale is the broad, notched (double-peaked, M-shaped) P wave in lead II, lasting 120 ms or more with its two peaks 40 ms or more apart, that is the classic surface-ECG marker of left atrial enlargement (left atrial abnormality). P pulmonaletall P wave · peaked P waveP pulmonale is the tall, peaked P wave (amplitude greater than 2.5 mm, i.e. 0.25 mV, in lead II) that is the classic surface-ECG marker of right atrial enlargement (right atrial abnormality). Right atrial enlargement (RAE)RAE · right atrial abnormality · RAARight atrial enlargement (right atrial abnormality) is an ECG pattern of increased right atrial depolarization voltage that raises the amplitude of the early (initial) part of the P wave, usually without prolonging total P-wave duration, because the right atrium is activated before the left. Right axis deviation (RAD)RAD · right axis deviation · right QRS axis deviationA mean frontal-plane QRS axis more positive than +90 degrees (that is, +90 to +180 degrees in adults). Right ventricular hypertrophy (RVH)RVH · right ventricular hypertrophy · RV hypertrophyAn electrocardiographic pattern of increased right ventricular mass characterized by right axis deviation and prominent anterior forces: a dominant R wave in V1 (R/S ratio of 1 or more, or a tall R wave, 6 mm in one criterion set), a deep S wave in V5 or V6, and often ST depression with T-wave inversion in the right precordial leads V1 to V3 (a secondary ST-T abnormality; the older label 'right ventricular strain' is discouraged). Sokolow-Lyon criteriaSokolow-Lyon index · Sokolow Lyon · SV1 + RV5/V6 · Sokolow-Lyon voltageThe Sokolow-Lyon criteria are a voltage-based ECG method for diagnosing left ventricular hypertrophy from QRS amplitudes.

Ischemia & infarction17

Acute pericarditis (ECG pattern)Pericarditis · Acute pericarditis EKG · Diffuse ST elevation with PR depression · Stage 1 pericarditisThe defining feature is diffuse ST-segment elevation spread across more than one region rather than one coronary territory (often in all leads except aVR and V1), concave upward in shape and classically accompanied by widespread PR-segment depression. Coronary territoryvascular territory · myocardial territory · coronary distribution · culprit territoryThe region of myocardium supplied by a given coronary artery. The leads that show ST elevation identify the affected region, and their pattern points to the likely culprit vessel. De Winter T wavesde Winter pattern · de Winter ST-T complex · de Winter sign · dewinter T wavesAn ST-elevation MI equivalent pattern consisting of upsloping ST depression of at least 1 mm at the J point in the precordial leads (1 to 3 mm across V1 to V6 in the original description), continuing into tall, prominent, symmetric T waves, without ST elevation in the precordial leads. Hyperacute T waveHyperacute T waves · Hyperacute T-wave changesBroad-based, symmetric T waves, usually of increased amplitude and often with a slightly depressed ST takeoff, that are among the earliest ECG signs of acute ischemia from coronary occlusion. IschemiaMyocardial ischemia · Cardiac ischemia · IschaemiaAn imbalance between myocardial oxygen supply and demand; its onset is the first step toward myocardial infarction. Myocardial infarctionMI · Heart attackDeath (necrosis) of myocardial cells caused by prolonged ischemia. The Fourth Universal Definition requires a rise and/or fall of cardiac troponin with at least one value above the 99th-percentile upper reference limit plus at least one sign of acute ischemia (symptoms, new ischemic ECG changes, new pathologic Q waves, imaging evidence of new loss of viable myocardium or a new regional wall-motion abnormality, or coronary thrombus on angiography or autopsy). Myocardial injuryMyocardial current of injury · Current of injuryIn current troponin-based usage, myocardial injury means a cardiac troponin value above the 99th-percentile upper reference limit; it is acute when the troponin rises and/or falls, and myocardial infarction is acute injury occurring with evidence of acute myocardial ischemia. NSTEMINon-ST-elevation myocardial infarction · Non-STEMI · Non-ST-segment elevation myocardial infarctionAn acute myocardial infarction (a rise and/or fall of cardiac troponin with at least one value above the 99th-percentile upper reference limit, with evidence of acute ischemia) in a patient without ST-segment elevation at presentation. Pathologic Q wavepathological Q wave · significant Q wave · pathologic Q waves · infarction Q waveAn abnormal initial negative QRS deflection that usually indicates established myocardial necrosis; it appears when viable myocardium beneath the recording electrode has been lost. Poor R wave progressionPRWP · poor R-wave progression · slow R wave progression · poor precordial R wave progressionFailure of the R wave amplitude to increase normally across the precordial leads. Reciprocal changesreciprocal ST changes · mirror changes · reciprocal ST depression · reciprocal changesST-segment depression in leads whose positive pole points roughly opposite (about 180 degrees away) to leads showing acute ST elevation, appearing as a mirror image of the ST elevation recorded over the injured area. Sgarbossa criteriaSgarbossa's criteria · modified Sgarbossa criteria · Smith-modified Sgarbossa criteria · Sgarbossa scoreA three-part scoring rule for diagnosing acute MI in the presence of left bundle branch block, based on ST deviation that breaks the expected discordant pattern; the same criteria have also been tested in ventricular paced rhythm. ST depressionSTD · ST-segment depressionDownward displacement of the ST segment below the isoelectric baseline, usually measured at the J point. ST elevationSTE · ST-segment elevation · ST segment elevationUpward displacement of the ST segment above the isoelectric (TP or PR) baseline, measured at the J point; when due to ischemia it reflects injury currents from acutely injured myocardium, usually from acute coronary occlusion. STEMIST-elevation myocardial infarction · ST-segment elevation myocardial infarctionAn acute myocardial infarction with diagnostic new ST elevation, which usually reflects acute coronary occlusion. T wave inversionTWI · inverted T waves · T-wave inversion · T wave inversionsA T wave whose main deflection is negative (below the baseline). In adults the T wave is normally upright in I, II and V3 to V6 and inverted in aVR, and it may be upright or inverted in III, aVL and V1; in adolescents and young adults it may also be inverted in V2 and slightly inverted in aVF. Wellens syndromeWellens sign · Wellens' syndrome · Wellens pattern · LAD coronary T-wave syndromeA pattern of deeply biphasic (type A) or deeply and symmetrically inverted (type B) T waves in the precordial leads V2 to V3 (sometimes extending to other precordial leads), recorded during a pain-free interval after an episode of angina and signifying a critical stenosis high in the left anterior descending artery.

Repolarization & inherited syndromes6

Brugada patternBrugada · type 1 Brugada · Brugada type 1 · Brugada ECG patternThe diagnostic type 1 pattern is coved ST-segment elevation of at least 2 mm (0.2 mV) followed by a negative T wave in one or more of the right precordial leads V1 to V2, recorded in the standard 4th or a higher (2nd or 3rd) intercostal space. Early repolarizationER · early repolarization pattern · ERP · benign early repolarizationJ-point elevation of at least 0.1 mV (1 mm) in two or more contiguous inferior and/or lateral leads, appearing as either a slur or a distinct notch (J wave) at the end of the QRS complex, with or without ST-segment elevation. Long QT syndromeLQTS · long QT · congenital long QT syndrome · hereditary long QT syndromeAn inherited disorder of ventricular repolarization marked by abnormal prolongation of the heart-rate-corrected QT interval (QTc). Prominent U waveprominent U waves · large U wave · tall U wave · giant U waveAn abnormally tall U wave, the small, low-frequency deflection that follows the T wave. QT prolongationprolonged QT · prolonged QTc · QTc prolongation · long QTcA QT interval (rate-corrected as QTc) that exceeds normal limits; the 2009 AHA/ACCF/HRS statement treats a QTc of 450 ms or longer in men and 460 ms or longer in women as prolonged, and a QTc above 500 ms is associated with a 2- to 3-fold higher risk of torsades de pointes. Short QT syndromeSQTS · short QT · short QT interval syndrome · congenital short QT syndromeAn inherited channelopathy defined by an abnormally short rate-corrected QT interval.

Electrolyte & drug effects6

Digoxin effectDig effect · Digitalis effect · Digoxin ECG effect · Digitalis repolarization changeThe expected ECG changes in a patient taking digoxin: down-sloping ST-segment depression with a scooped-out ('reverse tick') appearance, flattened or inverted T waves, and increased U-wave amplitude. Digoxin toxicityDig toxicity · Digitalis toxicity · Digoxin poisoning · Digitalis intoxicationA clinical and electrophysiologic syndrome of digoxin excess whose cardiac hallmark is increased automaticity combined with impaired conduction. HypercalcemiaHigh calcium · Elevated Ca2+ · High Ca · Raised serum calciumAn elevated serum calcium level (a normal total calcium is roughly 8.6 to 10.6 mg/dL). HyperkalemiaHigh potassium · Elevated K+ · High K · Raised serum potassiumAn elevated serum potassium level that affects the myocyte membrane potential and cardiac conduction and produces a recognizable sequence of ECG changes, although the ECG is an insensitive guide to the level. HypocalcemiaLow calcium · Decreased Ca2+ · Low Ca · Reduced serum calciumA low serum calcium level (one review defines hypocalcemia as a serum calcium below 8 mg/dL). HypokalemiaLow potassium · Low K · Decreased K+ · Reduced serum potassiumA low serum potassium level that prolongs ventricular repolarization (the QT interval).

Pacing & devices9

Atrial pacingAtrial pace · Atrial paced beat · AAI pacing · AAIR pacingPacing delivered to the atrium, seen on the ECG as a pacemaker stimulus (spike) followed, after a short latency, by a paced P wave. Cardiac resynchronization therapy (CRT)Biventricular pacing · BiV pacing · CRT-P · CRT-DCardiac resynchronization therapy is a pacing therapy that aims to restore or preserve ventricular synchrony by pacing the left ventricle in timed relation to the right ventricle, in heart failure linked to ventricular dyssynchrony such as that caused by left bundle branch block. Dual-chamber pacingDual chamber pace · DDD pacing · DDDR pacing · AV sequential pacingPacing from a device with leads in both the right atrium and the right ventricle that can sense and pace both chambers, classically the DDD mode (DDDR when rate modulation is added). Failure to captureLoss of capture · Non-capture · Noncapture · UndercaptureA malfunction in which a pacemaker spike is delivered but is not followed by depolarization of the intended chamber, so the ECG shows a spike with no following P wave (atrial noncapture) or QRS complex (ventricular noncapture). Failure to senseUndersensing · Under-sensing · Loss of sensing · Sensing failureA malfunction (undersensing) in which the pacemaker fails to detect the heart's own depolarizations and so paces asynchronously: spikes appear regardless of native P waves or QRS complexes, often too many of them and sometimes soon after a native beat. Paced rhythmPaced · Paced beat · Electronic pacing · Pacemaker rhythmA cardiac rhythm generated or triggered by an implanted electronic pacemaker rather than the heart's own conduction system, recognized on the ECG by pacemaker spikes followed by depolarization of the paced chamber. Pacemaker fusion beatPacemaker fusion · Paced fusion beat · Paced fusion complexA complex produced when a paced stimulus and the heart's own depolarization activate the same chamber at the same time, giving a QRS (or P wave) whose shape lies between a fully paced beat and a native beat. Pacemaker spikePacing spike · Pacer spike · Pacing artifact · Pacing artefactA narrow, sharp deflection on the ECG (a stimulus artifact) marking the instant the pacemaker delivers its pulse, followed by depolarization of the chamber when the pulse captures. Ventricular pacingVentricular pace · Ventricular paced beat · VVI pacing · VVIR pacingPacing delivered to the ventricle. When the lead stimulates ventricular muscle, the ECG shows a pacemaker spike followed by a broad QRS (often more than 120 ms), because activation spreads slowly from the pacing site.

Recording & method11

12-lead ECG12-lead EKG · twelve-lead ECG · standard ECG · resting ECGThe standard diagnostic recording that shows the heart's electrical activity in 12 leads: 6 limb leads (I, II, III, aVR, aVL, aVF) that view the heart in the frontal (vertical) plane and 6 chest (precordial) leads (V1 through V6) that view it in the horizontal plane, all derived from 10 electrodes (4 on the limbs, 6 on the chest). Artifactartefact · noise · interference · ECG artifactAny recorded deflection that does not come from the heart's electrical activity. Augmented limb leadsaVR aVL aVF · augmented unipolar leads · Goldberger leads · augmented voltage leadsThe three frontal-plane limb leads aVR, aVL and aVF, introduced by Goldberger in 1942. Dextrocardiadextrocardia · mirror-image dextrocardia · mirror-image ECGA congenital positional anomaly in which the heart lies in the right hemithorax with its base-to-apex axis pointing to the right. ECG calibrationstandardization · calibration pulse · cal mark · standardization markThe reference settings that make ECG amplitudes and intervals comparable between recordings. Einthoven triangleEinthoven's triangle · Einthoven triangle of leads · Einthoven's triangle of leadsA model that places the right-arm, left-arm and left-leg electrodes at the corners of an equilateral triangle with the heart at its center. Lead IILead 2 · II · limb lead IIA standard limb lead that records the potential difference between the left leg (positive) and the right arm (negative), lying at +60 degrees in the frontal plane. Limb leadsfrontal plane leads · extremity leads · bipolar and augmented limb leadsThe six leads that view the heart in the frontal (vertical) plane: the three standard limb leads of Einthoven (I, II and III), each recording the potential difference between a pair of limb electrodes, and the three augmented limb leads (aVR, aVL and aVF). Precordial (chest) leadschest leads · V leads · unipolar chest leads · horizontal plane leadsThe six chest leads (V1 through V6) that view the heart in the horizontal plane, each recording the potential at its chest electrode relative to Wilson's central terminal. Rhythm striprhythm lead · monitoring strip · rhythm tracing · rhythm monitoring stripA prolonged recording from one lead, used mainly to assess heart rate and rhythm rather than waveform shape across leads; a standard rhythm strip is 25 cm long (10 seconds). Right-sided and posterior leadsV3R-V6R · V4R · V7-V9 · posterior leadsExtra chest electrode positions that extend the standard 12-lead ECG to the right ventricle and the posterobasal (inferobasal) wall of the left ventricle, areas the standard leads show poorly.

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