Electrical alternans
Also calledQRS alternans · Beat-to-beat amplitude alternans
Definition
Alternation 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. Together with low QRS voltage it is a sign of pericardial effusion with cardiac tamponade; the two signs are attributed to the damping effect of the fluid and the heart swinging within it. QRS alternation during a narrow-QRS supraventricular tachycardia strongly suggests an accessory pathway in the tachycardia circuit. T-wave alternans is a beat-to-beat change in T-wave amplitude, shape or orientation; at the microvolt level it is too small to see and needs computer analysis. It indicates latent instability of repolarization and has been studied as a marker of ventricular arrhythmia risk, but its clinical value has not been fully defined.
Sources
- Adler Y, Charron P, Imazio M, et al. 2015 ESC Guidelines for the diagnosis and management of pericardial diseases. Eur Heart J. 2015;36(42):2921-2964. doi.org/10.1093/eurheartj/ehv318
- Green M, Heddle B, Dassen W, et al. Value of QRS alteration in determining the site of origin of narrow QRS supraventricular tachycardia. Circulation. 1983;68(2):368-373. doi.org/10.1161/01.cir.68.2.368
- Al-Khatib SM, Stevenson WG, Ackerman MJ, et al. 2017 AHA/ACC/HRS guideline for management of patients with ventricular arrhythmias and the prevention of sudden cardiac death. Circulation. 2018;138(13):e272-e391. doi.org/10.1161/CIR.0000000000000549
- Samesima N, God EG, Kruse JCL, et al. Brazilian Society of Cardiology guidelines on the analysis and issuance of electrocardiographic reports - 2022. Arq Bras Cardiol. 2022;119(4):638-680. doi.org/10.36660/abc.20220623
- Rautaharju PM, Surawicz B, Gettes LS. AHA/ACCF/HRS recommendations for the standardization and interpretation of the electrocardiogram: part IV: the ST segment, T and U waves, and the QT interval. Circulation. 2009;119(10):e241-e250. doi.org/10.1161/CIRCULATIONAHA.108.191096
Last reviewed 2 October 2026. Every definition in the EKG Dictionary cites the guideline, consensus statement or original paper it comes from.