Diagnosing Ventricular Tachycardia

Key Diagnostic Criteria

The American Heart Association recommends that ventricular tachycardia (VT) can be diagnosed on ECG by identifying a wide QRS complex (>120 ms), AV dissociation, fusion beats, and specific morphological features in leads V1-V6 and aVR 1, 2
QRS duration typically >120 ms in adults, though in infants VT may present with QRS <90 ms but different from sinus QRS morphology 3
The European Society of Cardiology notes that QRS morphology different from the patient's normal QRS during sinus rhythm suggests VT 1
QRS complexes in precordial leads that are all positive or all negative (concordance) strongly suggest VT, according to the American College of Cardiology 4
R-S interval (onset of R wave to nadir of S wave) >100 ms in any precordial lead implies VT, as stated by the American College of Cardiology and the Journal of the American College of Cardiology 4, 5

The American Heart Association states that presence of AV dissociation (ventricular rate faster than atrial rate) is pathognomonic of VT 1, 4
Fusion beats (combination of supraventricular and ventricular complexes) strongly indicate VT, according to the Journal of the American College of Cardiology 5
Independent P waves continuing unrelated to the QRS complexes during tachycardia suggest VT, as noted by the European Heart Journal 3
The American College of Cardiology recommends that presence of initial R wave in lead aVR suggests VT 4
Initial R or Q wave >40 ms in aVR suggests VT, according to the American College of Cardiology 4

The American College of Cardiology states that R-wave peak time ≥50 ms in lead II suggests VT 4
QR complexes (indicating myocardial scar) are present in approximately 40% of patients with post-MI VT, as reported by the Journal of the American College of Cardiology 5
Similar morphology between premature ventricular beats during sinus rhythm and the tachyarrhythmia strongly suggests VT, according to the European Heart Journal 3
Patients with prior myocardial infarction who develop wide QRS tachycardia are more likely to have VT, as stated by the Journal of the American College of Cardiology 5
VT rates in infants may range from 200-500 beats/min, with slight variation in R-R intervals, as noted by the European Heart Journal 3

Relying solely on QRS width criteria can be misleading when patients have pre-existing bundle branch blocks or are taking certain antiarrhythmic medications, according to the Journal of the American College of Cardiology 5
Electrolyte abnormalities or metabolic disorders can cause wide QRS complexes that mimic VT, as stated by the American College of Cardiology 4
When the diagnosis is unclear, it is safer to treat as VT rather than SVT, according to the Journal of the American College of Cardiology 5

Echocardiography should be performed to determine ventricular function and potential structural abnormalities, as recommended by the European Heart Journal 3
24-hour Holter monitoring may be worthwhile in complex ventricular arrhythmias, according to the European Heart Journal 3

AV dissociation, where the ventricular rate exceeds the atrial rate, is diagnostic of ventricular tachycardia (VT). This finding alone confirms VT in patients presenting with wide‑complex tachycardia. 6
Capture beats—intermittent normal‑looking QRS complexes occurring during a wide‑complex tachycardia—prove that the rhythm is VT. 6

Positive concordance (all precordial QRS complexes uniformly positive) suggests VT or a pre‑excitation mechanism, providing strong diagnostic guidance. 6

A QRS duration greater than 120 ms defines a wide‑complex tachycardia and serves as the initial threshold for considering VT in the acute setting. 6

In patients with a pre‑existing bundle‑branch block, interpretation of the tachycardia QRS morphology must be compared with the baseline ECG to avoid misclassification. This comparison is essential for accurate VT diagnosis. 6