Characteristics of Ventricular Tachycardia

Core Defining Features

• The European Society of Cardiology defines ventricular tachycardia as three or more consecutive ventricular beats at a rate exceeding 100 bpm with a wide QRS complex, originating from the ventricles below the atrioventricular node 1
• Nonsustained VT is defined as ≥3 beats terminating spontaneously in <30 seconds 1
• Sustained VT is defined as duration >30 seconds or requiring termination due to hemodynamic compromise in <30 seconds 1

Critical Diagnostic ECG Features

• The American College of Cardiology, American Heart Association, and European Society of Cardiology guidelines provide specific morphologic criteria that strongly suggest VT, including absence of RS complexes in all precordial leads V1-V6 and RS interval >100 ms in any precordial lead 7, 2, 3, 4
• AV dissociation with ventricular rate faster than atrial rate is diagnostic of VT, present in ~30% of cases but highly specific 2, 3, 4
• Fusion complexes are pathognomonic for VT 2, 3, 4

Morphologic Subtypes

• Monomorphic VT is characterized by a single, stable QRS morphology throughout the tachycardia, most commonly associated with structural heart disease, particularly prior myocardial infarction 1
• Polymorphic VT is characterized by continuously changing or multiform QRS morphology at cycle length 180-600 ms, with torsades de pointes being a specific type associated with prolonged QT/QTc 1

Physical Examination Findings

• Physical examination can reveal evidence of AV dissociation, including irregular cannon A waves in jugular venous pulse, variable intensity of first heart sound, and beat-to-beat variability in systolic blood pressure 2, 3, 4

Clinical Context

• The American Heart Association recommends that when wide-complex tachycardia cannot be definitively diagnosed despite careful ECG evaluation, it should be treated as VT, as most wide-complex tachycardias are ventricular in origin 2, 3, 4, 8
• A history of prior myocardial infarction with first occurrence of wide-complex tachycardia after the infarct strongly indicates VT 2, 3, 4

Critical Diagnostic Pitfalls

• The differential diagnosis of wide-complex tachycardia includes SVT with pre-existing bundle branch block, SVT with aberrant conduction due to tachycardia, and SVT with conduction over accessory pathway (pre-excitation) 7, 2, 6
• Adenosine should be used with extreme caution when diagnosis is unclear, as it may precipitate ventricular fibrillation in patients with coronary artery disease 3