Not all VT is the same. The subtype determines the prognosis, the treatment, and sometimes whether the patient needs a defibrillator or just a calcium channel blocker.
The short answer: patients with scar. The long answer is more nuanced.
Prior myocardial infarction is the most common cause of sustained monomorphic VT. Scar tissue from the infarct creates the reentry substrate. In the first two years after MI, sudden cardiac death (usually VT degenerating to VF) is the leading cause of death. Among patients with ischemic cardiomyopathy and untreated sustained VT, two-year mortality approaches 30%.
80% of wide complex tachycardias in patients with structural heart disease are VT.Dilated cardiomyopathy, hypertrophic cardiomyopathy, and infiltrative diseases (sarcoidosis, amyloidosis) all produce fibrosis that supports reentry. The scar pattern is different from ischemic disease: patchy, mid-myocardial, or epicardial rather than subendocardial. This matters for ablation, because the circuits may not be reachable from inside the heart. One-third of inducible VTs in dilated cardiomyopathy are bundle branch reentry, a form that is essentially curable with catheter ablation.
About 10% of all monomorphic VT occurs in patients with no detectable structural heart disease. These idiopathic VTs carry an excellent prognosis (near-normal life expectancy) and often respond to catheter ablation with cure rates above 90%. The mechanisms are triggered activity and abnormal automaticity rather than scar-based reentry, and the treatment is fundamentally different.
The most common idiopathic VT, accounting for 80-90% of outflow tract tachycardias. The mechanism is triggered activity: catecholamine-driven delayed afterdepolarizations (DADs) mediated by cyclic AMP. It presents in young, otherwise healthy patients as repetitive monomorphic VT or frequent PVCs, often triggered by exercise or stress.
The EKG signature: LBBB morphology (the impulse originates in the RV, so it activates the LV late, mimicking left bundle branch block) with an inferior axis (tall R waves in II, III, aVF, because the outflow tract sits high in the chest and the impulse travels downward).
The diagnostic trick: RVOT VT responds to adenosine. This is unusual for VT and diagnostically useful; scar-based reentrant VT does not terminate with adenosine. It also responds to beta-blockers and calcium channel blockers.
Treatment: Catheter ablation is curative in over 90% of cases. The 2022 ESC guidelines recommend ablation as first-line for symptomatic RVOT VT.
The second most common idiopathic VT, accounting for 10-15% of cases. It uses a reentrant circuit involving the left posterior fascicle of the His-Purkinje system and a verapamil-sensitive slow pathway (calcium-dependent conduction). It affects young patients aged 15-40, with a 60-80% male predominance.
The EKG signature: RBBB morphology with left axis deviation (the most common subtype involves the left posterior fascicle). The QRS is relatively narrow for VT, often only 120-140ms, which makes it easy to misdiagnose as SVT with aberrancy.
The diagnostic trick: Fascicular VT responds to IV verapamil. This distinguishes it from RVOT VT (which responds to adenosine) and from scar-based VT (which responds to neither).
Treatment: Verapamil for acute termination. Catheter ablation is highly effective for long-term cure.
A macroreentrant circuit that uses the His-Purkinje system itself. The impulse travels antegrade down one bundle branch, through the interventricular septum, and retrograde up the other bundle branch, then back through the His bundle to start again. The most common form travels down the right bundle and up the left, producing an LBBB-morphology VT.
It requires pre-existing conduction disease (prolonged HV interval, baseline bundle branch block) and is most common in nonischemic dilated cardiomyopathy and post-valve surgery patients. It accounts for roughly one-third of inducible VTs in dilated cardiomyopathy.
Treatment: Ablation of the right bundle branch cures the arrhythmia. But these patients usually need an ICD anyway, because they typically have additional scar-based VT substrates.
A group of genetic conditions that create VT substrate in hearts that look structurally normal on echocardiography. The substrate is molecular (ion channel dysfunction) or ultrastructural (desmosomal defects), not macroscopic scar. These syndromes disproportionately kill young, apparently healthy people.
Congenital prolongation of ventricular repolarization that predisposes to torsades de pointes. Three subtypes account for 90% of genotyped cases, and each has different triggers, T-wave morphology, and treatment response.
| Subtype | Gene / Channel | Triggers | T-wave | Treatment |
|---|---|---|---|---|
| LQT1 (40-55%) | KCNQ1 / IKs loss | Exercise (especially swimming), emotional stress | Broad-based | Beta-blockers (highly effective) |
| LQT2 (30-35%) | KCNH2 / IKr loss | Sudden auditory stimuli (alarm clocks), emotion, postpartum | Low-amplitude, notched | Beta-blockers + K+ supplementation |
| LQT3 (5-10%) | SCN5A / Na+ gain | Rest, sleep (bradycardia-dependent) | Late-onset, peaked, long ST segment | Mexiletine; beta-blockers less effective |
All subtypes: avoid QT-prolonging drugs (crediblemeds.org maintains the definitive list). ICD for cardiac arrest survivors and patients with syncope despite beta-blockers. Left cardiac sympathetic denervation (LCSD) for refractory cases.
Prevalence: 1 in 2,000 to 10,000, predominantly affecting Southeast Asian men. Caused by SCN5A loss-of-function sodium channel mutations in 20-30% of cases (the rest are genetically unresolved). The reduced sodium current creates a transmural voltage gradient in the right ventricular outflow tract: the epicardium loses its action potential dome (due to unopposed Ito), but the endocardium doesn't. This dispersion triggers phase 2 reentry and VF.
The EKG: Type 1 (diagnostic) pattern is coved ST elevation of 2mm or more in V1-V3, followed by a negative T wave. This pattern may be spontaneous or provoked by IV sodium channel blockers (ajmaline, procainamide, flecainide).
Clinical pattern: VT/VF occurs at rest, during sleep, or with fever. Not during exercise (unlike CPVT and LQT1).
Treatment: ICD for cardiac arrest survivors and patients with syncope plus spontaneous Type 1 ECG. Quinidine (blocks Ito, restores the action potential dome) for patients with recurrent ICD shocks. Epicardial ablation of the RVOT substrate is an emerging approach that can normalize the Brugada pattern.
Prevalence: 1 in 2,000 to 5,000. Caused by mutations in desmosomal genes (plakophilin-2 is most common). Defective desmosomes weaken cell-to-cell mechanical coupling, leading to myocyte death during mechanical stress, fibrofatty replacement of the right ventricular myocardium, and a progressive reentrant substrate.
The EKG: Epsilon waves (small notches after the QRS in V1-V3, representing delayed RV activation through scar), T-wave inversions in V1-V3, and prolonged terminal QRS activation.
The VT: LBBB morphology (RV origin), often triggered by exercise. This is the syndrome behind many cases of sudden death in young athletes.
Treatment: Activity restriction (exercise promotes disease progression). Beta-blockers. ICD for cardiac arrest survivors and patients with hemodynamically significant VT. Catheter ablation for recurrent VT, often requiring both endocardial and epicardial approaches because the substrate sits in the outer wall.
Rare (1 in 10,000) but exceptionally dangerous: 30-50% of untreated patients experience cardiac events by age 30. Caused by mutations in the cardiac ryanodine receptor (RYR2, 60-65% of cases) or calsequestrin (CASQ2). The defective ryanodine receptor leaks calcium from the sarcoplasmic reticulum during catecholamine stimulation, generating DADs and triggered activity.
The hallmark: Bidirectional VT, with the QRS axis alternating 180 degrees beat to beat. This pattern is pathognomonic for CPVT. The resting ECG is completely normal; arrhythmias appear only with exercise or catecholamine infusion. Exercise stress testing is the diagnostic test: progressive ventricular ectopy with increasing workload, from isolated PVCs to couplets to bidirectional VT.
Treatment: Nadolol (beta-blocker) at maximum tolerated dose, mandatory for all patients. Flecainide as add-on therapy for breakthrough arrhythmias (it directly inhibits the ryanodine receptor, targeting the molecular defect). ICD is a double-edged sword: the shock itself releases catecholamines, which can trigger more VT, creating a vicious cycle. LCSD for drug-refractory cases. Competitive sports are prohibited.
| Subtype | ECG Clue | Responds To | Prognosis |
|---|---|---|---|
| Scar reentry (post-MI) | Wide QRS, AV dissociation, concordance | Amiodarone, procainamide, cardioversion | High mortality without ICD |
| RVOT VT | LBBB + inferior axis | Adenosine, beta-blockers, ablation | Excellent |
| Fascicular VT | RBBB + left axis, narrow QRS (120-140ms) | Verapamil, ablation | Excellent |
| Bundle branch reentry | LBBB morphology, baseline conduction disease | Right bundle ablation | Depends on underlying CMP |
| Torsades de pointes | Twisting axis, prolonged QT at baseline | IV magnesium, overdrive pacing | Good if cause corrected |
| CPVT (bidirectional) | Alternating QRS axis, normal resting ECG | Nadolol, flecainide | High risk without treatment |
Post-MI, LVEF ≤30%: ICD reduces mortality by 31% (MADIT-II). Without an ICD, two-year mortality from sustained VT approaches 30%.
Heart failure, LVEF ≤35%: ICD reduces mortality by 23% (SCD-HeFT). Amiodarone performed no better than placebo. NNT: approximately 14 over five years.
VT storm + ICD + failing drugs: Catheter ablation reduces the composite of death, VT storm, and ICD shocks by 28% compared to drug escalation (VANISH).
Idiopathic VT: Catheter ablation success rate exceeds 90%. Life expectancy approaches the general population.
Stable monomorphic VT, acute: IV procainamide terminates VT in 67% of cases versus 38% for amiodarone, with fewer adverse events (PROCAMIO). Despite this, amiodarone remains more commonly used in practice.