Ventricular tachycardia

Ventricular tachycardia is defined by at least three consecutive ventricular-origin beats, usually at a rate above 100 beats per minute.¹ The abnormal rhythm bypasses the normal conduction sequence that begins in the sinoatrial node and travels through the atria and specialized conduction system. On an electrocardiogram, VT commonly produces broad QRS complexes, although a broad-complex rhythm may have other causes and should be assessed cautiously.

VT may arise from a single re-entry circuit, several circuits, or an area of enhanced automaticity in ventricular muscle. Monomorphic VT has a relatively consistent QRS shape and often reflects scar-related re-entry, whereas polymorphic VT changes its QRS appearance from beat to beat. The distinction helps guide urgent treatment and later investigation.

The most common serious substrate for VT is structural heart disease, particularly prior myocardial infarction and cardiomyopathy.² Other causes include myocarditis, heart failure, congenital heart disease, electrolyte disturbance, medication toxicity, and inherited disorders such as long QT syndrome or catecholaminergic polymorphic ventricular tachycardia. Some patients have idiopathic VT arising from anatomically characteristic sites in an otherwise normal heart.

Symptoms depend on the rate, duration, ventricular function, and whether the rhythm is sustained. Palpitations, dizziness, chest discomfort, shortness of breath, and fainting may occur; cardiac arrest can be the first presentation. A rapid rhythm is especially dangerous when it markedly reduces cardiac output, but even apparently tolerated VT warrants prompt medical assessment.

Diagnosis begins with a 12-lead electrocardiogram when available, alongside assessment of blood pressure, consciousness, oxygenation, and reversible triggers. A regular wide-complex tachycardia is generally treated as VT until a specialist establishes another diagnosis, because misclassifying VT as supraventricular tachycardia can be hazardous.³ Evaluation commonly includes blood tests, echocardiography, coronary assessment when indicated, cardiac magnetic resonance imaging, and review of family history.

Unstable VT with hypotension, shock, ischemic chest pain, pulmonary edema, or altered mental status requires synchronized cardioversion; pulseless VT is a shockable cardiac-arrest rhythm treated with defibrillation and cardiopulmonary resuscitation.⁴ Stable cases may receive intravenous antiarrhythmic therapy under monitoring. Long-term strategies can include beta blockers, treatment of coronary or structural disease, catheter ablation, and an implantable cardioverter-defibrillator (ICD) when the risk of sudden cardiac death is substantial.¹

Not all VT has the same prognosis: brief nonsustained episodes and idiopathic monomorphic VT can behave very differently from sustained scar-related VT in a damaged ventricle. Nonsustained VT usually ends spontaneously within 30 seconds, while sustained VT lasts longer or must be terminated earlier because of hemodynamic compromise.

Some inherited syndromes produce polymorphic VT despite a structurally normal heart. Brugada syndrome, long QT syndrome, and catecholaminergic polymorphic ventricular tachycardia are electrical diseases in which fever, drugs, sudden adrenergic stress, or exercise can influence risk.⁵ The ECG pattern may be absent between episodes, so clinical history and relatives can be diagnostically important. In selected patients, ablation can target a ventricular focus or scar channels, reducing recurrent shocks and VT burden, but it does not remove every cause of sudden death risk.⁶

Monomorphic VT

Ventricular tachycardia with a largely uniform QRS appearance from beat to beat, often associated with a stable re-entry circuit.

Polymorphic VT

Ventricular tachycardia whose QRS shape varies continuously or repeatedly; it may occur with acute ischemia or inherited electrical disorders.

Nonsustained VT

A ventricular tachycardia episode that terminates spontaneously, conventionally within 30 seconds.

Ventricular fibrillation

A chaotic ventricular rhythm that produces no effective coordinated cardiac output and causes cardiac arrest.

Implantable cardioverter-defibrillator

A device that detects dangerous ventricular rhythms and can deliver pacing or a shock to terminate them.