(See also Overview of Arrhythmias Overview of Arrhythmias The normal heart beats in a regular, coordinated way because electrical impulses generated and spread by myocytes with unique electrical properties trigger a sequence of organized myocardial... read more .)
Some experts use a cutoff rate of ≥ 100 beats/minute for ventricular tachycardia (VT). Repetitive ventricular rhythms at slower rates are called accelerated idioventricular rhythms or slow VT; they are usually benign and are not treated unless associated with hemodynamic symptoms.
Most patients with VT have a significant heart disorder, particularly prior myocardial infarction Acute Myocardial Infarction (MI) Acute myocardial infarction is myocardial necrosis resulting from acute obstruction of a coronary artery. Symptoms include chest discomfort with or without dyspnea, nausea, and/or diaphoresis... read more or a cardiomyopathy Overview of Cardiomyopathies A cardiomyopathy is a primary disorder of the heart muscle. It is distinct from structural cardiac disorders such as coronary artery disease, valvular disorders, and congenital heart disorders... read more . Electrolyte abnormalities (particularly hypokalemia Hypokalemia Hypokalemia is serum potassium concentration 3.5 mEq/L ( 3.5 mmol/L) caused by a deficit in total body potassium stores or abnormal movement of potassium into cells. The most common cause is... read more or hypomagnesemia Hypomagnesemia Hypomagnesemia is serum magnesium concentration 1.8 mg/dL ( 0.70 mmol/L). Causes include inadequate magnesium intake and absorption or increased excretion due to hypercalcemia or drugs such... read more ), acidemia, hypoxemia, and adverse drug effects contribute. The long QT syndrome Long QT Syndrome and Torsades de Pointes Ventricular Tachycardia Torsades de pointes is a specific form of polymorphic ventricular tachycardia in patients with a long QT interval. It is characterized by rapid, irregular QRS complexes, which appear to be twisting... read more (congenital or acquired) is associated with a particular form of VT, torsades de pointes.
Ventricular tachycardia may be monomorphic or polymorphic and nonsustained or sustained.
Monomorphic VT: Single abnormal focus or reentrant pathway and regular, identical-appearing QRS complexes
Polymorphic VT: Several different foci or pathways and irregular, varying QRS complexes
Nonsustained VT: Lasts < 30 seconds
Sustained VT: Lasts ≥ 30 seconds or is terminated sooner because of hemodynamic collapse
VT frequently deteriorates to ventricular fibrillation Ventricular Fibrillation (VF) Ventricular fibrillation causes uncoordinated quivering of the ventricle with no useful contractions. It causes immediate syncope and death within minutes. Treatment is with cardiopulmonary... read more and thus cardiac arrest Cardiac Arrest Cardiac arrest is the cessation of cardiac mechanical activity resulting in the absence of circulating blood flow. Cardiac arrest stops blood from flowing to vital organs, depriving them of... read more .
Symptoms and Signs of Ventricular Tachycardia
Ventricular tachycardia of short duration or slow rate may be asymptomatic. Sustained VT is almost always symptomatic, causing palpitations, symptoms of hemodynamic compromise, or sudden cardiac death.
Diagnosis of Ventricular Tachycardia
Diagnosis of ventricular tachycardia is by ECG (see figure Broad QRS ventricular tachycardia Broad QRS ventricular tachycardia ). Any wide QRS complex tachycardia (QRS ≥ 0.12 second) should be considered VT until proved otherwise.
Diagnosis is supported by ECG findings of dissociated P-wave activity, fusion or capture beats, uniformity of QRS vectors in the V leads (concordance) with discordant T-wave vector (opposite QRS vectors), and a frontal-plane QRS axis in the northwest quadrant. Differential diagnosis includes supraventricular tachycardia Reentrant Supraventricular Tachycardias (SVT) including Wolff-Parkinson-White Syndrome Reentrant supraventricular tachycardias (SVT) involve reentrant pathways with a component above the bifurcation of the His bundle. Patients have sudden episodes of palpitations that begin and... read more conducted with bundle branch block or via an accessory pathway (see figure Modified Brugada Criteria for ventricular tachycardia Modified Brugada criteria for ventricular tachycardia ). However, because some patients tolerate VT surprisingly well, concluding that a well-tolerated wide QRS complex tachycardia must be of supraventricular origin is a mistake. Using drugs appropriate for supraventricular tachycardia (eg, verapamil, diltiazem) in patients with VT may cause hemodynamic collapse and death.
Pearls & Pitfalls
Broad QRS ventricular tachycardia
The QRS duration is 160 millisecond. An independent P wave can be seen in II (arrows). There is a leftward mean frontal axis shift.
Treatment of Ventricular Tachycardia
Acute: Sometimes synchronized direct-current cardioversion, sometimes class I or class III antiarrhythmics
Long-term: Usually an implantable cardioverter-defibrillator
Treatment of acute ventricular tachycardia depends on symptoms and duration of VT.
Pulseless VT requires defibrillation Defibrillation Cardiopulmonary resuscitation (CPR) is an organized, sequential response to cardiac arrest, including Recognition of absent breathing and circulation Basic life support with chest compressions... read more with ≥100 joules.
Stable sustained VT can be treated with synchronized direct-current cardioversion Direct-Current (DC) Cardioversion-Defibrillation The need for treatment of arrhythmias depends on the symptoms and the seriousness of the arrhythmia. Treatment is directed at causes. If necessary, direct antiarrhythmic therapy, including antiarrhythmic... read more with ≥100 joules.
Stable sustained VT can also be treated with IV class I or class III antiarrhythmic drugs (see table Antiarrhythmic Drugs Antiarrhythmic Drugs (Vaughan Williams Classification) ). Lidocaine acts quickly but is frequently ineffective. If lidocaine is ineffective, IV procainamide may be given, but it may take up to 1 hour to work. IV amiodarone is frequently used but does not usually work quickly. Failure of IV procainamide or IV amiodarone is an indication for cardioversion.
Nonsustained VT does not require immediate treatment unless the runs are frequent or long enough to cause symptoms. In such cases, antiarrhythmics are used as for sustained VT.
The primary goal is preventing sudden death, rather than simply suppressing the arrhythmia. It is best accomplished by use of an implantable cardioverter-defibrillator Implantable Cardioverter-Defibrillators (ICD) The need for treatment of arrhythmias depends on the symptoms and the seriousness of the arrhythmia. Treatment is directed at causes. If necessary, direct antiarrhythmic therapy, including antiarrhythmic... read more (ICD). However, the decision about whom to treat is complex and depends on the estimated probability of life-threatening VTs and the severity of underlying heart disorders (see table Indications for Implantable Cardioverter-Defibrillators Indications for Implantable Cardioverter-Defibrillators in Ventricular Tachycardia and Ventricular Fibrillation ).
Long-term treatment is not required when the index episode of ventricular tachycardia resulted from a transient cause (eg, during the 48 hours after onset of myocardial infarction) or a reversible cause (acid-base disturbances, electrolyte abnormalities, proarrhythmic drug effect).
In the absence of a transient or reversible cause, patients who have had an episode of sustained VT typically require an ICD. Most patients with sustained VT and a significant structural heart disorder should also receive a beta-blocker. If an ICD cannot be used, amiodarone may be the preferred antiarrhythmic for prevention of sudden death.
Because nonsustained VT is a marker for increased risk of sudden death in patients with a structural heart disorder, such patients (particularly those with an ejection fraction < 0.35) require further evaluation. Such patients should receive an ICD.
When prevention of VTs is important (usually in patients who have an ICD and are having frequent episodes of VT), antiarrhythmics or transcatheter or surgical ablation Ablation for Cardiac Arrhythmia The need for treatment of arrhythmias depends on the symptoms and the seriousness of the arrhythmia. Treatment is directed at causes. If necessary, direct antiarrhythmic therapy, including antiarrhythmic... read more of the arrhythmogenic substrate is required. Any class Ia, Ib, Ic, II, or III antiarrhythmic drug Drugs for Arrhythmias The need for treatment of arrhythmias depends on the symptoms and the seriousness of the arrhythmia. Treatment is directed at causes. If necessary, direct antiarrhythmic therapy, including antiarrhythmic... read more can be used. Because beta-blockers are safe, they are the first choice unless contraindicated. If an additional drug is required, sotalol is commonly used, then amiodarone.
Transcatheter ablation Ablation for Cardiac Arrhythmia The need for treatment of arrhythmias depends on the symptoms and the seriousness of the arrhythmia. Treatment is directed at causes. If necessary, direct antiarrhythmic therapy, including antiarrhythmic... read more is used most commonly in patients who have VT with well-defined syndromes (eg, right ventricular outflow tract VT or left septal VT [Belhassen VT, verapamil-sensitive VT]) and otherwise healthy hearts.
Any wide-complex (QRS ≥ 0.12 second) tachycardia should be considered ventricular tachycardia (VT) until proved otherwise.
Patients who do not have a pulse should be cardioverted.
Synchronized cardioversion or antiarrhythmic drugs may be tried if the patient is stable.
Patients who had an episode of sustained VT without a transient or reversible cause typically require an implantable cardioverter-defibrillator (ICD).