Ventricular Tachycardia

Ventricular tachycardia (VT or V-tach) refers to any rhythm faster than 100 beats/min arising distal to the bundle of His. It is the most common form of wide complex tachycardia, with a high associated mortality rate. ^[1] The rhythm may arise from the working ventricular myocardium, the distal conduction system, or both. VT can be classified as sustained or nonsustained, with a generally accepted cutoff of 30 seconds.

VT is further classified according to the electrocardiographic (ECG) appearance. If the QRS complex remains identical from beat to beat, as occurs when VT originates from a single focus or circuit, it is classified as monomorphic (see the first two images below). If the QRS morphology changes from beat to beat, the VT is classified as polymorphic (see the third image below).

Torsade de pointes, often referred to as torsade, is an uncommon form of polymorphic VT characterized by a gradual change in the amplitude and twisting of the QRS complexes around the isoelectric line. Torsade de pointes is associated with a prolonged QT interval, which may be congenital or acquired. ^[2]  Torsade usually terminates spontaneously but frequently recurs and may degenerate into ventricular fibrillation (VF), and therefore can be fatal if not diagnosed and managed.

Accelerated idioventricular rhythm, sometimes termed slow VT, is a variant of VT that produces a rate of 60-120 beats/min. It typically occurs in patients with underlying heart disease (ischemic or structural), is transient, and only rarely is associated with hemodynamic compromise or collapse. Treatment of the dysrhythmia itself usually is not required unless significant hemodynamic impairment develops.

Further classification of VT can be made on the basis of the substrate and the location of the earliest activation.

In the United States, the most common setting for VT is ischemic heart disease, in which myocardial scar tissue is the substrate for electrical reentry. VT can also be seen in other conditions that create a myocardial scar, such as the following:

• Dilated cardiomyopathy
• Hypertrophic cardiomyopathy
• Arrhythmogenic right ventricular dysplasia/cardiomyopathy (ARVD/ARVC) 
• Chagas disease (trypanosomiasis) ^[3]
• Tetralogy of Fallot and associated surgical scar

VT may also occur in the absence of structural heart disease. VT in this setting may result from enhanced automaticity, which most commonly originates in the right ventricular outflow tract or from the fascicles of the cardiac conduction system. Bundle-branch reentrant VT occurs in patients with conduction system disease distal to the bundle of His.

Finally, functional reentrant VTs can occur in structurally normal hearts, in patients with inherited channelopathies including:

• Long QT syndrome
• Short QT syndrome
• Catecholaminergic polymorphic VT (CPVT)
• Brugada syndrome
• Familial ventricular tachycardia

Torsade de pointes can be triggered by the following:

• Electrolyte deficiencies (eg, hypokalemia, hypocalcemia, hypomagnesemia)
• Antiarrhythmic drugs including class IA agents (eg, quinidine, procainamide, disopyramide), class IC agents (eg, flecainide), and class III agents (eg, sotalol, amiodarone).
• Other drugs that prolong the QT interval including phenothiazines, tricyclic antidepressants, lithium carbonate, ziprasidone,cisapride, highly active antiretroviral drugs, high-dose methadone, anthracycline chemotherapeutic agents (eg, doxorubicin, daunomycin),

Certain prescription medications are associated with a nonshockable rhythm. A study concluded that the use of drugs known to increase torsade risk (most commonly citalopram and roxithromycin) was associated with a reduced likelihood of presenting with a shockable rhythm and thus a less likely to return to spontaneous circulation. ^[4]

Patients with frank hemodynamic compromise from acute VT require emergency management with electrical cardioversion. Although cardioversion treats VT, it does not prevent recurrence of VT, and patients may experience repeated episodes of recurrent VT after cardioversion; this phenomenon is termed VT storm. These patients additionally require acute antiarrhythmic therapy, ablation therapy, or both.

The mainstays of long-term treatment for clinically stable patients with VT are the various antiarrhythmic drugs. However, cardiologists are increasingly making use of interventional therapy with devices and ablation procedures designed to abort VT or to destroy arrhythmogenic tissue in the heart.

Causes of ventricular tachycardia (VT) include the following ^[5] :

• Ischemic heart disease (most common)
• Structural heart disease (eg, nonischemic cardiomyopathy, arrhythmogenic right ventricular cardiomyopathy [ARVD] or cardiomyopathy, hypertrophic cardiomyopathy)
• Congenital structural cardiac disorders (eg, tetralogy of Fallot) and associated surgical scar)
• Acquired channelopathies, most commonly from drugs that prolong the QT interval (eg, class IA and class III antiarrhythmics, phenothiazines, methadone, many others)
• Inherited channelopathies (eg, long QT syndrome, short QT syndrome, Brugada syndrome, and catecholaminergic polymorphic ventricular tachycardia)
• Electrolyte deficiencies (eg, hypokalemia, hypocalcemia, hypomagnesemia)
• Systemic diseases that affect the myocardium (eg, sarcoidosis, amyloidosis, systemic lupus erythematosus, hemochromatosis, rheumatoid arthritis)
• Sympathomimetic agents, including intravenous (IV) inotropes and illicit drugs such as methamphetamine or cocaine
• Digitalis toxicity, which can lead to biventricular tachycardia
• Exposure to extreme heat and humidity appears to raise the risk for VT in the setting of preexisting cardiovascular disease ^[6]

Hypokalemia is an important arrhythmia trigger, followed by hypomagnesemia. Hyperkalemia may also predispose to VT and ventricular fibrillation (VF), particularly in patients with structural heart disease. Other triggers include sleep apnea and atrial fibrillation (AF), which can increase VT risk in patients with preexisting structural heart disease.

QT prolongation, which may be acquired or inherited, can lead to VT. Acquired QT prolongation is observed with certain potassium channel–blocking medications. Most of the causative drugs block the delayed rectifier cardiac potassium current, I_Kr. These agents include class IA and class III antiarrhythmics, azithromycin, and many others. Congenital long QT syndrome is a group of genetic disorders involving abnormal cardiac ion channels (most commonly, potassium channels responsible for ventricular repolarization).

In both acquired and congenital long QT syndromes, prolonged repolarization predisposes to torsade de pointes. Other inherited ion channel abnormalities may cause idiopathic VF and familial polymorphic VT in the absence of QT prolongation.

Inherited long QT syndrome

Long QT syndrome is characterized by QT interval prolongation, T-wave abnormalities, and polymorphic VT. Persons with this syndrome are predisposed to episodes of polymorphic VT. These episodes can be self-limited, resulting in syncope, or they may transition into VF and thus can cause sudden cardiac death.

Long QT syndromes have been identified by eponyms (ie, Romano-Ward syndrome, Jervell and Lange-Nielsen (JLN) syndrome, Andersen-Tawil syndrome, and Timothy syndrome). However, current practice is moving away from using eponyms and toward denoting these syndromes as numbered types (eg, LQT1 through LGT12, and JLN1, JLN2) on the basis of identified underlying mutations.

LQTS results from mutations of genes encoding for cardiac ion channel proteins, which cause abnormal ion channel kinetics. At least 10 genes have been identified in LQTS with mutations in the KCNQ1, KCNH2, SCN5A, KCNE1, and KCNE2 genes responsible for the majority of cases.

Brugada syndrome

Brugada syndrome is characterized by the specific ECG pattern of right bundle-branch block and ST-segment elevation in the early precordial leads, most commonly V1-V3, without any structural abnormality of the heart. It causes idiopathic VT or VF and carries a high risk for sudden cardiac death.

At least nine genes are known to cause Brugada syndrome (SCN5A, GPD1L, CACNA1C, CACNB2, SCN1B, KCNE3, SCN3B, HCN4, and KCND3), but SCN5A accounts for about 20% of cases, with other known "minor" genes comprising another 15% of cases. ^[7] Brugada syndrome is inherited in an autosomal dominant fashion.

Catecholaminergic polymorphic ventricular tachycardia

Catecholaminergic polymorphic VT (CPVT) is characterized by polymorphic VT that can be triggered by stress, exercise, or even strong emotional states. It can be induced by catecholamine administration. Patients may present with syncope or with sudden cardiac death if the dysrhythmia degrades into VF. Physical examination or electrocardiography (ECG) during rest will likely be normal.

CPVT may be caused by mutations in the CASQ2 or RYR2 genes. An additional locus has been mapped to chromosome 7p22-p14. This disorder shares clinical characteristics with the bidirectional VT sometimes seen in digitalis toxicity.

Familial ventricular tachycardia

Familial VT is characterized by paroxysmal VT in the absence of cardiomyopathy or another identifiable electrophysiologic disorder. Familial VT is rare; investigation of families with paroxysmal VT will frequently reveal disorders such as Brugada syndrome, long QT syndrome, or catecholaminergic polymorphic VT.

Dilated cardiomyopathy

Dilated cardiomyopathy is a highly heterogeneous disorder that can predispose to ventricular tachyarrhythmias such as VT. Its genetic causes are myriad and involve mutations in genes coding for proteins that make up cardiac sarcomeres, including actin, myosin, and troponin. It is noteworthy that genes such as PSEN1 and PSEN2, which are responsible for early-onset Alzheimer disease, have also been implicated in dilated cardiomyopathy.

Most familial dilated cardiomyopathies are inherited in an autosomal dominant fashion. X-linked inheritance of dilated cardiomyopathy has been described in patients with mutations in the DMD gene (Duchenne muscular dystrophy) and the TAZ gene (Barth syndrome). Autosomal recessive inheritance has been described in mutations of the TNNI3 gene, which encodes troponin I.

Hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy is usually inherited in an autosomal dominant fashion with incomplete penetrance. Mutations in four genes that encode sarcomeric proteins—TNNT2, MYBPC3, MYH7, ­and TNNI3—account for approximately 90% of cases. ^[8] Most people with symptomatic hypertrophic cardiomyopathy will experience them at rest. Less often, a person with this disorder will experience an initial episode of VT or VF with significant exertion.

Arrhythmogenic right ventricular dysplasia

Arrhythmogenic right ventricular dysplasia/cardiomyopathy (ARVD/ARVC) is considered a genetic disorder as most cases (up to 90%) are familial, and there is geographical clustering. The remaining cases result from an acquired etiology such as viral myocarditis; however, it is thought that patients with a genetic predisposition are more likely to develop myocarditis.

ARVD/ARVC is characterized by replacement of the free wall of the right ventricle with fibrous tissue and the development of right ventricular hypertrophy. This disorder frequently results in sustained VT, which may degrade into VF.

The genetics of ARVD are extremely heterogeneous with numerous causative genes (ie, DSP, PKP2, DSG2, DSC2, JUP) implicated in the pathogenesis of this disorder, which is inherited in an autosomal dominant fashion with incomplete penetrance. ^[9]  

At the cellular level, ventricular tachycardia (VT) is caused by electrical reentry or abnormal automaticity. Myocardial scarring from any process increases the likelihood of electrical reentrant circuits. These circuits generally include a zone where normal electrical propagation is slowed by the scar. Ventricular scar formation from a prior myocardial infarction (MI) is the most common cause of sustained monomorphic VT.

VT in a structurally normal heart typically results from mechanisms such as triggered activity and enhanced automaticity. Torsade de pointes, seen in the long QT syndromes, is likely a combination of triggered activity and ventricular reentry. ^[10]

During VT, cardiac output is reduced as a consequence of decreased ventricular filling from the rapid heart rate and the lack of properly timed or coordinated atrial contraction. Ischemia and mitral insufficiency ^[11] may also contribute to decreased ventricular stroke output and hemodynamic intolerance.

Hemodynamic collapse is more likely when underlying left ventricular dysfunction is present or when heart rates are very rapid. Diminished cardiac output may result in diminished myocardial perfusion, worsening inotropic response, and degeneration to ventricular fibrillation (VF), resulting in sudden death.

In patients with monomorphic VT, mortality risk correlates with the degree of structural heart disease. Underlying structural heart diseases such as ischemic cardiomyopathy, dilated cardiomyopathy, hypertrophic cardiomyopathy, Chagas disease, and right ventricular dysplasia have all been associated with degeneration of monomorphic or polymorphic VT to VF. ^[3] Even without such degeneration, VT can also produce congestive heart failure and hemodynamic compromise, with subsequent morbidity and mortality.

If VT is hemodynamically tolerated, the incessant tachyarrhythmia may cause a dilated cardiomyopathy. This may develop over a period of weeks to years and may resolve with successful suppression of the VT. ^[12] A similar course is occasionally seen in patients with frequent premature ventricular contractions or ventricular bigeminy, despite the absence of sustained high rates. ^[13]

Ventricular tachycardia (VT) and coronary artery disease (CAD) are common throughout most of the developed world. In developing countries, VT and other heart diseases are relatively less common.

The incidence of VT in the United States is not well quantified, because of the clinical overlap of VT with ventricular fibrillation (VF). Most sudden cardiac deaths are caused by VT or VF, ^[14] at an estimated rate of approximately 300,000 deaths per year in the United States, or about half of the estimated cardiac mortality. ^[15]

A review of nationwide data from 1999 to 2020 reported a total of 123,945 deaths reported due to VT alone, another 16,777 were associated with VT and nonischemic cardiomyopathy (NICM) and 15,888 deaths involved both VT and ischemic cardiomyopathy (ICM). ^[16]

Age-related demographics

VT is unusual in children but may occur in the postoperative cardiac setting or in patients with associated congenital heart disease. The incidence of ischemic VT increases with age, regardless of sex, as the prevalence of CAD increases. VT rates peak in the middle decades of life, in concert with the incidence of structural heart disease. Idiopathic VT can be observed at any age.

Race- and sex-related demographics

 ICM-related deaths occur more frequently among men, Whites, and Hispanics, whereas NICM-related deaths are more frequent among women and Black Americans. ^[16]  

The prognosis in patients with ventricular tachycardia (VT) varies with the specific cardiac process, but it is predicted best by left ventricular function. Patients with VT may suffer heart failure and its attendant morbidity as a result of hemodynamic compromise. In patients with ischemic cardiomyopathy and nonsustained VT, sudden-death mortality approaches 30% in 2 years. In patients with idiopathic VT, the prognosis is excellent, with the major risk being injury incurred during syncopal spells.

Morbidity from VT is associated with hemodynamic collapse. Resuscitated survivors may suffer ischemic encephalopathy, acute renal insufficiency, transient ventricular dysfunction, aspiration pneumonitis, and trauma related to resuscitation efforts.

Data from the Harmonizing Outcomes with Revascularization and Stents in Acute Myocardial Infarction Trial suggest that VT or ventricular fibrillation occurring before coronary angiography and revascularization in the setting of ST-segment elevation myocardial infarction has a strong association with increased 3-year rates of death and stent thrombosis. ^[17]

Appropriate treatment can significantly improve the prognosis in selected patients. Beta-blocker therapy can reduce the risk of sudden cardiac death from VT, and implantable cardioverter-defibrillators can terminate malignant arrhythmias.

The prognosis does not always correlate with left ventricular function. Patients with long QT syndrome, right ventricular dysplasia, or hypertrophic cardiomyopathy may be at increased risk for sudden death despite relatively well preserved left ventricular function. These possibilities should be considered in any patient with a strong family history of premature sudden death.