Ventricular tachycardia

Ventricular tachycardia is a type of ventricular arrhythmia with at least three consecutive ventricular beats occurring at greater than 100 beats per minute. If left untreated, ventricular tachycardia can lead to ventricular fibrillation and cardiac arrest.

Epidemiology 

Ventricular tachycardia is the major cause of sudden cardiac death with an estimated rate of 300,000 deaths each year in the United States ¹. Risk factors of ventricular tachycardia include hypertension, valvular disease, coronary artery disease, and cardiomyopathy ². 

Clinical presentation 

Patients with ventricular tachycardia most often report palpitations, which may be associated with chest pain, dizziness, presyncope or syncope, or dyspnea. Patients are classified as stable if they have no or minimal symptoms and maintain a normal blood pressure, while unstable patients have hypotension, altered mental status, signs of shock or acute heart failure, or ischemic chest pain.

ECG of ventricular tachycardia demonstrates at least three consecutive beats of a wide QRS complex with a rate of at least 100 beats per minute ⁸. The rhythm in ventricular tachycardia is generally but not always regular. The width of the QRS complex is at least 120 milliseconds by definition in wide complex tachycardia, but even longer durations (>160 milliseconds) are more specific to ventricular tachycardia compared to other causes of wide complex tachycardia.

Ventricular tachycardia can be divided into two categories based on duration: nonsustained (less than 30 seconds) and sustained (lasting at least 30 seconds). Nonsustained ventricular tachycardia is usually asymptomatic and detected during cardiac monitoring. Sustained ventricular tachycardia may present with mild symptoms but can deteriorate rapidly into a life-threatening condition.

Pathology 

Etiology 

The vast majority of patients with ventricular tachycardia have significant underlying heart disease. The damaged, fibrotic myocardium can alter electrical pathways to the ventricles. 

Some of the common causes of ventricular tachycardia include ¹:

• myocarditis
• ischemic heart disease 
• hypertrophic cardiomyopathy
• right ventricular cardiomyopathy
• congenital heart disease
• valvular heart disease
• long QT syndrome
• myocardial infarction
• metabolic/electrolyte abnormalities

Radiographic features 

Because most serious cases of ventricular tachycardia are related to structural heart disease, especially ischemic heart disease, imaging is indicated to evaluate for structural abnormalities resulting in a myocardial scar.

US

Echocardiography is part of first-line imaging in patients presenting with ventricular tachycardia ⁹. The main utility is assessing for structural abnormalities, as well as valvular and pump function. Wall thinning and motion abnormalities point to abnormal regions of the ventricle, although the resolution of changes in echo density are generally insufficient for detailed visualization of scar ⁹.

Angiography

Coronary angiography is the other part of first-line imaging for patients with ventricular tachycardia in order to identify significant coronary artery disease that would cause ischemic cardiomyopathy ⁹.

MRI

Cardiac MRI is widely considered the gold standard for identifying ventricular tachycardia substrate ⁹. Late gadolinium enhancement detects specific patterns and distribution of myocardial fibrosis and improvement of disease diagnoses ³.

Nuclear medicine

Nuclear imaging can detect abnormal myocardial perfusion, silent ischemia, and metabolism ⁴ in patients with ventricular tachycardia by utilizing radio-labeled tracers bound to metabolically active molecules ³. 

CT 

Cardiac CT is an alternative technique to assess myocardial structure and function, specifically ventricular wall thickness and myocardial fibrosis ^3,5. However, the contrast resolution in myocardium is poorer on CT than in MRI.

Treatment and prognosis 

Initial management of ventricular tachycardia depends on the hemodynamic stability of the patient. Unstable patients require emergent synchronized cardioversion, while stable patients require urgent management such as pharmacologic cardioversion using antiarrhythmic drugs.

Depending on the underlying cause of ventricular tachycardia, appropriate therapy can be prescribed. Implantable cardioverter-defibrillators are the mainstay of therapy for patients with ventricular tachycardia due to systolic heart failure. Catheter ablation is increasingly indicated as a primary treatment for ventricular tachycardia, particularly in patients with multiple Implantable cardioverter-defibrillator shocks or with prior infarct scar ⁶. Pharmacologic options for ventricular tachycardia are limited. Antiarrhythmic drugs, such as amiodarone and sotalol, and beta-blockers are often prescribed for recurrent ventricular tachycardia ⁷.