Idiopathic Ventricular Tachycardia

Definition, Etiology, PathogenesisTop

Idiopathic ventricular tachycardias (VTs) primarily include several types of focal arrhythmias (outflow tract VT, fascicular VT, papillary muscle VT) in patients without coronary artery disease (CAD) or structural heart disease. Rarely there may be annular VT. These arrhythmias are idiopathic and generally associated with a good prognosis. They may present as frequent premature ventricular contractions (PVCs) or episodes of sustained VT, usually monomorphic.

Clinical Features and Natural HistoryTop

Symptoms range from none (asymptomatic) to paroxysmal palpitations. Symptom severity depends on the hemodynamic significance of the arrhythmia. Patients with very frequent PVCs (>10% of total beats in 24 hours) may develop cardiomyopathy. Symptoms are frequently exacerbated by stress or exercise.

DiagnosisTop

Electrocardiography (ECG):

1) Outflow tract VT can arise from the right ventricular outflow tract or the left ventricular outflow tract. It is the most common type, either in the form of monomorphic PVCs or monomorphic VT. The hallmark is an inferior axis on ECG (positive QRS in the inferior leads; Figure 1).

2) Fascicular VT: The most common origin is the left posterior fascicle of the left bundle branch. ECG during tachycardia reveals a slightly widened QRS (usually <140 milliseconds, not as wide as in other VTs) with right bundle branch block (RBBB) and a left axis deviation (negative QRS in the inferior leads).

3) Papillary muscle VT: Similar to fascicular VT but with a wider QRS (>140 ms).

Differential Diagnosis

Differential diagnosis should include other types of VT or supraventricular tachycardia with aberrancy. It is important to exclude structural heart disease and to analyze QRS morphology during the arrhythmia. VT in arrhythmogenic right ventricular cardiomyopathy can resemble benign right outflow tachycardia; determination of the nature of ventricular arrhythmia in these cases is an evolving field requiring expert input.

TreatmentTop

Classification of antiarrhythmic drugs: see Table 1 in Cardiac Arrhythmias.

Antiarrhythmic agents: see Table 2 in Cardiac Arrhythmias.

1. Fascicular VT commonly responds to verapamil (IV or oral).

2. When outflow tract VT/PVCs are suspected, beta-blockers, diltiazem, or verapamil should be considered. This type of VT may also respond to class Ic antiarrhythmics.

3. Catheter ablation is indicated in patients with focal PVCs/VT or fascicular VT who do not respond to antiarrhythmic drugs, are not willing to take medications on a long-term basis, or cannot tolerate the drugs.

FiguresTop

Figure 3.4-11. Episode of monomorphic right ventricular outflow tract tachycardia.