Ventricular tachycardia

Ventricular tachycardia is three or more consecutive ventricular impulses with a frequency of 120 per minute.

Symptoms of ventricular tachycardia depend on its duration and range from no sensation or sense of heartbeat to hemodynamic collapse and death. Diagnosis is by ECG. Treatment of ventricular tachycardia, except for very short episodes, includes cardioversion and antiarrhythmic drugs depending on symptoms. If necessary, long-term treatment with an implantable cardioverter-defibrillator is prescribed.

Some experts use 100 beats per minute as the limit for ventricular tachycardia. A repetitive ventricular rhythm at a lower rate is called an enhanced idioventricular rhythm, or slow ventricular tachycardia. This condition is usually benign and does not require treatment until hemodynamic symptoms develop.

Most patients with ventricular tachycardia have significant cardiac disease, most commonly previous myocardial infarction or cardiomyopathy. Electrolyte abnormalities (especially hypokalemia or hypomagnesemia), acidosis, hypoxemia, and drug side effects may also contribute to the development of ventricular tachycardia. Long QT syndrome (congenital or acquired) is associated with a special form of ventricular tachycardia called torsades depointes.

Ventricular tachycardias may be monomorphic or polymorphic, sustained or unsustained. Monomorphic ventricular tachycardia arises from a single abnormal focus or accessory pathway and is regular, with identical QRS complexes. Polymorphic ventricular tachycardia arises from several different foci or pathways and is irregular, with different QRS complexes. Unsustained ventricular tachycardia lasts < 30 s, sustained ventricular tachycardia lasts 30 s or terminates more quickly due to hemodynamic collapse. Ventricular tachycardia often progresses to ventricular fibrillation followed by cardiac arrest.

Symptoms of ventricular tachycardia

Short-term or low-rate ventricular tachycardia may be asymptomatic. Sustained ventricular tachycardia almost always leads to the development of dramatic symptoms such as palpitations, signs of hemodynamic failure, or sudden cardiac death.

Diagnosis of ventricular tachycardia

The diagnosis is established based on ECG data. Any tachycardia with a wide ventricular complex (QRS 0.12 s) should be regarded as ventricular tachycardia until proven otherwise. The diagnosis is confirmed by revealing on the electrocardiogram dissociation of the P waves, extended or captured complexes, unidirectionality of the QRS complex in the chest leads (concordance) with a discordant T wave (directed against the direction of the ventricular complex) and a frontal direction of the QRS axis in the northwest quadrant. Differential diagnosis is performed with supraventricular tachycardia combined with bundle branch block or with an additional conduction pathway. However, because some patients tolerate ventricular tachycardia surprisingly well, the conclusion that a well-tolerated wide-complex tachycardia must be supraventricular is a mistake. Use of drugs used for supraventricular tachycardia (eg, verapamil, diltiazem) in patients with ventricular tachycardia may result in hemodynamic collapse and death.

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Treatment of ventricular tachycardia

Emergency treatment of ventricular tachycardia. Treatment depends on the symptoms and duration of ventricular tachycardia. Ventricular tachycardia with hypertension requires synchronized direct cardioversion with 100 J. Stable, sustained ventricular tachycardia may respond to intravenous agents, usually lidocaine, which is rapidly acting but rapidly inactivated. If lidocaine is ineffective, intravenous procainamide may be used, but administration may take up to 1 hour. Failure of procainamide is an indication for cardioversion.

Nonsustained ventricular tachycardia does not require emergency treatment unless the beats become very frequent or the episodes are long enough to cause symptoms. In such cases, antiarrhythmic drugs are prescribed as for sustained ventricular tachycardia.

Long-term treatment of ventricular tachycardia

The primary goal is to prevent sudden death rather than simply suppress arrhythmia. This is best achieved by implanting a cardioverter-defibrillator. However, deciding who to treat is always difficult and depends on the identification of potentially life-threatening ventricular tachycardias and the severity of the underlying cardiac pathology.

Long-term treatment is not used if the detected attack of ventricular tachycardia is a consequence of a transient (for example, within 48 hours after the development of myocardial infarction) or reversible (disorders associated with the development of acidosis, electrolyte imbalance, pararrhythmic effect of antiarrhythmic drugs) cause.

In the absence of a transient or reversible cause, patients who have had an episode of sustained ventricular tachycardia usually require ICDF. Most patients with sustained ventricular tachycardia and significant structural heart disease should also receive beta-blockers. If ICDF is not possible, amiodarone should be the antiarrhythmic drug of choice to prevent sudden death.

Since nonsustained ventricular tachycardia is a marker of increased risk of sudden death in patients with structural heart disease, such patients (especially those with an ejection fraction of less than 0.35) require further evaluation. There is emerging evidence for the need to implant an ICD in such patients.

If VT prevention is necessary (usually in patients with ICD who suffer from frequent episodes of ventricular tachycardia), antiarrhythmic drugs, radiofrequency or surgical ablation of arrhythmogenic substrates are used. Any antiarrhythmic drug of class Ia, Ib, Ic, II, III can be used. Since beta-blockers are safe, in the absence of contraindications they become the drugs of choice. If another drug is needed, sotalol is prescribed, then amiodarone.

Catheter radiofrequency ablation is more often performed in patients with ventricular tachycardia with clearly identifiable sources [eg, right ventricular outflow tract ventricular tachycardia, left septal ventricular tachycardia (Belassen ventricular tachycardia, verapamil-sensitive ventricular tachycardia)] and otherwise healthy hearts.

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