Ventricular tachycardia definition

The common ventricular arrhythmias include (1) premature ventricular complexes (PVCs), (2) ventricular tachycardia, and (3) ventricular fibrillation. Again, these arrhythmias may result in a wide variety of symptoms. PVCs often cause no symptoms or only mild palpitations. Ventricular tachycardia may be a life-threatening situation associated with hemodynamic collapse or be totally asymptomatic. Ventricular fibrillation, by definition, is an acute medical emergency necessitating cardiopulmonary resuscitation (CPR). 

Ventricular tachycardia (VT) is the result of uncontrolled electrical activity in the ventricle. This activity may be coordinated or uncoordinated. The definitive therapy for Ventricular is external stimulation by an electric field sufficiently large to reset the electrical activity of most ventricular cells. This ends the previous (uncontrolled) electrical activity and allows the reestablishment of normal cardiac activity. As explained earlier, this requires depolarization of a critical mass of tissue by a high-voltage discharge. When high-voltage therapy is delivered, an attempt is made to synchronize the delivery with a detected R-wave. A synchronized shock is termed cardioversion, whereas an unsynchronized shock is termed defibrillation because VF has no coherent electrical activity, and therefore no basis for synchronization (Figure 15.6). 

CAST-11 compared moricizine with placebo. The protocol for the CAST-11 was modified in an attempt to enroll patients more likely to experience serious arrhythmias and to observe for early risk of antiarrhythmic drugs. The qualifying ejection fraction was lowered to < 0.40, a higher dose of moricizine could be used, and the definition of disqualifying ventricular tachycardia was changed to allow patients with more serious arrhythmias to be entered into the trial. CAST II was subsequently terminated prematurely because patients treated with moricizine had an increased cardiac mortality rate during the first... 

Frequent shocks can occnr for several reasons. Most commonly they are due to repetitive episodes of supraventricular tachycardia or ventricular tachycardia, or a lead/lCD sensing problon. The definition of frequent shocks varies among physicians and patients, but more than three shocks within 24 h are probably appropriate and this situation is frequently referred to as electrical storm. Freqnent shocks are associated with depression and reduced mental health. The canses and evaluation of a patient with frequent shocks are summarized in Table 20.6. 

Flecainide slows conduction in all cardiac cells including the anomalous pathways responsible for the Wolff-Parkinson-White (WPW) syndrome. Together with encainide and moricizine, it underwent clinical trials to establish if suppression of asymptomatic premature beats with antiarrhythmic drugs would reduce the risk of death from arrhythmia after myocardial infarction. The study was terminated after preliminary analysis of 1727 patients revealed that mortality in the groups treated with flecainide or encainide was 7.7% compared with 3.0% in controls. The most likely explanation for the result was the induction of lethal ventricular arrhythmias possibly due to ischaemia by flecainide and encainide, i.e. a proarrhythmic effect. In the light of these findings the indications for flecainide are restricted to patients with no evidence of structural heart disease. The most common indication, indeed where it is the drug of choice, is atrioventricular re-entrant tachycardia, such as AV nodal tachycardia or in the tachycardias associated with the WPW syndrome or similar conditions with anomalous pathways. This should be as a prelude to definitive treatment with radiofrequency ablation. Flecainide may also be useful in patients with paroxysmal atrial fibrillation. 

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