Contrary to conventional wisdom, a significant number of sudden arrhythmic deaths result from re-entrant ventricular tachycardia that occurs in patients with chronic heart disease in the absence of acute infarction. These arrhythmias can be safely studied in a controlled setting using electrophysiological testing. Programmed electrical stimulation of the ventricle (also termed VT stimulation studies) has a remarkable sensitivity for reproducing monomorphic ventricular tachycardia associated with infarct related myocardial scars and offers a fairly reliable means of identifying patients at risk for sudden death. Patients with LV dysfunction (LV ejection fraction <40%) who are inducible for monomorphic VT have a risk of sudden cardiac death of approximately 30% over the ensuing year.

The patients at highest risk for sudden death include those who have survived a cardiac arrest not occurring in the context of an acute infarction, and those presenting with sustained VT. These patients are best treated with implantable cardiac defibrillators. The role of VT stimulation studies in such patients is primarily to confirm the diagnosis and exclude focal ventricular arrhythmias or unusual supraventricular arrhythmias indistinguishable from VT that are amenable to RF ablation. Occasionally, suppression of VT inducibility with drugs such as amiodarone and sotalol may be an acceptable alternative to implantable cardioverter defibrillator (ICD) implant.

VT stimulation studies are more valuable for patients with severe heart disease and unexplained syncope. Such patients may have had a self-limiting arrhythmia causing their syncope. Inducibility of monomorphic VT is a fairly specific finding in this patient population especially if their heart disease is based on coronary artery disease. In addition, electrophysiological studies can unmask severe His-Purkinje conduction disease requiring pacemaker implantation. One major drawback of VT stimulation studies is the low sensitivity for ventricular arrhythmia in nonischaemic dilated cardiomyopathy. In these patients, if the clinical suspicion is high, a negative study may well represent a false negative. A second problem with VT studies is the uncertain reliability of induced polymorphic VT or ventricular fibrillation as end points. Recent data from subgroup analysis of the Multicenter Unsustained Tachycardia Trial (MUSTT) suggests that such arrhythmias may be just as important as monomorphic VT for predicting mortality in the face of severe LV dysfunction.

Perhaps the most important role of VT study is in primary prevention of sudden death. Two recent randomised trials have demonstrated conclusively that patients with depressed LV function and non-sustained VT (defined as three or more beats of VT at a rate >120bpm) will benefit from ICD implantation if they are inducible for sustained VT.1,2 Clinical trials are in progress to determine if ICD implantation would benefit patients with low LVEF and heart failure alone without resorting to an EP study. Pending their results, patients with LV dysfunction who manifest non-sustained VT should undergo VT stimulation studies to see if they would benefit from an ICD. This strategy appears to be cost effective.

The risks of invasive electrophysiological studies are related to venous (and rarely arterial) cannulation and from the arrhythmias induced. Injury to the vascular structures and venous thrombosis occurs rarely (less than 2%). Cardiac perforation from catheter placement is equally rare (0.4%); death from the procedure occurred in 0.12% in one study4 and underlines the importance of trained personnel and well equipped laboratories for these studies.

No comments: