Case Report A 68-year-old male with coronary artery disease presented with three episodes of syncope within two weeks. Each episode was sudden, unexpected and without prodrome. One episode (witnessed by his neighbor) occurred after he stepped off his lawnmower tractor. He passed out suddenly but then awoke. When he tried to get up again, he passed out a second time. He was unconscious for about 30 seconds each time. There were no preceding symptoms. Another episode occurred when he was sitting on his kitchen chair where his wife saw him collapse suddenly and without seizure activity. He was a little confused after awakening from the 30-second episode. There is no other history of syncope, except for a syncopal episode 30 years ago when he was giving blood. This patient had a renal transplant evaluation two years ago, during which time a dobutamine stress echocardiogram was notable for monomorphic ventricular tachycardia degenerating into ventricular fibrillation requiring direct current (DC) shock. Coronary angiography at that time demonstrated multivessel coronary artery disease. He underwent coronary bypass graft surgery without sequelae. The electrocardiogram (ECG) at that time demonstrated normal sinus rhythm and nonspecific ST and T wave changes without intraventricular conduction delay. The physical examination was unremarkable on initial evaluation. The ECG indicated atrial fibrillation and a left bundle branch block. An echocardiogram revealed normal left ventricular function. An electrophysiology study was then performed. The HV interval was 85 ms in atrial fibrillation. Double premature right ventricular apical extrastimuli (500/250/190 ms) induced a sustained monomorphic ventricular tachycardia with a right bundle branch block morphology, a left superior axis and a cycle length of 240 ms (Figure 1). There was no association between the tachycardia and His-Purkinje activation. Attempts to pace terminate ventricular tachycardia were unsuccessful. Within 45 seconds, the rhythm degenerated to ventricular fibrillation, at which time he lost consciousness. He required a direct current shock to return him to normal sinus rhythm. Consequently, there was evidence for sinus node dysfunction and episodic 2:1 infra-Hisian block (Figure 2). The HV intervals varied, but were as long as 180 ms, implying strong evidence for infra-Hisian conduction system disease (Figure 3). Conducted beats demonstrated right bundle branch block morphology with a left superior axis alternating with left bundle branch block; therefore, he had bilateral bundle branch block consistent with trifascicular disease (Figure 4). He remained bradycardic. The results of the study suggested possible etiologies for syncope: 1) bradycardia due to infra-Hisian conduction disease; 2) bradycardia due to sinus node dysfunction; 3) tachycardia due to atrial fibrillation; and 4) monomorphic ventricular tachycardia. Moreover, the patient was at risk for life-threatening ventricular arrhythmias independent of the need for treatment of his syncope. A transesophageal echocardiogram was performed demonstrating no clots in the left atrium as he remained in sinus rhythm after DC shock. We proceeded to place a dual-chamber implantable cardioverter-defibrillator (ICD). The patient remains fully anticoagulated after this. Discussion The diagnosis of syncope can usually be made by taking a proper history and performing a complete physical exam. This patient's syncope was sudden in onset, not associated with any particular activity or prodrome (consistent with Stokes Adams attacks), and the physical exam was normal. The history is most suggestive of an arrhythmia, probably a tachycardia, as the cause given the sudden onset of syncope without prodrome. Common causes of syncope without structural heart disease include situational circumstances, vasovagal reflex syncope (i.e., neurocardiogenic), orthostatic hypotension, and others. This patient's history and physical exam did not identify any of these causes. There is a distant history of what may have been neurocardiogenic syncope, but the prior episode does not share any similarity to the most recent syncopal events. The most recent episodes are recurrent and occur within a short timeframe, suggesting an arrhythmic cause. The evaluation of patients with syncope also involves careful review of the ECG. This patient presented with a concerning sudden onset of syncope. The new onset of a left bundle branch block was worrisome, and he had coronary artery disease as well. Despite the fact that he had normal ventricular function, he was at risk for conduction system disease and ventricular tachycardia. No further noninvasive evaluation would be helpful in this patient at this time. T wave alternans testing and signal-averaged ECG for patients with atrial fibrillation and left bundle branch block would not be useful. Therefore, the next indicated test is an electrophysiology study. A tilt table test could have been performed to evaluate for a neurocardiogenic cause for syncope, but this would not have uncovered the ventricular tachyarrhythmias, bradycardia, and alternating bundle branch block that developed during the electrophysiology test. For these reasons, a tilt table test in this case could have been misleading. Based on the history, despite the prior history of syncope, the most likely problem was a serious arrhythmia and not neurocardiogenic syncope. Thus, a tilt table test was not performed at this time. While an ICD might not prevent syncope due to ventricular tachycardia in this patient, it can still be lifesaving. The ICD can provide dual-chamber back-up pacing to protect against bradycardia, which may have caused the syncope. The use of electrophysiological testing in patients with underlying coronary artery disease has changed over the years. Now we have evidence proving that ICDs are required for primary prevention of ventricular tachycardia and ventricular fibrillation for patients who have a reduced left ventricular ejection fraction and heart failure symptoms irrespective of syncope. These data are based on a variety of multi-center controlled clinical trials demonstrating the advantage of an ICD irrespective of any particular symptoms. Electrophysiologic testing can help evaluate sinus node dysfunction, conduction system disease, and the presence of supraventricular and ventricular arrhythmias, but there are issues regarding sensitivity and specificity of the test dependent on the population. Electrophysiological testing is still indicated in patients with syncope who have structural heart disease, even if the left ventricular ejection fraction exceeds 0.35. This is particularly true if there is evidence for conduction system disease, as patients with bundle branch block and structural heart disease with preserved ventricular function are at risk for ventricular arrhythmia and conduction block. ICDs are indicated for syncope patients with structural heart disease who have inducible ventricular tachycardia, even if the ejection fraction is over 0.40. For patients with syncope who do not have structural heart disease but do have sustained monomorphic ventricular tachycardia, ablation without an ICD is preferable. It is important to realize that several forms of ventricular tachycardia can masquerade as idiopathic ventricular tachycardia when indeed it is not. Consider the presence of arrhythmogenic right ventricular dysplasia, for example. In some cases, further evaluation utilizing a cardiac MRI scan may be useful. Electrophysiologic testing may not be useful in specific conditions that may lead to cardiac arrest and syncope, such as catecholaminergic ventricular tachycardia, idiopathic ventricular fibrillation, Long QT syndrome, Brugada syndrome, and other causes. Our patient did well after the ICD implant. He did have recurrent atrial fibrillation, but since he was not clearly symptomatic from this, rate control and anticoagulation were chosen instead of attempting to maintain sinus rhythm. He is now functional and has not had recurrent syncope. The electrophysiology study can be a powerful tool to diagnose the cause for syncope. For our patient, the electrophysiology test unleashed the tiger. It provided several potential important arrhythmic mechanisms for syncope so we could prevent recurrent syncopal episodes. It also allowed us to properly prescribe appropriate and potentially life-saving device therapy.