Case Report A 32-year-old male was referred to the electrophysiology clinic for evaluation of a recent onset of dizziness that occurred while he was upright and was generally associated with exertion. This especially concerned him since he was working as a bricklayer. During one episode at work, he found himself down on the floor but was not sure if he actually passed out. Episodes occurred once every few weeks and had been occurring for several months. He was taking no specific medications and was otherwise in good health, but did smoke one pack of cigarettes per day and drank four to six beers daily on the weekend. On physical examination, his blood pressure was 145/88. His heart rate was 64 bpm and regular. He was modestly overweight, with distribution of fat consistent with a beer belly. The examination was otherwise unremarkable except for trace pedal edema. A 12-lead ECG showed sinus rhythm, rate 60, with a left bundle branch block. There were no previous ECGs immediately available. Due to our concerns about his presentation, an echocardiogram and a perfusion scan were performed. The left ventricular ejection fraction was 38% without evidence for valvular heart disease. The left ventricle was mildly dilated but not hypertrophied. A rest and exercise Sestamibi scan showed no perfusion defect. He was able to exercise to stage 4 of the Bruce protocol without any ST-T changes. A Holter monitor showed asymptomatic short episodes of Wenckebach block at heart rates at 100 bpm. What would you do next? Discussion Patients who complain of episodic dizziness, palpitations and syncope are commonly referred for electrophysiology evaluation. The proper evaluation can be challenging but, in this case, an aggressive approach was taken due to his symptoms, the presence of left bundle branch block, and evidence for structural heart disease, which was probably related to non-ischemic cardiomyopathy. A proper evaluation of symptoms in patients with LV dysfunction is important, as these may represent potentially serious and recurrent arrhythmias or even lead to cardiovascular collapse and ultimately death. It was not completely clear if this patient had syncope or not, but he did have recurrent, debilitating dizziness that compelled us to proceed further. We did not have an explanation for his syncope or dizziness despite the asymptomatic Wenckebach on the Holter monitor. Even though an implantable loop recorder may document a symptomatic arrhythmia, it was not recommended as this patient was at risk of having a serious, life-threatening arrhythmia. Similarly, proceeding directly to tilt table testing was not recommended. For patients with a left bundle branch block and impaired ventricular function, cardiac electrophysiology testing is warranted, especially if there is no immediate need to proceed to defibrillator implantation. In this case, as episodes of dizziness were distributed over a six-month period and the most recent episode was a few weeks before presenting to the clinic, immediate hospitalization was not recommended. Instead, he was scheduled for outpatient cardiac electrophysiology testing. In recent times, electrophysiologists often forgo electrophysiology testing for patients with syncope who have evidence for impaired ventricular function. When there is a presence of structural heart disease with a low ejection fraction, based on accepted criteria, such patients may be directly implanted with a cardioverter defibrillator (ICD). However, this patient did not meet any criteria for an ICD as he had no demonstrable heart failure, he had a left ventricular ejection fraction exceeding 35%, there was no history of long-standing ventricular dysfunction, and he was not otherwise medically treated for the structural heart disease. We proceeded with a complete electrophysiology study. During that study, spontaneously but more reproducibly with atrial pacing and isoproterenol, the following phenomenon was noted (Figure 1). No other abnormalities were seen. The patient had AV Wenckebach block below the AV node. The block was below the initial part of the His bundle. Intra-Hisian Wenckebach periodicity was seen with further progressive delay in conduction below the distal common His or right bundle. The electrophysiology study (Figure 1) showed normal sinus rhythm. The first and second beats were associated with split His potentials indicating intra-Hisian disease. Therefore, the conduction disease is not only within the His bundle, but below it as well. Wenckebach periodicity can occur below the AV node and is more likely when conduction system disease is present in the His Purkinje system, as was the case in our patient. Such patients often present with a history of exercise-related symptoms because heart block increases with increasing sinus rate when catecholamine levels are higher and AV conduction via the AV node is facilitated. More rapid bombardment of the His-Purkinje system leads to greater block due to conduction system abnormalities and increases the refractory period of the His Purkinje system. This is in contradistinction to AV Wenckebach in the AV node. It is important to note that a complete electrophysiology study was performed. There were no supraventricular or ventricular tachycardias induced. In patients like this with non-ischemic cardiomyopathy and His Purkinje disease, a complete electrophysiology study must still be performed since inducible tachyarrhythmias, such as bundle branch reentry tachycardia and other tachycardias, may be the cause of symptoms. This patient s cardiomyopathy was treated with a beta-blocker and an ACE inhibitor. He was counseled to stop smoking and stop drinking. In addition, his truncal obesity was a concern to us, as this also increases his risk of death. He was also educated about the risks of obesity on coronary artery disease and heart failure. He was scheduled to meet with a dietician to start a weight loss program, but instead agreed to begin a fad diet instead. Due to his symptoms and the Wenckebach block in the His Purkinje system, a permanent dual chamber pacemaker was placed. We were not compelled to collect more information from an endless loop recorder or an implantable loop recorder to document spontaneous episodes, as this would not have altered our management plan. He did not meet criteria for an ICD, and certainly did not meet criteria at this point for a CRT device. This case demonstrates several conundrums associated with evaluating patients presenting with dizziness. Following a structured and well thought-out plan while eliminating the possibilities at each step will help the clinician arrive at the most likely diagnosis. In follow-up, his ejection fraction improved and he denied any further symptoms. He maintains an active lifestyle and continues to work as a brick layer to support his family. He also recently became the proud father of a baby girl.