Introduction

In patients with aortic valve surgery, syncopal episodes are usually due to complete atrioventricular (AV) block. Damage to the conduction system in this group of patients is commonly due to surgical trauma, hematoma, extending calcification and ischemia. This case reveals an unusual mechanism of syncope in a patient with aortic valve replacement. The diagnosis was undertaken using an implantable loop recorder (ILR).

Case Report

A 55-year-old male patient experienced 3 syncope episodes within a year. All episodes occurred at daytime. One episode occurred while he was sitting and the two others, in upright position. He had no prodromal symptoms. In all of the episodes, he became conscious immediately after syncopal attack. There were no neurological symptoms or loss of sphincter control. In the last episode, he had a nose fracture. Except for the fracture, he was asymptomatic.

Upon admission, he was conscious and was able to give his full history. He had aortic valve replacement (AVR) with a bileaflet metallic prosthetic valve 3 years ago and he has been on oral anticoagulant medication. His physical and neurological examination was normal except for the nasal fracture and prosthetic valve sounds. A 12-lead ECG revealed normal sinus rhythm with a rate of 76 bpm.

Transthoracic and transesophageal echocardiography revealed normal prosthetic aortic valve function. Carotid sinus massage, 24-hour Holter monitoring and tilt-table test showed no abnormalities. Electrophysiological examination showed normal sinus and AV nodal functions. (AH interval: 78 msn, HV interval: 47 msn, basal cycle length: 760 msn, corrected sinus node recovery time: 515 msn, AV node Wenckebach interval: 300 msn) With ventricular stimulation, no ventricular tachycardia (VT) was induced. A neurologic workup with cranial and carotid imaging was also normal. To determine the cause of the syncopal attacks, an ILR (Reveal Plus Medtronic Inc. Minneapolis) was implanted subsequently.

Four months after implantation, the patient would awaken from sleep with a feeling of nausea, lightheadedness and sweating. The ILR revealed a sinus pause of 31 seconds interrupted by a junctional beat after 20 seconds. (Figure 1) A dual chamber pacemaker with lower rate 60 bpm and a long fixed AV delay (275 msc) was implanted. The patient had no syncopal episodes during one-year follow-up. Assessment of the pacemaker data showed predominantly intrinsic rhythm (88%) with atrial pacing at 10% and atrial sensing and ventricular pacing at 2%.

Discussion

Complete AV block is a known complication of aortic valve surgery and may also be seen in various aortic root diseases (1- 5). Surgical trauma to the conduction system during AVR has been described in autopsy reports on subjects who died after surgery (6). Apart from surgical trauma; ischemia, dissecting hematomas, and extending calcification or granulomas may affect the conduction system. New conduction defects were also found in 33% of patients after AVR, with left branch bundle block (BBB) being the most commonly encountered anomaly (7). A new and persistent BBB acquired after AVR is associated with an increased adverse event rate (8).

Recurrent episodes of unexplained syncope may be due to many factors. Electrophysiology studies can be useful for evaluating sinus node function, AV nodal and His-Purkinje system conduction. The diagnostic yield of electrophysiology studies in patients with a structurally normal heart and a normal ECG is low (1% ventricular tachycardia, 10% bradycardia) whereas in patients with organic heart disease, the yield is over 50% (21% ventricular tachycardia, 34% bradycardia) (9). Patients with an abnormal ECG also have a significant diagnostic yield (17% ventricular tachycardia, 19% bradycardia). A negative electrophysiology study does not necessarily exclude an arrhythmic cause of syncope and has a poor predictive value in nonischemic cardiomyopathy, long QT syndrome, mitral valve prolapse, and the Brugada syndrome (10). The use of implantable loop recorders leads to successful documentation of bradyarrhythmias in patients with previously unexplained syncope (11).

In our case, prolonged sinus arrest was the cause of the syncopal attacks. When bradycardic episode occurs before an episode of asystole, the cause of the asystole is attributed to an increased vagal tone. But the sudden onset of patients’ attacks and negative tilt-table test makes the diagnosis of neurally mediated syncope, unlikely.

This case study demonstrates that in patients with aortic valve replacement, AV block is not the only cause of syncope. ILRs are useful diagnostic tools for patients who exhibit infrequent symptoms and have normal results of conventional diagnostic tests.