‘Let's Pause A Minute…And Think’ – Syncope Due to Prolonged Atrioventricular Block

A 67-year-old gentleman presented with a history of recurrent syncope with tremors and head injury. There were no other features in the history suggestive of obvious precipitants, and neither examination nor initial investigations suggested obvious causes. The leading differential was a seizure disorder. Subsequent investigations with electroencephalogram and magnetic resonance imaging of his brain were unremarkable. On subsequent cardiac evaluation, echocardiography revealed a structurally normal heart, and sinus rhythm with resting right bundle branch block was recorded on an electrocardiogram (ECG). A loop recorder was implanted to investigate for syncope of unclear etiology. Atrioventricular block and ensuing ventricular asystole of 66.6 seconds was captured, followed by return of intrinsic sinus rhythm (Figure). This was associated with his usual symptoms. Given recurrent episodes despite medical therapy, he underwent permanent pacemaker implantation, which abated his syncopal events. Syncope is a transient loss of consciousness due to cerebral hypoperfusion of various etiologies. A detailed history can narrow differential causes and assist greatly in determining appropriate investigations and management. This is important, as episodes can recur during work-up and might result in significant morbidity or mortality, such as intracranial hemorrhage from head injury. The causes of syncope can be broadly classified into neurally mediated reflex syncopal syndromes, orthostatic-related causes, cardiac syncope, or conditions that mimic syncope. Neurally mediated syndromes include neurocardiogenic syncope, carotid sinus syncope, or situational fainting such as post micturition or with coughing. Cardiogenic syncope includes arrhythmogenic causes or structural heart disease. Orthostatic-related causes may include autonomic dysfunction such as in diabetes or Parkinson disease. Finally, syncope mimics may consist of transient ischemic attacks, epilepsy, metabolic disorders, or intoxication. Our patient presented with features (ie, tremors) that suggested a seizure disorder. However, tremors in themselves are rather nonspecific. Cardiogenic syncope can be associated with involuntary muscle activity that can resemble tremors or seizure-like activity, and a significant proportion of patients can be misdiagnosed with seizure.1Zaidi A Clough P Cooper P Scheepers B Fitzpatrick AC Misdiagnosis of epilepsy: many seizure-like attacks have a cardiovascular cause.J Am Coll Cardiol. 2000; 36: 181-184Crossref PubMed Scopus (345) Google Scholar,2Bergfeldt L Differential diagnosis of cardiogenic syncope and seizure disorders.Heart. 2003; 89: 353-358Crossref PubMed Scopus (94) Google Scholar Pre-existing patient risk factors might increase the likelihood of cardiogenic syncope. In common with our case, patients older than 60 years are more likely to have cardiogenic syncope rather than syncope due to noncardiac causes. The initial ECG demonstrated interventricular abnormalities, which is more suggestive of cardiac syncope,3Sutton R Ricci F Fedorowski A Risk stratification of syncope: current syncope guidelines and beyond.Auton Neurosci. 2021; 238102929PubMed Google Scholar and is classified as a high-risk feature on evaluation of syncope.4Brignole M Moya A de Lange FJ et al.2018 ESC Guidelines for the diagnosis and management of syncope.Eur Heart J. 2018; 39: 1883-1948Crossref PubMed Scopus (943) Google Scholar Nonetheless, in this case, the cause of recurrent syncope was uncertain. The current guidelines recommend the use of an implantable loop recorder or cardiac monitor, particularly when an arrhythmogenic cause is suspected.4Brignole M Moya A de Lange FJ et al.2018 ESC Guidelines for the diagnosis and management of syncope.Eur Heart J. 2018; 39: 1883-1948Crossref PubMed Scopus (943) Google Scholar,5Shen WK Sheldon RS et al.Writing Committee Members2017 ACC/AHA/HRS guideline for the evaluation and management of patients with syncope: Executive summary: a report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines and the Heart Rhythm Society.Heart Rhythm. 2017; 14: e218-e254Abstract Full Text Full Text PDF PubMed Scopus (17) Google Scholar Various ambulatory devices provide cardiac event monitoring over wide-ranging periods, where longer duration monitoring is preferred if the diagnosis is elusive, while shorter duration monitoring, such as with a Holter monitor, would be reasonable if symptoms are frequent. Ultimately, extended monitoring by the loop recorder revealed the underlying cause, and appropriate intervention was instituted with good patient outcomes. In conclusion, careful consideration of the patient's risk factors and thorough initial investigation including an ECG may help prioritize investigations in the ambulatory setting. It is important to select cardiac event monitors of appropriate duration to investigate for recurrent syncope of uncertain cause.