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A patient in their 80s with a history of hypertension controlled with Dyazide presented to the emergency department with 1 episode of syncope. The patient reported a weird sensation of feeling hot and light-headed and felt they should lie down but suddenly awoke on the floor with considerable head and left shoulder pain. The patient also had a few near-fainting spells in the week prior to this index syncopal event. In the emergency department, the patient’s vital signs were stable without considerable orthostatic changes in blood pressure and heart rate. Results of laboratory tests, including serum electrolyte levels and cardiac enzymes, were normal. Cranial computed tomographic findings revealed no acute pathologic changes, and echocardiogram findings showed mild concentric left ventricular hypertrophy with preserved left ventricular systolic function. Two 12-lead electrocardiograms (ECGs) obtained on arrival to the emergency department and the day following admission are shown in the Figure.
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Because the patient was taking Dyazide, which contains the diuretics hydrochlorothiazide and triamterene, for treatment of hypertension, the differential diagnosis of syncope in this elderly patient should include orthostatic hypotension as a potential cause. However, this diagnosis is not supported because the patient had long-term use of Dyazide but experienced frequent presyncopal or syncopal episodes only within a short time frame without considerable orthostatic hypotension on physical examination.
The striking finding pointing to the cause of syncope is a change from LAFB to LPFB in the setting of RBBB. Right bundle-branch block with stable LAFB on ECG without clinical symptoms is a relatively common type of bifascicular block in adults (1%-1.5%),1 of which only a small percentage of people will develop clinically significant atrioventricular (AV) block at a rate of 1% to 2% per year.2,3 However, changing between LAFB and LPFB in the presence of preexisting RBBB, a form of trifascicular block,4,5 suggests a rare situation in which permanent conduction block in the right bundle branch is accompanied by intermittent block between 2 fascicules of the left bundle branch. From a mechanistic point of view, trifascicular block indicates His-Purkinje system diseases involving both right and left bundle branches that often herald the development of high-degree or complete AV block. Low-intensity exercise could immediately result in AV block in these patients.6 According to the recent European Society of Cardiology guidelines on cardiac pacing and cardiac resynchronization therapy, pacemaker implantation is recommended as a class I indication (level C) for patients with trifascicular block with or without symptoms.5 It should be emphasized that an electrophysiology study to determine if the patient requires pacemaker implantation under this situation is not necessary.
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CME Disclosure Statement: Unless noted, all individuals in control of content reported no relevant financial relationships. If applicable, all relevant financial relationships have been mitigated.
Corresponding Author: Gan-Xin Yan, MD, PhD, Lankenau Medical Center, Wynnewood, PA 19096 (firstname.lastname@example.org); Tong Liu, MD, PhD, Tianjin Key Laboratory of Ionic-Molecular Function of Cardiovascular Disease, Department of Cardiology, Tianjin Institute of Cardiology, Second Hospital of Tianjin Medical University, Tianjin 300211, People’s Republic of China (email@example.com).
Published Online: February 21, 2022. doi:10.1001/jamainternmed.2021.8528
Conflict of Interest Disclosures: Dr Yan is supported by the Sharpe-Strumia Research Foundation. No other disclosures were reported.
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