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Challenges in Clinical Electrocardiography
October 2018

Syncope With Bifascicular Block Due to Infra-Hisian Wenckebach Conduction Abnormality

Author Affiliations
  • 1Division of Cardiovascular Medicine, University of California (Davis) Medical Center, Sacramento
JAMA Intern Med. 2018;178(10):1408-1410. doi:10.1001/jamainternmed.2018.3951

A man in his 70s with a history of type 2 diabetes and hypertension presented with syncope. He reported symptoms while ambulating with sudden onset of weakness and diaphoresis followed by loss of consciousness for several minutes. There was no reported seizure activity, and he denied preceding chest pain, palpitations, or shortness of breath. After regaining consciousness, he returned to baseline.

In the emergency department, the patient was alert and asymptomatic. Electrocardiogram (ECG) showed normal sinus rhythm, right bundle branch block (RBBB), and left anterior fascicular block (LAFB) (Figure 1). Vital signs included blood pressure, 151/83 mm Hg; heart rate, 72 beats per minute; respiratory rate, 18 per minute; and oxygen saturation, 98% while breathing ambient air. Orthostatic assessment revealed no significant decrease in blood pressure with sitting or standing. Physical examination, including cardiopulmonary and neurology screen, had normal results. Laboratory data revealed normal glucose, electrolytes, and serial cardiac troponin I of less than 0.02 ng/mL (reference range, <0.05 ng/mL; 1-to-1 correspondence with nanograms per liter). Transthoracic echocardiogram revealed a left ventricular ejection fraction of 55% with normal left ventricular wall motion and mild concentric left ventricular hypertrophy.

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    1 Comment for this article
    Louis Janeira |
    I don't agree with this statement, necessarily. Bifascicular block with prolonged PR interval indicates either intra-atrial conduction delay, AV node delay or infranodal delay. Based on surface ECG alone, it isn't possible to say for sure. AV node delay would be the most common, I realize. By your definition, there would never be TFB, as this would be the same as CHB. Your own case presentation makes my point. The PR interval seems to be just a bit over 200 ms and you proved the problem was infra nodal. The paced AH seems to be normal and constant (to my eye).