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Researchers find possible mechanism for unexplained syncope

Brignole M. J Am Coll Cardiol. 2011;doi:10.1016/j.jacc.2010.12.045.

Mehta N. J Am Coll Cardiol. 2011;doi:10.1016/j.jacc.2011.01.039.

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In a small population of men and women, idiopathic paroxysmal atrioventricular block led to a form of syncope currently unexplained in terms of known mechanisms.

The study included 18 patients (50% women; mean age, 55 years) who presented with unexplained syncope at four centers. At the time of presenting, all patients had normal baseline electrocardiogram; the absence of structural heart disease; and paroxysmal third-degree atrioventricular block with abrupt onset and absence of other rhythm disturbances before or during the block.

Researchers followed the patients for a mean of 4 years and found that in all of them, prolonged ECG monitoring indicated paroxysmal complete atrioventricular block with one or multiple consecutive pauses; they also documented multiple episodes of atrioventricular block in 11 patients. Additionally, during follow-up time, no patients developed permanent atrioventricular block or had further recurrences of syncope upon permanent cardiac pacing.

According to the researchers, if it had not been for the documentation of paroxysmal atrioventricular block at the time of syncope, the patients in the study would have probably been categorized as affected by an atypical form of neurally mediated syncope.

In an accompanying editorial, Niraj Mehta, MD, Maria Zildany Pinheiro Tavora, MD, and Carlos A. Morillo, MD, of the Syncope and Autonomic Dysfunction Unit, McMaster University – Hamilton Health Sciences, Hamilton, Ontario, Canada, said permanent pacemaker therapy may be the treatment of choice among these patients.

“More studies need to be performed to establish the true efficacy of this therapy, given the benign prognosis from the patients described by Brignole et al,” they said. “In true Holmesian deductive reasoning, it appears ‘elementary’ that we are presented with new evidence for idiopathic paroxysmal AV block as a potential cause of unexplained syncope, thereby unraveling another mystery in the syncope saga.”

Disclosure: Drs. Mehta, Tavora and Morillo report no relevant financial disclosures.

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