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A man in his late 50s with a history of remote coronary artery bypass grafting presented with unstable angina and underwent percutaneous coronary intervention with a drug-eluting stent. He was discharged and prescribed ticagrelor, 90 mg twice daily, in addition to his home regimen of aspirin and metoprolol tartrate. Three months later, he experienced worsening exertional dyspnea and had multiple episodes of syncope. He had no history of syncopal episodes or arrhythmias. His baseline transthoracic echocardiogram results demonstrated normal systolic function and no significant valvular disease. Ambulatory electrocardiogram (ECG) monitoring results showed 31 episodes of high-grade atrioventricular (AV) block (AVB), with ventricular pauses ranging from 3.0 to 13.0 seconds occurring during the day and at night (Figure 1). Among them, 4 episodes were associated with presyncope.
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D. Switch ticagrelor to clopidogrel
The key to the correct diagnosis is in the detailed analysis of the ECG rhythm strip, which elucidates a plausible mechanism of bradyarrhythmia in this case. The initial part of the rhythm demonstrates normal P and QRS wave morphologies with normal intervals, followed by a simultaneous prolongation of the P-P and P-R intervals manifesting as sinus bradycardia and AVB with a 10-second pause (Figure 2). The pause leads to junctional and ventricular escape beats followed by a resumption of a normal sinus rhythm and AV nodal (AVN) conduction. This pattern is a result of the transient suppression of sinus node (SN) activity and AVN conduction. Such a phenomenon usually suggests a sudden increase in parasympathetic activity or vagal tone because SN and AVN are innervated by vagal efferent fibers rather than structural abnormalities of SN and AVN.1,2
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Corresponding Author: Takahiro Tsushima, MD, University Hospitals Cleveland Medical Center, Department of Medicine, Case Western Reserve University, 11100 Euclid Ave, Cleveland, OH 44106 (email@example.com).
Published Online: September 18, 2019. doi:10.1001/jamacardio.2019.3306
Conflict of Interest Disclosures: None reported.
Additional Contributions: We thank Mohammed Osman, MD, Case Western Reserve University, for discussions regarding this article. He did not receive any compensation for his contribution.
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