A man in his mid-50s with a history of mitral valve repair presented to the emergency department with complaints of recent-onset palpitation within the last hour. On physical examination, the patient showed a rhythmic tachycardia with a rate of 178 beats/min and blood pressure of 130/80 mm Hg. The 12-lead electrocardiogram (ECG) revealed a regular tachycardia with a rate of 178 beats/min; no obvious P waves were recognizable (Figure 1A). The QRS complexes displayed 2 different morphologies occurring with a definite allorhythmic distribution: pairs of beats exhibiting complete right bundle branch block (RBBB) and QRS duration of 140 milliseconds followed by a third beat with normal configuration and QRS duration of 70 milliseconds. This trigeminal variation in intraventricular conduction occurred without any change in cycle length and was maintained. Adenosine administration quickly slowed the ventricular rate allowing recognition of an atrial tachycardia with a rate of 178/min and a 2:1 atrioventricular (AV) ratio (Figure 1B).
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Atypical atrial flutter with RBBB aberration and conduction improvement every third beat resulting from concealed type I (Wenckebach) second-degree block in the right bundle branch with 3:2 ratio
C. Start treatment with low-molecular-weight heparin and amiodarone
The atrial rate during adenosine administration was identical to the ventricular rate during tachycardia, implying that the arrhythmia in Figure 1A reflects an atrial tachycardia with 1:1 AV conduction. The medical history strongly suggests a macroreentrant circuit (macroreentrant atrial tachycardia, also called atypical atrial flutter) developing around the atriotomy scar related to mitral valve surgery, possibly a left-sided atrial flutter such as mitral annular flutter. The R-R interval prolongation due to the shift from 1:1 to 2:1 AV ratio restored the normal right bundle branch conduction resulting in narrow QRS complexes. This supports an intermittent phase 3 RBBB. The most challenging issue in the tracing on presentation is the periodic disappearance of the RBBB aberration. The key to the correct diagnosis is the unexpected normalization of the QRS morphology occurring periodically, every third beat, despite constant cycle lengths.1- 4
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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: Vincenzo Carbone, MD, Outpatient Cardiology, via Europa, 84 S Giuseppe Vesuviano, Naples 80047, Italy (email@example.com).
Published Online: September 7, 2022. doi:10.1001/jamacardio.2022.2902
Conflict of Interest Disclosures: None reported.
Additional Contributions: We thank the patient for granting permission to publish this information.
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