Spontaneous Onset of Atrioventricular Nodal Reentrant Tachycardia With High Grade Intranodal Block
A 45-year-old man with no significant medical history presented with exertional palpitations. A diagnostic electrophysiological study demonstrated a supraventricular tachycardia with a cycle length of 330 ms (180bpm), prominent electrical alternans, a short RP interval, and P-wave morphology consistent with retrograde atrial activation of the atrioventricular (AV) node (Figure 1). The mechanism of the tachycardia was determined to be AV nodal reentrant tachycardia (AVNRT) as proven by: (1) concentric retrograde atrial activation, (2) reproducible termination with ventricular premature extrastimuli not reaching the atrium, (3) no atrial advancement with delivery of premature ventricular beats delivered in the tachycardia during His refractoriness, (4) variable retrograde ventriculo-atrial conduction and unchanged tachycardia cycle length during ventricular premature beats, and (5) persistence of tachycardia with AV block (2 to 5 demonstrate that neither the ventricle or the atrium were required for the tachycardia to persist). An intracardiac recording of the tachycardia is shown in Figure 2.
During the study, we observed spontaneous initiation of tachycardia associated with transient complete intranodal block and followed by high grade intranodal block (Figure 3). Retrograde atrial activation continued regularly at the tachycardia cycle length (Figure 4). A 12-lead ECG obtained shortly after demonstrated 2:1 AV conduction, followed by spontaneous reversion to more typical 1:1 AV relationship (Figure 5). After radiofrequency ablation between the os of the coronary sinus and the tricuspid annulus (the AV node “slow pathway” region), the patient has had no recurrent symptoms.
The editor of Images in Cardiovascular Medicine is Hugh A. McAllister, Jr, MD, Chief, Department of Pathology, St Luke’s Episcopal Hospital and Texas Heart Institute, and Clinical Professor of Pathology, University of Texas Medical School and Baylor College of Medicine.
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