Atrioventricular Nodal Reentrant Tachycardia Disguised as Atrial Fibrillation: Expect the Unexpected in EP

In this brief case report, authors from the Florida Hospital Zephyrhills describe an unexpected finding during one of their EP cases.

Case Description:

A 53-year-old female was referred from a physician’s clinic and admitted for syncope after experiencing palpitations. The palpitations lasted about 30 minutes to 1 hour, occurring 2-3 times per week. She has had 3 syncopal episodes in 3 months. The ECG showed normal sinus rhythm (NSR) with left atrial enlargement and premature atrial complexes. An event monitor was utilized and consequently showed several episodes of supraventricular tachycardia with p-wave morphology, which was undistinguishable. The cycle length varied from 220 to 280 milliseconds (ms). The tracings appear most likely to be atrial tachycardia/atrial fibrillation. Propafenone (Rhythmol) 225 mg twice daily was started and ablation therapy was discussed with the patient. Upon arrival to the hospital, the patient was in NSR and prepped for atrial fibrillation ablation. Once in the EP lab, the patient was induced into a tachycardia with catheter manipulation with a cycle length of 380 ms and regular. The septal ventriculo-atrial (VA) time was less than 60 ms. Sensed premature ventricular complexes (PVCs), or PVC on His, were placed, which did not advance the tachycardia or the subsequent cycle length. Impairment of the ventricle resulted in VAV response. The tachycardia was persistent and degenerated into atrial fibrillation (AF). Corvert (ibutilide) 1 mg was administered to convert the patient to sinus rhythm. The tachycardia was then induced with decremental atrial burst pacing from 400 ms to 300 ms. The tachycardia was not inducible with single or double atrial extra stimuli. Atrio-ventricular nodal effective refractory period (AVNERP) was atrial limited to 600/400 ms and demonstrated no clear jump. The atrial effective refractory period (AERP) was measured at 600/280 ms. VA conduction was present and concentric; the VA Wenkebach cycle length was measured at 330 ms. The patient intrinsically altered her rhythm from AVNRT to AF to sinus rhythm on several occasions. When in AF, the atrial cycle length varied around 210 ms with a rate-dependant right bundle branch block (RBBB). At this point, the AF ablation procedure was aborted and an AVNRT ablation was undertaken. A 4 millimeter (mm) ablation catheter was utilized to ablate the slow pathway region. In the 2-month follow-up visit to the clinic, the patient has not had any reoccurrence of syncope, palpitations, or tachycardia.

Discussion:

This case is a good reminder of the unexpected findings in EP. As staff members, these types of challenging studies bring about the motivation to want to learn more about EP. As we discovered upon researching our findings after the case was complete, “paroxysmal atrial fibrillation is often misdiagnosed and patients may erroneously be considered for pulmonary vein isolation.”¹ It is also worth noting and exemplified in our patient that “AVNRT is an uncommon AF trigger seen more frequently in younger patients.”²