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  • In our clinic the intracardiac electrogram

    2019-05-20

    In our clinic, the intracardiac electrogram recorded by the ICD showed repetitive non-reentrant ventriculoatrial synchrony (RNRVAS), which was associated with hypotension and chest discomfort (Fig. 1). We suspected that the RNRVAS caused the hypotension; therefore, we performed electrophysiologic and hemodynamic studies. A 24-h ambulatory electrocardiograph also indicated RNRVAS that was initiated by either a premature ventricular or atrial beat. The EPS indicated that a single ventricular extrastimulus from the right ventricular apex reproducibly induced and termed the RNRVAS. Under the setting for DDIR, the b catenin inhibitor rate was lowered to 70bpm and 80bpm, and RNRVAS was induced repetitively. The shortened AV delay caused heart failure due to increasing ventricular pacing. Other setting changes such as prolonging the lowered rate interval were not effective in preventing RNRVAS. During RNRVAS, the patient\'s systolic blood pressure decreased by approximately 20mmHg (60–70mmHg) compared to that during the atrial pacing ventricular sensing rhythm (80–90mmHg, Fig. 2). During the atrial pacing ventricular pacing rhythm, his blood pressure also decreased compared to that during the ventricular sensing rhythm. In addition, the site of earliest retrograde atrial activation during RNRVAS was recorded on the electrograms of the His bundle (Fig. 3). Because this atrial activation involved only a single retrograde pathway with a decremental conduction property, we considered it to be retrograde VA conduction occurring via the fast AV nodal pathway. The elective replacement indicator was triggered in the ICD; therefore, we replaced the ICD with another device (7278 PROTECTA®, Medtronic, Minneapolis, MN, USA), to manage the ventricular pacing mode and to provide functional AAI/R pacing that was equipped with a safe dual-chamber ventricular support that would allow automatic switching between AAI and DDD mode pacing. The parameters after replacement were as follows: MVP mode (AAI, 80bpm and DDD, 80–120bpm), paced AV delay 180ms, and PVARP 320ms. Cumulative percentages of pacing and sensing were atrial pacing (AP)–ventricular sensing (VS) 97.3%, AP 99.1%, and ventricular pacing 1.8%. Thus far, no report of RNRVAS following ICD replacement has been reported. After this replacement, the patient\'s hypotension improved.
    Discussion RNRVAS is becoming a well-known pacemaker for arrhythmia, as DDD or DDI modes have often been selected in clinical situations [1–4]. This arrhythmia occurs in cases of intact retrograde VA conduction. Furthermore, the pacemaker must be programmed with a sufficiently long PVARP so that retrograde conduction does not induce endless loop tachycardia. One final prerequisite is a sufficiently high base rate to ensure a relatively short atrial escape interval and an even shorter interval from the retrograde atrial depolarization, thus rendering the atrial tissue physiologically refractory. Functional undersensing occurs when the retrograde P wave is not sensed because it coincides with the PVARP. Because of the relatively high rate and the failure to reset the atrial timing cycle, atrial pacing is delivered while the atrial myocardium is physiologically refractory, resulting in functional atrial non-capture. Functional undersensing and non-capture play critical roles in maintaining RNRVAS. After the ineffective atrial pacing, the AV interval times out, and a ventricular paced event occurs, by which time, the AV node and atrial myocardium are fully recovered, facilitating retrograde conduction. Thus, RNRVAS is caused by the sequence of a combination of an AV paced rhythm with repeated functional atrial undersensing and non-capture [5]. In the present case, RNRVAS onset was recorded (Fig. 1). The pattern was consistent with ventricular pacing from the right ventricular ICD lead, which led to retrograde conduction in PVARP and produced an atrial refractory period in the atrium. Thus, programmed atrial pacing during the atrial refractory period caused a functional atrial non-capture. This repeated AV synchronous rhythm, RNRVAS has been described previously.