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  • Clinical symptoms consist of the

    2019-06-19

    Clinical symptoms consist of the pacemaker syndrome, including palpitations and hemodynamic instability, as in our case. The definitive management of RNRVAS requires sufficient time for the atrial tissue to recover from the refractory period. Barold et al. reviewed several general modes that could prevent RNRVAS [1]. First, the atrial escape interval must be prolonged to allow the atrial myocardium to recover. Second, the lower Urolithin A rate should be decreased or the lower rate increased. Third, the sensor-driven upper rate should also be decreased. Lastly, the AV delay must be shortened. In addition, a higher base rate is effective for suppressing atrial fibrillation. However, some of these management options are not clinically appropriate. Other algorithms to prevent RNRVAS have also been suggested; however, to our knowledge, automatic switching between AAI and DDD has not yet been reported. Furthermore, ablation of a retrograde pathway, which involves maintaining RNRVAS, may be a therapeutic option, provided that the retrograde pathway is not the AV nodal fast pathway, as determined from the EPS. The mechanism by which RNRVAS is prevented via automatic mode switching between AAI and DDD involves the termination of the inappropriate synchronous atrial and ventricular pacing mode using an AV conduction check. The MVP mode (Medtronic, Minneapolis, MN, USA) [6,7] is one such switching mode. During a sequential atrial and ventricular pacing rhythm in the MVP mode, an AV conduction check is scheduled every 1, 2, 4, and 8min for up to 16h following a transition from AAI to DDD. The AV conduction check is temporary, consists of only 1 beat, and uses an AAI pacing mode to monitor for conducted ventricular sensing. In this case, during RNRVAS, the scheduled AV conduction check in the MVP mode allowed both atrial and ventricular sensing, which did not initiate retrograde VA conduction because the AV node had not recovered from the refractory period (Fig. 4). Hence, the RNRVAS was terminated. In addition, the MVP mode has other algorithms, including a dynamic atrial refractory period and postventricular premature beat option, which can prevent RNRVAS given that the atrial escape interval is prolonged after a non-conducted P wave or ventricular premature beat. To suppress atrial fibrillation, a higher rate of atrial pacing with a dual-chamber pacing mode and a long AV delay, a relatively fast lower rate, or both has recently been applied in clinical situations. Overdrive pacing over intrinsic atrial activity may reduce paroxysmal atrial fibrillation by affecting the pattern of atrial depolarization and suppressing premature atrial beats. However, an increase in the cumulative proportion of right apex ventricular pacing is associated with an increased risk of death and heart failure, most likely through ventricular desynchronization and hemodynamic deterioration [8]. It is difficult to prevent unnecessary right ventricular pacing in patients with a dual-chamber ICD with prolonged settings for the AV delay alone. Thus, there are many possible clinical situations where RNRVAS might arise. In this case, atrial pacing prevented atrial fibrillation; hence, we maintained atrial pacing. However, AV-sequential and RNRVAS ventricular pacing led to hemodynamic instability and deterioration. To prevent unnecessary ventricular pacing, including RNRVAS with atrial pacing, the MVP mode was employed to provide the AAI or AAIR mode for monitoring AV conduction, and to provide an automatic switching to DDD or DDDR mode when the AV block persisted beyond a single dropped ventricular beat [4]. The MVP mode successfully addresses a high rate of atrial pacing and consequently prevents unnecessary ventricular pacing, including both RNRVAS and AV sequential pacing.
    Conclusion
    Conflict of interest
    Introduction Failure of an implantable cardioverter defibrillator (ICD) to deliver therapy for sustained ventricular tachycardia (VT) or ventricular fibrillation (VF) can result in fatality. Recently, there has been great concern over Riata lead insulation breaches. There have been reports of insulation breaches with or without externalization of conductors in the Riata family of leads [1–7]. There is also considerable debate about how to manage patients with an electrically silent Riata lead malfunction with or without a fluoroscopically detected insulation breach. We report a case of an apparently normal ICD lead that failed to deliver shock during high-voltage shock testing.