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  • There are few learning points that can be

    2019-05-09

    There are few learning points that can be derived from this case. While VDD is an acceptable mode in young patients, one XL184 should be cautious of using this mode in elderly patients with sick sinus syndrome, unless retrograde VA conduction is absent. A single PVC can trigger a ventricular paced rhythm with retrograde p waves that will persist until the sinus rate increases, which may be limited in patients with sinus node dysfunction. This is especially true in patients with intact but slow VA conduction and those with slow intra-atrial conduction due to longer time taken from retrograde atrial depolarization to reach atrial lead electrode. Potential for RNRVAS can be unmasked during atrial lead threshold evaluation in patients with complete XL184 block. Here, pacing the atrium at a faster rate in DDD mode may initiate RNRVAS once atria loose capture. In addition, subsequent atrial capture will not resume even at suprathreshold levels due to RNRVAS, and it may lead to a false diagnosis of atrial lead dysfunction. To minimize the risk of VA synchrony, lower basal rate and shorter AV delay should be programmed for patients with VDD pacer. Similar programming is recommended for patients with complete heart block and those with a biventricular implantable cardioverter defibrillator (ICD) to prevent RNRVAS. NCAP is an algorithm available in DDD mode (pacemaker or ICD) and is primarily intended to prevent triggering of atrial tachyarrhythmia by delaying atrial pacing within the atrial myocardial refractory period. With NCAP, a sensed atrial event occurring in the PVAR period starts NCAP period, typically 300ms, during which atrial pacing is inhibited. If lower rate pacing is scheduled to occur during this period, the VA interval is extended until the NCAP expires. Furthermore, when an atrial pacing is delayed by NCAP, subsequent paced AV delay is shortened to maintain a stable ventricular rate. This delay allows the atrial myocardium to recover and ensure capture. Occasionally, other algorithms such as extension of atrial escape interval after PVC and synchronous atrial pacing upon detection of PVC can be utilized to prevent this type of arrhythmia.
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