Barold S S, Abe H, Nagatomo T
Electrophysiology Institute, Broward General Hospital, Fort Lauderdale, Florida, USA.
Pacing Clin Electrophysiol. 2000 Oct;23(10 Pt 1):1527-31. doi: 10.1046/j.1460-9592.2000.01527.x.
Paradoxical shortening of the paced AV delay (atrial paced-ventricular paced or Ap-Vp interval) was observed at rest in the DDD and DDDR modes in three patients with implanted CPI Vigor DR pacemakers programmed with a long AV delay and a relatively narrow difference between the lower and upper rates. This behavior is related to the VA extension algorithm designed to prevent the sensor-driven atrial pacing rate from exceeding the programmed upper rate whenever a sensed conducted QRS complex continually follows an atrial stimulus. We found that this algorithm also becomes manifest at rest and may cause shortening of the Ap-Vp intervals. The VA extension algorithm is best conceptualized in terms of a separate atrial upper rate that functions on exercise and at rest. The atrial and ventricular upper rates are equal but the atrial upper rate is initiated by an atrial-paced or sensed event and the ventricular upper rate is initiated by a paced or sensed ventricular event. Under certain circumstances delay in the release of the atrial stimulus Ap to conform to the atrial upper rate interval produces variable abbreviation of the paced AV (Ap-Vp) delays with resultant variation in the duration of the atrial escape intervals despite fundamental ventricular-based lower rate timing.
在三名植入了CPI Vigor DR起搏器的患者中，当以长房室延迟以及较低和较高心率之间相对较窄的差异进行编程时，在DDD和DDDR模式下静息时观察到起搏房室延迟（心房起搏-心室起搏或Ap-Vp间期）出现矛盾性缩短。这种现象与VA延长算法有关，该算法旨在防止每当感知到的传导QRS波群持续跟随心房刺激时，传感器驱动的心房起搏率超过编程的上限心率。我们发现，该算法在静息时也会表现出来，并可能导致Ap-Vp间期缩短。VA延长算法最好从一个独立的心房上限心率来理解，它在运动和静息时都起作用。心房和心室的上限心率相等，但心房上限心率由心房起搏或感知事件启动，心室上限心率由起搏或感知的心室事件启动。在某些情况下，为符合心房上限心率间期而延迟释放心房刺激Ap会导致起搏房室（Ap-Vp）延迟出现可变缩短，尽管基于心室的基本较低心率定时不变，但心房逸搏间期的持续时间会因此而变化。
