Brownlee R R, Neff P H, Tyers G F
Med Instrum. 1978 Mar-Apr;12(2):94-9.
New ventricular synchronous demand (VVT) pacemaker functions have been developed that provide improved performance in electromagnetic interference (EMI) environments and improved sensing of ventricular premature contractions. All previous ventricular synchronous pacemakers had an inherent design conflict between choosing the optimal (relatively long) input refractory interval needed for limiting the maximum pulse delivery rate and choosing the optimal (relatively short) input refractory interval (sensing dead time) following either a sensed or paced cardiac contraction. The necessary compromise resulted in a device that in the presence of EMI, stimulated at a rate (approximately 150 ppm) which was dangerously fast for certain patients, yet was insensitive to early poststimulation (400 to 500 msec) premature ventricular contractions, resulting in a risk of T-wave stimulation. Partly because of these deficiencies, the VVT function has not been widely employed by the medical profession: instead, the ventricular inhibited (VVI) pacemaker has evolved as the treatment of choice for the cardiac patient with intermittent heart block, even though total inhibition by certain EMI radiators is a potentially serious problem. New VVT structures have been developed that allow control separation of the maximum EMI discharge rate and the sensing refractory interval by employing independent input and output refractory intervals. New low-power digital devices provide building blocks applicable to the developed architectures.
新型心室同步按需（VVT）起搏器功能已被开发出来，其在电磁干扰（EMI）环境中性能得到改善，对室性早搏的感知能力也有所提高。以往所有的心室同步起搏器在选择限制最大脉冲发放率所需的最佳（相对较长）输入不应期与选择在感知或起搏心脏收缩之后的最佳（相对较短）输入不应期（感知盲区）之间存在内在的设计冲突。这种必要的折衷导致了一种装置，在存在电磁干扰时，它以对某些患者来说危险地快的速率（约150次/分钟）进行刺激，但对刺激后早期（400至500毫秒）的室性早搏不敏感，从而产生T波刺激的风险。部分由于这些缺陷，VVT功能尚未被医学界广泛采用：相反，心室抑制（VVI）起搏器已发展成为间歇性心脏传导阻滞心脏病患者的首选治疗方法，尽管某些电磁干扰辐射器的完全抑制是一个潜在的严重问题。已开发出新型VVT结构，通过采用独立的输入和输出不应期，实现了最大电磁干扰放电率和感知不应期的控制分离。新型低功耗数字设备为适用于已开发架构提供了组件。
