Techniques for improving cardiac performance with implantable devices.

A variety of pacing techniques are available to improve cardiac performance in patients who have bradyarrhythmias. These approaches include the preservation of AV synchrony and rate responsiveness, whereby pacing rate is varied according to some physiologic marker such as the atrial rate. New rate responsive pacemakers utilize other sensors to govern pacing rate and these units may monitor QT interval duration, respiratory rate, activity, venous oxygen saturation, temperature, or pH. Additional sensors are presently being investigated and prototype stroke volume and pressure monitoring devices should be available in the near future. All of these approaches require clinical evaluation and their eventual widespread application must be preceded by thorough studies of benefit, risk, and cost.