Sensing and Detection

Reduction of Ventricular Oversensing Oversensing is defined as sensing of unintended nonphysiological signals or physiological signals that do not accurately reflect local depolarization.1 Nonphysiological signals usually arise from extracardiac electromagnetic interference. Electrical artifacts are a common cause of oversensing from leads with insulation failure or intermittent fracture resulting in make-break potentials. Physiological signals may be intracardiac (P, R, or T waves) or...

Inappropriate Detection Due to Oversensing

ICD sensing circuits are designed to be highly sensitive so that low amplitude EGM waveforms during fibrillation can be sensed adequately.5 As a result, oversensing of cardiac and noncardiac signals in ICDs occurs and is one of the major sources of inappropriate ICD therapy. Oversensing on the ventricular sensing channel of an ICD (ventricular oversensing) causes inappropriate VT VF detection due to overestimation of the true cardiac rate. Oversensing on the atrial sensing channel (atrial...

The Long List of Inventions and Observations that Led to the Pacemaker

Pulse Theory and Observations that Bradycardia Leads to Syncope Today physicians and athletes routinely measure the pulse. Although it is fairly simple to measure, especially compared to our now sophisticated imaging tools like magnetic resonance imaging, the pulse is still considered one of the vital signs. The knowledge that the pulse was a critical sign of health goes back to the ancient Egyptians. In 1875 George Ebers purchased an Egyptian scroll written in 1553 BC that described the...

Time Dependence of the Anodal and Cathodal Refractory Periods

Mehra et al.27 observed that immediately following implantation of a pacemaker the anodal refractory period was shorter than the cathodal refractory period, but after several weeks the cathodal refractory period became shorter than the anodal refractory period. Figure 14 suggests one hypothesis to explain this observation.28 After a pacemaker electrode is implanted, tissue adjacent to the electrode is healthy and excitable. However, within a few weeks a region of inexcitable scar tissue...