Evaluation of extent of shortening versus velocity of shortening at the endocardium and midwall in hypertensive heart disease

with the transmission of the monitor). This type of monitor has been shown previously to be accurate and reliable in nonpacemaker patients.2,3 Our study shows the monitor to reflect accurately the heart rate in patients with pacemakers, even with maximum unipolar output. In 2 patients, double counting occurred for just a few seconds immediately after the pacemaker was programmed to maximum output in unipolar mode. In all other patients, the monitors were able to discern between the QRS and the pacemaker spike in both VVI and DDD mode. No double counting occurred when the pacemakers were programmed at the usual clinical setting; double counting occurred only at high unipolar output in just 2 patients and for just a few seconds. The only other problem with sensing (and therefore heart rate display) occurred in a patient with atrial fibrillation and intermittent pacing at high unipolar output, when the intrinsic QRS complexes were not counted. This finding can be explained by an error detection algorithm incorporated into the microprocessor program, designed to reject artifactual signals, which presumably rejected the intrinsic complexes due to their low amplitude compared with the pacing spike or paced QRS complex. One limitation of the study is that the heart rate comparisons were performed with the patients at rest. It may be that during dynamic exercise, when rapid changes in heart rate occur, heart rate readings could be less precise, although probably not to a significant degree.4 Other limitations are the small sample size and that most of the patients had pacemakers from 1 manufacturer (Medtronic). Our results apply to this particular brand of heart rate monitors, and it is possible that other brands could affect pacemakers differently.