Statistical analysis of pacemaker follow up data. Rate stability and reliability

In a rate stable pacemaker, pacemaker rate reflects battery voltage level and should remain constant or be slightly depleted with time in a linear fashion until failure occurs. Linear regression techniques are therefore particularly suited to the analysis of pacemaker rate data. Data on model 8114/8114A Starr Edwards pacemakers followed at the University of Oregon Health Sciences Center were studied. For a given pacemaker both the slope of the regression line and the standard deviation about the regression line are proportional to the original rate. Natural indices of rate depletion and rate stability for each pacemaker can therefore be calculated by dividing the slope and the standard deviation, respectively, by the intercept of the corresponding regression line. This model pacemaker has a small average standard deviation so that significant variations from the line of regression, indicating impending pulse generator failure, can be detected in spite of random fluctuations. Emergency and prophylactic replacements can therefore be kept to a minimum so that pulse generator lifetime is maximized. Success in extending pulse generator longevity can be measured by actuarial techniques, which show this pacemaker to have a median battery depletion time of 38 months and a median replacement time of 35 months.