Performance of implantable cardiac rhythm management devices.

Our data represent use, follow-up, and management decisions from eight independently functioning centers and most importantly, actuarial survival of ICRMD's that have been implanted for a sufficient time period to allow assessment of time versus failure. General patterns of possible target durations for adequate performance for present or future generations of similar clinical devices may be suggested by the data that we have presented. However, it would be inappropriate to conclude from these data that any presently implanted ICRMD would have a particular functional reliability. Furthermore, these data only summarized device hardware performance and cannot and must not be used to determine either short-term or long-term individual patient status, management, or outcome.

Performance of implantable cardiac rhythm management devices.

Our data represent use, follow-up, and management decisions from seven independently functioning centers and most importantly, actuarial survival of ICRMDs that have been implanted for sufficient time period to allow assessment of time versus failure. General patterns of possible target durations for adequate performance for present or future generations of similar clinical devices may be suggested by the data that we have presented. However, it would be inappropriate to conclude from these data that any presently implanted ICRMD would have a particular functional reliability. These data, furthermore, only summarized device hardware performance and cannot and must not be used to determine either short-term or long-term individual patient status, management, or outcome.

An exponential formula for heart rate dependence of QT interval during exercise and cardiac pacing in humans: reevaluation of Bazett's formula.

A new exponential formula to characterize the human RR-QT relation was evaluated in comparison with Bazett's formula in 16 subjects: 10 healthy, normal men (ages 18 to 30 years) who exercised on a stationary bicycle, and 6 patients (ages 50 to 80 years; 2 women and 4 men) with rate-programmable VVI pacemakers whose rates were changed by an external programmer. The RR and QT intervals for heart rate in the range of 50 to 180 beats/min were measured from electrocardiographic tracings recorded at a paper speed of 100 mm/s. The data from each subject were fitted separately by 4 formulas by an appropriate regression analysis using a statistical package program: (F1) QT = A1 - B1*Exp(-k1*RR); (F2) QT = A2[1-Exp-(-k2*RR)]; (F3) QT = A3* square root (RR) + B3; and (F4) QT = A4* square root (RR), where all A, B, and k are regression parameters. The relative goodness of fit of data by the 4 formulas was assessed by the mean-squared residual and the Akaike Information Criterion using Wilcoxon signed-ranks tests. This analysis confirmed that F1 is the best model among the formulas tested and F4 (Bazett's formula) is the least acceptable for both exercised and paced groups. The deviations from Bazett's formula were more striking for the paced group than for the exercised group, as reflected by the mean-squared residual values for F4 (715 +/- 86 for the paced group vs 384 +/- 41 for the exercised group, p less than 0.005).(ABSTRACT TRUNCATED AT 250 WORDS)

Optimal resources for implantable cardiac pacemakers. Pacemaker Study Group.

In this document, the 1974 Inter-Society Commission for Heart Disease Resources (ICHD) report, Implantable Cardiac Pacemakers, has been revised and updated to emphasize the increased complexity of present-day pacing, to propose realistic guidelines for various aspects of pacing practivce, and to identify the resources needed for delivery of this important mode of health care. The first section of the report describes the several types of pacemakers currently available, how they function, and how and to what purpose they may be modified through noninvasive programming. Recommendations are given for a modified and updated version of the widely accepted ICHD code for identification of pacing modes. The emphasis of the second section of the report is on physical and personnel resources. Matters considered in some depth include the training and qualification of the various medical, technical, and paramedical specialists involved in an implantation procedure; requirements for, and methods of achieving, short and long-term surveillance of pacemaker patients; and the role of the hospital, the manufacturers, and the FDA in this new era of complex dual-chamber, multiprogrammable pacemakers.

Optimal resources for implantable cardiac pacemakers.

In this document, the 1974 Inter-Society Commission for Heart Disease Resources (ICHD) report, Implantable Cardiac Pacemakers, has been revised and updated to emphasize the increased complexity of present-day pacing, to propose realistic guidelines for various aspects of pacing practice, and to identify the resources needed for delivery of this important mode of health care. The first section of the report describes the several types of pacemakers currently available, how they function, and how and to what purpose they may be modified through noninvasive programming. Recommendations are given for a modified and updated version of the widely accepted ICHD code for identification of pacing modes. The emphasis of the second section of the report is on physical and personnel resources. Matters considered in some depth include the training and qualification of the various medical, technical, and paramedical specialists involved in an implantation procedure; requirements for, and methods of achieving, short- and long-term surveillance of pacemaker patients; and the role of the hospital, the manufacturers, and the FDA in this new era of complex dual-chamber, multiprogrammable pacemakers.

Ventricular refractory periods in relation to rate and test-site VT intervals in anesthetized and conscious dogs: a canine model for conscious state measurements.

The functional relationship of ventricular effective refractory period (ERP) with basic cycle length (BCL) of stimulated ventricular depolarization and VT intervals of test-site unipolar ventricular electrograms were studied in five conscious and eight anesthetized (sodium pentobarbital, 30 mg/kg) open-chested dogs. The range of BCLs studied was 300 to 1000 ms, achieved through ventricular stimulation following chemically-induced complete AV block. In the conscious animal model developed for this study, two-to-four ventricular electrode leads were exteriorized and the ventricular rate was maintained by an implanted programmable VVI pacemaker. In all animals studied, the BCL-ERP relation was closely represented by the empirical equation ERP = A-B.Exp(-k.BCL), and the VT-ERP relation over the same range of BCLs was linear: ERP = C + D.VT. The correlation coefficients were in the range of 0.991 to 0.999. The mean values of the parameters in the above equations determined by the appropriate non-linear or linear regression analysis showed significant differences between the two groups of animals studied. In three conscious animals a strong linear correlation between the test-site VT intervals and simultaneously measured QT intervals measured from the lead II surface electrogram was demonstrated (r = 0.993 to 0.998). For a fixed site of stimulation, the morphology of ventricular depolarization complexes as well as the corresponding T-waves remained essentially unaltered with BCL for both myocardial and surface electrograms. The possible applications of developed canine model and the results of the present study include: (1) the study of the rate-dependent effects of cardioactive drugs on ventricular electrophysiology and, (2) the improved design of electronic refractory periods of rate programmable pacemakers.

A digital module for cardiac pacemaker assessment.

The accuracy of a digital pacemaker testing module incorporated into a digital recording electrocardiograph has been tested against two other methods of waveform recording. Measurements of rate (pulse interval), pulse width, pulse amplitude and ratio of trailing edge to the leading edge amplitude were found to be highly accurate. The pulse shapes were faithfully recorded. The practical clinical use of the method is discussed.

Clinical experience with a programmable pacemaker.

As part of a study to evaluate a new programmable pacemaker, 15 patients received lithium-powered R-wave inhibited, unipolar pulse-generators (CPI Model 0505). Five were initial implants (Group I) and 10 were pulse generator replacements (Group II). The follow-up period ranged from 1 to 18 months (mean 11 months). There were 5 deaths unrelated to the pacemaker. Three instances of pacemaker failure were identified and were characterized by a sudden loss of pacemaker output. THe malfunction, traced to a 10 kHz timing crystal, has been corrected in subsequently manufactured pulse-generators. In 11 patients, the pacemakers were programmed at a pulse width which was twice the threshold determined at 3 months. Four were programmed at 0.1 ms, three at 0.2 ms and four at 0.4 ms. Although no complications were seen in patients programmed at 0.1 ms pulse width, it might be advisable to leave pacemakers at 0.2 ms or greater for chronic pacing in patients with a pulse width threshold at 0.05 mg.