Walk test at increased levels of heart rate in patients with dual-chamber pacemaker and with normal or depressed left ventricular function

Systemic peripheral vascular resistance as a determinant of functional cardiac reserve in response to exercise in patients with heart disease

Resting cardiac function is a poor indicator of functional cardiac reserve that is invoked during exercise. The objective of this study was to investigate the relationship between functional cardiac reserve and systemic vascular resistance (SVR) using an ambulatory radionuclide monitoring system (the Vest system) in patients with heart disease. The study population consisted of 29 patients (all male [mean +/- SD age, 63 +/- 10 years]), 23 with coronary artery disease, 3 with dilated cardiomyopathy, and 3 with hypertensive heart disease. All patients underwent cardiopulmonary stress testing using a ramped treadmill protocol and the Vest system. The anaerobic threshold (AT) was autodetermined using the V-slope method. Systemic vascular resistance was calculated using the mean blood pressure and cardiac output as determined using the Vest system parameters. All patients exercised beyond the AT until exhaustion. Resting left ventricular ejection fraction, peak ejection ratio, and peak filling ratio increased with the AT (P < .01 for all). Resting SVR decreased with the AT (P < .01). The percentage changes from rest to the AT in SVR correlated with those from rest to the AT in ejection fraction, peak ejection ratio, and peak filling ratio (r = -0.735, r = -0.510, and r = -0.697, respectively; P < .01). These findings indicate that SVR as recorded using the Vest system is a good determinant of functional cardiac reserve in patients with heart disease. Therefore, cardiopulmonary function testing combined with the Vest system is a good modality for the evaluation of functional cardiac reserve.

Pacing Evaluation-Atrial SUpport Study in Cardiac Resynchronization Therapy (PEGASUS CRT): design and rationale

BACKGROUND

Cardiac resynchronization therapy (CRT) has been demonstrated to be an effective heart failure (HF) therapy. All pivotal trials of CRT to date have used atrial-synchronous biventricular pacing wherein there is no or minimal atrial pacing. In clinical practice, however, physicians often program CRT devices to have atrial rate support pacing, either by increasing the lower rate limit or by activating the rate sensor.

OBJECTIVE

The purpose of this study is to evaluate the effect of empiric atrial support pacing in patients with HF who have received a CRT defibrillator (CRT-D) device.

METHODS

PEGASUS CRT is a multicenter, 3-arm, randomized clinical trial of approximately 1200 patients receiving a CRT-D device. For the first 6 weeks after implant, devices are programmed to DDD with a lower rate limit of 40 beats/min. At 6 weeks, patients are randomized to DDD-40, DDD-70, or DDDR-40. All randomized patients are followed for 1 year, and at each visit, mortality, HF events, quality of life, New York Heart Association class, and atrial and ventricular arrhythmic episodes are evaluated. An exercise substudy will also be conducted, enrolling a minimum of 375 patients. Patients in this substudy will complete 2 cardiopulmonary exercise tests to evaluate the effect pacing mode has on exercise capacity. This randomized controlled trial will address whether empiric atrial support pacing is of clinical benefit to patients with HF who receive a CRT-D device.

Haemodynamic effects of dual-chamber pacing versus ventricular pacing during a walk test in patients with depressed or normal left ventricular function

PURPOSE

Dual-chamber rate-modulated pacing provides haemodynamic benefits compared with ventricular pacing at rest, but it is unclear whether this also holds true during physical exercise in patients with heart failure. This study assessed the haemodynamic response to a walk test during dual-chamber pacing and ventricular pacing in patients with depressed or normal left ventricular (LV) function.

METHODS

Twelve patients with an LV ejection fraction <50% and 11 patients with an LV ejection fraction >or=50% underwent two randomised 6-min walk tests under dual-chamber rate-modulated pacing and ventricular pacing at a fixed rate of 70 beats/min. All patients had a dual-chamber pacemaker implanted for complete heart block. LV function was monitored by a radionuclide ambulatory system.

RESULTS

In patients with depressed LV function, the change from dual-chamber pacing to ventricular pacing induced a decrease in end-systolic volume at the peak of the walk test (P<0.05), with no difference in end-diastolic volume. As a consequence, higher increases in LV ejection fraction (P<0.0001) and stroke volume (P<0.01) were observed during ventricular pacing. No difference in cardiac output was found between the two pacing modes. In patients with normal LV function, the change from dual-chamber pacing to ventricular pacing induced a significant decrease in cardiac output (P<0.005 at rest and P<0.05 at the peak of the walk test).

CONCLUSION

Compared with dual-chamber rate-modulated pacing, ventricular pacing improves cardiac function and does not affect cardiac output during physical activity in patients with depressed LV function, whereas it impairs cardiac output in those with normal function.

Early and late effects of coronary artery bypass grafting on cardiac haemodynamics during daily physical activities in patients with coronary artery disease

This study investigated the early and late effects of coronary artery bypass grafting (CABG) on left ventricular (LV) function during different physical daily activities in patients with multivessel coronary artery disease (CAD). In ten patients with multivessel CAD, cardiac haemodynamics were assessed during a 6-min walk test and during stair climbing 8+/-2 days before (study 1) and 15+/-3 days (study 2) and 120+/-3 days (study 3) after CABG. LV function was monitored by an ambulatory radionuclide system. In study 1, the walk test induced a significant increase in relative end-diastolic volume (EDV) and end-systolic volume (ESV) and no change in LV ejection fraction as compared to rest. In both study 2 and study 3, EDV increased significantly and ESV was unchanged. As a consequence, LV ejection fraction rose from 48%+/-8% to 52%+/-10% and from 48%+/-7% to 51%+/-6%, respectively (both P<0.05). In study 1, stair climbing induced a significant increase in EDV and ESV and as a consequence LV ejection fraction decreased from 46%+/-8% to 42%+/-9% (P<0.05) as compared to rest. In both study 2 and study 3, EDV increased significantly whereas ESV did not change. As a consequence, LV ejection fraction rose from 48%+/-8% to 52%+/-7% and from 48%+/-8% to 51%+/-7%, respectively (both P<0.05). In conclusion, CABG has beneficial effects on cardiac performance during moderate or more intense physical activity in patients with multivessel CAD and these effects are due to improvement in systolic function. Radionuclide monitoring of LV function provides an objective method for quantitative evaluation of cardiac performance after CABG.