Hemodynamic aspects of biventricular pacing in heart failure

Abstract

Background and aims: Biventricular pacing or cardiac resynchronization therapy (CRT) is an established treatment option for selected heart failure (HF) patients. We aimed at evaluating acute and longer-term hemodynamic effects of different pacemaker programmings in CRT patients. For the latter purpose, 10 CRT patients also received an implantable hemodynamic monitor (IHM), allowing for long-term hemodynamic monitoring during ambulatory periods.

Study I The hemodynamic effects of varying the atrioventricular delay (AVD) within a clinical relevant range (± 40 ms) were investigated in 27 CRT patients in different body positions and during exercise. Nine patients with 3rd degree AV block, and left ventricular ejection fraction ≥ 45% served as controls. A small but significant reduction in cardiac output (CO) was found when AVD was shortened, while prolongation had no effect. The magnitude of individual CO response to AVD modifications was larger in CRT patients compared with controls, differed substantially between individuals and was associated with left atrial size.

Study II We evaluated the accuracy of an algorithm based on pressure waveform characteristics from the IHM to track CO changes. The proposed method (CO IHM) was compared to a non-invasive reference method (inert gas rebreathing, RB) in 12 HF patients. The median inter-patient correlation coefficient (r = 0.83) as well as bias (-0.39 L/min, 11%) and limits of agreements (± 1.57 L/min) were found to be acceptable and appeared favorable compared with 2 clinically accepted methods: Doppler echocardiography and impedance cardiography. CO IHM was subsequently applied in study III and IV for the determination of CO.

Study III We investigated the acute hemodynamic effects of different biventricularly paced heart rates (HRs) in 10 CRT patients who had also received an IHM. Increasing the paced HR in the range 60-100 bpm reduced cardiac filling pressures and increased CO. Moreover, a positive force frequency relationship, usually blunted in HF patients, was observed in the right ventricle.

Study IV The hemodynamic effects of programming different basic HRs (60 or 80 bpm) were investigated during 2-week periods in a single-blind cross-over study. Hemodynamic data was continuously recorded with the IHM and at the end of each study period patients were assessed by quality of life (QoL), a 6-minute walk test (6MWT) and Brain Natriuretic Peptide (BNP). During pacing at 80 bpm compared with 60 bpm, filling pressures were reduced and CO was increased. However, during the period of pacing at 80 bpm there was a trend of increased filling pressures and stroke volume over time suggestive of a potential gradual deterioration with increased HR. QoL-score, the 6MWT and BNP-levels were unchanged comparing the 2 study periods.

Conclusions Varying the AVD within a clinical relevant range in CRT patients has little effect on CO. However, the CO response varies largely between individual patients, suggesting that AVD optimization should be performed routinely not to miss those who may gain a potentially important hemodynamic benefit. A simple IHM algorithm can track CO changes in HF patients with reasonable accuracy. This method was subsequently used to demonstrate beneficial short-term effects of pacing with an elevated HR both at rest and during periods of ambulatory living. Considering the potentially large hemodynamic and clinical effects of differential HR programming in CRT patients, this issue demands further evaluation.