Acute and chronic haemodynamic effects of biventricular pacing and of switching to different pacing modalities in heart failure patients

Long-term outcomes of cardiac resynchronization therapy by left ventricular ejection fraction

AIMS

Despite our prior report suggesting heart failure (HF) risk reduction from cardiac resynchronization therapy with defibrillator (CRT-D) in mild HF patients with higher left ventricular ejection fraction (LVEF > 30%), data on mortality benefit in this cohort are lacking. We aimed to assess long-term mortality benefit from CRT-D in mild HF patients by LVEF > 30%.

METHODS AND RESULTS

Among 1274 patients with mild HF and left bundle branch block enrolled in MADIT-CRT, we analysed long-term effects of CRT-D vs. implantable cardioverter defibrillator (ICD) therapy only, and reverse remodelling to CRT-D (left ventricular end-systolic volume percent change ≥ median at 1 year), on all-cause mortality and HF for the LVEF ≤ 30% and LVEF > 30 subgroups using Kaplan-Meier and Cox analyses. During long-term follow-up, CRT-D vs. ICD was associated with reduction in all-cause mortality in both patients with LVEF > 30% and LVEF ≤ 30% [hazard ratio (HR) 0.47, 95% confidence interval (CI) 0.25-0.85, P = 0.036 vs. HR 0.69, 95% CI 0.49-0.98, P = 0.013, interaction P = 0.261]. The efficacy of CRT-D vs. ICD only to reduce HF was similar in those with LVEF above and below 30% (HR 0.36, 95% CI 0.35-0.61, P < 0.001 vs. HR 0.46, 95% CI 0.35-0.61, P < 0.001; interaction P = 0.342). Patients with CRT-D-induced reverse remodelling had significant mortality reduction when compared to ICD, with either LVEF > 30% or LVEF ≤ 30% (HR 0.17 and 0.39), but no mortality benefit was seen in patients with less reverse remodelling. HF events, however, were reduced in both CRT-D-induced high and low reverse remodelling vs. ICD only, in both LVEF subgroups.

CONCLUSIONS

In MADIT-CRT, left bundle branch block patients with higher LVEF (> 30%) derive long-term mortality benefit from CRT-D when exhibiting significant reverse remodelling.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov ID NCT00180271, NCT01294449, and NCT02060110.

A mechanistic investigation into how long-term resynchronization therapy confers ongoing cardiac functional benefits and improved exercise capacity

The exact mechanisms underpinning the longer term benefits of cardiac resynchronization therapy (CRT) were not fully understood. It was still unclear whether there was any ongoing functional benefit conferred by the partial resynchronization of ventricular contraction. To resolve this, a randomized controlled double-blind crossover trial was conducted to investigate the impact of temporary cessation of CRT on cardiac function both at rest and during peak exercise. Fifteen patients with severe heart failure and a CRT device implanted at least 3 months previously were randomly assigned to have the CRT mode switched to either off or on during exercise tests with central hemodynamic measurements (including noninvasive cardiac output measured using rebreathing methods), then crossed over on separate days to the opposite CRT mode. There were no significant changes in hemodynamic variables at rest with either mode of CRT. When CRT was acutely turned off, there was 19% lower peak exercise cardiac power (2.10 +/- 0.46 vs 2.59 +/- 0.75 W; p <0.005), 6% lower mean arterial pressure (92 +/- 12 vs 98 +/- 13 mm Hg; p <0.05), and 11.5% lower peak cardiac output (10.4 +/- 1.9 vs 11.8 +/- 2.5 L/min; p <0.05). Exercise capacity was also diminished with lower peak oxygen uptake (15.7 +/- 4.3 vs 17.2 +/- 4.9 ml/kg/min; p <0.01) and shorter exercise duration (542 +/- 204 vs 587 +/- 212 seconds; p <0.05). These changes were seen without differences in peak respiratory exchange ratio and peak systemic vascular resistance. In conclusion, these observations provided evidence that after CRT, left ventricular resynchronization continued to confer cardiac functional benefits manifest during peak exercise, but imperceptible at rest.

Effects of cardiac resynchronization therapy on coronary blood flow: evaluation by transthoracic Doppler echocardiography

BACKGROUND

Relatively limited and conflicting data are available on the effects of cardiac resynchronization therapy (CRT) on coronary blood flow (CBF).

AIMS

To investigate changes in the left anterior descending coronary artery (LAD) flow under different CRT pacing modes by means of transthoracic Doppler echocardiography (TTE).

METHODS

Twenty-two responders to CRT (67+/-11 years) with idiopathic dilated cardiomyopathy underwent TTE assessment of LAD flow and Tissue Velocity Imaging during 4 programming modes: intrinsic conduction (IC), right ventricular pacing (RV), simultaneous biventricular pacing (BVP), BVP with left ventricular (LV) pre-activation.

RESULTS

Mean coronary flow velocity (CFV) was increased by simultaneous BVP (p=0.0063 vs. IC) and BVP with LV pre-activation (p<0.0001 vs. IC; p=0.027 vs. simultaneous BVP). Peak CFV and LAD flow velocity/time integral were highest during BVP with LV pre-activation. A reduction in septal-to-lateral delay and an increase in peak systolic velocity in the basal septum were observed during simultaneous BVP and BVP with LV pre-activation.

CONCLUSIONS

In CRT responders with idiopathic dilated cardiomyopathy, an increase in LAD flow, assessed by TTE, was observed during simultaneous BVP and BVP with LV pre-activation. This was associated with an improvement in regional myocardial contraction and a decrease in intraventricular dyssynchrony.

How, why, and when may atrial defibrillation find a specific role in implantable devices? A clinical viewpoint

This viewpoint article discusses the potential for incorporation of atrial defibrillation capabilities in modern multi-chamber devices. In the late 1990s, the possibility of using shock-only therapy to treat selected patients with recurrent atrial fibrillation (AF) was explored in the context of the stand-alone atrial defibrillator. The failure of this strategy can be attributed to the technical limitations of the stand-alone device, low tolerance of atrial shocks, difficulties in patient selection, a lack of predictive knowledge about the evolution of AF, and, last but not least, commercial considerations. An open question is how atrial defibrillation capability may now assume a specific new role in devices implanted for sudden death prevention or cardiac resynchronization. For patients who already have indications for implantable devices, device-based atrial defibrillation appears attractive as a "backup" option for managing AF when preventive pharmacological/electrical measures fail. This and several other personalized hybrid therapeutic approaches await exploration, though assessment of their efficacy is methodologically challenging. Achievement of acceptance by patients is an essential premise for any updated atrial defibrillation strategy. Strategies that are being investigated to improve patient tolerance include waveform shaping, pharmacologic modulation of pain, and patient-activated defibrillation (patients might also perceive the problem of discomfort somewhat differently in the context of a backup therapy). The economic impact of implementing atrial defibrillation features in available devices is progressively decreasing, and financial feasibility need not be a major issue. Future studies should examine clinically relevant outcomes and not be limited (as occurred with stand-alone defibrillators) to technical or other soft endpoints.

Cardiac resynchronization therapy in clinical practice: need for electrical, mechanical, clinical and logistic synchronization

Considering the relatively short history of cardiac resynchronization therapy (CRT), the amount of available evidence of efficacy is impressive, and effectiveness studies are now required. Transfer of our experimentally gained knowledge into the real world raises issues that call for synchronization among the many specialists involved in chronic heart failure (CHF) management and CRT decision making. From an economic perspective, the demonstrated ability of CRT to reduce hospitalizations could help ease the burden on health systems derived from the growing incidence of CHF. Recent American College of Cardiology/American Heart Association guideline revisions should encourage a synchronized approach to rational deployment of CRT in selected patients. Nevertheless, current QRS criteria for CRT candidacy do not directly address the key issue of identification of patients with a pacing-correctable mechanical dyssynchrony (and in clinical trials, 25-30% of implanted patients did not respond to CRT). Echocardiography could become an important adjunct (or even an alternative) to QRS duration for patient selection; routine implementation would require use of straightforward, reproducible measurements, possibly obtainable on standard equipment. Echocardiography could also help optimize site location, although this would not eliminate lead placement problems. A series of issues remain open for investigation, including the potential of CRT in patients with atrial fibrillation, impact of devices with defibrillation ability, effects of electrical/pharmacological tailoring, need for confirmation that efficacy of CRT extends into the long term and possible use of CRT in mild CHF. Interdisciplinary synchronization in the various phases of CRT (screening, proposing, implementing, optimizing and monitoring) should eventually help develop a coordinated system for patient referral.

Changes in pulse pressure variability during cardiac resynchronization therapy in mechanically ventilated patients

INTRODUCTION

The respiratory variation in pulse pressure (PP) has been established as a dynamic variable of cardiac preload which indicates fluid responsiveness in mechanically ventilated patients. The impact of acute changes in cardiac performance on respiratory fluctuations in PP has not been evaluated until now. We used cardiac resynchronization therapy as a model to assess the acute effects of changes in left ventricular performance on respiratory PP variability without the need of pharmacological intervention.

METHODS

In 19 patients undergoing the implantation of a biventricular pacing/defibrillator device under general anesthesia, dynamic blood pressure regulation was assessed during right ventricular and biventricular pacing in the frequency domain (power spectral analysis) and in the time domain (PP variation: difference between the maximal and minimal PP values, normalized by the mean value).

RESULTS

PP increased slightly during biventricular pacing but without statistical significance (right ventricular pacing, 33 +/- 10 mm Hg; biventricular pacing, 35 +/- 11 mm Hg). Respiratory PP fluctuations increased significantly (logarithmically transformed PP variability -1.27 +/- 1.74 ln mm Hg2 versus -0.66 +/- 1.48 ln mm Hg2; p < 0.01); the geometric mean of respiratory PP variability increased 1.8-fold during cardiac resynchronization. PP variation, assessed in the time domain and expressed as a percentage, showed comparable changes, increasing from 5.3% (3.1%; 12.3%) during right ventricular pacing to 6.9% (4.7%; 16.4%) during biventricular pacing (median [25th percentile; 75th percentile]; p < 0.01).

CONCLUSION

Changes in cardiac performance have a significant impact on respiratory hemodynamic fluctuations in ventilated patients. This influence should be taken into consideration when interpreting PP variation.