Biventricular Pacing in the Early Postoperative Period After Cardiac Surgery

Multidisciplinary approach to long-standing left bundle branch block with dyssynchrony and aortic stenosis: case report

Background

Cardiac resynchronization therapy (CRT) is recommended for patients with symptomatic heart failure in sinus rhythm with left ventricular ejection fraction (LVEF) ≤ 35%, QRS duration ≥ 150 ms, and left bundle branch block (LBBB) morphology. However, when severe left ventricular dysfunction and cardiogenic shock are present, treatment paradigms are often limited to palliative medical therapy or advanced therapies with durable left ventricular assist device or heart transplant as the functional and survival benefit of CRT in these patients remains uncertain.

Case summary

A 77-year-old white man with long-standing LBBB with dyssynchrony, severely reduced LVEF of 4%, and severe bicuspid aortic stenosis (AS) presented with worsening heart failure symptoms. After multidisciplinary heart team evaluation and pre-operative optimization, the patient underwent a surgical aortic valve replacement with simultaneous intraoperative initiation of CRT with pacemaker (CRT-P) and temporary mechanical circulatory support. Echocardiography at 44 days and 201 days post-discharge showed an LVEF of 29% and 40%, respectively.

Discussion

This case demonstrates that reverse remodelling and native heart recovery were successfully achieved in a patient with advanced structural heart disease, presenting with cardiogenic shock, through an early and aggressive approach involving multidisciplinary heart team evaluation, treatment of severe AS with surgical aortic valve replacement, prophylactic intraoperative initiation of temporary mechanical circulatory support, and early initiation of CRT-P.

Stroke Volume Optimization: Utilization of the Newest Cardiac Vital Sign: Considerations in Recovery from Cardiac Surgery

The hemodynamic monitoring landscape is rapidly evolving from pressure-based and static parameters to more blood flow-based and dynamic parameters. Consensus guidelines for cardiac surgery state that the pulmonary artery catheter is neither required nor helpful in most patients. In the meantime, critical care has been searching for the alternatives to the pulmonary artery catheter and protocols for use. Best available evidence for any protocol developed suggests the inclusion of stroke volume optimization to determine fluid responsiveness. Additional strategies to using stroke volume to optimize hemodynamics, including case studies, are discussed.

Feasibility of speckle-tracking echocardiography for assessment of left ventricular dysfunction after cardiopulmonary bypass

OBJECTIVES

Effects of temporary biventricular pacing after cardiopulmonary bypass are unpredictable, and the utility of speckle-tracking echocardiography in this setting is unclear. Accordingly, speckle-tracking analysis of transgastric echocardiograms taken during cardiac surgery was assessed as a potential tool to measure strain, synchrony, and twist as indices to predict response.

DESIGN

Prospective observational study, in part, with a randomized controlled study of temporary permanent biventricular pacing after cardiopulmonary bypass.

SETTING

Single-center study at university-affiliated tertiary care hospital.

PARTICIPANTS

Twenty-one cardiac surgery candidates with ejection fraction ≤40% and QRS duration ≥100 ms or who were undergoing double-valve surgery.

INTERVENTIONS

Transgastric views of the basal, midpapillary, and apical levels of the left ventricle were acquired before and after bypass.

MEASUREMENTS AND MAIN RESULTS

Midpapillary sections were analyzable in 38% of patients. The remainder had epicardial borders extending beyond the field of view (24%) or inadequate image quality (38%). Only 9% of basal or apical sections were analyzable. Midpapillary radial strain and synchrony changed insignificantly after bypass. Variation in fractional area change correlated with changes in radial strain (p = 0.041) but not with synchrony.

CONCLUSIONS

Intraoperative transgastric echocardiography is inadequate for speckle-tracking analysis with current techniques. Intraoperative predictors of temporary biventricular pacing response are lacking.

Short-term reduction in intrinsic heart rate during biventricular pacing after cardiac surgery: a substudy of a randomized clinical trial

BACKGROUND

The Biventricular Pacing After Cardiac Surgery trial investigates hemodynamics of temporary pacing in selected patients at risk of left ventricular dysfunction. This trial demonstrates improved hemodynamics during optimized biventricular pacing compared with atrial pacing at the same heart rate 1 and 2 hours after bypass and reduced vasoactive-inotropic score over the first 4 hours after bypass. However, this advantage of biventricular versus atrial pacing disappears 12 to 24 hours later. We hypothesized that changes in intrinsic heart rate can explain variable effects of atrial pacing in this setting.

METHODS

Heart rate, mean arterial pressure, cardiac output, and medications depressing heart rate were analyzed in patients randomized to continuous biventricular pacing (n = 16) or standard of care (n = 18).

RESULTS

During 30-second testing periods without pacing, intrinsic heart rate was lower in the paced group 12 to 24 hours after bypass (76.5 ± 17.5 vs 91.7 ± 13.0 beats per minute; P = .040) but not 1 or 2 hours after bypass. Cardiac output (4.4 ± 1.2 vs 3.6 ± 1.9 L/min; P = .054) and stroke volume (53 ± 2 vs 42 ± 2 mL; P = .051) increased overnight in the paced group. Vasoactive medication doses were not different between groups, whereas dexmedetomidine administration was prolonged over postoperative hours 12 to 24 in the paced group (793 ± 528 vs 478 ± 295 minutes; P = .013).

CONCLUSIONS

These observations suggest that hemodynamic benefits of biventricular pacing 12 to 24 hours after cardiopulmonary bypass lead to withdrawal of sympathetic drive and decreased intrinsic heart rate. Depression of intrinsic rate increases the apparent benefit of atrial pacing in the chronically paced group but not in the control group. Additional study is needed to define clinical benefits of these effects.

Effects of biventricular pacing on left heart twist and strain in a porcine model of right heart failure

BACKGROUND

Biventricular pacing (BiVP) improves cardiac output (CO) in selected cardiac surgery patients, but response remains variable, necessitating a better understanding of the mechanism. Accordingly, we used speckle tracking echocardiography (STE) to analyze BiVP during acute right ventricular pressure overload (RVPO).

MATERIALS AND METHODS

In nine pigs, the inferior vena cava (IVC) was snared to decrease CO and establish a control model. Heart block was induced, the pulmonary artery snared, and BiVP initiated. Echocardiograms of the left ventricular midpapillary level were taken at varying atrioventricular delay (AVD) and interventricular delay (VVD) for STE analysis of regional circumferential strain (CS) and radial strain (RS). Echocardiograms were taken of the left ventricular base, midpapillary, and apex during baseline, IVC occlusion, and each BiVP setting for STE analysis of twist, apical and basal rotations, CS, RS, and synchrony. Indices were correlated against CO with mixed linear models.

RESULTS

During IVC occlusion, CO correlated with twist, apical rotation, RS, RS synchrony, and CS (P < 0.05). During RVPO with BiVP, CO only correlated with RS synchrony and CS (P < 0.05). During AVD and VVD variations, CO was associated with free wall RS (P < 0.008). CO correlated with septal wall CS during AVD variation and free wall CS during VVD variation (P < 0.008).

CONCLUSIONS

In an open chest model, twist, RS, RS synchrony, and CS analyzed by STE may be noninvasive surrogates for changes in CO. During RVPO, changes in RS synchrony and CS with varying regional strain contributions may be the primary mechanism in which BiVP improves CO. Lack of correlation of remaining indices may reflect postsystolic function.

In silico study of the haemodynamic effects induced by mechanical ventilation and biventricular pacemaker

In silico modeling of the cardiovascular system (CVS) can help both in understanding pharmacological or pathophysiological process and in providing information which could not be obtained by means of traditional clinical research methods due to practical or ethical reasons. In this work the numerical CVS was used to study the effect of interaction between mechanical ventilation and biventricular pacemaker by haemodynamic and energetic point of view. Starting from literature data on patients with intra and/or inter-ventricular activation time delay and treated using biventricular pacemaker, we used in silico simulator to analyse the effects induced by mechanical ventilatory assistance (MVA). After reproducing baseline and CRT conditions, the MVA was simulated changing the mean intrathoracic pressure value. Results show that simultaneous application of CRT and MVA yields a reduction of cardiac output, left ventricular end-diastolic and end-systolic volume when positive mean intrathoracic pressure is applied. In the same conditions, when MVA is applied, left ventricular ejection fraction, mean left (right) atrial and pulmonary arterial pressure increase.