Analysis of right ventricular function during bypass of the left side of the heart by afterload alterations in both normal and failing hearts

Outcomes With Phosphodiesterase-5 Inhibitor Use After Left Ventricular Assist Device: An STS-INTERMACS Analysis

BACKGROUND

Elevated right ventricular afterload following continuous-flow left ventricular assist device (CF-LVAD) may contribute to late right heart failure (LRHF). PDE5i (phosphodiesterase-5 inhibitors) are used to treat pulmonary hypertension and right heart dysfunction after CF-LVAD, but their impact on outcomes is uncertain.

METHODS

We queried Interagency Registry for Mechanically Assisted Circulatory Support from 2012 to 2017 for adults receiving a primary CF-LVAD and surviving ≥30 days from index discharge. Patients receiving early PDE5i (ePDE5i) at 1 month were propensity-matched 1:1 with controls. The primary outcome was the cumulative incidence of LRHF, defined using prevailing Interagency Registry for Mechanically Assisted Circulatory Support criteria; secondary outcomes included all-cause mortality and major bleeding.

RESULTS

Among 9627 CF-LVAD recipients analyzed, 2463 (25.6%) received ePDE5i and 1600 were propensity-matched 1:1 with controls. Before implant, ePDE5i patients had more severe RV dysfunction (13.1% versus 9.6%) and higher pulmonary vascular resistance (2.8±2.7 versus 2.2±2.4 WU), both P<0.001, but clinical factors were well-balanced after propensity-matching. In the unmatched cohort, ePDE5i patients had a higher 3-year cumulative incidence of LRHF, mortality, and major bleeding, but these differences were attenuated in the propensity-matched cohort: LRHF 40.8% versus 35.7% (hazard ratio, 1.14 [95% CI, 0.99-1.32]; P=0.07); mortality 38.6% versus 35.8% (hazard ratio, 0.99 [95% CI, 0.86-1.15]; P=0.93); major bleeding 51.2% versus 46.0% (hazard ratio, 1.12 [95% CI, 0.99-1.27]; P=0.06).

CONCLUSIONS

Compared with propensity-matched controls, adult CF-LVAD patients receiving ePDE5i had similar rates of LRHF, mortality, and major bleeding. While intrinsic patient risk factors likely account for more adverse outcomes with ePDE5i in the unmatched cohort, there is no obvious benefit of ePDE5i in the LVAD population.

Preoperative Right Heart Dysfunction and Gastrointestinal Bleeding in Patients with Left Ventricular Assist Devices

Gastrointestinal bleeding (GIB) is a common cause of morbidity among patients supported by left ventricular assist devices (LVADs). The aim of this study was to identify if pre-LVAD right ventricular (RV) dysfunction is associated with risk of GIB after LVAD implantation. Of 398 patients implanted with LVADs between July 2008 and July 2016, 130 (33%) developed GIB at a median of 2.6 months following LVAD implantation. Arteriovenous malformations (AVMs) were found in 42 (34%) GIB patients. Patients with GIB were older and more likely to have hypertension, diabetes, and ischemic cardiomyopathy. On pre-LVAD echocardiography, GIB patients had increased RV diastolic dimension (4.7 ± 0.8 vs. 4.4 ± 0.9 cm, p = 0.02), a higher rate of greater than mild tricuspid valve (TV) regurgitation (73 [60%] vs. 120 [47%], p = 0.006), and underwent TV repair more often (38 [30%] vs. 43 [16%], p = 0.0006) during LVAD implantation. After multivariable adjustment, preoperative greater than mild RV enlargement (hazard ratio [HR] 2.32, 95% CI 1.12-5.03; p = 0.03), TV regurgitation (HR 1.83, CI 1.02-3.44; p = 0.01), and TV repair (HR 3.76, confidence interval [CI] 1.02-4.44; p = 0.01) remained associated with risk of GIB. This finding was driven by the AVM-GIB subgroup. Preoperative RV enlargement and TV regurgitation are associated with post-LVAD AVM-related GIB.

Effect of left ventricular assist device implantation on right ventricular function: Assessment based on right ventricular pressure-volume curves

Right ventricular (RV) failure is significantly associated with morbidity and mortality after left ventricular assist device (LVAD) implantation. However, it remains unclear whether LVAD implantation could worsen RV function. Therefore, we aimed to investigate the effect of LVAD implantation on RV function by comparing RV energetics derived from the RV pressure-volume curve between before and after LVAD implantation. This exploratory observational study was performed between September 2016 and January 2018 at a national center in Japan. Twenty-two patients who underwent LVAD implantation were included in the analysis. We measured RV energetics parameters: RV stroke work index (RVSWI), which was calculated by integrating the area within the RV pressure-volume curve; RV minute work index (RVMWI), which was calculated as RVSWI × heart rate; and right ventriculo-arterial coupling, which was estimated as RV stroke volume/RV end-systolic volume. We compared RV energetics between before and after LVAD implantation. Although RVSWI was similar [424.4 mm Hg · mL/m² (269.5-510.3) vs. 379.9 mm Hg · mL/m² (313.1-608.8), P = 0.485], RVMWI was significantly higher after LVAD implantation [29 834.1 mm Hg · mL/m² /min (18 272.2-36 357.1) vs. 38 544.8 mm Hg · mL/m² /min (29 016.0-57 282.8), P = 0.001], corresponding to a significantly higher cardiac index [2.0 L/min/m² (1.4-2.2) vs. 3.7 L/min/m² (3.3-4.1), P < 0.001] to match LVAD flow. Right ventriculo-arterial coupling was significantly higher after LVAD implantation [0.360 (0.224-0.506) vs. 0.480 (0.343-0.669), P = 0.025], suggesting that the efficiency of RV performance improved. In conclusion, higher RVMWI with higher cardiac index to match LVAD flow and improved efficiency of RV performance indicate that LVAD implantation might not worsen RV function.

Preimplant Phosphodiesterase-5 Inhibitor Use Is Associated With Higher Rates of Severe Early Right Heart Failure After Left Ventricular Assist Device Implantation

Background Early right heart failure (RHF) occurs commonly in left ventricular assist device (LVAD) recipients, and increased right ventricular (RV) afterload may contribute. Selective pulmonary vasodilators, like phosphodiesterase-5 inhibitors (PDE5i), are used off-label to reduce RV afterload before LVAD implantation, but the association between preoperative PDE5i use and early RHF after LVAD is unknown. Methods and Results We analyzed adult patients from the INTERMACS registry (Interagency Registry for Mechanically Assisted Circulatory Support) who received a continuous flow LVAD after 2012. Patients on PDE5i were propensity-matched 1:1 to controls. The primary outcome was the incidence of severe early RHF, defined as the composite of death from RHF within 30 days, need for RV assist device support within 30 days, or use of inotropes beyond 14 days. Of 11 544 continuous flow LVAD recipients, 1199 (10.4%) received preoperative PDE5i. Compared to controls, patients on PDE5i had higher pulmonary artery systolic pressure (53.4 mm Hg versus 49.5 mm Hg) and pulmonary vascular resistance (2.6 WU versus 2.3 WU; P<0.001 for both). Before propensity matching, the incidence of severe early RHF was higher among patients on PDE5i than in controls (29.4% versus 23.1%; unadjusted odds ratio (OR), 1.32; 95% CI, 1.17-1.50). This association persisted after propensity matching (PDE5i, 28.9% versus control 23.7%; OR, 1.31; 95% CI, 1.09-1.57), driven by a higher incidence of prolonged inotropic support. Similar results were observed across a wide range of subgroups stratified by markers of pulmonary vascular disease and RV dysfunction. Conclusions Patients treated with preoperative PDE5i had markers of increased RV afterload and HF severity compared to unmatched controls. Even after propensity matching, patients receiving preimplant PDE5i therapy had higher rates of post-LVAD RHF.

Postoperative Care of the Cardiac Surgical Patient

The subspecialty of interventional cardiology began in 1977. Since then, the discipline of interventional cardiology has matured rapidly, particularly with regards to ischemic heart disease. As a result, more patients are undergoing percutaneous catheter interventional therapy for ischemic heart disease and fewer patients are undergoing surgical myocardial revascularization. Those patients referred for surgical revascularization are generally older and have more complex problems. Furthermore, as the population ages more patients are referred to surgery for valvular heart disease. The result of these changes is a population of surgical patients older and sicker than previously treated.

Can transventricular intracardiac impedance measurement discriminate haemodynamically unstable ventricular arrhythmias in human?

AIMS

To measure changes in transventricular impedance during arrhythmias.

METHODS AND RESULTS

Patients were studied during electrophysiological studies. A quadrapolar catheter was positioned at the right ventricular apex (RVA) and a decapolar catheter within the coronary sinus (CS). Transventricular impedance was measured by injecting a subthreshold biphasic rectangular pulse of 600 micro A between poles 1 of the CS catheter and pole 1 of the RVA catheter and the voltage measured between CS pole 10 and RVA catheter pole 4. Stroke impedance (SZ), surface ECG, intracardiac electrogram (IEGM), and invasive femoral artery blood pressure (FAP) were recorded. Twenty-eight patients were analysed, 5 with inducible, haemodynamically unstable ventricular tachycardia (VT) (HUSVT), 5 with stable VT (HSVT). During HUSVT, the SZ value reduced to 22% (range 0.15-0.32 P < 0.001) in comparison with sinus rhythm. For HSVT, the SZ value reduced to 58% (range 0.33-0.88) P < 0.01, significantly different from HUSVT (P < 0.01). There was a good correlation between reduction of SZ and arterial pulse pressure (PP) during arrhythmias (r = 0.95).

CONCLUSION

Changes in SZ strongly correlated with PP amplitude. Transventricular impedance fell significantly during unstable arrhythmias and may be useful as a sensor capable of haemodynamic discrimination.

Comparison of Electron Beam Computed Tomography With Magnetic Resonance Imaging in Assessment of Right Ventricular Volumes and Function

OBJECTIVE

Intraindividual comparison of right ventricular volumes and function using electron beam computed tomography (EBT) and magnetic resonance imaging (MRI).

METHODS

Twenty-seven patients with a known cardiac history were referred for evaluation of ventricular function parameters. The following standardized protocols were used: contrast-enhanced multislice mode EBT and gradient echo sequence MRI. Right ventricular end-diastolic volume (EDV), end-systolic volume (ESV), stroke volume (SV), and ejection fraction (EF) were calculated using a slice summation method. Interobserver variability was calculated.

RESULTS

The correlation between the 2 methods was: r = 0.901 for EDV, r = 0.938 for ESV, r = 0.823 for SV, and r = 0.953 for EF. Electron beam computed tomography overestimated EDV and ESV slightly when compared with MRI (P < 0.05). No significant differences (P > 0.05) were found between SV and EF. Mean values determined by EBT and MRI were as follows: 168.6 +/- 62.3 mL and 153.7 +/- 59.1 mL for EDV, 104.7 +/- 60.4 mL and 95.1 +/- 54.8 mL for ESV, 63.2 +/- 19.3 mL and 58.7 +/- 19.8 mL for SV, and 40.2% +/- 14.1% and 40.2% +/- 13.6% for EF, respectively. Interobserver variability ranged between 1.0% and 3.2%.

CONCLUSION

Electron beam computed tomography shows good agreement with a close correlation and an acceptable interobserver variability for right ventricular volumes and global function, with a small but significant overestimation of EDV and ESV when compared with MRI.

Effects of acute left ventricular unloading on right ventricular function in normal and chronic right ventricular pressure-overloaded lambs

OBJECTIVE

Right ventricular pressure overload occurs in several types of (congenital) heart disease, as well as in pulmonary disease. Clinical outcome in some of these patient groups might in part be related to left ventricular loading conditions. The effects of left ventricular unloading on the function of the hypertrophic right ventricle have not been studied. We aimed to study the effects of left ventricular unloading on right ventricular hemodynamics and contractility in an animal model of chronic right ventricular pressure overload.

METHODS

In lambs the pulmonary artery was chronically banded to increase right ventricular pressure to systemic levels. After 8 weeks, right ventricular contractility and hemodynamic function were assessed in these lambs, as well as in age-matched control animals, by using a combined pressure-conductance catheter in the right ventricle during baseline conditions and during complete bypass of the left ventricle.

RESULTS

In both groups acute left ventricular unloading significantly decreased left ventricular pressure to low levels while aortic pressure was maintained. In the right ventricle of the control group, both end-systolic and end-diastolic volumes increased with left ventricular unloading (P <.01) while end-systolic pressure was maintained. Cardiac output was unchanged despite decreased right ventricular contractility. In the banding group acute left ventricular unloading also decreased right ventricular contractility but increased cardiac output. During acute left ventricular unloading, diastolic stiffness was unchanged in the control group, whereas it was significantly decreased in the banding group.

CONCLUSIONS

Both in normal hearts and in hearts subject to chronic right ventricular pressure overload, acute left ventricular unloading decreases right ventricular contractility. Although no effects on cardiac output are encountered in normal hearts during left ventricular bypass, cardiac output is improved in right ventricular pressure-overloaded hearts, most likely related to improved right ventricular diastolic compliance.

Right ventricular support for off-pump coronary artery bypass grafting studied with bi-ventricular pressure--volume loops in sheep

OBJECTIVES

Tilting the heart during off-pump coronary artery bypass grafting (OPCABG) causes a strong decrease in cardiac output. It is hypothesized that this decrease is caused by reduced right ventricular filling and that right ventricular support is thus the best way to restore cardiac output. Simultaneous left and right ventricular pressure-volume loops were used to test this hypothesis.

METHODS

In seven sheep, the heart was tilted with the use of an Octopus device. After unsupported tilting, a novel right ventricular support, the Enabler, was activated at a pulsatile flow of 1.6 l/min. Pressure-volume loops of both ventricles were obtained using conductance catheters, and cardiac output was monitored with an aortic flow probe.

RESULTS

Tilting reduced cardiac output by 31% (4.4--3.1 l/min, P=0.001) and right ventricular end-diastolic volume by 44% (86--51 ml, P=0.005), while right ventricular end-diastolic pressure did not decrease. Left ventricular systolic pressure was not significantly reduced upon tilting and even increased in two animals. During Enabler right ventricular support, the cardiac output remained 23% lower than pre-tilting values (3.4 vs. 4.4 l/min, P=0.001).

CONCLUSIONS

Restricted right ventricular filling is the primary cause of the strong decrease in cardiac output during tilting. The Enabler right ventricular support can currently not restore cardiac output to pre-tilting values, mainly caused by its limited output and a decrease in right ventricular output upon Enabler activation. Constant monitoring of cardiac output is crucial during (unsupported or supported) tilting as blood pressure alone may not reflect the extent of the reduction in cardiac function.

The measurement of impedance to assess myocardial contractility and rhythm stability

By introducing an alternating current through the ventricular cavity via a multipolar catheter the potential difference measured between adjacent electrodes can be used to assess ventricular volume. This is possible by the measurement of intracardiac impedance. The data obtained can be used to construct pressure-volume loops allowing the continuous real-time assessment of myocardial contractility. Clinical applications of this research tool are now becoming apparent. Further derivations of impedance measurement have been incorporated into commercially available permanent pacing systems, allowing effective heart rate modulation.