Ventricular constraint in severe heart failure halts decline in cardiovascular function associated with experimental dilated cardiomyopathy

Beneficial effects of a cardiac support device on left ventricular remodeling after posterior myocardial infarction: an evaluation by echocardiography, pressure-volume curves and ventricular histology

PURPOSE

Posterior myocardial infarction (MI) can induce LV remodeling and ischemic mitral regurgitation (IMR). The protective effects of a cardiac support device (CSD) against LV remodeling and IMR after posterior MI have been poorly documented.

METHODS

Posterior MI was induced by ligation of the left circumflex coronary artery in beagle dogs. After 7 days, the dogs were randomized to a CSD placement (CSD group, n = 8) or no treatment (CTL group, n = 8).

RESULTS

At 3 months after MI, the LV remodeling was less marked and the LV and RV systolic functions were better in the CSD group than in the CTL group. Neither the RV nor LV diastolic function (min dP/dt, Tau and EDPVR) was disturbed by the CSD. IMR was consistently prevented in our canine model.

CONCLUSION

Early application of a CSD after posterior MI can attenuate LV remodeling without causing any deterioration of the biventricular diastolic function.

Diastolic ventricular support with cardiac support devices: an alternative approach to prevent adverse ventricular remodeling

Heart failure is a global epidemic with limited therapy. Abnormal left ventricular wall stress in the diseased myocardium results in a biochemical positive feedback loop that results in global ventricular remodeling and further deterioration of myocardial function. Mechanical myocardial restraints such as the Acorn CorCap and Paracor HeartNet ventricular restraints have attempted to minimize diastolic ventricular wall stress and limit adverse ventricular remodeling. Unfortunately, these therapies have not yielded viable clinical therapies for heart failure. Cellular and novel biopolymer-based therapies aimed at stabilizing pathologic myocardium hold promise for translation to clinical therapy in the future.

Ovine models for chronic heart failure

PURPOSE

Testing and optimizing of surgical therapies for chronic heart failure (CHF) requires large animal models. CHF has been induced in several large animal species. Sheep have modest body mass increase and demonstrate docile behavior and are therefore a preferred species in research on surgical therapies for CHF METHODS: A literature search for existing ovine CHF models was performed, using search terms "sheep" and "heart failure". Relevant secondary references were traced.

RESULTS

Rapid ventricular pacing produces rapid-onset CHFE Its severity ranges from moderate left ventricular failure to severe biventricular failure, depending on length and frequency of pacing. Its counterpart in human CHF is tachycardia-induced HF since it is reversible upon cessation of pacing. Myocardial damage models include CHF induced by cardiototoxic drugs and ischemia. Ischemia-based models include coronary microembolization, occlusion and ischemia/reperfusion models. The microembolization model is relevant to diabetic cardiomyopathy. Coronary occlusion models exhibit variable functional impairment, some with aneurysm formation, and some with mitral valve regurgitation, depending on occlusion localization. They are relevant to CHF following non-reperfused myocardial infarction. Coronary occlusion/reperfusion models are relevant to the occurrence of human ãã despite coronary artery recanalization. Pressure overload of left and right ventricle is induced by aortic and pulmonary artery banding, respectively. Hypertrophy precedes CHF as in patients with valve stenosis and hypertension. Volume overload is induced by valve damage or shunt creation. Atrioventricular valve regurgitation is the most important clinical counterpart.

CONCLUSION

Several ovine CHF models exist. Since they exhibit important cardiac pathology differences, the choice of model should be based on the specific experimental question.

Device therapy for remodeling in congestive heart failure

Heart failure is a progressive condition which begins after an inciting event that leads to neurohormonal activation and cardiac remodeling. Medical therapy with beta-blockers and angiotensin-converting enzyme inhibitors has been shown to attenuate neurohormonal changes and left ventricular remodeling. Despite optimal medical therapy, patients often progress, and other therapeutic modalities have been sought to interrupt and reverse the process of remodeling. Various devices have been developed and entered into clinical trials with the intent of promoting reverse remodeling by directly altering the mechanical properties or shape of the left ventricle. This article reviews devices currently undergoing clinical trials.

Effect of passive cardiac containment on ventricular synchrony and cardiac function in awake dogs

OBJECTIVE

Passive restraint of the left ventricle (LV) has been shown to have beneficial effects on acute hemodynamics and reverse remodeling in both animal and human models. The goals of this study were to test whether a left ventricular support device (LVSD) improves LV synchrony and/or affects cardiac performance.

METHODS

Ten dogs were chronically instrumented to measure hemodynamics and LV volume (sonomicrometry). Congestive heart failure (CHF) was induced by repeated intracoronary microembolization via a chronically implanted coronary catheter. The LVSD was implanted after establishment of CHF in five animals, and five animals were observed as controls. All animals were then observed for 8 weeks. A mathematical model to measure LV synchrony was used to evaluate LV motion over time.

RESULTS

Mean arterial pressure and LV pressures was significantly increased after LVSD therapy, and LV pressure-volume relationships were shifted leftwards, although no change was seen in ejection fraction, end-systolic elastance, or LV dP/dt versus control. There was no significant change in diastolic function in LVSD animals compared with control animals. End-diastolic volumes were reduced by 15% after 8 weeks with LVSD treatment, versus an increase of 8% in control animals (p<0.05). Synchrony was significantly improved with LVSD therapy compared with control (9% vs 76% of baseline) in 1 of 11 ventricular dimension axes (Anterior-Apex).

CONCLUSIONS

LVSD therapy provided only minimal improvement in ventricular synchrony and partially improved hemodynamics. Further study into mechanisms of benefit are warranted.

Passive Ventricular Constraint Prevents Transmural Shear Strain Progression in Left Ventricle Remodeling

Background— Passive ventricular constraint provides external cardiac support to reduce left ventricular (LV) wall stress and myocardial stretch, which are primary determinants of LV remodeling. Altered wall strain results in cytokine and reactive oxygen species production, which, in turn, stimulates apoptosis and extracellular matrix disruption and could be an important trigger for adverse global LV dilatation and remodeling. The effects of the Acorn cardiac support device (CSD) on regional transmural LV wall strains, however, remain unknown.

Methods and Results— Thirty-three sheep had transmural radiopaque beadsets surgically inserted into the anterior basal and lateral equatorial LV walls, with additional markers silhouetting the left ventricle. Eight animals had CSD implanted (myocardial infarction [MI]+CSD). One week thereafter, the MI+CSD group and 10 animals without CSD (MI) underwent posterior LV infarction by snaring obtuse marginal coronary arteries. Fifteen animals (Sham) had no infarction or CSD. 4D marker dynamics were measured with biplane videofluoroscopy 1 and 8 weeks postoperatively. LV volumes, sphericity index, and transmural circumferential, longitudinal, and radial systolic strains were analyzed. Compared with Sham, infarction (MI) dilated the heart, reduced sphericity index (LV length/width), and increased longitudinal–radial shear strains in the inner half of both the anterior and lateral LV walls. CSD prevented this shear strain perturbation, minimized LV end diastolic volume increase, and augmented the LV sphericity index.

Conclusions— Prophylactic CSD prevented infarct-induced shear strain progression not only in myocardium adjacent to, but also remote from, the infarct. CSD also prevented LV dilatation and sphericalization. By attenuating shear strain abnormalities, CSD could prevent the heart from entering into a positive feedback loop of further LV dilatation and exaggeration of LV wall stress and may reduce biochemical triggers portending adverse LV remodeling.

Efficacy of the Acorn Cardiac Support Device in animals with heart failure secondary to high rate pacing

AIM

To utilise an ovine model of tachycardia induced progressive dilated cardiomyopathy and heart failure to investigate the efficacy of passive ventricular constraint with the Acorn cardiac support device as a heart failure treatment.

METHODS

(a) Moderate heart failure was produced in 16 sheep by pacing for 3 weeks. Half were implanted and half sham implanted with the CSD. Pacing continued at a higher rate for an additional 3 weeks. Cardiac function was assessed by echocardiography and manometry. (b) Moderate heart failure was produced (as above) in 27 sheep, 9 were implanted with CSD, pacing was restarted for 4 weeks, the initial CSD implants were terminated and another 9 animals were CSD implanted (severe heart failure), pacing was restarted in the remaining 18 animals for an additional 4 weeks (total 12 weeks) and then all animals were terminated. Cardiac function was assessed using echocardiography and treadmill exercise testing.

RESULTS

(a) After 6 weeks of rapid pacing CSD implant animals had significantly better cardiac function both when compared with pre implant values and with non-implanted animals at termination. (b) CSD implantation at both moderate and severe failure resulted in significant improvements in cardiac function both when compared with pre implant values and with non-implanted animals at termination. When compared to pre implant values the improvement was greatest in severe implant animals.

CONCLUSION

In this ovine model of tachycardia induced progressive heart failure, CSD implantation in either moderate or severe heart failure resulted in improved cardiac function, reduced left ventricular volume and mitral regurgitation both when compared with function at time of implant and with non implanted control animals.

Development of a new animal model of chronic mitral regurgitation in rats under transesophageal echocardiographic guidance

Large animal models (dog and sheep) are often used for the investigation of the pathophysiology of chronic mitral regurgitation (MR). A major limitation of large animal models is cost. The aim of this study was to develop a new animal model of chronic MR. Left thoracotomy was performed in 34 rats. Under the guidance of transesophageal echocardiography, a fine needle was inserted into the left ventricle (LV) to damage the mitral leaflets and produce MR. Serial transthoracic echocardiography was performed to assess LV remodeling and function. Left atrial and LV diameters were significantly larger, and LV fractional shortening was lower in the MR group than in the sham group. The 150-day survival was 59% in the MR group and 100% in the sham group (P < .01). This new animal model of chronic MR may be used in the study of the pathophysiology of chronic MR and pharmacologic therapies.

Global Left Ventricular Remodeling with the Acorn Cardiac Support Device: Hemodynamic and Angiographic Findings in Dogs with Heart Failure

Preventing progressive left ventricular (LV) remodeling is paramount in the treatment of heart failure. In recent years, several surgical approaches have been implemented with the objective of improving LV function through amelioration of progressive LV remodeling. These included surgical reduction of LV size, the so-called Batista procedure, dynamic cardiomyoplasty and mitral valve repair to limit or eliminate functional mitral regurgitation. While the Batista procedure and dynamic cardiomyoplasty have for all practical purposes been abandoned, the lessons learned from these procedures gave rise to a new generation of devices aimed at preventing progressive LV dilation and restoring LV shape by passive mechanical containment of the failing LV. One such device is the Acorn Cardiac Support Device (CSD) or the CorCap. Studies in dogs with intracoronary microembolization-induced moderate and advanced heart failure have shown that long-term monotherapy with the CSD not only prevents progressive LV dilation but, in effect, partially reverses this phenotype. These studies have also shown that the CSD restores, albeit in part, progressive LV chamber sphericity and attenuates functional mitral regurgitation. These benefits were accompanied by improvement in global LV function along with improvements of remodeling at the cellular level. The findings were largely responsible for initiating safety and feasibility clinical trials with the CSD and ultimately, the initiation of the Acorn efficacy trial that was completed in 2004. This review will focus on studies conducted in dogs with heart failure and, specifically on hemodynamic, angiographic and echocardiographic results from these studies that provided support for the CSD as a successful technology targeting "reverse LV remodeling" for the treatment of heart failure.

Changes in right ventricular dimensions and performance after passive cardiac containment

BACKGROUND

Previous studies have shown that the cardiac support device (CSD) improves left ventricular structure and function in patients with heart failure by preventing further cardiac enlargement. The aim of this study was to identify effects on the right ventricle (RV).

METHODS

Ten male patients with idiopathic dilated cardiomyopathy underwent electron-beam computed tomographic (CT) examination within 1 month before, and 6 to 9 months after CSD implantation. The RV end-diastolic and end-systolic volumes (EDV, ESV) and diameters (EDD, ESD), stroke volume (SV), ejection fraction (EF), total and forward RV output (RVO, fRVO), and tricuspid regurgitation fraction (TRF) were calculated.

RESULTS

The EDV measurements decreased from 182.1 +/- 49.6 to 137.5 +/- 37.0 mL, ESV from 114.8 +/- 47.0 to 68.3 +/- 23.8 mL, EDD from 48.2 +/- 6.6 to 41.6 +/- 7.1 mm, and ESD from 39.6 +/- 6.9 to 32.7 +/- 6.5 mm (p < 0.05 for each). Ejection fraction increased from 38.5 +/- 8.9 to 52.0% +/- 7.7% and fRVO from 4.0 +/- 0.8 to 4.6 +/- 1.1 L/min (each with p < 0.05). TRF decreased from 18.2 +/- 14.1 to 10.4% +/- 13.5%, whereas SV and RVO remained nearly unchanged. Postoperatively, RV volumes, EF, and fRVO were not different from 15 age- and gender-matched normal control patients.

CONCLUSIONS

Implantation of a CSD leads to a decrease in RV size and improved RV performance. These data together with the results of previous studies demonstrating improved left ventricular structure and function confirm the biventricular nature of recovery with the CSD.

Passive external cardiac constraint improves segmental left ventricular wall motion and reduces akinetic area in patients with non-ischemic dilated cardiomyopathy

OBJECTIVE

To verify changes in left ventricular (LV) volumes and regional myocardial wall motion after implantation of a textile cardiac support device (CSD) for passive external constraint in non-ischemic dilated cardiomyopathy.

METHODS

In nine male patients participating in a non-randomized clinical trial LV volumes were determined and the segmental LV wall motion was studied by contrast-enhanced electron-beam CT in a sectionwise manner at three ventricular levels (base, middle and apex of ventricle) before and 32+/-6 months after CSD implantation. In 16 myocardial segments ejection fraction and wall thickening were measured semiautomatically after drawing the myocardial contours. The wall motion score index was calculated based on semiquantitative visual grading in each segment.

RESULTS

The global LV volumes decreased significantly from 304.3 +/- 90.9 to 231.5 +/- 103.9 ml at end-diastole and from 239.7 +/- 83.7 to 164.0 +/- 97.7 at end-systole (P<0.05). Overall ejection fraction increased from 14.8 +/- 8.2 to 25.7 +/- 17.1% (P<0.05). A segment-by-segment analysis demonstrated a significant increase of regional ejection fraction in the basal myocardium as well as in the mid-inferior, mid-inferolateral, and mid-anterolateral myocardium. Overall wall thickening increased from 16.4 +/- 13.3 to 24.2 +/- 18.1% (P<0.05), but without significant differences in a segment-by-segment comparison. The mean wall motion score index improved from 2.70 +/- 0.26 to 2.20 +/- 0.71 (P<0.05), with an increased wall motion in eight (89%) patients. A section-by-section analysis demonstrated significantly improved wall motion in the inferior and lateral segments at each ventricular level. Postoperatively, the number of akinetic and markedly hypokinetic segments decreased significantly (P<0.05) from 56 (39%) to 26 (18%) and from 76 (53%) to 56 (37%), respectively.

CONCLUSION

CSD implantation improves segmental wall motion, predominantly in the inferior and lateral myocardium, and reduces the number of akinetic and hypokinetic segments.