Cardiomyoplasty: comparison of latissimus dorsi muscles of three large mammals with that of human

Induction of chronic cardiac insufficiency by arteriovenous fistula and doxorubicin administration

OBJECTIVES

Large animal experimental models of chronic heart failure (HF) permit repeated invasive assessment of cardiovascular function, and evaluation of new medical or surgical therapies. The existing models however fail to achieve stable and long-term HF. The aim of this study was to create a simple and stable chronic model of HF in goat, using both arteriovenous fistula and weekly intravenous doxorubicin injections.

METHODS

After a preliminary experiment on four goats receiving weekly 1 to 2 mg/kg of doxorubicin, six adult female goats, having had an arteriovenous fistula without signs or symptoms of heart failure, received weekly two different dosages of doxorubicin for 13 weeks: group A (n = 3) received 0.5 mg/kg and group B (n = 3) received 1 mg/kg. After a three-month period without medication, both groups received again 1 mg/kg for four weeks. Cardiac function was assessed by repeated electrocardiographic and echocardiographic examinations.

RESULTS

Four goats died during the medication period (one in group A, three in group B). During the period without medication a stable ventricular hypocontractility with left ventricular dilation was observed. Left ventricular dysfunction was more pronounced in group B, and was associated with clinical symptoms of HF.

CONCLUSIONS

Arteriovenous fistula alone did not produce HF. Its association with doxorubicin injections provides a simple and stable chronic model of HF. This association allows reduction of the required doxorubicin dose and toxicity in animals and in the environment. Depending of the dose of doxorubicin, it is possible to obtain a model of heart dilatation and ventricular hypokinesia with or without clinical symptoms of HF, with a different mortality.

Cardiomyoplasty: the benefits of electrical prestimulation of the latissimus dorsi muscle in situ

BACKGROUND

Ischemic damage in the latissimus dorsi muscle may limit the success of cardiomyoplasty. Electrical prestimulation of the muscle in situ is known to enhance thoracodorsal perfusion to the distal latissimus dorsi muscle immediately after grafting. In this study we asked whether prestimulation was also beneficial under typical postoperative conditions.

METHODS

Ten sheep were randomly assigned to two equal groups. In one group the latissimus dorsi muscle was stimulated continuously in situ at 2 Hz for 2 weeks; in the other group the muscle was not stimulated. Regional blood flows in the muscle were determined sequentially (1) under baseline conditions, (2) immediately after surgical mobilization, handling, and reattachment at 80% of the resting length, and (3) after 5 days.

RESULTS

Manipulation of the unstimulated muscle resulted in an acute global reduction in blood flow with no improvement after 5 days. The distal region was most severely affected (26.2%+/-4.2% of baseline blood flow). Electrical prestimulation significantly reduced regional blood flow under baseline conditions but rendered the whole muscle more resistant to the surgical manipulations; blood flow was significantly better-preserved immediately afterwards, and there was complete recovery to baseline levels after 5 days.

CONCLUSIONS

Electrical prestimulation of the latissimus dorsi muscle in situ reduces the acute distal ischemia caused by surgical manipulations, and promotes subsequent recovery of blood flow to baseline levels after a few days. Use of a prestimulated graft may therefore improve the outcome of skeletal muscle cardiac assistance.

Myocardial oxygen consumption is affected by dynamic cardiomyoplasty in dogs with adriamycin-induced cardiomyopathy

The purpose of the study was to investigate a possible myocardial sparing effect by dynamic cardiomyoplasty. We directly measured cardiac work and myocardial oxygen consumption after dynamic cardiomyopathy in dogs with adriamycin-induced cardiomyopathy. Ten dogs with cardiomyopathy induced by 4 weekly intracoronary infusions of adriamycin were studied. Five dogs underwent right latissimus dorsi cardiomyoplasty with progressive myostimulation, and five served as controls. Right heart and coronary sinus catheterizations were performed at 0, 10, and 15 weeks. Four and two dogs, respectively, the cardiomyoplasty and the control group, survived until 15 weeks. Cardiac work was not different between the control and the cardiomyoplasty groups (p = 0.42). Myocardial oxygen consumption was less in the cardiomyoplasty group (185.70 +/- 37.22; 165.75 +/- 25.86; 161.40 +/- 54.14 J/min at 0, 10, and 15 weeks, respectively) compared to the control group (147.80 +/- 70.99; 275.00 +/- 103.24; 263.50 +/- 52.75 J/min at 0, 10, and 15 weeks, respectively, p = 0.019). Mechanical cardiac efficiency was not meaningfully different between the cardiomyoplasty group (16.08% +/- 5.39%; 20.51% +/- 5.89%; 20.67% +/- 11.98% at 0, 10, and 15 weeks, respectively) compared to the control group (15.29% +/- 8.06%; 9.40% +/- 1.22%; 13.40% +/- 2.29% at 0, 10, and 15 weeks, respectively, p = 0.093). Acute changes of the cardiosynchronization ratio (2:1, 1:1, OFF) did not affect myocardial oxygen consumption or cardiac work within the cardiomyoplasty group. Dynamic cardiomyoplasty reduced myocardial oxygen consumption in dogs with adriamycin-induced cardiomyopathy.

Functional properties of conditioned skeletal muscle: implications for muscle-powered cardiac assist

Latissimus dorsi (LD) muscles of six canines were studied to assess changes induced by electrical conditioning and to quantify the capacity of these muscles to perform hemodynamic work. Muscles were conditioned using burst stimuli delivered over an 8-wk period. Contralateral LD were used as control. Muscles were tested in situ to simulate anticipated linear-pull cardiac assist conditions. This training process reduced muscle mass and cross-sectional area by 16 and 17%, respectively. Muscle phenotype shifted to a predominantly "slow" form by coordinate reduction of myosin heavy chain (MHC) 2A expression and increased expression of the MHC beta/slow form. Force generation was reduced by 54%, and contractile duration increased 13%. Fatigue resistance was markedly enhanced, and chronic stroke work increased from 0.19 to 0.72 mJ/g. The highest steady-state power output (2.06 mW/g) was obtained from one muscle fully converted to a slow phenotype. These data suggest that single LD trained via conventional techniques can provide energy sufficient for partial cardiac assistance but cannot sustain work levels needed to achieve total circulatory support.