Heterotopic transplantation of the failing rat heart as a model of left ventricular mechanical unloading toward recovery

The left ventricular assist device (LVAD) is usually used in patients with end-stage heart failure as a bridge to transplantation. Recently, some studies have reported functional recovery with the use of an LVAD, although the mechanisms responsible for recovery are not fully understood. We investigated the functional recovery of the infarcted, failing rat heart in response to mechanical unloading after heterotopic transplantation. Heart failure was induced in Lewis rats by ligating the left anterior descending artery. After 4 weeks, the infarcted hearts were harvested and heterotopically transplanted. The transplanted infarcted heart was removed after 2 weeks of unloading and examined for hypertrophy and fibrosis, as well as for mRNA levels encoding for brain natriuretic peptide, sarco(endo)plasmic reticulum Ca(2+)-ATPase2a (SERCA2a), and beta1- and beta2-adrenergic receptors. Normal and infarcted rats without transplantation served as control animals. The infarcted heart was hypertrophied as evidenced by an increase in heart weight and myocyte diameter. After unloading the infarcted heart for 2 weeks, there was a decrease in heart weight and myocyte diameter. However, the percentage of myocardial fibrosis increased after unloading. The mRNA expression of brain natriuretic peptide and the beta2-adrenergic receptor significantly improved after mechanical unloading. The levels of SERCA2a mRNA tended to increase after unloading. In conclusion, unloading the failing, infarcted heart can help normalize left ventricular hypertrophy and cardiac gene expression. This unloading model appears to partially mimic the conditions of hemodynamic support with an LVAD in heart failure patients and potentially offers insights into the mechanisms of functional recovery.     

Importance of preserving the apex and plication of the base in left ventricular volume reduction surgery

OBJECTIVE: Volume reduction surgery for dilated cardiomyopathy has not yielded predictable outcomes. The purpose of this study was to clarify the efficacy of modified volume reduction surgery in preserving the left ventricular apex and reducing the left ventricular diameter at the base to maintain fiber continuity. METHODS: Heart failure was induced with propranolol in 12 dogs, and the animals were randomized into 2 groups. In one group the left ventricular wall was plicated between the 2 papillary muscles from the middle to the apex (apex-sacrificing volume reduction surgery, group A, n = 6), and in the other group plication was done from the base to the middle (apex-sparing volume reduction surgery, group B, n = 6). Left ventricular function was then compared between the groups by using echocardiography and sonomicrometry crystals. RESULTS: After volume reduction surgery, the fractional area change at the base in group B was greater than that in group A (40% +/- 3% vs 27% +/- 4%, P =.003). Cardiac output in group B was better than that in group A (2.5 +/- 0.2 vs 1.8 +/- 0.2 L/min, P =.023). Left ventricular end-diastolic pressure in group A was higher than that in group B (16 +/- 2 vs 8 +/- 1 mm Hg, P =.001). Fractional shortening in the long axis, as assessed by means of sonomicrometry, was better in group B than in group A. CONCLUSIONS: Apex-sparing volume reduction surgery capable of maintaining left ventricular fiber continuity provided better left ventricular function in both the systolic and diastolic phases than apex-sacrificing volume reduction surgery in the acute heart failure model. This modification might improve the results of left ventricular volume reduction surgery.     

Mitral annuloplasty as a ventricular restoration method for the failing left ventricle: a pilot study

BACKGROUND AND AIM OF THE STUDY: Undersized mitral annuloplasty (MAP) is effective in patients with dilated cardiomyopathy and functional mitral regurgitation (MR) since, as well as addressing the MR, the MAP may also reshape the dilated left ventricular (LV) base. However, the direct benefits of this possible reshaping on LV function in the absence of underlying MR remain incompletely understood. The study aim was to identify these benefits in a canine model of acute heart failure. METHODS: Six dogs underwent MAP with a prosthetic band on the posterior mitral annulus, using four mattress sutures. The sutures were passed individually through four tourniquets and exteriorized untied via the left atriotomy. Sonomicrometry crystals were implanted around the mitral annulus and left ventricle to measure geometry and regional function. Acute heart failure was induced by propranolol and volume loading after weaning from cardiopulmonary bypass; an absence of MR was confirmed by echocardiography. MAP was accomplished by cinching the tourniquets. Data were acquired at baseline, after induction of acute heart failure, and after MAP. RESULTS: MAP decreased mitral annular dimensions in both commissure-commissure and septal-lateral directions. Concomitantly, the diastolic diameter of the LV base and LV sphericity decreased (i.e., improved) from 37.4 +/- 9.3 to 35.9 +/- 10 mm (p = 0.063), and from 67.9 +/- 18.6% to 65.3 +/- 18.9% (p = 0.016), respectively. Decreases were evident in both LV end-diastolic pressure (from 17 +/- 7 to 15 +/- 6 mmHg, p = 0.0480 and Tau (from 48 +/- 8 to 45 +/- 8 ms, p <0.01), while fractional shortening at the LV base increased from 7.7 +/- 4.5% to 9.4 +/- 4.5% (p = 0.045). After MAP, increases were identified in both cardiac output (from 1.54 +/- 0.57 to 1.65 +/- 0.57 1/min) and Emax (from 1.86 +/- 0.9 to 2.41 +/- 1.31 mmHg/ml). CONCLUSION: The data acquired suggest that isolated MAP may have certain benefits on LV dimension/function in acute heart failure, even in the absence of MR. However, further investigations are warranted in a model of chronic heart failure.     

Prevention of myocardial reperfusion injury by poly(ADP-ribose) synthetase inhibitor, 3-aminobenzamide, in cardioplegic solution: in vitro study of isolated rat heart model.

OBJECTIVE: Cardioplegic arrest remains the method of choice for myocardial protection in cardiac surgery. Poly(adenosine 5'-diphosphate-ribose) synthetase (PARS) inhibitor has been suggested to attenuate the ischemia-reperfusion injury in myocardial infarction by preventing energy depletion associated with oxidative stress. We investigated the efficacy of a cardioplegic solution containing a PARS inhibitor, 3-aminobenzamide (3-AB), for myocardial protection against ischemia-reperfusion injury caused by cardioplegic arrest. METHODS: Isolated hearts were set on a Langendorff apparatus and perfused. The hearts were arrested for 90 min with a cardioplegic solution given at 30-min intervals and then reperfused for 20 min. The hearts of rat in the 3-AB(-) group (n = 8) were perfused with a standard cardioplegic solution and terminal warm cardoplegia, whereas the 3-AB(+) group (n = 8) received these solutions supplemented with 3-AB (100 microM). Left ventricular function and release of cardiac enzymes were monitored before and after cardioplegic arrest. After reperfusion, NAD+ (nicotinamide-adenine dinucleotide) levels were assessed, and the tissues were examined immunohistochemically for oxidative stress and apoptosis. RESULTS: During reperfusion, the 3-AB(+) group showed significantly higher (P = 0.005)dp/dt and lower creatine phosphokinase (CPK) level and glucotamic-oxaloacetic transaminase (GOT) in the effluent (CPK; P = 0.003 GOT; P < 0.001) The cardiomyocytes of the 3-AB(+) group also preserved a higher NAD+ level (P < 0.001). Immunohistochemical study of oxidative stress revealed a lesser extent (P = 0.007) of nuclear staining and a lower fraction of apoptosis in the 3-AB(+) group. CONCLUSION: Cardioplegic solution supplemented with 3-AB provides efficient myocardial protection in cardioplegic ischemic reperfusion by suppressing oxidative stress and overactivation of PARS.     

Effect of edaravone, a novel free radical scavenger, supplemented to cardioplegia on myocardial function after cardioplegic arrest: in vitro study of isolated rat heart

Cardioplegic arrest has been the main mechanism of myocardial protection during open-heart surgery; however, it causes myocardial injury during ischemia-reperfusion. Free radical scavengers are widely known to attenuate ischemia-reperfusion injury in various settings. We investigated the effects of edaravone, a novel free radical scavenger that was originally used for cerebral protection, on myocardial function during ischemia-reperfusion after cardioplegic arrest. Rat hearts were excised and perfused using Langendorff apparatus. The hearts were cardioplegically arrested for 90 min using St. Thomas’ Hospital cardioplegic solution (ST solution) at 4°C every 45 min and then reperfused for 20 min. The hearts were divided into 4 groups (n = 13 in each group). In Group ST, the hearts were arrested using the ST solution alone. In Groups L, M, and H, the hearts were arrested using the ST solution supplemented with a low-dose (1 μM), moderate dose (10 μM), and high dose (100 μM) of edaravone, respectively. Left ventricular function (+dp/dt _max) and the levels of the cardiac enzymes released were measured before and after cardioplegic arrest. At the end of the study, the water content and the tissue oxidative stress (8-hydroxy-2′-deoxyguanosine) of the heart were measured. During reperfusion, the edaravone-treated groups showed a greater functional recovery with regard to the +dp/dt _max (P < 0.05). The lactate level was the lowest (P < 0.01) in Group M. The water content of the hearts in the edaravone-treated groups was significantly lower (P < 0.05) than that in Group ST. Oxidative stress was significantly lower (P < 0.01) in the edaravone-treated hearts than in Group ST, and it was the lowest in Group M. The addition of edaravone to the cardioplegic solution ameliorates the impairment in myocardial function by reducing the oxidative stress after cardioplegic arrest. In this study, the maximum improvement in the myocardial function was achieved by addition of a moderate dose (10 μM) of edaravone.     

Taurine prevents myocardial ischemia/reperfusion-induced oxidative stress and apoptosis in prolonged hypothermic rat heart preservation

Taurine (2-aminoethanesulfonic acid) is a potent antioxidant and inhibits cell apoptosis in ischemic reperfusion injury. In this study we evaluated whether addition of taurine to St. Thomas' cardioplegic solution enhances its myocardial protective effects in prolonged hypothermic heart preservation in rats. Hearts isolated from male Sprague–Dawley rats were mounted on a Langendorff apparatus to estimate baseline cardiac function, then arrested and stored in St. Thomas' cardioplegic solution, with taurine (10 mM; taurine group, n = 8) or without taurine (control group, n = 8), for 6 h at 4°C. After storage, the hearts were reperfused and heart rate (HR), coronary flow (CF), left ventricular developed pressure (LVP), and positive maximum left ventricular developing pressure (max LV dp/dt) were measured. The LV tissue was examined immunohistochemically for determining DNA oxidative stress and cell apoptosis. Compared with control groups, recovery of LVP (P < 0.001), max LV dp/dt (P < 0.001), and coronary flow (P < 0.001) were significantly enhanced, whereas glutamic oxaloacetic transaminase (P < 0.01), lactate dehydrogenase (P < 0.05), creatine phosphate kinase (P < 0.01), 8-hydroxy-2′-deoxyguanosine index (P < 0.01), caspase-3 mRNA expression (P < 0.05), and percentage of TUNEL-positive cardiomyocytes (P < 0.05) were reduced in the taurine group. Addition of taurine to St. Thomas' cardioplegic solution improved cardiac function recovery for prolonged hypothermic rat heart preservation by suppressing DNA oxidative stress and cell apoptosis.