A pressure overload model to track the molecular biology of heart failure.

OBJECTIVES

Pressure overload plays an important role in left ventricular remodelling and the development of heart failure. The underlying molecular mechanisms behind these processes are poorly understood at the myocyte level. To investigate this, we developed an ovine model of pressure overload-induced heart failure, in which serial left ventricular biopsies were obtained.

METHODS

Adult male sheep were chronically banded with a novel variable aortic constriction device. This was progressively inflated via a subcutaneous port to increase left ventricular afterload. The animals were monitored clinically and echocardiographically. Serial left ventricular endomyocardial biopsies were obtained via the right external carotid artery under fluoroscopic guidance. They were used to measure mRNA expression of the genetic regulators of apoptosis by reverse transcription polymerase chain reaction. In a subset of the animals, once left ventricular failure had been established, the constriction device was deflated to produce unloading of the left ventricle.

RESULTS

Ten of the 17 sheep banded developed left ventricular failure. Over the first 3-4 weeks, left ventricular mass index increased acutely (88+/-18 vs. 44+/-10 g/m(2), P<0.01) followed by gradual left ventricular dilatation (diastolic left ventricular internal diameter 4.1+/-0.7 vs. 3.2+/-0.3 cm, P<0.01). Ventricular function remained stable until 7-8 weeks postoperatively, when there was significant deterioration (fractional shortening 17+/-8 vs. 40+/-8%, P<0.01) associated with clinical heart failure. Expression of the pro-apoptotic genes (bax and Fas) increased significantly following inflation of the constriction device and persisted through the transition to left ventricular failure. Following deflation of the constriction device, myocardial contractility gradually improved over a 3 week period (fractional shortening 32+/-1 vs. 17+/-8%).

CONCLUSIONS

Progressively increasing the afterload on the left ventricle produces a clinical and echocardiographical picture of chronic heart failure. Obtaining myocardial tissue during this transition will allow the molecular correlates of pressure overload-induced heart failure and potential myocardial recovery to be investigated.