Main determinants of postinfarction remodeling

In the acute phase, thrombolysis limits infarct size, transmurality, and infarct expansion; beyond the acute phase, ventricular remodeling is influenced predominantly by the patency of the infarct-related artery, ventricular loading conditions, neurohumoral activation, and local tissue growth factors.

The magnitude of remodeling changes relates roughly to infarct size. In small infarcts, the ratio of cavity volume to mass is normal, suggesting normalization of wall stress. In moderate-to-large infarcts, however, volume is further increased out of proportion to mass as filling pressure rises, suggesting that the stimulus to volume enlargement is still present. Ventricular dilation without a concomitant increase in mass may become mechanically disadvantageous.

Infarct expansion is more often associated with large transmural infarcts. In nontransmural infarcts, very small residual islands of myofibrils and preservation of interstitial collagen may play a role in limiting infarct expansion.

Although infarct size is a major determinant of ventricular remodeling, late patency of the infarct-related artery or collateral flow to the infarct may confer survival benefit. Myocardial reperfusion reduces infarct size and improves later regional and global ventricular function. Healing markedly accelerates when flow is reestablished to the infarct zone, and a blood-filled vasculature may also serve as a scaffold.

In patients not receiving thrombolysis, the degree of infarct-related artery perfusion was a more important predictor than infarct size of left ventricular volume change from 48 hours to 1 month after infarction. Reperfusion may salvage endocardial tissue and restore function in the infarct border zone. Reperfused infarcts with contraction band necrosis may have greater tensile strength and less propensity to expansion.

The Total Occlusion Study of CAnada (TOSCA) demonstrated the benefit of primary stenting compared with angioplasty alone in terms of late patency, restenosis, and the need for revascularization in a large group of patients with nonacute coronary occlusion. However, the remodeling benefit of acute percutaneous revascularization of the occluded infarct-relat-ed artery is unknown.

Left ventricular remodeling can also occur in patients with a patent infarct-related artery. Left ventricular dilatation after primary percutaneous transluminal coronary angioplasty has been observed in 30% of patients despite sustained infarct-related artery patency and preservation of regional and global function. The significance, in terms of clinical outcome, of left ventricular dilatation in patients with sustained infarct-related artery patency remains to be established.

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