Background-Several studies suggest that patients with ischemic cardiomyopathy benefit less from cardiac resynchronization therapy. In a novel animal model of dyssynchronous ischemic cardiomyopathy, we investigated the extent to which the presence of infarction influences the short-term efficacy of cardiac resynchronization therapy. Methods and Results-Experiments were performed in canine hearts with left bundle branch block (LBBB, nϭ19) and chronic myocardial infarction, created by embolization of the left anterior descending or left circumflex arteries followed by LBBB (LBBBϩleft anterior descending infarction [LADi; nϭ11] and LBBBϩleft circumflex infarction [LCXi; nϭ7], respectively). Pacing leads were positioned in the right atrium and right ventricle and at 8 sites on the left ventricular (LV) free wall. LV pump function was measured using the conductance catheter technique, and synchrony of electrical activation was measured using epicardial mapping and ECG. Average and maximal improvement in electric resynchronization and LV pump function by right ventricularϩLV pacing was similar in the 3 groups; however, the site of optimal electrical and mechanical benefit was LV apical in LBBB hearts, LV midlateral in LBBBϩLCXi hearts and LV basal-lateral in LBBBϩLADi hearts. The best site of pacing was not the site of latest electrical activation but that providing the largest shortening of the QRS complex. During single-site LV pacing the range of atrioventricular delays yielding Ն70% of maximal hemodynamic effect was approximately 50% smaller in infarcted than noninfarcted LBBB hearts (PϽ0.05). Conclusions-Cardiac resynchronization therapy can improve resynchronization and LV pump function to a similar degree in infarcted and noninfarcted hearts. Optimal lead positioning and timing of LV stimulation, however, require more attention in the infarcted hearts. (Circ Arrhythm Electrophysiol. 2010;3:361-368.)

The above findings confirm that post-MI pharmacological treatment can increase capillary density in the remodeled left ventricle. Whereas prevention of left ventricular hypertrophy normalizes capillary density without actually affecting capillary number, increased capillary to myocyte ratio (at preserved hypertrophic response) indicates actual capillary growth.

Our findings indicate that MI-induced collagen deposition in the spared myocardium can be affected by chronic therapy with low-dose aspirin or methylprednisolone. The effects on interstitial collagen seemed reflected in an altered left ventricular diastolic function.

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