Cardiomyoplasty. Latissimus dorsi muscle function and blood flow during isolation.

Cardiomyoplasty is a new surgical treatment for heart failure in which skeletal muscle assists the heart. However, for the first 2 weeks postoperatively, the latissimus dorsi muscle (LDM) remains unstimulated, and during the next 2 weeks, the LDM is stimulated with only one pulse every other heart beat. Thus, for the initial 4 postoperative weeks, minimal systolic assistance is provided. The present study determined if the LDM is capable of providing early assistance. Cardiomyoplasty surgery involves severing the perforating intercostal arteries to the LDM, detaching the LDM from its distal insertion, and wrapping it around the heart. At each of these steps, we measured LDM force development, shortening, and blood flow in six dogs. At control, LDM shortening, work, and power decreased during a 2 min fatigue test: fatigue indices (final/ initial value) for shortening, work, and power were 47.6 +/- 6.9%, 47.5 +/- 7.1%, and 46.9 +/- 6.6%, respectively. Blood flow increased in the proximal (P), mid (M), and distal (D) LDM during the fatigue test. After partial vascular isolation, initial shortening, work, and power decreased by 29.4%, 32.5%, and 31.7% from their respective control values. During the fatigue test, fatigue indices for shortening, work, and power were 24.7 +/- 3.3%, 19.5 +/- 4.6%, and 22.2 +/- 4.7%, respectively, all significantly (p < 0.05) less than control values. Resting blood flows were unaltered. During exercise, flow to the P increased, whereas flow did not increase in M (p < 0.05). Loss of LDM function was most apparent after mobilizing and reattaching the muscle. Initial shortening, work, and power significantly decreased (p < 0.05) by 74.1%, 76.8%, and 74.4%, from their respective control values. During a fatigue test, final values for shortening, work, and power were all near zero. Resting blood flow decreased in the M and D (p < 0.05) and, during exercise, blood flow increased only in P. Thus, LDM function was severely depressed during the isolation procedure. This functional loss is associated with inadequate blood flow responses. Therefore, preconditioning and/or revascularization is needed if the LDM is to provide cardiac assistance shortly after cardiomyoplasty surgery.