The data suggest that magnesium infusion during a coronary occlusion has a significant benefit in reducing the IS in this model. Magnesium may have a beneficial clinical role in AMI, especially if administered before reperfusion as a bolus followed by a constant infusion.
We investigated the possibility of preventing further aggravation of muscle ischemia and necrosis in newly mobilized, unconditioned latissimus dorsi muscle (LDM) by utilizing short increments of stimulation with intervening rest periods. Adult St. Croix sheep (N = 12) weighing 30 +/- 8 kg were used in this study. Fatigue tests (30 min) using different stimulation regimens before and after LDM mobilization were performed on all animals; the length of time to return to baseline levels was also measured. Our investigation yielded results that contradict the conventional wisdom that any electrical stimulation damages newly mobilized LDM and will cause a considerable decrease in contractile force (CF). Stimulation regimens using continuous contractions at 30 and 60 contractions per minute (CPM) for 30 minutes were damaging to the LDM. CF also dropped significantly and returned slowly to baseline values: at 60 CPM, CF dropped to 50 +/- 4% and did not return to baseline even after 90 minutes of rest; at 30 CPM, CF dropped to 61 +/- 4% and baseline was restored after 80 minutes of rest. Electrical stimulation using continuous contractions at a slower rate (15 CPM) was tolerable, although a 23% decrease in CF was noted (p < 0.05 when compared to 60 CPM). These results did not satisfy us that such a regimen would be useful for cardiac assistance immediately after cardiomyoplasty. The work-rest regimen at 30 CPM also gave poor results: CF decreased to 75 +/- 2% and baseline was restored after 80 minutes of rest. Promising results were seen when utilizing a work-rest regimen at 15 CPM. The newly mobilized LDM showed no visible signs of fatigue: CF decreased minimally to 92 +/- 3% (p < 0.05 when compared to 30 CPM), and light microscopic analysis of biopsies revealed no morphological damage exceeding that typically seen after subtotal mobilization. Such results open avenues for future investigations: beginning electrical stimulation immediately after cardiomyoplasty (using a single impulse and a slow rate of contraction); decreasing the length of time necessary to obtain full cardiac assistance; and beginning partial cardiac assistance immediately after cardiomyoplasty (if needed) for approximately 30 minutes several times a day.
The hemodynamic effects of cardiomyoplasty (CMP) have been investigated in many centers, but the question of whether it is necessary to stimulate the latissimus dorsi muscle (LDM) 24 hours a day has not been answered. The main goal of our investigation was to determine whether hemodynamic results after CMP were impaired when continuous electrical stimulation (ES) was off for 12 hours a day. A model of chronic heart failure was created in 12 sheep by performing an arteriovenous anastamosis and administering doxorubicin. Two weeks after the anastomosis, CMP was performed in eight sheep (experimental series); ES training was begun at 2 weeks after CMP. After completion of the initial ES conditioning (8 weeks after CMP), one group of sheep continued to receive ES 24 hours daily. Another group of sheep had only 12 hours of ES daily. Hemodynamic parameters were investigated 2 weeks later with the stimulator turned on and then off. With doxorubicin administration, arteriovenous anastamosis created a stable model of biventricular heart failure (right atrial pressure 20 +/- 3 mmHg vs 6 +/- 2 mmHg at baseline; pulmonary capillary wedge pressure 18 +/- 3 mmHg vs 9 +/- 2 mmHg; left ventricular end-diastolic area 15.2 +/- 1.2 cm2 vs 6.4 +/- 0.7 cm2; left ventricular ejection fraction 0.38 +/- 0.6 vs 0.65 +/- 0.7). Cardiomyoplasty improved hemodynamic status in all eight experimental sheep. However, when the investigation was performed with the stimulator off, this improvement was statistically insignificant. With stimulation on, there was decreased right atrial pressure, pulmonary capillary wedge pressure, left ventricular end-diastolic volume, and increased left ventricular ejection fraction. With the stimulator turned off for 12 hours daily, hemodynamic measurements did not differ from data with continuous ES for 24 hours daily. Because hemodynamic results do not seem to be impaired, we recommend daily, periodic cessation of stimulation to prevent damage to the LDM after CMP.
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