Preconditioning of the latissimus dorsi muscle in cardiomyoplasty: vascular delay or chronic electrical stimulation

In vitro evaluation of the distribution of blood flow within a canine bipedicled latissimus dorsi muscle flap

OBJECTIVE

To identify the predominant perforating artery in the canine latissimus dorsi muscle and demonstrate that perfusion of the predominant perforating artery improves blood flow in segments of the latissimus dorsi muscle that are located distally from the thoracodorsal artery.

SAMPLE POPULATION

Latissimus dorsi muscles dissected from 7 dogs.

PROCEDURES

Colored microspheres were used to determine the degree of perfusion of the latissimus dorsi muscle via the thoracodorsal artery, predominant perforating artery, or the thoracodorsal artery and predominant perforating artery together. The latissimus dorsi muscle was divided into 4 proximal to distal segments relative to the thoracodorsal artery (segments A, B, C, and D, respectively).

RESULTS

The perforating artery, located at the level of the fifth intercostal space, predominantly supplied perfusion to segments B, C, and D. The number of microspheres received by segment C was significantly higher when the thoracodorsal artery and perforating artery were used for muscle perfusion (181.40 +/- 44.90 microspheres/300 g of tissue for every 3,000 spheres injected), compared with use of the thoracodorsal artery alone (60.00 +/- 13.70 microspheres/300 g of tissue for every 3,000 spheres injected).

CONCLUSIONS AND CLINICAL RELEVANCE

Blood flow via the predominant perforating artery improves perfusion to the middle part of the latissimus dorsi muscle in dogs. A bipedicled latissimus dorsi muscle flap would provide a healthier muscle for cardiac assist in the treatment of dilated cardiomyopathy in dogs.

Effects of acute dynamic cardiomyoplasty in a goat model of chronic ventricular dilatation: part 1

BACKGROUND

The acute effects of cardiomyoplasty in an experimental model of chronic dilated heart have not been thoroughly investigated. Therefore, a model of chronic left ventricular (LV) dilatation was created to accurately determine actual changes shortly after passive and active wrapped skeletal muscle.

METHODS

A carotid-jugular shunt model in 8 goats was used to induce progressive dilatation of the cardiac ventricles. Geometric modifications induced by the arteriovenous shunt were monitored by transthoracic echocardiography. After 8 weeks, cardiomyoplasty was performed, and the acute hemodynamic changes obtained with static cardiomyoplasty soon after the wrapping procedure were determined. Hence, hemodynamic variables recorded during assisted cardiac beats were then compared with data collected with unassisted cardiac beats using the conductance catheter method to generate pressure-volume loops.

RESULTS

During electrical stimulation of the unconditioned skeletal muscle wrapped around the dilated left ventricle, a significant increase in stroke volume (117 +/- 48 mL versus 87 +/- 38 mL; p < 0.05) was observed. Early wrapped latissimus dorsi muscle activation also induced a reduction in LV end-systolic volume (from 51 +/- 28 mL to 27 +/- 14 mL; p < 0.05) when compared with unassisted LV contraction.

CONCLUSIONS

In a chronic model of cardiac dilatation, acute dynamic cardiomyoplasty was shown to increase LV contractile performance and reduce LV volume. Further evaluation is necessary to show the effects of a conditioned wrapped muscle on LV systolic function and dimensions in the long-term.

Avoiding ischemia in latissimus dorsi muscle grafts: electrical prestimulation versus vascular delay

BACKGROUND

Surgical mobilization of the latissimus dorsi muscle produces regional ischemic damage that may compromise its function in clinical applications such as cardiomyoplasty. We compared the effectiveness of two procedures designed to maintain blood flow throughout the mobilized muscle.

METHODS

Adult pigs were assigned to two experimental groups: an electrically prestimulated group (n = 10) and a vascular delay group (n = 10). In the prestimulated group the left latissimus dorsi muscle was activated in situ at 2 Hz for 24 h/d. In the vascular delay group, the intercostal perforating arteries to the left latissimus dorsi muscle were divided. Two weeks later, hyperemic blood flow was measured by means of fluorescent microspheres immediately before and after mobilizing the latissimus dorsi muscle and again after recovery for a further 2 days.

RESULTS

In the prestimulated group, blood flow was not significantly depressed in any region of the muscle immediately after mobilization, and blood flow increased significantly in proximal (p = 0.01), middle (p = 0.02), and distal (p = 0.007) regions following recovery. In muscles subjected to vascular delay the proximal and middle regions showed no significant changes in blood flow after mobilization or recovery, but flow in the distal region was 50% lower after mobilization (p = 0.003), and it remained significantly depressed even after recovery (p = 0.008).

CONCLUSIONS

Prestimulation was significantly more effective than vascular delay in preserving distal blood flow. Because it is also less invasive and initiates metabolic transformation before mobilization, this technique should allow cardiac assistance to be introduced at an earlier postoperative stage without compromising the viability of the grafted muscle.

Can latissimus dorsi muscle stimulation benefit heart during training period after vascular delay?

We hypothesized that a two-stage vascular delay procedure followed by 5 weeks of conditioning of the latissimus dorsi muscle (LDM) could benefit the heart during the training period and greatly increase cardiac assistance when examined with maximum potential. In mongrel dogs (n = 10), left ventricle (LV) dysfunction was induced by intracoronary injections of latex microspheres [90 +/- 2 micro diameter]. Vascular delay of the LDM was performed in one group (n = 6), whereas the other group (control, n = 4) did not undergo vascular delay. After 2 weeks, CMP was performed in all animals followed by LDM conditioning. After 5 weeks of muscle training, we examined left ventricular function at 20 Hz-4 volts, 33 Hz-4 volts, and 50 Hz-10 volts stimulation by assessing peak aortic pressure (AoP), left ventricular pressure (LVP), maximum LV +dP/dt, stroke volume (SV), stroke work (SW), stroke power (SP), and aortic flow. LDM assisted beats were compared with nonstimulated beats. LDM stimulation caused significant increases in pressure and flow in the vascular delay group. At 20 Hz-4 volts, absolute increases were LVP (10.2 +/- 0.6) mm Hg, AoP (9.8 +/- 1.7) mm Hg, SV (1.8 +/- 0.4) ml, SW (5.3 +/- 1.0) gm x m, SP (40.8 +/- 12.7) gm x m/sec, max LV dP/dt (104.8 +/- 53.2) mm Hg/sec, and peak aortic flow (0.9 +/- 0.3) L/min. At 33 Hz-4 volts, the absolute increases were LVP (13.6 +/- 1.3) mm Hg, AoP (12.1 +/- 2.4) mm Hg, SV (2.7 +/- 0.7) ml, SW (7.4 +/- 1.4) gm x m, SP (72.7 +/- 16.5) gm x m/sec, max LV dP/dt (294 +/- 19) mm Hg/sec, and peak aortic flow (1.8 +/- 0.5) L/min. At 50 Hz-10 volts, the absolute increases were LVP (17.7 +/- 0.7) mm Hg, AoP (21.1 +/- 1.9) mm Hg, SV (6.0 +/- 1.1) ml, SW (14.6 +/- 2.2) gm.m, SP (128.2 +/- 15.3) gm x m/sec, max LV dP/dt (352 +/- 62) mm Hg/sec, and peak aortic flow (3.3 +/- 0.4) l/min (p < 0.05). The percentage increases were significantly larger in the vascular delay group compared with controls at 50 Hz-10 volts LDM stimulation. By using a two-stage vascular delay procedure, LDM stimulation can provide meaningful cardiac assistance during training periods. Furthermore, brief periods of maximal potential benefit (demand cardiomyoplasty) can be achieved during the training period.