The effect of basic fibroblast growth factor on the blood flow and morphologic features of a latissimus dorsi cardiomyoplasty

Bio-technologies for a glandular stem cell cardiomyopexy

The glandular stem cell cardiomyopexy should become a treatment option for end-stage heart failure. It combines an expected regenerative potential of transformed adult glandular stem cells into cardiomyocytes within the myocardium or onto the myocardium of the recipient and the potential of a hypercapillarized latissimus dorsi muscle (LDM) wrapped around the heart for stem cell nutrition and girdling.

Critical appraisal of the mouse model of myocardial infarction

In order to critically evaluate the utility of a mouse model of myocardial infarction (MI) for therapeutic studies, we investigated survival, haemodynamic measurements and histopathology in mice with an occluding suture placed at one of three distinct sites along the left anterior descending coronary artery. The suture was placed at the atrioventricular juncture (High), or at two sites more distally towards the base (Middle and Low). In the High group, only 33% of animals survived 7 days after MI (P < 0.05 compared to all other groups). Only the Middle group had significantly reduced haemodynamics compared to sham-operated animals (maximum left ventricular pressure: 55.9 +/- 3.5 versus 80.8 +/- 5.1 mmHg, maximum change in pressure over time : 2003 +/- 172 versus 4402 +/- 491, P < 0.01). Histological examination showed morphological changes in all MI groups. The Middle group had larger lesions than the Low group (P < 0.05). Lesions in the anterior and lateral walls correlated, albeit weakly, with cardiac function. Power calculations indicated that, despite a certain amount of intragroup variation, the Middle Suture model may be useful for therapeutic studies to assess the effects of treatment on cardiac function and overall lesion size.

Growth factors improve latissimus dorsi muscle vascularization and trophicity after cardiomyoplasty

BACKGROUND

Dynamic cardiomyoplasty consists of wrapping the electrostimulated latissimus dorsi muscle (LDM) around the failed heart. Partial ischemia followed by atrophy of the middle and distal part of the LDM were observed in 30% of clinical cases after LDM flap elevation from its origin. In the current study, we hypothesized that local administration of growth factors at the LDM/epicardial interface could improve muscle vascularization and trophicity.

METHODS

In 24 sheep, dynamic cardiomyoplasty was performed using the left LDM. A multiperforated catheter was positioned at the LDM/epicardial interface for a weekly administration, during a 1-month period, of the following factors: basic fibroblast growth factor (bFGF, n = 6), vascular endothelial growth factor (VEGF, n = 6), and regenerating agent (RGTA, n = 6). Six sheep injected with phosphate-buffered saline (used for dilution of the growth factors) were used as a control group. At 3 months, angiographic, histologic, and histomorphometric studies were performed.

RESULTS

Angiographic studies of the animals treated with growth factors demonstrated hypervascularization due to the development of new vessels. Histomorphometric and histologic studies showed a significant increase in the number of capillaries and arterioles (100 fields/muscle) in the groups treated with bFGF (443.0 +/- 101.2, p < 0.01), RGTA (293.2 +/- 29.3, p < 0.05), and VEGF (246.5 +/- 45.9, p < 0.05), as compared with the control group (81.5 +/- 11.4). A significantly lower atrophy score was observed in the groups treated with bFGF (1.4 +/- 0.18, p < 0.05), RGTA (1.59 +/- 0.17, p < 0.05), and VEGF (1.96 +/- 0.14, NS), as compared with the control group (2.48 +/- 0.16).

CONCLUSIONS

Local administration at the heart/muscle interface of growth factors increases muscle vascularization and avoids muscle atrophy in an experimental cardiomyoplasty model, both of which are advantageous to the contracting LDM. The local growth factors delivery system used in this study appears efficient, easy to implant, and manipulate and safe.

Improved viability of latissimus dorsi muscle grafts after electrical prestimulation

Surgical mobilization of the latissimus dorsi muscle (LDM) produces fiber degeneration, particularly in the distal part of the graft, that may compromise its function in clinical applications such as dynamic cardiomyoplasty. In five rats, the left LDM was stimulated continuously at 10 HZ. After 5 weeks, vessels perforating the chest wall were divided and the left LDM was mobilized as a pedicle graft based on the thoracodorsal artery. Twenty-four hours later, animals were killed and left and right LDMs were incubated with the vital stain nitroblue tetrazolium. Five control rats underwent a similar procedure without prestimulation. Mobilization of the LDM resulted in a loss of viability in the distal third of the muscle graft. This was reduced significantly by prestimulation (P = 0.006). Blood flow to the distal LDM graft is known to be augmented by electrical stimulation in situ before mobilization; the present results show that there is an associated enhancement of viability. The clinical implications of this finding are discussed.

Angiogenesis in the latissimus dorsi muscle using different regimens of electrical stimulation and pharmaceutical support

It is our contention that the prevention of ischemia-reperfusion injuries immediately after latissimus dorsi muscle (LDM) mobilization and enhancement of angiogenesis will be effective in improving cardiomyoplasty results. The investigations were performed on adult sheep. Three hours after LDM mobilization, various stages of leukocyte-endothelium interaction were revealed: leukocytes binding to the endothelium, leukocyte destruction of endothelium, and leukocytes leaving capillaries through gaps in the endothelium. Fifty-six days after mobilization various stages of necrosis were discernible. The area occupied by capillaries was 3.45 +/- 0.26% vs. 3.99 +/- 0.24% in control muscle; most of the endothelial cells exhibited morphologic degeneration. Electrical stimulation with 60 CPM actually decreased the capillary density to 2.15 +/- 0.7%, and most of the endothelial cells were damaged, with disrupted plasma membranes. Muscle subjected to 15 CPM increased the percent of capillaries to 5.01 +/- 0.56%, and endothelial cells appeared normal in ultrastructure. Pharmaceutical support prevented muscle damage and accelerated revascularization. After 56 days of autologous biological glue (ABG) application, the area occupied by capillaries was 5.57 +/- 0.24%. This increased to 8.47 +/- 0.72% when aprotinin (proteinase inhibitor) was added to ABG, and to 9.40 +/- 1.24% with pyrrolostatin (free radical scavenger). Both ABG application with aprotinin and electrical stimulation at 15 CPM prevent the LDM from postmobilization damage, and increase angiogenic potential.

Multistep approach to electrical stimulation after cardiomyoplasty

Still a controversial procedure, cardiomyoplasty (CMP) improves the failing heart's ability to contract by using a latissimus dorsi muscle (LDM), but to date, hemodynamic results correlate poorly with clinical improvement. The following two causes for apprehension bar attempting to change the conventional electrical stimulation (ES) protocol to improve CMP results: (1) fear of beginning ES for LDM-assisted contraction immediately postmobilization and CMP and (2) fear of stopping or slowing ES during sleep periods.

METHODS

In ten different experimental series, I used animal models of CMP to determine how to apply ES to newly mobilized LDM, how to begin partial cardiac assist immediately post-CMP, and how to suspend ES for 12 hours daily.

RESULTS

From my experimental series I noted the following three results. (1) Different ES regimens applied 1 hour postmobilization changed the contractile force (CF). After a 30-minute fatigue test, CF decreased by 34% +/- 3% with continuous ES at 30 contractions per minute (cpm), by 23% +/- 2% with continuous ES at 15 cpm, by 25% +/- 5% with ES in a work-rest regimen at 30 cpm, and by 8% +/- 3% with ES in a work-rest regimen at 15 cpm. (2) Imitation of partial cardiac assist immediately postmobilization slightly decreased CF. Sixteen days postmobilization, during a 30-minute fatigue test in animals in which ES had been started immediately after mobilization, CF decreased by only 6% +/- 3% and did not change when ES was combined with imitation of cardiac assist for 30 minutes twice daily (work-rest regimen). (3) ES cessation for 24 hours daily or 12 hours daily in CMP model created no difference in ejection fraction (EF) with ES (54% +/- 4% vs 53% +/- 5%, respectively (or in left ventricular end-diastolic volume (LVEDV, 234.3 ml +/- 1.0 ml vs 24.8 mL +/- 0.6 mL, respectively) or in LV end-systolic volume (LVESV; 12.1 mL +/- 0.7 mL vs 12.8 mL +/- 0.7 mL, respectively).

CONCLUSION

For improving angiographic potential in the LDM, ES can be started safely immediately post-CMP at 15 cpm (a 1:4 or 1:5 regimen) and single impulses per burst. For partial cardiac assist and for improving LDM performance, cardiac assist can be used for 30 minutes twice daily immediately post-CMP. To rest the muscle and save it from overuse, muscle contraction can be either stopped or slowed down during hours of sleep.

Vascular delay and administration of basic fibroblast growth factor augment latissimus dorsi muscle flap perfusion and function

Ischemia of the distal latissimus dorsi muscle flap occurs when the entire muscle is acutely elevated. Although this level of ischemia may not be critical if the muscle is to be used as a conventional muscle flap, the ischemia causes decreased distal muscle function if it is used for dynamic muscle flap transfer. This experiment was designed to determine whether or not the administration of exogenous basic fibroblast growth factor (bFGF), combined with a sublethal ischemic insult (i.e., vascular delay), would further augment muscle perfusion and function. Both latissimus dorsi muscles of nine canines were subjected to a bipedicle vascular delay procedure immediately followed by thoracodorsal intraarterial injection of 100 microg of bFGF on one side and by intraarterial injection of vehicle on the other. Ten days later, both latissimus dorsi muscles were raised as thoracodorsally based island flaps, with perfusion determined by laser-Doppler fluximetry. The muscles were wrapped around silicone chambers, simulating cardiomyoplasty, and stimulating electrodes were placed around each thoracodorsal nerve. The muscles were then subjected to an experimental protocol to determine muscle contractile function. At the end of the experiment, latissimus dorsi muscle biopsies were obtained for measurement of bFGF expression. The results demonstrated that the administration of 100 microg of bFGF immediately after the vascular delay procedure increases expression of native bFGF. In the distal and middle muscle segments, it also significantly increased muscle perfusion by approximately 20 percent and fatigue resistance by approximately 300 percent. The administration of growth factors may serve as an important adjuvant to surgical procedures using dynamic muscle flap transfers.

Dynamic cardiomyoplasty: at the crossroads

BACKGROUND

Dynamic cardiomyoplasty remains a promising, but still unproven surgical treatment for patients with end-stage heart failure. Lack of a clear survival advantage and ongoing misunderstanding of its mechanism of action have hindered its acceptance as a treatment alternative for patients with end-stage heart failure. This review seeks to update current clinical results and practice of dynamic cardiomyoplasty and to present its likely mechanism of action.

METHODS

The method involved a literature review.

RESULTS

More than 600 patients have undergone dynamic cardioplasty since 1985. Improvement in average New York Heart Association class was noted in 80% to 85% of hospital survivors. Operative mortality has decreased from 31% in Phase I to less than 3% in the ongoing Phase III trial. Clinical work as well as recent animal work supports the hypothesis that through a combination of long-term elastic constraint and active dynamic assist, dynamic cardiomyoplasty decreases myocardial wall stress associated with the remodeling process of progressive heart failure.

CONCLUSIONS

Though dynamic cardiomyoplasty can be shown to limit the remodeling process of heart failure in animal studies and some patients, its ultimate role in the treatment of heart failure will depend on the outcome of randomized, controlled studies.

Multicenter trial of dynamic cardiomyoplasty for chronic heart failure. The American Cardiomyoplasty Group

OBJECTIVES

The purpose of this study was to prospectively assess the effect of dynamic cardiomyoplasty in patients with symptomatic chronic heart failure.

BACKGROUND

Since the first procedure was performed in 1985, dynamic cardiomyoplasty has been developed for use in patients with chronic heart failure. The aging population in developed countries has made heart failure a growing public health concern. Heart transplantation is appropriate or available for only a small proportion of these patients because of limited donor supply. Effective alternatives to transplantation are needed.

METHODS

Eight centers in North and South America performed 68 cardiomyoplasty procedures between May 1991 and September 1993. Data were prospectively collected every 6 months and compared with preoperative values using paired t tests, chi-square tests and actuarial survival analyses.

RESULTS

Patients had a mean (+/- SD) age of 57 +/- 1 years and were predominantly male (53 [78%] of 68). Heart failure etiology was classified as idiopathic in 47 (69%) of 68 patients and ischemic in 21 (31%). The in-hospital mortality rate was 12% (8 of 68), and the survival rate at 6 and 12 months was 75 +/- 5% and 68 +/- 6%, respectively. Objective improvements were seen at 6 months (n = 49) in left ventricular ejection fraction (23 +/- 1% vs. 25 +/- 1%, p = 0.05), stroke volume (50 +/- 2 vs. 56 +/- 3 ml/beat, p = 0.02) and left ventricular stroke work index (26 +/- 1 vs 30 +/- 2 g/m2 per beat, p = 0.01). Improvements in mean New York Heart Association functional class (3 +/- 0.04 vs. 1.8 +/- 0.1, p = 0.0001) and activity of daily living score (59 +/- 3 vs. 80 +/- 2, p = 0.0001) were also observed. There were no significant changes at 6 months in peak oxygen consumption (15 +/- 1 vs. 16 +/- 1 ml/kg per min), cardiac index (2.26 +/- 0.08 vs. 2.33 +/- 0.08 liters/min per m2), pulmonary capillary wedge pressure (19 +/- 2 vs. 18 +/- 1 mm Hg) or heart rate (87 +/- 2 vs. 82 +/- 3 beats/min).

CONCLUSIONS

These data suggest that dynamic cardiomyoplasty improves ventricular systolic function, reduces symptoms of heart failure and improves objective measures of quality of life in patients with congestive heart failure. This improvement occurred without changes in peak exercise capacity, ventricular filling pressure or actuarial survival.

Heparin and basic fibroblast growth factor are associated with preservation of latissimus cardiomyoplasties in goats: a retrospective study

BACKGROUND

Chronic electrical stimulation of cardiomyoplasties often leads to atrophy and fibrosis of the skeletal muscle. In this retrospective study, we re-examined the data in our previous work, which suggested that muscle was preserved by treatment with basic fibroblast growth factor (bFGF).

METHODS

Histologic sections were reviewed for evidence of atrophy, and fibrosis from four groups of goats with latissimus dorsi cardiomyoplasty: (1) unstimulated; (2) 2-Hz stimulated x 6 weeks; (3) 2-Hz stimulated with heparin infusion (50 units/hour) x 6 weeks; and (4) 2-Hz stimulated with bFGF (80-micrograms bolus/week) x 6 weeks.

RESULTS

Muscle degeneration, as indicated by fat replacement of muscle fibers, was 56.95% +/- 9.16% (mean +/- S.E.) in the 2-Hz stimulated compared with 16.43% +/- 6.22% in unstimulated muscles. In 2-Hz = bFGF and 2 Hz-Heparin (Hep) groups, degeneration was 11.60% +/- 3.04% and 20.36% +/- 5.03%, respectively. bFGF treatment was associated with a greater latissimus blood flow than in the 2-Hz-untreated and 2 Hz-Hep groups (p < 0.05).

CONCLUSIONS

bFGF's protection against degeneration may have involved angiogenesis and myogenesis, whereas that of heparin appears to have involved only myogenesis. While the mechanism(s) of the effects of heparin and bFGF remain to be defined, we conclude that they may be a useful adjunct for cardiomyoplasty.