Skeletal muscle ventricles with improved thromboresistance: 28 weeks in circulation

Stroke Volume Validation and Energy Evaluation for the Dynamic Training of Skeletal Muscle Ventricles

Skeletal muscle ventricles used for cardiac assistance were trained dynamically by shifting volume within an elastic training device. To optimize this dynamic training that is by variation of stimulation patterns and application of drugs, methods for stroke volume and energy evaluation were required.

A volume shift induced by a muscle contraction resulted in a pressure rise in the training device. Stroke volume was calculated by relating the pressure difference of a muscle contraction to the device's compliance. For validation of the calculated stroke volume, a mock system was built to simulate muscle contractions under various conditions. The stroke volume measured independently and calculated by means of the pressure rise inside the training device, showed an approximately one-to-one relation (R=0.996). Calculation of delivered energy from skeletal muscle ventricles thereby became possible.

This method offers a simple, reliable and practical procedure to quantify the dynamic training of skeletal muscle ventricles for use in cardiac assistance.

Pericardium-lined skeletal muscle ventricles: up to two years' in-circulation experience

BACKGROUND

Skeletal muscle ventricles (SMVs) are autologous pumping chambers constructed from skeletal muscle. Skeletal muscle ventricular rupture and thromboembolism have complicated chronic models of this method of skeletal muscle cardiac assist.

METHODS

The SMVs were constructed from the latissimus dorsi muscle in 10 dogs. The inner surface of each SMV was lined with autologous pericardium harvested at the time of SMV construction. After a 3-week period of vascular delay and 6 weeks of electrical conditioning to convert the muscle to a fatigue-resistant state, SMVs were connected to the descending thoracic aorta and stimulated to contract during cardiac diastole.

RESULTS

Initial hemodynamics revealed that SMV contraction at 33 Hz increased diastolic pressure 24.7% (60.8 +/- 7.3 mm Hg versus 80.3 +/- 8.8 mm Hg). Skeletal muscle ventricle relaxation decreased presystolic pressure 14.4% (59.9 +/- 7.7 mm Hg versus 51.3 +/- 7.5 mm Hg) and decreased peak systolic pressure 4.1% (90.2 +/- 7.3 mm Hg versus 86.5 +/- 5.8 mm Hg). Hemodynamics were assessed at 1 to 2 weeks, then at 1, 2, 3, and 6 months, and at 6-month intervals thereafter. Hemodynamic performance remained stable for the duration of this study. After 2 years of pumping continuously in circulation, SMV contraction resulted in a 34.8% augmentation of diastolic pressure (63.6 +/- 6.6 mm Hg versus 85.3 +/- 6.4 mm Hg), a 17.2% decrease in presystolic pressure (54.7 +/- 3.73 mm Hg versus 45.3 +/- 4.1 mm Hg), and a 4.2% decrease in peak systolic pressure (95.3 +/- 10.4 mm Hg versus 91.3 +/- 12.3 mm Hg). Three dogs survived to 2 years with the SMVs in circulation. No animal showed evidence of thromboembolism during serial echocardiography or at autopsy and no SMVs ruptured.

CONCLUSIONS

These data demonstrate that SMVs can provide effective hemodynamic assist over an extended period without specific complications related to the SMVs.

Skeletal muscle ventricles in circulation: decreased incidence of rupture

BACKGROUND

Skeletal muscle ventricles (SMVs) are muscular pumping chambers constructed for cardiac assist. Skeletal muscle ventricles can be connected to the circulation in a variety of configurations for both left and right heart assist; when connected to the aorta and stimulated to contract during diastole, they function in a similar fashion as an intraaortic balloon pump.

METHODS

Skeletal muscle ventricles were constructed in 18 dogs using the left latissimus dorsi muscle. In 10 of these dogs (group 1), the inner surface of the SMV was lined with autogenous pericardium obtained at the time of construction of the SMV. For the remaining 8, the SMVs were lined by fibrous tissue that forms in reaction to the synthetic mandrel around which the latissimus muscle is wrapped. After the muscles were electrically conditioned to a fatigue-resistant state, the mandrels were removed from the SMVs and the SMVs were connected to the descending thoracic aorta with a specially constructed base cap and two polytetrafluoroethylene conduits.

RESULTS

Initial hemodynamic recordings revealed that the mean diastolic blood pressure increased by 24.7% in group 1 and by 29.8% in group 2. Diastolic augmentation was well maintained over time; augmentation in surviving group 1 animals was 30.0% after 18 months of pumping continuously in circulation. Long-term survival was greater in the dogs whose SMVs were constructed using an inner pericardial lining. At 90 days in circulation, 60% of the dogs in group 1 were alive with functioning SMVs, whereas only 13% of the dogs in group 2 were alive. The incidence of SMV rupture in the fibrouslined SMVs was 63%, whereas the incidence in the pericardial-lined SMVs was 0%. No evidence of thromboembolism occurred in either group.

CONCLUSIONS

Lining the inner surface of an SMV with pericardium appears to provide structural integrity, which helps to prevent the complication of SMV rupture in this model of cardiac assist.

Endothelial lined skeletal muscle ventricles: open and percutaneous seeding techniques

Twelve bilateral skeletal muscle ventricles (SMVs) were constructed in six dogs by wrapping each latissimus dorsi muscle around a cylindrical, plastic mandrel (volume 30 cc). After 6 to 10 weeks, five dogs had one of their SMVs seeded with allogeneic cultured canine endothelial cells (8 x 10(6) cells/pouch) via an open technique, whil the contralateral SMV was seeded by percutaneous injection of cells into the space around the mandrel. After 1 week, the SMVs were excised. Viable, adherent endothelial cells were present in all seeded pouches; this was confirmed via fluorescent microscopy with several endothelial cell markers; KLH-2, dilacetylated low-density lipoprotein and antibodies to von Willebrand factor. The inner lining of the SMVs were also examined with scanning and transmission electron microscopy; the highest concentration of cells were seen at the apex where a continuous endothelial monolayer was observed. No significant difference in the distribution or the morphology of the endothelial lining was noted between the open and percutaneous seeding techniques. These data show that SMVs can be seeded with an endothelial monolayer using both open and percutaneous techniques.

Chronic morphologic changes of skeletal muscle ventricles in circulation

Skeletal muscle ventricles (SMVs) were constructed either extrathoracically or intrathoracically in 44 dogs using the left latissimus dorsi muscle. These SMVs functioned as aortic counterpulsators for from several hours to 216 days. In this study, the relationship between the morphologic changes in the SMVs and their time course in the circulation was evaluated retrospectively. The average volume of the SMV chamber after it had been excised and fixed in formalin was 21.3 +/- 11.0 mL (mean +/- the standard deviation) for extrathoracic SMVs and 20.0 +/- 7.5 mL for intrathoracic SMVs. The volume of the SMV chamber did not correlate with the time course in the circulation. The SMV wall was mainly composed of three components: muscular, fibrous, and fatty aspects. The overall thickness of the wall appeared to be preserved over time in the circulation. However, the thickness of the muscular component tended to decrease over time. SMV rupture occurred in 15 dogs between postoperative days 4 and 39. All ruptures occurred at the suture line between the SMV and the vascular conduits. There was some degree of thrombus in 24 SMVs. Before SMVs can be applied clinically for the purpose of cardiac assist, problems with rupture and thrombus formation must be solved. A better understanding of the morphologic changes that take place in the SMV over time also is needed.

Dynamic training of skeletal muscle ventricles. A method to increase muscular power for cardiac assistance

BACKGROUND

Skeletal muscle can be used for cardiac assistance after electrical stimulation over a period of several weeks. This will adapt it to do chronic work with no resulting fatigue. The result of this procedure, however, is a reduction of 80% in muscle power, > 60% in muscle mass, and approximately 85% in contractile speed. To minimize these disadvantages, the following study was done to develop and test a method to dynamically train skeletal muscle ventricles (SMVs).

METHODS AND RESULTS

Barrel-shaped SMVs were tested in 15 Jersey calves. They were made from the latissimus dorsi muscle, which was wrapped around an elastic silicone training device. Six SMVs were used extrathoracically in a single layer and nine intrathoracically in a double layer. With dynamic training preserving contractile speed, the output increased to approximately 5 L/min, the systolic pressure increased to > 200 mm Hg, and power developed to approximately 10 W after 3 months of dynamic training. The contractile speed of dynamically trained SMVs was between 250 and 700 mm/s. The diameter of the latissimus dorsi muscle increased to three times that of the corresponding contralateral muscle.

CONCLUSIONS

The combination of electrical conditioning with dynamic training of the SMVs resulted in a strong muscle pump that did not develop fatigue. Dynamic training for skeletal muscle represents a new and promising method for providing powerful autologous cardiac assist.

Skeletal muscle ventricles with efferent valved homograft

Skeletal muscle ventricles (SMVs) were constructed from the latissimus dorsi muscle in seven beagles. Following 3 weeks of vascular delay and 6 weeks of electrical conditioning, the SMVs were connected in series with the thoracic aorta using a valved aortic homograft for the efferent limb. The SMVs were stimulated to contract synchronously during diastole. Effective aortic diastolic counterpulsation was achieved in all dogs, with an average 24.2% +/- 15.3% improvement in diastolic pressure. In two animals surviving beyond 3 months, increase in SMV function was noted over time. Appropriate aortic homograft valve function was documented by echocardiogram. Acute reversible heart failure was induced with propranolol in one dog alive after 126 days. A 61.3% reduction in cardiac output and a 37.6% reduction in mean arterial blood pressure were achieved. During profound low cardiac output, SMV stimulation with 33 Hz and 50 Hz improved cardiac output by 16.9% and 17.8%, improved the tension time index by 14.9% and 16.1%, and improved the endocardial viability ratio by 34.1% and 34.1%, respectively. These results again demonstrate the long-term effectiveness of SMVs as aortic counterpulsators. A valve in the efferent limb of the SMV system functions appropriately over time and may improve the efficiency of the system.