Larry W. Stephenson

Cardiomyoplasty : probable mechanism of effectiveness using the pressure-volume relationship

The mechanism of effectiveness of cardiomyoplasty was evaluated in the setting of chronic left ventricular dysfunction in terms of the pressure-volume relationship. The distal branches of the left coronary artery were ligated in 12 sheep. Seven sheep died and the 5 survivors underwent cardiomyoplasty using a left latissimus dorsi graft 10 to 12 weeks later. These muscle grafts were then electrically conditioned for 2 months. The systemic pressure and cardiac output were not different between the postinfarction and postcardiomyoplasty period with the pacemaker off or on. However, the pressure-volume loops were altered by cardiomyoplasty in all 5 animals. Emax, which is an index of ventricular contractility, increased after cardiomyoplasty from 2.66 +/- 0.92 to 4.59 +/- 1.73 mm Hg/mL (mean +/- the standard deviation; p < 0.05), but did not change between the pacemaker off and on situations. The pressure-volume area, which strongly correlates with myocardial oxygen consumption, decreased after cardiomyoplasty (1,932 +/- 615 mm Hg.mL), compared with before cardiomyoplasty (3,776 +/- 1,201 mm Hg.mL) (p < 0.05), but did not change between pacemaker off and on. The probable mechanism responsible for the effectiveness of cardiomyoplasty is an active support or constraint of the damaged myocardium by the latissimus dorsi and the prevention of further ventricular dilation. This suggests that left ventricular systolic function can be augmented by cardiomyoplasty, but that it is a secondary mechanism of action.

Skeletal muscle ventricles: Left ventricular apex to aorta configuration

Skeletal muscle ventricles (SMVs) were constructed from the latissimus dorsi muscle in 6 dogs. After 3 weeks of vascular delay followed by 6 weeks of 2-Hz continuous electrical conditioning, a valved conduit was placed between the left ventricular apex and the SMV and a second valved conduit, between the SMV and the aorta. The SMV was stimulated to contract during diastole at a 1:2 ratio with the heart. The SMV pumped 47% of the systemic blood flow initially (0.73 ± 0.23 versus 1.54 ± 0.42 L/min) and 40% after 3 hours. Skeletal muscle ventricle stimulation resulted in a 58% increase in mean diastolic pressure initially (52 ± 9 to 82 ± 11 mm Hg; p < 0.05) and a 73% increase (45 ± 7 to 78 ± 8 mm Hg) after 3 hours of continuous pumping. This was associated with a 68% increase in the endocardial viability ratio initially and a 63% increase at 3 hours. The systolic tension-time index decreased by 26% initially and 25% at 3 hours. This study indicates that the SMV configuration of left ventricular apex to aorta may be particularly suitable for left ventricular assist.

Skeletal muscle ventricles as left atrial-aortic pumps: short-term studies.

In 5 dogs, skeletal muscle ventricles (SMVs) were constructed from the latissimus dorsi muscle and placed in the left hemithorax. After a 3-week vascular delay period, SMVs were electrically preconditioned with 2-Hz stimulation for 6 weeks. At a second operation, SMVs were connected between the left atrium and thoracic aorta by afferent and efferent aortic root homografts, and stimulated to contract in a 1:2 diastolic mode. At a mean left atrial pressure of 12.4 +/- 1.3 mm Hg and a burst stimulation frequency of 33 Hz, SMV stroke volume was initially 43% of that of the native left ventricle, achieving a flow equivalent to 21% of cardiac output (194 +/- 38 versus 902 +/- 85 mL/min). At 50-Hz stimulation, this figure rose to 27% (246 +/- 41 mL/min; p less than 0.05). Skeletal muscle ventricle power output (the product of stroke work and contraction rate) at 33 Hz was 0.016 +/- 0.003 W, increasing to 0.024 +/- 0.004 W at 50 Hz (p less than 0.05), corresponding to 14% and 22%, respectively, of left ventricular power output (0.11 +/- 0.012 W). After 4 hours of continuous pumping, four of the SMVs were still generating flows of more than 70% of starting values and more than 60% of initial power output. This study demonstrates that SMVs can function in the systemic circulation at physiologic left atrial preloads.

History of Cardiac Surgery

After the development of general anesthetics such as ether and chloroform during the middle of the nineteenth century, investigators began to study techniques to repair heart wounds in the animal laboratory. Soon, simple operations in humans for heart wounds were reported.

Functional assessment of skeletal muscle ventricles after pumping for up to four years in circulation

BACKGROUNDnThe successful treatment of cardiac failure by heart transplantation is severely limited by the shortage of donor organs, and alternative surgical approaches are needed. An experimental approach that holds considerable promise is the skeletal muscle ventricle (SMV), an auxiliary blood pump formed from a pedicled graft of latissimus dorsi muscle and connected to the circulation in a cardiac assist configuration. Adaptive transformation, or conditioning, by electrical stimulation enables the skeletal muscle to perform a significant proportion of cardiac work indefinitely without fatigue.nnnMETHODSnIn 10 dogs, SMVs were constructed from the latissimus dorsi muscle, lined internally with pericardium, and conditioned by electrical stimulation to induce fatigue resistant properties. The SMVs were connected to the descending thoracic aorta via two 12-mm Gore-Tex conduits and the aorta was ligated between the two grafts. The SMV was stimulated to contract during the diastolic phase of alternate cardiac cycles. The animals were monitored at regular intervals.nnnRESULTSnAt initial hemodynamic assessment, SMV contraction augmented mean diastolic blood pressure by 24.6% (from 61 +/- 7 to 76 +/- 9 mm Hg). Presystolic pressure was reduced by 15% (from 60 +/- 8 to 51 +/- 7 mm Hg) after an assisted beat. Four animals died early, 1 from a presumed arrhythmia, and 3 during propranolol-induced hypotension. The other 6 animals survived for 273, 596, 672, 779, 969, 1,081, and 1,510 days. Diastolic augmentation was 27.4% at 1 year (93 +/- 9 vs 73 +/- 6 mm Hg; n = 5), 34.7% at 2 years (85 +/- 6 vs 63 +/- 7 mm Hg; n = 3), 21.2% (89 +/- 10 vs 73 +/- 8 mm Hg; n = 2) at 3 years, and 34.5% (78 vs 58 mm Hg; n = 1) after 4 years in circulation. After 4 years, the isolated SMV was able to maintain a pressure of over 80 mm Hg while ejecting fluid at 20 mL/s. No animal showed evidence of SMV rupture or thromboembolism.nnnCONCLUSIONSnThe SMVs in this study provided effective and stable hemodynamic assistance over an extended period of time. There was no evidence that the working pattern imposed on the muscular wall of the SMV compromised its viability. Areas of fibrofatty degeneration were suggestive of early damage that future protocols should seek to minimize.

Pericardium-lined skeletal muscle ventricles in circulation up to 589 days

Skeletal muscle ventricles (SMVs) were constructed from the latissimus dorsi muscle in 15 beagles. The animals were divided into two groups based on modifications in the SMV construction: group I consisted of 5 animals and group II of 10 animals. After a 3-week vascular delay and 6 to 8 weeks of 2-Hz electrical conditioning, the SMVs were connected to the thoracic aorta. In group I, counterpulsation at 33 Hz resulted in an initial 24.4% augmentation of the mean diastolic pressure, a 27.1% decrease in the presystolic pressure, and a 15.9% increase in the endocardial viability ratio. In group II, the mean diastolic pressure rose by 24.7%, the presystolic pressure decreased by 14.3%, and the endocardial viability ratio increased by 24.5%. During propranolol-induced heart failure, the percentage increase in the mean diastolic pressure was improved (12.9% before propranolol infusion versus 27.6% during propranolol infusion), as was the percentage increase in the endocardial viability ratio (11.2% versus 28.7%). Under low cardiac output conditions, SMV contraction resulted in small but statistically significant increases in the total cardiac output (4.3% at 33 Hz, 7.6% at 85 Hz). One animal in group I survived for 589 days with a functioning SMV before progressive dilation of the SMV (impending rupture) developed. Delayed rupture of the SMV sewing ring anastomosis occurred in 2 dogs. Five animals in group II are all alive, with functioning SMVs in the circulation for 377 to 464 days. No animals in group II had rupture of their SMV or showed evidence of thrombus formation.

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.

Doxorubicin-Induced Canine CHF:

Abstractu2003 Background. The dog is the most commonly used laboratory animal for heart surgery research. It has been difficult, however, to develop a canine chronic heart failure model, particularly without associated significant tachycardia. Our objective is to utilize intracoronary doxorubicin at various doses to evaluate a chronic model of left ventricular dysfunction and develop a dose‐response relationship. Methods. In 18 dogs, we evaluated their hemodynamic function, placed an in‐dwelling intracoronary catheter, and then administered four weekly infusions of doxorubicin at 5 mg (n = 6), 10 mg (n = 6), or 15 mg (n = 6). Hemodynamic measurements were taken again at 4–5 weeks after infusion, and a final measurement at 14–18 weeks. Results (See table). In the low dose group, all six animals survived the post‐infusion period. Cardiac output changed from 2.9 ± 0.2 to 2.2 ± 0.5. The medium dose group had a mortality of 33% (2/6 dogs), with a moderate decrease in cardiac output (3.1 ± 0.4 to 2.3 ± 0.3 L/min). The high dose group had a mortality of 67% (4/6 dogs), with a dramatic decrease in cardiac output (3.0 ± 0.2 L/min to 1.6 ± 0.7 L/min (p < 0.05). None of the dogs developed a significant tachycardia. Conclusion. This study reconfirms that doxorubicin, when given into the coronary arteries, induces cardiac dysfunction. It appears to be dose‐dependent, but more importantly, in doses where the LV dysfunction yields overt heart failure; the mortality over 14 weeks is significant and likely unacceptable for most chronic heart failure studies. (J Card Surg 2003; 18:301‐306)

Pericardium-Lined Skeletal Muscle Ventricles: Up to Two Years' In-Circulation Experience1

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

Skeletal muscle for cardiac assistance.

The last few years have witnessed considerable interest in the use of skeletal muscle to assist the heart. This review outlines developments of particular relevance and importance to this field during the past 12 months. The use of conditioned, fatigue resistant latissimus dorsi muscle has been proposed for cardiomyoplasty, for constructing separate pumping chambers, and for powering alternative assist systems. Although the cardiomyoplasty procedure has been applied clinically, the other techniques remain experimental, but promising, modes of support.