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.     

Variable Effects of Cardiomyoplasty on Left Ventricular Function

Abstract: Cardiomyoplasty (CMP) has been considered as a possible treatment for patients with heart failure. Symptomatic improvements occur almost uniformly among survivors with CMP, but changes in left peak ventricular systolic pressure (PVSP) and stroke volume vary in patients. This study examined whether there is variability present shortly after cardiomyoplasty surgery. Cardiomyoplasty was performed in 11 mongrel dogs with normal ventricular function. Nine to twelve days after CMP, left ventricular (LV) function was evaluated by simultaneously measuring LV volume (conductance catheter) and pressurc (Millar catheter). The latissimus dorsi muscle (LDM) was stimulated synchronously with ventricular systole in a ratio of 1:4 to 1:7 to avoid muscle fatigue. Data were analyzed on a beat by beat basis. The PVSP, and maximum dP/dt (+dP/ dt ) increased, but the absolute value of minimum dP/dt (-dP/dt ) decreased in stimulated beats in 7 dogs while 4 dogs did not respond. The net changes in stimulated beats versus nonstimulated beats of PVSP were 6.1 ± 1.8 mm Hg (4.3%), of stroke work was 4.5 ± 1.9 gm. m (29.5%), of +dP/dt was 185 ± 47 mm Hg/s (So/,), and of -dP/dt was 168 ± 43 mm Hg/s (7.8%) (p < 0.05) for all these net changes in the responding group while these variations were not significant in the nonresponding group. From the results of our study, active LDM assist improves left ventricular systolic function, occurring in only 7 of 11 experiments. This improvement is inconsistent and varied individually. The integrity of the LDM, tightness of wrapping, and adhesions might contribute to the variability which is present early after surgery and before the LDM is converted into a fatigue resistance muscle.     

Vascular delay of the latissimus dorsi provides an early hemodynamic benefit in dynamic cardiomyoplasty.

OBJECTIVES: Dynamic cardiomyoplasty (CMP) as a surgical treatment for chronic heart failure improves functional class status for most patients. However, significant hemodynamic improvement with latissimus dorsi muscle (LDM) stimulation has not been consistent. The current protocols do not allow early LDM stimulation after CMP surgery. We hypothesized that vascular delay of LDM would increase myocardial assistance after CMP and allow early (48-h) LDM stimulation after CMP. METHODS: Mongrel dogs (n = 24) were divided in four groups: 1) controls (n = 6), single-stage CMP; 2) Group ES (n = 6), single-stage CMP with early LDM stimulation beginning 48 h, postoperatively; 3) Group VD (n = 6), vascular delay of the LDM followed by CMP without early LDM stimulation, and 4) Group VDES (n = 6), vascular delay of LDM (14-18 days), followed by CMP with early stimulation (48 h postoperatively). Two weeks after CMP, global cardiac dysfunction was induced by injecting microspheres into the left coronary artery. LDM-assisted (S) beats were compared with nonstimulated beats (NS) by measuring aortic pressure (AoP), LV pressure, aortic flow, and by calculating first derivative of LV contraction (+/-dP/dt), stroke volume (SV), and stroke work (SW). RESULTS: In ES, LDM stimulation had no effect on the hemodynamic parameters. In the other groups, LDM stimulation significantly (p < 0.05) increased AoP, LVP, dP/dt, SV, and SW. However, these increases were much larger in VD and VDES. In VD, LDM stimulation increased peak AoP by 21.5+/-3.8 mm Hg, LVP by 22.1+/-4.1 mm Hg, dP/dt by 512+/-163 mm Hg/sec, SV by 10.4+/-2.3 mL, and SW by 22.1+/-5.4 g/m(-1). Similarly, in VDES, LDM stimulation increased peak AoP by 24.1+/-4.7 mm Hg, LVP by 26.2+/-4.3 mm Hg, dP/dt by 619+/-47 mm Hg/sec, SV by 6.5+/-0.7 mL, and SW by 16.7+/-4.1 g/m(-1). CONCLUSIONS: In dogs with global LV dysfunction, CMP after vascular delay resulted in a significant improvement in hemodynamic function measured 2 weeks after surgery. This improvement was not provided by single-stage CMP with or without early stimulation. Vascular delay of the LDM before surgery may play an important role for early benefit after CMP, shorten the overall muscle training period, as well as increase hemodynamic response to LDM stimulation.     

Optimal Electrical Stimulation for Latissimus Dorsi Muscle After Cardiomyoplasty

A bstract The aim of this study was to evaluate the functional state of latissimus dorsi muscle (LDM) during electrical stimulation following cardiomyoplasty. Both single pulses and bursts of impulses were used for electrical stimulation. In 15 dogs, studies were carried out for 2 months, while in 19 patients, the follow-up period after cardiomyoplasty was 10 ± 3.1 months. The LDM was punctured by needle electrodes at various intervals following cardiomyoplasty, and the changes of the rheomyosignal (RMS) curve were registered on the "Reostim-06." During the follow-up study, it was found that: (1) signal amplitude decreased 30%; (2) the contraction duration of LDM increased 38%; (3) the contraction velocity decreased 43%; and (4) relaxation velocity decreased 61%. There is a correlation between LDM mechanical contractile force and RMS indices (r = 0.8). The RMS index was a function of the electrical burst duration and the number of impulses in the bursts. Thus, RMS parameters can characterize the functional state of LDM, and they may be used in designing a new generation of electromyostimulators for optimal LDM stimulation at different periods after cardiomyoplasty.     

Hemodynamic Response To In Situ Latissimus Dorsi Muscle Stimulation: Implications in Dynamic Cardiomyoplasty

A bstract Dynamic cardiomyoplasty (DCM) involves the electrical stimulation of a pedicled latissimus dorsi muscle flap wrapped around the failing ventricle as a means of cardiac assist. To further elucidate a potential neurohumoral mechanism for improvement of cardiac output after myoplasty, we evaluated the hemodynamic effects of in situ stimulation of the latissimus dorsi muscle (in the absence of cardiomyoplasty). In seven mongrel dogs, a nerve cuff electrode (Medtronic 6901) was placed around the left thoracodorsal nerve (TDN). This was attached to a pulse generator (Medtronic, Itrel 7420), delivering a 4.0 volt, 0.19 second on, 0.81 second off, 33 Hz, 210 microsecond pulse width, cyclic bursts similar to that used in DCM. Stroke volume index (SVI) and other hemodynamic parameters as well as plasma norepinephrine (NE) levels were measured at five stages: baseline, stimulator on at 0, 2, and 5 minutes, and stimulator off at 30 minutes after. The animals were then subjected to 4 weeks of rapid pacing at 240 beats/min (Medtronic 8329) to induce heart failure, and as the rapid pacing was discontinued, measurements were repeated as above. After rapid pacing, cardiac function was significantly depressed, and NE was elevated (133 ± 69 versus 500 ± 353 pg/mL, p < 0.05). In the normal hearts, TDN stimulation increased SVI, heart rate, systemic pressure, and NE levels. In heart failure, however, no significant changes in cardiac function and NE levels were noted. In conclusion, our data indicate that in the normal hearts, afferent impulses from TDN stimulation alone may augment cardiac function by means of a neurohumoral effect that is not seen in severe heart failure. The implications of these findings in DCM are discussed.     

Cardiomyoplasty Benefits in Experimental Myocardial Dysfunction

Beneficial effects of cardiomyoplasty have been documented and the use of this technique in the treatment of dilated cardiomyopathy have been suggested. This study was undertaken to evaluate the effectiveness of stimulated preconditioned latissimus dorsi muscle flaps wrapped around the heart in order to restore ventricular contractility in six adult mongrel dogs with induced myocardial dysfunction by administration of beta blockers and volume loading. Hemodynamic and two-dimensional echocardiographic evaluation were performed 1 week after the surgical procedure and immediately after heart failure induction. With synchronous pulse train electrical stimulation, cardiac output increased from 1.46 +/- 0.13 (+/- SD) to 2.01 +/- 0.16 L/min (p less than 0.01), pulmonary wedge pressure decreased from 15.5 +/- 1.2 to 11.3 +/- 1.6 mmHg (p less than 0.01) and left ventricular end-diastolic pressure from 18.3 +/- 2.4 to 13.5 +/- 1.4 mmHg (p less than 0.04). Echo derived left ventricular ejection fraction increased from 39.3 +/- 2.4 to 59.6 +/- 2.9% (p less than 0.01) and segmental wall shortening from 15.4 +/- 1.2 to 26.3 +/- 1.7% (p less than 0.01), inclusive when the muscle flap was wrapped only around the left ventricle. In conclusion, this study suggests that cardiomyoplasty may be an alternative method of treatment for irreversible cardiomyopathy, including in patients with a great cardiac enlargement in which muscle flap may only be wrapped partially around the heart.     

New hopes for dynamic cardiomyoplasty from use of Doppler flow wire in evaluation of demand stimulation.

BACKGROUND: There are no data regarding real cardiac assistance in demand dynamic cardiomyoplasty (DDCMP). A test of the use of Doppler flow wire is presented to demonstrate cardiac assistance in DDCMP. METHODS: Comparative study in hospitalized care. A peripheral Flex Doppler flow wire of 0.018 inch was advanced through a 4F introducer femoral arterial in seven DDCMP patients (age=57.1+/-6.2 years; NYHA= 1.4+/-0.5). A short period of 10 sec with stimulator off and a following period of 15 sec with clinical stimulation were recorded. We measured the maximum peak aortic flow velocity (MPAV) in all beats. Latissimus dorsi (LD) mechanogram was simultaneously recorded. RESULTS: Statistical analysis showed an increase not only in MPAV in assisted period versus rest, but also in assisted beats versus unassisted (8.42+/-6.98% and 7.55+/-3.07%). CONCLUSIONS: Intravascular Doppler proved real systolic assistance in DDCMP; in DDCMP systolic assistance is correlated to the LD wrap speed of contraction, suggesting that demand stimulation could be the most effective protocol in dynamic cardiomyoplasty.     

Acute Hemodynamic Effects of Cardiac Resynchronization Therapy in Patients with Poor Left Ventricular Function During Cardiac Surgery

Abstract   Background: Cardiac resynchronization therapy improves systolic function in patients with heart failure and left ventricular (LV) dyssynchrony. However, the effect of biventricular (BiV) pacing on perioperative hemodynamics in cardiac surgery is not well known. We investigated the acute hemodynamic response using LVdP/dt_max in patients with depressed LV function and conduction disturbances undergoing cardiac surgery. Methods: Patients with LV ejection fraction of ≤35%, QRS duration of >130 ms, and left bundle branch block undergoing aortocoronary bypass and valve surgery were included. Temporary atrial and left and right ventricular pacing wires were applied, and LVdP/dt_max was measured with a high fidelity pressure wire in the left ventricle at the end of cardiopulmonary bypass. Responders had a ≥10% increase in LVdP/dt_max. Results: Eleven patients (age 63 ± 11 years, eight males) with a LV ejection fraction 0.29 ± 0.06% were included. Compared with right ventricular pacing (782 ± 153 mmHg/sec), there was a significant improvement in the mean LVdP/dt_max during simultaneous BiV pacing (849 ± 174 mmHg/sec; p = 0.034) and sequential BiV pacing with the LV 40 ms advanced (880 ± 157 mmHg/sec; p = 0.003). Improvement during LV pacing alone was not significant (811 ± 141 mmHg/sec). Six patients were responders with simultaneous and nine with sequential BiV pacing. Only sequential BiV pacing had a significant improvement in LV systolic pressure (p = 0.02). Conclusions: BiV pacing results in acute hemodynamic improvement of LV function during cardiac surgery. Optimization of the interventricular pacing interval contributes to the effect of the therapy.     

Dynamic cardiomyoplasty for long-term cardiac assist

The principle of cardiomyoplasty is long-term electrostimulation of a latissimus dorsi muscle (LDM) wrapped around the failing heart. Technically, this procedure consists of placing the left LDM flap around the heart via a window created by partial resection of the 2nd or 3rd rib, and subsequent muscle electrostimulation in synchrony with ventricular systole. The aim of cardiomyoplasty is to support ventricular function in ischemic or dilated cardiomyopathies, or to partially replace the ventricular myocardium after large aneurysm or tumor resections. Our clinical experience at Broussais Hospital involves 44 patients. The functional class and quality of life improved after cardiomyoplasty. Improvement of the ventricular performance and limitation of cardiac dilatation were demonstrated over the long-term. The actuarial survival at 6 years was 71%. Risk factors influencing perioperative mortality were: age >65 years, associated surgical procedures, pulmonary vascular hypertension, and patients hemodynamically unstable or on inotropic drug support. Preoperative risk factors influencing the long-term mortality were: permanent NYHA functional class 4, cardiothoracic ratio >0.60, LV ejection fraction <15%, bi-ventricular heart failure, and atrial fibrillation. Cardiomyoplasty does not preclude the use of future orthotopic heart transplantation.     

Muscle contraction and relaxation described by tactile stiffness

We developed a tactile sensor system that measures the stiffness of objects (tactile stiffness) and used it to describe the time course of muscle contraction and relaxation. We examined fatigue resistance of the latissimus dorsi muscle (LDM), which is preconditioned for cardiomyoplasty. Time to peak, ripple of LDM, and time constant were calculated from the time course of LDM contraction and relaxation as described by tactile stiffness. We compared conditioned and unconditioned LDMs using these 3 parameters. The time course can be described by tactile stiffness. Tactile stiffness fell exponentially during LDM relaxation. In mean values, time to peak increased 230%, ripple decreased 20%, and time constants increased 424%. Significant differences were shown in 3 parameters between conditioned and unconditioned LDMs (p < 0.05). Our tactile sensor system can describe the time course of LDM contraction and relaxation. Examining the difference in time courses, we might detect the level of LDM preconditioning for cardiomyoplasty.     

Vascular delay and intermittent stimulation: keys to successful latissimus dorsi muscle stimulation

Background. The goal of this study was to obtain physiologically significant increases in peak left ventricular (LV) systolic pressure and stroke volume with latissimus dorsi muscle (LDM) stimulation in cardiomyoplasty (CMP). We hypothesized that preserving LDM integrity by vascular delay and intermittent stimulation would significantly increase LDM cardiac assistance.

Methods. In 4 control dogs and 12 dogs that had undergone a vascular delay (VD) procedure, LV dysfunction was induced by intracoronary microsphere injections. Cardiomyoplasty surgery was performed 14 days later, followed by progressive LDM conditioning. In the control dogs and in 6 of the VD dogs, the LDM was stimulated 24 hours per day (VD plus constant stimulation [CS]). In the other 6 VD dogs, LDMs were stimulated on a daily schedule of 10 hours on and 14 hours off (VD plus interrupted stimulation [IS]). Latissimus dorsi muscle stimulated beats were compared with nonstimulated beats 9 weeks later.

Results. In the control dogs, LDM stimulation had minimal effects. In VD + CS and VD + IS, LDM stimulation increased peak LV pressure, stroke volume, stroke work, and stroke power (p < 0.05). However, these changes were greater in the VD + IS group, in which LDM stimulation increased peak aortic pressure by 17.6 ± 1.7 mm Hg, peak LV pressure by 19.7 ± 1.1 mm Hg, peak positive LV dp/dt by 398 ± 144 mm Hg per second, stroke volume by 5.1 ± 0.7 mL, stroke work by 10.9 ± 0.9 gm · m, and stroke power by 122.7 ± 11.6 gm · m per second (p < 0.05 compared with VD + CS). Quantitative morphometric analysis showed minimal LDM degeneration in the VD + IS group (7.5% ± 1.1%), and VD + CS group (10.5% ± 4.5%) compared with the control group (29.5% ± 4.5%, p < 0.05).

Conclusions. VD and IS considerably increased the LV assistance with LDM stimulation. Further studies of this combined approach to CMP should be planned.     

Effects of Wrapping Tightness on Acute Cardiac Function in Dynamic Cardiomyoplasty

Background. It has not been clarified how tightly the heart should be wrapped for maximal augmentation of cardiac function in cardiomyoplasty.

Methods. Hearts in acute failure induced by propranolol were wrapped with the left latissimus dorsi muscle, loosely (loose CMP), moderately (moderate CMP), and tightly (tight CMP) in each of 5 pigs. To measure the pressure between the latissimus dorsi muscle and the left ventricle (LV), a Millar pressure catheter with a latex balloon was placed on the anterior wall of the LV. Left ventricular wall tension was calculated according to Laplace's law, using the difference between the LV pressure and the balloon pressure.

Results. In the loose CMP, moderate CMP, and tight CMP groups, the mean balloon pressures during unassisted beats were 8.2, 10.4, and 13.2 mm Hg, respectively. During unassisted beats, the mean LV wall tension values were 38,683, 29,938 (p < 0.05 versus loose CMP), and 26,652 (p < 0.05 versus loose CMP) dynes/cm, respectively, the peak LV pressures were 76.8, 73.8, and 65 (p < 0.05 versus loose CMP) mm Hg, respectively, and the stroke volumes were 12.8, 9.2, and 8.5 (p < 0.05 versus loose CMP) mL, respectively. During assisted beats, the mean LV wall tension values were 20,059, 11,290, and 7,893 (p < 0.05 versus loose CMP) dynes/cm, respectively, the peak LV pressures were 94.1, 98.1, and 92.0 mm Hg, respectively, and the stroke volumes were 13.8, 11.6, and 9.4 (p < 0.05 versus loose CMP) mL, respectively.

Conclusions. During unassisted beats, tight CMP (13 mm Hg) had the advantage of diminishing LV wall tension, but the disadvantage of diminishing LV pressure and stroke volume, compared with loose CMP (8 mm Hg). Moderate CMP (10 mm Hg), however, had the advantage of diminishing LV wall tension without a decrease in LV pressure and stroke volume.     

Preparation of a skeletal muscle ventricle in sheep: severe damage to the Latissimus dorsi muscle due to mobilization before preconditioning

As part of a study examining the use of a skeletal muscle ventricle for cardiac assistance in sheep, a new concept of muscle preconditioning was put into practice. We aimed to produce a latissimus dorsi muscle (LDM) capable of performing chronic work immediately after the construction of a skeletal muscle ventricle. The left LDM was detached from the thoracic wall, divided longitudinally and reattached in situ to achieve vascular delay. The right LDM was left unaffected. Thereafter, preconditioning of both LDM was started according to the clinically approved stimulation protocol for cardiomyoplasty. Preconditioning of the unaffected right LDM in situ resulted in a complete muscle fiber transformation with no signs of degeneration or necrosis. Mobilization of the left LDM before preconditioning led to a distinct damage of the muscle. During conditioning, the increase in burst duration from 2 to 3 impulses in sheep A and from 3 to 5 impulses in sheep B resulted in a homogenous degeneration of the muscle fibers of the left LDM. Histomorphological analysis showed a dramatic increase in the percent perimysial and endomysial connective tissue. The applied concept of muscle prefabrication proved to be a failure. Muscle splitting and mobilization followed by vascular delay and in situ conditioning as a concept of muscle prefabrication should be strictly avoided.     

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.     

Combination of preconditioning and delayed flap elevation: evidence for improved perfusion and oxygenation of the latissimus dorsi muscle for cardiomyoplasty

BACKGROUND: Atrophy and fibrosis of the distal part of the latissimus dorsi muscle (LDM) wrap is a recognized complication of cardiomyoplasty that has been attributed to ischemia. Failure of the muscle wrap contributes to the late attrition seen in clinical cardiomyoplasty. In this study we examined the role of two-staged mobilization and of preconditioning by electrical stimulation on the regional perfusion and oxygenation of the LDM. METHODS: In a rabbit model (n = 36) the LDM was preconditioned as follows: group A muscles received preconditioning in situ; group B muscles were partially mobilized by dividing the intercostal perforators and then preconditioned; and group C muscles were completely mobilized and wrapped around a silicone-rubber mandrel before conditioning. Controls received no conditioning. The preconditioning regimen consisted of 2 weeks of continuous stimulation at 2.5 Hz. At completion of preconditioning the muscles were fully mobilized and mounted on a muscle-testing apparatus. Purpose-built microelectrodes measured regional PO2 and perfusion using a diffusible gas tracer technique. Muscles were weighed and processed for fiber typing and capillary counting. RESULTS: All preconditioned muscles demonstrated fiber transformation, with increased fatigue resistance. Perfusion of preconditioned muscles both at rest and during contraction was higher than control in the proximal part of the muscle. Distal regions of group B muscles had higher perfusion and capillary density than any other group (p < 0.05). Distal regions of group C had the lowest perfusion and capillary density, and showed muscle atrophy and histologic evidence of necrosis. During fatigue testing there was a decrease in the PO2 in the distal regions of the control and group C muscles (p < 0.05), whereas it was maintained at resting levels in both group A and B muscles. CONCLUSIONS: Conditioning in situ improves perfusion of the distal LDM and prevents a fall in tissue PO2 during contraction. Two-stage mobilization further improves distal perfusion and capillary density. In contrast, shortterm elevation followed by conditioning produces impaired distal perfusion, decrease in PO2, and fiber necrosis in the distal muscle. The present study suggests that partial mobilization of the LDM performed at the same time as placement of electrodes for preconditioning may prepare the LDM better for the demands of cardiomyoplasty.     

Assisted Circulation Using Cardiomyoplasty Together with Aortomyoplasty

Abstract: Both dynamic cardiomyoplasty and counterpulsation by the synchronous paced contraction of skeletal muscles in aortomyoplasty can improve ventricular function. The goal of this study was to clarify the effect of cardiomyoplasty combined with aortomyoplasty on cardiac dysfunction in dogs. The percentage of increase in various hemodynamic parameters was calculated during assisted and unassisted cardiac cycles and was compared for three groups: cardiomyoplasty only (Group A), aortomyoplasty only (Group B), and both methods combined (Group C). In Group A, the left ventricular pressure (LVP), systolic aortic pressure (systolic AoP), and dp/dt of LVP (LVdp/dt) increased significantly; the diastolic aortic pressure (diastolic AoP) did not change; and the endocardial viability ration (EVR) decreased during assisted cardiac cycles. In Group B, the diastolic AoP and EVR were improved significantly, but the LVP, LVdp/dt, and systolic AoP were unchanged during assisted cardiac cycles. In contrast to Groups A and B, all parameters were improved in Group C during assisted cardiac cycles. Cardiac assistance using cardiomyoplasty together with aortomyoplasty was more effective than either procedure used alone.     

Activity-rest stimulation protocol improves cardiac assistance in dynamic cardiomyoplasty.

OBJECTIVE: No data have ever been published regarding cardiac assistance in demand dynamic cardiomyoplasty (DDCMP). We tested the efficacy of the Doppler flow wire in measuring beat-to-beat aortic flow velocity and evaluating cardiac assistance in demand cardiomyoplasty patients. METHODS: The technique was tested in seven patients (M/F=6/1; age=57.1+/-6.2 years; atrial fibrillation/sinus rhythm=1/6; NYHA=1.4+/-0.5). Measurements were done using a 0.018inch peripheral Doppler flow wire advanced through a 5F arterial femoral sheath. Three 1-min periods with the stimulator off and three 1-min periods with clinical stimulation were recorded. We measured peak aortic flow velocity in all beats. Latissimus dorsi (LD) mechanogram was simultaneously recorded. RESULTS: Comparison between pre-operative and follow-up data showed significantly higher values of tetanic fusion frequency (TFF) and ejection fraction at follow-up, whereas mean NYHA class was significantly lower. Statistical analysis showed an increase in aortic flow velocity not only in assisted versus rest period, but also in assisted versus unassisted beats (8.42+/-6.98% and 7.55+/-3.07%). A linear correlation was found between the increase in flow velocity and LD wrap TFF (r(2)=0.53). CONCLUSIONS: In DDCMP, systolic assistance is significant and correlated to LD speed of contraction; demand stimulation protocol maintains muscle properties and increases muscle performance.     

Evaluation of stimulation parameters on aortomyoplasty, using Latissimus Dorsi muscle in a goat model: an acute study.

OBJECTIVE: Dynamic aortomyoplasty using Latissimus Dorsi muscle (LDM) has been shown to improve myocardial function. However, systematic examination of the effects of stimulation parameters on aortic wrap function has not been done. Thus, the present study measures the direct effect of stimulation voltage, pulse train duration, frequency of the pulses, and the duration of the stimulation delay from R wave on the aortic wrap function. METHODS: In eight female goats, the left LDM was wrapped around the descending aorta. The muscle was then subjected to electrical stimulation, altering frequency of stimulation pulses (16.6, 20, 25, 33 and 50 Hz), amplitude (2, 4, 6, 8 and 10 V), and number of pulses (2, 4, 6, 8 and 10 pulses) in a train stimulation. Left ventricular, aortic pressure, and pressure generated by LDM on aorta (wrap pressure) was measured. The changes in hemodynamic parameters mentioned above were calculated and compared for different stimulation parameters during unassisted and assisted cardiac cycles. RESULTS: Aortomyoplasty counterpulsation using LDM provided significant improvement in wrap pressure (78 mmHg +/- 2), aortic diastolic pressure, and changes in aortic diastolic pressure from 2 to 4 V (P < 0.05). Further increase in amplitude did not make any significant improvements of the above mentioned parameters. Significant augmentation of wrap pressure (82 mmHg +/- 2), aortic diastolic pressure (79 mmHg +/- 3) and changes in aortic diastolic pressure (12 mmHg +/- 1) occurred at 6 pulses (P < 0.05). Other changes in number of pulses did not show any significant improvements. Significant improvement of wrap pressure (80 mmHg +/- 2), aortic diastolic pressure (73 mmHg +/- 3) and changes in aortic diastolic pressure (12 mmHg +/- 1) was observed with a frequency of 33 Hz. To examine a wide range of delays from the onset of the QRS complex to LDM stimulation, stimulation was delivered randomly. The exact delay was determined from the ECG signal and superimposed LDM stimulation pulses. CONCLUSIONS: In this study we present a new measurement, wrap pressure. We also present that in aortomyoplasty using LDM, the most significant improvement in wrap pressure, aortic diastolic pressure and changes in aortic diastolic pressure occurs when the stimulation consists of an amplitude of 4 V, a frequency of 33 Hz and a train stimulation of 6 pulses.     

Adynamic Cardiomyoplasty: Effect on Cardiac Efficiency and Contractile Reserve in Dogs with Adriamycin-Induced Cardiomyopathy

ASTRACT The girdling effect of the skeletal muscle wrap seems to be the primary mechanism of action of cardiomyoplasty. It is associated with a myocardial sparing effect. Myocardial sparing effect has been shown with an active muscle wrap or an active muscle wrap acutely turned"OFF". The purpose of the study was to evaluate the effect of a passive skeletal muscle wrap on cardiac energetics parameters and contractile reserve in a canine model of cardiomyopathy. Six dogs with adriamycin-induced cardiomyopathy were studied. Three dogs underwent right latissimus dorsi adynamic cardiomyoplasty and 3 served as controls. Cardiac and coronary sinus catheterizations were performed at 0 and 6 weeks. A dobutamine stress test was performed at 6 weeks. Myocardial oxygen consumption was not reduced in the cardiomyoplasty group (139.20 ± 86.90 Joules/min) compared to the control group (95.10 ± 12.60 Joules/min, P = 0.27) at 6 weeks. Mechanical cardiac efficiency was increased in the cardiomyoplasty group (33.15 ± 4.40%) compared to the control group (24.50 ± 2.70%, P = 0.049) at 6 weeks. Left ventricular end diastolic diameter index was reduced in the cardiomyoplasty group (38.00 ± 1.70 mm/m²) compared to the control group (46.30 ± 1.55 mm/m², P = 0.049) at 6 weeks. Indices of diastolic function-dp/dt, and tau were not significantly affected by adynamic cardiomyoplasty. Max dp/dt was increasing more in the cardiomyoplasty group than in the control group (P = 0.07) during dobutamine stress test. Mechanical cardiac efficiency was better preserved by the adynamic cardiomyoplasty. Myocardial contractile reserve might be better preserved with cardiomyoplasty.     

Effects of a new cardiomyoplasty technique on cardiac function

OBJECTIVE: The current cardiomyoplasty technique was modified to maintain the resting tension of the latissimus dorsi muscle and to prevent lateral movement of the heart during muscle stimulation. The aim of this study is to compare the short term hemodynamic effects of the new cardiomyoplasty wrap (W1) with those of the clinically applied cardiomyoplasty wrap (W2). Preliminary indications of the long-term hemodynamic effects of W1 are presented. METHODS: In three acute experiments in sheep mean central venous pressure (MCVP), mean arterial pressure (MAP), mean cardiac output (MCOP), mean left ventricular systolic pressure (MLVSP), and mean left ventricular diastolic pressure (MLVDP) were measured for 30s before and five minutes after applying each procedure with and without stimulation of the muscle graft. The same parameters were also recorded 5min after removing each muscle wrap. Hemodynamic changes associated with unstimulated muscle wraps were compared to the baseline data. Hemodynamic effects of muscle stimulation were determined by comparing the assisted to the preceding unassisted cardiac cycle. The long-term effects of W1 on the hemodynamics of another three sheep were studied at 6-12months after the operation. The viability of the muscles used in the chronic experiments were evaluated by morphometric analysis. RESULTS: Unstimulated W2 significantly increased mean central venous pressure and reduced mean cardiac output. It also increased mean left ventricular diastolic pressure and reduced peak negative dP/dt. Unstimulated W1 had no deleterious effect on mean central venous pressure, mean left ventricular diastolic pressure or peak -dP/dt, but it also reduced mean cardiac output and increased mean left atrial pressure (MLAP). Synchronised muscle stimulation, in both techniques, augmented the mean arterial pressure, mean cardiac output and mean left ventricular systolic pressure. In W2, however, myostimulation was also associated with a significant increase of the mean left ventricular diastolic pressure. In two long-term experiments significant hemodynamic assistance was observed at 6months and at 1yr after W1. In those sheep 68% of the cross-sectional area of the muscle was well preserved. CONCLUSIONS: Unstimulated cardiomyoplasty wraps acutely impair left ventricular function in sheep. The new technique, however, may offer significant long-term hemodynamic assistance and adequate preservation of the structural and functional integrity of the muscle flap for up to 1yr.