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

Inadequacy of Augmentation Index for Monitoring Arterial Stiffness: Comparison with Arterial Compliance and Other Hemodynamic Variables

PURPOSE

Augmentation Index (AI_x) is used clinically for monitoring both wave reflections and arterial stiffness, which when increased is a risk factor of cardiovascular mortality and morbidity. We hypothesize that AI_x is not solely related to vascular stiffness as described by arterial compliance and other hemodynamic parameters since AI_x underestimates wave reflections.

METHODS

Aortic pressure and flow datasets (n = 42) from mongrel dogs were obtained from our experiments and Mendeley Data under various conditions. Arterial compliances based on the Windkessel model (C_t), the stroke volume (SV) to pulse pressure (PP) ratio (C_v = SV/PP), and at inflection pressure point (C_Pi) were computed. Other relevant hemodynamic factors are also computed.

RESULTS

AI_x was poorly associated with arterial stiffness calculated from C_t (r = 0.299, p = 0.058) or C_Pi (r = 0.203, p = 0.203), even when adjusted for heart rates. C_t and C_v were monotonically associated. Alterations in inflection pressure (P_i) did not follow the changes in pulse pressure (PP) (r = 0.475, p = 0.002), and P_i was quantitatively similar to systolic pressure (r = 0.940, p < 0.001).

CONCLUSION

AI_x is neither linearly correlated with arterial stiffness, nor with arterial compliance and several cardiac and arterial parameters have to be considered when AI_x is calculated.

Augmentation index in the assessment of wave reflections and systolic loading

BACKGROUND

Augmentation index (AI_x) is used to quantify the augmented systolic aortic pressure that impedes ventricular ejection. Its use as an index of wave reflections is questionable. We hypothesize that AI_x is quantitatively different from the reflection coefficient under varied physiological conditions.

METHODS

42 datasets of aortic pressure and flow waveforms were obtained during induced hypertension (methoxamine infusion) and vasodilation (nitroprusside infusion) in our mongrel dog experiments (n = 5) and from Mendeley data during various interventions (vasoconstrictors, vasodilators, pacing, stimulation, hemorrhage and hemodilution). Wave reflections and principal components of reflection coefficients were computed for comparison to AI_x and heart rate normalized AI_x. RESULTS: Principal reflection coefficient, Γ₁, increased in hypertension and decreased in vasodilation, hemorrhage and hemodilution. AI_x followed the trend in many cases but was consistently lower than Γ₁ in almost all the subjects. The Bland-Altman analysis also showed that both AI_x and normalized AI_x underestimated Γ₁. The relationship between augmentation index and reflection coefficient was explained by a linear regression model (r² = 0.23, p < 0.01) in which AI_x followed directional changes in Γ₁ and the normalization of AI_x resulted in a linear model that explained less variation in the relationship between AI_x and Γ₁.

CONCLUSION

AI_x is a reasonable clinical trend indicator, albeit not an accurate surrogate measure of the amount of wave reflections.

Performance of Dynamic and Isovolumetric Trained Skeletal Muscle Ventricles

BACKGROUND

Dynamic training and maintaining muscle tension are important factors during skeletal muscle ventricle (SMV) conditioning that may improve SMV performance. This study sought to determine the effects of dynamic muscle training and progressive SMV resting pressure expansion on SMV pumping capability.

MATERIALS AND METHODS

SMVs were constructed in 14 goats using the left latissimus dorsi muscle. SMVs were conditioned with a 40 ml constant-volume isovolumetric implant (n = 5, IsoVol group) or a compliant, pneumatic system that allowed dynamic shortening and direct exposure to resting pressures. Dynamic SMV resting pressure was either progressively increased from 40 to 100 to 120 mmHg (n = 5, HiP group) or maintained at 40 mmHg (n = 4, LowP group) during conditioning. After 8 to 10 weeks of electrical stimulation conditioning, SMVs were connected to a counterpulsation mock circulation system and SMV pumping performance evaluated across a range of pressures and stimulation parameters.

RESULTS

SMV pumping performance was similar in each group. Stroke works generally increased with pressure and reached a plateau in all groups above 80 mmHg (120 msec contraction approximately 80 mJ/stroke; 480 msec contraction approximately 180 mJ/stroke). Stroke volumes decreased with pressure except at high stimulation levels where loading effects were observed. Chronic changes in SMV volume significantly effected pumping performance.

CONCLUSIONS

These data suggest that acute pumping performance is not different between 8 to 10 weeks of dynamic or isovolumetric training if SMV volume is not constrained. A potentially improved SMV conditioning protocol is proposed that determines, positions, and maintains SMV volume near the initial volume for maximal isovolumetric pressure during conditioning.

Ventricular constraint in dilated cardiomyopathy: a new, compliant textile mesh exerts prophylactic and therapeutic properties

BACKGROUND

Dilated cardiomyopathy is associated with a progressive decrease in cardiac function, leading to end-stage heart failure. We aimed to stop this process by mechanically constraining the heart with a new, compliant textile mesh.

METHODS

In 16 male Munich minipigs (50 +/- 7 kg), dilated cardiomyopathy with congestive heart failure was induced through 4 weeks of rapid ventricular pacing (220 beats/min). In the early-mesh group (n = 8), a polyvinylidene fluoride mesh was positioned around both ventricles before pacing was started. In the other group (n = 8), experimental dilated cardiomyopathy through rapid pacing was induced (no mesh). After mesh grafting, rapid pacing was continued (late mesh).

RESULTS

Rapid pacing in the no-mesh group (control group) significantly decreased both systolic (cardiac output, peak systolic pressure, and the derivative of pressure increase [dP/dt(max)]) and diastolic (minimum rate of pressure rise [dP/dt(min)] and left ventricular end-diastolic pressure) variables, whereas these variables remained almost unchanged in the early-mesh group. In the late-mesh group the passive-elastic constraint not only prevented further deterioration but even exerted reverse remodeling to some extent (dP/dt(max) and left ventricular end-diastolic pressure, P < .05).

CONCLUSIONS

Ventricular constraint with the new mesh seems to be a prophylactic and therapeutic option in cardiac insufficiency caused by ventricular dilation. This passive-elastic cardioplasty induced reverse remodeling of dilated hearts and significantly improved diastolic and systolic ventricular function.

Ischemic Preconditioning of Skeletal Muscle

BACKGROUND

The time course of the late phase of ischemic preconditioning (IPC) was determined in latissimus dorsi muscle (LDM) flaps using viability and function as the endpoints.

MATERIALS AND METHODS

LDM flaps from Sprague-Dawley rats were allocated into 6 groups. LDMs were preconditioned with 2 30-minute periods of ischemia separated by 10 minutes of reperfusion and subjected to a 4-hour ischemic insult after 24, 48, 72, and 96 hours from IPC. LDMs were evaluated for percent necrosis and muscle contractile function and compared with controls.

RESULTS

The late phase of IPC provides significant protection against necrosis up to 72 hours. Conversely, when the end point used was muscle contractile function, the protection only lasted 48 hours.

CONCLUSION

The time course of late-phase protection in skeletal muscle is 2-3 days. Late phase IPC appears to protect muscle flaps during the most critical time period following elevation.

Reverse remodeling by net cardioplasty in a model of dilated cardiomyopathy: results of an animal study

AIM

End-stage heart failure is a growing clinical problem with only a few satisfactory therapeutical options. Dilated cardiomyopathy (DCM) is associated with a progressive decline in cardiac function. Our hypothesis was to arrest this worsening of cardiac function by mechanically containing the dilated heart with a special net.

METHODS

In 16 pigs (50+/-7 kg) DCM congestive heart failure was initiated by rapid ventricular pacing (220 b/m). In series 1 (n=8) a polyester net was placed around both ventricles before pacing was induced, whereas in series 2 (n=8) ventricular wrapping was performed when DCM was established.

RESULTS

Comparing hemodynamic data before re-operation of group 11-animals, the decrease of CO and dp/dt(max) was significantly lower in series 1 than in series 2 compared to the baseline values before pacing (CO: series 1:-22.6+/-3.3%, series 2:-52.4+/-6.4%, p<0.05; dp/dt: series 1: +16.4+/-2.8%, series 2: -51.5+/-5.9%, p<0.05). In series 2, after net implantation, we could furthermore show that deterioration of the animal stopped and hemodynamic data improved significantly in the following 2 weeks (CO: +62.9+/-10.5% and dp/dt +37.0+/-6.8%).

CONCLUSION

Ventricular containment with a polyester net seems to be a therapeutic option in cardiac insuffiency caused by ventricular dilation. This cardioplasty induced a reverse remodeling of the dilated hearts with a significant improvement in diastolic and systolic ventricular function.

A review of the concept of circulatory bioassist focused on the "new" demand dynamic cardiomyoplasty: the renewal of dynamic cardiomyoplasty?

After the initial enthusiasm, the dynamic cardiomyoplasty lost its reputation owing to the poor long-term results, caused by the muscular degeneration subsequent to chronic continuous electrical stimulation of the latissimus dorsi. An activity-rest stimulation protocol that avoids full transformation of the skeletal muscle, maintaining muscular properties over time, has been successfully tried. This "demand" stimulation protocol showed in humans good results improving NYHA class, ejection fraction value, and survival. The discussion about the capability of this and a unique kind of cardiocirculatory bioassist is due to be reopened. In fact, heart transplant, percutaneous circulatory-supporting device, multisites stimulation therapy, and total artificial heart have some drawbacks, one of which is the economic cost. In developing countries the more economic demand dynamic cardiomyoplasty may still play a role.

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.

Cardiocirculatory bio-assist: is it time to reconsider demand dynamic cardiomyoplasty? Review and future perspectives

In the last 15 years, dynamic cardiomyoplasty has remained an experimental procedure even after the enthusiastic short- and mid-term results, mainly because of the disappointing long-term outcome caused by muscular degeneration secondary to chronic continuous electrical stimulation of the latissimus dorsi. In Italy, a group of muscular pathologists, cardiologists, and cardiac surgeons conducted an experiment of an activity-rest stimulation protocol in humans that should avoid complete transformation of the skeletal muscle, maintaining its properties overtime. This "demand" stimulation protocol gave good results, improving New York Heart Association class, ejection fraction value, and survival. Even though dynamic cardiomyoplasty was excluded from the recent international guidelines for the management of heart failure, the discussion on the ability of this unique kind of cardiocirculatory bio-assistance is due to be reopened, thanks to the results of the new stimulation protocol. Heart transplantation, circulatory supporting devices, multisite stimulation therapy, and the total artificial heart are not always and in all countries the best solutions: the great economic cost, the numerous contraindications, the need for immunosuppression and antithrombotic therapy, and the troublesome follow up constitute important drawbacks. For patients in whom transplant surgery cannot be performed, as well as in developing countries, the nonprohibitively expensive demand dynamic cardiomyoplasty may still play a role.

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.

Reducing the vascular delay period in latissimus dorsi muscle flaps for use in cardiomyoplasty

Although the mechanism by which vascular delay benefits skin flaps is not completely understood, this topic has been extensively studied and reported on in the literature. In contrast, little has been documented about the effects of vascular delay in skeletal muscle flaps. Recent animal studies tested the effectiveness of vascular delay to enhance latissimus dorsi muscle flap viability for use in cardiomyoplasty and found that it prevented distal flap necrosis. However, these studies did not define the optimal time period necessary to achieve this beneficial effect. The purpose of this study was to determine how many days of "delay" can elicit the beneficial effects of vascular delay on latissimus dorsi muscle flaps. To accomplish this, 90 latissimus dorsi muscles of 45 male Sprague-Dawley rats were randomly subjected to vascular delay on one side or a sham procedure on the other. After predetermined delay periods (0, 3, 7, 10, and 14 days) or a sham procedure, all latissimus dorsi muscles were elevated as single pedicled flaps based only on their thoracodorsal neurovascular pedicle. Latissimus dorsi muscle perfusion was measured using a Laser Doppler Perfusion Imager just before and immediately after flap elevation. The muscles were then returned to their original vascular beds, isolated from adjacent tissue with Silastic film, sutured into place to maintain their original size and shape, and left there for 5 days. After 5 days, the latissimus dorsi muscle flaps were dissected free, scanned again (Laser Doppler Perfusion Imager-perfusion measurements), and the area of distal necrosis was measured using digitized planimetry of magnified images. The authors' results showed that delay periods of 3, 7, 10, and 14 days significantly increased (p < 0.05) blood perfusion and decreased (p < 0.05) distal flap necrosis when compared with sham controls. On the basis of these findings, the authors conclude that in their rat latissimus dorsi muscle flap model the beneficial effects of vascular delay are present as early as 3 days. If these findings also hold true in humans, they could be useful in cardiomyoplasty by allowing surgeons to shorten the amount of time between the vascular delay procedure and the cardiomyoplasty procedure in these very sick patients.

New advances in dynamic cardiomyoplasty: Doppler flow wire shows improved cardiac assistance in demand protocol

No data have been published on real cardiac assistance with demand dynamic cardiomyoplasty. We tested the utility of a Doppler flow wire in measuring beat by beat aortic flow velocity and evaluating cardiac assistance in demand cardiomyoplasty patients. The technique was tested in seven patients (M/W = 6/1; age, 57.1+/-6.2 years; atrial fibrillation/ sinus rhythm = 1/6; New York Heart Association [NYHA] classification = 1.4+/-0.5). Measurements were done using a 0.018 inch peripheral Doppler flow wire advanced through a 5 French arterial femoral sheath. Three 1 minute periods with the stimulator off, and three 1 minute periods with clinical stimulation were recorded. We measured peak aortic flow velocity in all beats. Latissimus dorsi mechanogram was simultaneously recorded. Comparison between preoperative and follow-up data showed significantly higher values of tetanic fusion frequency 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 the 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 increase in flow velocity and latissimus dorsi wrap tetanic fusion frequency (r2 = 0.53). In demand dynamic cardiomyoplasty, systolic assistance is significant and correlated to the latissimus dorsi speed of contraction; a demand stimulation protocol maintains muscle properties and increases muscle performance.

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.

Dynamic cardiomyoplasty as a therapeutic alternative: current status

Dynamic cardiomyoplasty was proposed as an alternative surgical treatment for severe cardiomyopathies and has been performed worldwide in more than 1,000 patients. Patients indicated for this procedure are specifically those with dilated or ischemic cardiomyopathies. The ventricular function improvement observed after dynamic cardiomyoplasty derived from the direct action of synchronized skeletal muscle flap contraction and from a girdling effect that helps to reverse chamber remodeling and to decrease ventricular wall stress. Although long-term benefits of this procedure may be limited by skeletal muscle flap ischemic compromise, technological advances incorporated in the new myostimulators will possibly decrease this complication incidence. Clinical improvement has been reported as a consistent finding in cardiomyoplasty follow-up and the overall 5-year survival after this procedure ranges from 39 % to 54 %. On the other hand, the mortality after cardiomyoplasty has been significantly higher for patients in persistent New York Heart Association functional class IV, showing that this procedure needs to be indicated earlier than the heart transplantation. In this regard, only the results of an ongoing randomized trial will potentially define cardiomyoplasty influence on the survival of patients with severe heart failure. In the meantime, however, there are clearly several functional class III patients whose quality of life and exercise capacity have worsened despite the use of maximum medical therapy, justifying dynamic cardiomyoplasty indication.

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.

Surgical therapies for heart failure

Heart transplantation remains the best hope for patients with end-stage heart failure unresponsive to conventional therapy, but the number of transplant candidates continues to exceed the number of available donor hearts. Despite major advances in the medical management of heart failure, researchers continue to explore alternative surgical therapies designed to augment cardiac function. Many of these surgical therapies are still in the experimental or clinical trial phases. Surgical approaches include coronary revascularization, mitral valve repair or replacement, cardiomyoplasty, left ventricular volume reduction surgery, and bridging to recovery with the use of ventricular assist devices. Although cardiac surgeons have gained considerable experience in the treatment of patients with heart failure, many improvements and innovations lie ahead.