Eric Solien

Conformational adaptation of muscle: Implications in cardiomyoplasty and skeletal muscle ventricles

In dynamic cardiomyoplasty and other forms of muscle-powered cardiac assist, the stretch that should be applied to the skeletal muscle to obtain optimal resting tension remains unclear. To test the hypothesis that skeletal muscle is capable of conformational adaptation over time, the effect of altered resting tension on the chronic performance of a skeletal muscle ventricle was studied. In 7 mongrel dogs, skeletal muscle ventricles constructed from the lastissimus dorsi muscle were stimulated to contract for 12 weeks against an implantable mock circulation. The preload pressure was altered, thereby varying the resting tension of the latissimus dorsi. One group (group I; n = 5) was maintained at a preload of 80 mm Hg, whereas a second group (group II; n = 2) was maintained at 20 mm Hg. Adaptation to preload was observed. After 12 weeks, the pressure increase generated by the skeletal muscle ventricle at a preload of 20 mm Hg was only 35 +/- 2 mm Hg for group I compared with 44 +/- 5 mm Hg for group II. At a preload of 80 mm Hg, the pressure increase was 61 +/- 4 mm Hg for group I and only 34 +/- 6 mm Hg for group II. Adaptation of the latissimus dorsi to a new resting tension has important implications in the use of skeletal muscle for cardiac assist. Stretching the latissimus dorsi to its in situ length during cardiomyoplasty is not required for future muscle performance to be optimal.

Importance of adaptive stimulation of the latissimus dorsi muscle in cardiomyoplasty

During cardiac synchronized latissimus dorsi (LD) stimulation, adaptive duration (AD) allows the pulse train length to be set as a percentage of the cardiac cycle. The LD contraction duration adjusts to variations in heart rate (HR). The effects of AD on LD work output and blood flow (BF) were investigated in nine dogs that underwent skeletal muscle ventricle (SMV) construction. The SMVs were stimulated according to the cardiomyoplasty protocol. BF and the pressure increase (delta P) generated during SMV contraction were monitored biweekly for 3 months. SMV contraction time increased significantly after training (P < 0.0001). The trained SMV could only partially contract at duration settings of 25% and 30%. Before training, the increase in mean pressure and BF during 35% AD increased proportionally with increasing HR. After training, BF and mean pressure decreased with increasing HR because of reduced peak pressure generation during partial SMV contractions. When duration was fixed at 200 msec, BF increased with HR to 80 bpm but decreased with additional increases in HR. At high rates and fixed duration, inadequate relaxation between contractions resulted in the inefficient muscle performance and reduced BF. AD did not impair BF and allowed the appropriate autoregulatory response to occur in the trained and untrained LD so that the supply-to-demand ratio did not become compromised over a large range of HR.

Ventriculocoronary artery bypass results using a mesh-tipped device in a porcine model ☆

BACKGROUND In this report we describe the in vivo evaluation of a device and ventriculocoronary artery bypass procedure that creates a permanent transmyocardial channel between the left ventricle and a coronary artery. METHODS The transmyocardial device, an L-shaped titanium tube with a meshed distal tip and an exterior polyester cuff, was implanted from the base of the left ventricle to the proximal left anterior descending coronary artery in 11 healthy juvenile domestic pigs using a beating-heart approach. Flow rates were measured at implant. Patency was assessed at explant for surviving animals at 2 (n = 3) and 4 weeks (n = 4). RESULTS Flow through the transmyocardial device after implantation was 74% of base line. Forward flow occurred during systole. Luminal patency was 100% at 2 weeks and 75% at 4 weeks. Histologic analysis showed little to no intimal proliferation at the coronary interface. CONCLUSIONS This short-duration study shows promise for perfusing ischemic myocardium with systolic flow. The transmyocardial titanium conduit and treated coronary artery patency was good at 2 and 4 weeks and warrants further studies.

Clinical evaluation of the eSVS Mesh: First-in-Man trial outcomes.

In coronary artery bypass graft surgery, saphenous vein graft (SVG) patency is much lower than that of the internal mammary artery (IMA). To address this problem, an external support device, the eSVS Mesh was developed. A prospective randomized First-in-Man feasibility trial was conducted in 90 patients after institutional ethics committee approval at seven international centers. The left IMA was used to bypass the anterior descending artery. A mesh-supported (treated) saphenous vein was randomized to either the right or the circumflex coronary system, and an unsupported (control) vein was grafted to the opposing territory. Device diameters available for use were 3.0, 3.5, 4.0, and 4.5 mm. Primary end-points were 30 day adverse cardiac and cerebral events and angiographic patency at 9–12 months. Eighty-five of 90 patients returned for 30 day clinical follow-up (94%). Five patients refused to return, but by telephone contacts were asymptomatic. There was one late noncardiac death and 73 patients returned for angiography (82%), thus 12 additional patients were lost to follow-up at 1 year. Overall patency rate was 49% for the treated versus 81% for controls (p < 0.001). Subset analysis revealed significantly lower patency at one center and with use of the 3.0 mm device (p < 0.05). Removing these data, patency was 72% vs. 81% (p = NS). Sternal wound infection was higher than expected at 5.0%, but this was center specific. The eSVS Mesh is safe, but at up to 1 year, patency is equivalent to untreated vein grafts after removal of outlying data. This study provides insight into operative events and parameters that may optimize outcomes and point to potential improvements in the external SVG support device. Furthermore, longer term studies are pending.

Saphenous Vein Graft Wrapping by Nitinol Mesh: A Word of Caution.

We read the article by Rescigno et al, “Saphenous Vein Graft Wrapping by Nitinol Mesh: A Word of Caution,” with interest.1 While the authors raise several excellent points, the word of caution suggested in the titlemay be that interpretation of the computed tomography (CT) angiogram in Nitinolwrapped vein grafts may not be definitive. The authors note in the one angiogramperformed that a vein interpreted on CT as having disease was normal. Further, when other patients with “occluded” grafts underwent stress testing, two were slightly positive, all others were negative and no further testing was done. This is inconclusive evidence for true graft occlusion. Other investigators have also noted that mesh-wrapped grafts that were interpreted to be occluded or have string sign using CT angiography were actually shown to be fully patent using ciné angiography (personal communication). It is known that there is shadowing and scatter of CT signals with the Nitinol mesh (►Fig. 1), whichmay be further obscured by the healing process or when the dye is added making the result open to misinterpretation. Due to this effect and until more accurate CT scanning protocols can be established, we recommend that meshwrapped graft patency assessments be performed using ciné angiography. Rescigno et al raise two important points with which we concur. First, including the mesh in each anastomosis makes the construction more difficult. Second, the impact of the fibrin sealant on the vein is unknown. Therefore, both factors may potentially impact outcomes. Others have had the same opinion (eSVS Mesh focus group).2 Thus, the recommended implantation technique was recently changed such that the mesh is placed 2 to 3 mm from the cut end of the vein and not included in either proximal or distal anastomoses. Fibrin sealant is also not used to adhere the vein to the mesh.3 Studies incorporating this new approach are ongoing. Fig. 1 Computed tomography imaging of a Nitinol mesh showing scatter with blurring that may confound interpretation when coupled with dye and the healing vein itself.