THE VIENNA SMV-PROJECT

FIRST RESULTS FROM CHRONIC EXPERIMENTS IN GOAT

W. Girsch, H. Lanmüller, M. Rab, LP. Kamolz, U. Windberger, H.Schima,

R. Avanessian, M. Greher, M. Ulrich, H. Beck, W. Haslik and R. Seitelberger

Medical School, University of Vienna, Austria

SUMMARY

A new type of skeletal muscle ventricle (SMV) constructed of biological materials only was designed as an aortic counterpulsation device: The SMV consists of an aortic homograft, enlarged to a pouch with pericardium and is anastomosed in parallel to the descending aorta. The latissimus dorsi muscle (LDM) is wrapped around the pouch. Stimulation electrodes are applicated to the thoracodorsal nerve and R-wave triggered burst stimulation is applied during cardiac diastole. In a series of acute experiments in sheep the hemodynamic efficacy was demonstrated and a standardised surgical procedure was established. A series of chronic experiments in goat was scheduled in order to evaluate the reliability and patency of this new type of SMV and its overall influence to the circulation.

Methods: In one goat an unconditioned LDM was used for SMV construction. In two goats the LDM was preconditioned by means of a newly developed fully implantable ECG-triggered multi-channel-stimulator and the SMV was constructed.

Results: The goats survived the procedure without any complications. The goats survived the procedure without any complications. The SMV was in circulation for four, five and six months in these first animals, stimulated chonically at a rate of 1:5 compared with the native heart rate. Reconstitution of the resected third rib caused compression of muscle and nerve in the first animal. Consecutive loss of muscle force terminated this experiment. Second and third goat were sacrificed as scheduled. In all three animals the SMV was found patent at the end of the experiment.

Conclusion: Goat turned out to be appropriate for this kind of experiments. The configuration produced distinct hemodynamic changes required for aortic counterpulsation. Several problems seen in the first and second experiment necessitated modifications of the surgical procedure. The observed results still are promising and the experiments will be continued.

INTRODUCTION

A new type of skeletal muscle ventricle (SMV) constructed of biological materials only was designed as an aortic counterpulsation device: The SMV consists of an aortic homograft, enlarged to a pouch with pericardium and is anastomosed in parallel to the descending aorta. The latissimus dorsi muscle (LDM) is wrapped around the pouch (fig. 1). Stimulation electrodes are applicated to the thoracodorsal nerve and R-wave triggered burst stimulation is applied during cardiac diastole. In a series of acute experiments in sheep the hemodynamic efficacy was demonstrated and a standardised surgical procedure was established [1]. A series of chronic experiments in goat was scheduled in order to evaluate the reliability and patency of this new type of SMV and its overall influence to the circulation.

Fig. 1: Scheme of the SMV model

MATERIALS AND METHODS

3 female adult alpine goats, weighing about 50kg, underwent the experimental procedure. In one goat an unconditioned LDM was used for SMV construction. In one goat an unconditioned LDM was used for SMV construction. In two goats the LDM was preconditioned by means of a newly developed fully implantable ECG-triggered multi-channel-stimulator and a new stimulation protocol. 4 ring-shaped stimulation electrodes were applied to the epineurium of the thoracodorsal nerve while the LDM was left untouched [2,3,4]. During 8 weeks the LDM was conditioned to perform 30 contractions per minute fatigue-free around the clock (the protocol is presented in detail by H. Lanmüller)

Prior to the main surgical procedure the pericardium and the entire thoracic aorta had been excised from fresh goat cadavers. These ”homografts” were cryopreserved according to approved techniques [5,6].

The SMV construction was performed as a standardized procedure using a left side lateral flank incision. The serratus muscle was detached from the thoracic wall. A segment of the third rib was resected subperiostally and the fifth and sixth rib were removed and preserved as pedicled vascularized grafts. Enlarging the circumference of the homograft with strips of homologous pericardium created a neoventricle of about 50ml. This biological conduit was anastomosed in parallel to the descending aorta (fig 2a, b). The LDM was wrapped around the ne oventricle, applying near physiologic resting tension to the muscle and the free end of the muscle was fixed to the sixth rib. Two ECG-sensing electrodes were fixed directly to the heart and the electrode leads were connected with the implanted stimulation unit. Finally the thorax was reconstructed by means of the rib grafts and the mobilized serratus muscle.

At the end of the procedure functional electrical stimulation (FES) was started. R-wave triggered burst stimulation at a rate of 1:5 with the native heart rate and limited to maximum 30 contractions per minute was applied during cardiac diastole to simulate aortic counterpulsation.

2a

Fig. 2: Intraoperative situs

- after completion of proximal anastomosis (2a)
- and connected to the circulation on both ends (2b)

2b

RESULTS

The goats survived the procedure without any complications. The SMV was in circulation for four, five and six months in these first animals, stimulated chronically at a rate of 1:5 compared with the native heart rate.

Activation of the SMV during diastole augmented the diastole to systolic pressure levels. Ultrasound investigation revealed a reduction of the SMV-diameter of about 30% during LDM contraction, causing arterial back-flow in the most proximal part of the aorta.

3a

3b

Fig. 3: Hemodynamic measurements (arterial pressure curve derived from the brachiocephaliv trunk) during ECG-triggered activation of the SMV (ECG curve interrupted by FES-pulse trains) at different R-R intervals (3a -35%, 3b - 45%, 3c -60%)

Reconstitution of the resected third rib caused compression of muscle and nerve in the first animal. Consecutive loss of muscle force terminated this experiment. Second and third goat were sacrificed as scheduled. In all three animals the SMV was found patent at the end of the experiment.

CONCLUSIONS

Goat turned out to be appropriate for this kind of experiments. The configuration produced distinct hemodynamic changes required for aortic counterpulsation. Several problems seen in these first experiments necessitated modifications of the surgical procedure. The observed results still are promising and the experiments will be continued.

REFERENCES

1. Girsch, W. Koller, R. Lanmüller, H. Rab, M. Avanessian, R. Schima, H. Wolner, E. Seitelberger, R. Experimental development of an electrically stimulated biological skeletal muscle ventricle for chronic aortic counterpulsation. Eur J Cardiothorac Surg 13(1):78-83, 1998.

2. Koller, R. Girsch, W. Liegl, Ch. Gruber, H. Holle, J. Losert, U. Mayr, W,. Thoma, H. Long term results of nervous tissue alterations caused by epineurial electrode application: An experimental study in rat sciatic nerve. PACE 15(1):108-115, 1992.

3. Mayr, W. Bijak, M. Girsch, W. Holle, J. Lanmüller, H. Thoma, H. Zrunek, M. Multichannel stimulation of phrenic nerves by epineurial electrodes: Clinical experience and future developements. ASAIO J 39(3):729-735, 1993.

4. Lanmüller, H. Sauermann, S. Unger, E. Schnetz, G. Mayr, W. Bijak, M. Girsch, W. Multifunctional implantable nerve stimulator for cardiac assistance by skeletal muscle. Artif Organs 23(4):352-359, 1999.

5. Grabenwöger, M. Grimm, M. Eybl, E. Moritz, A. Müller, MM. Bock, P. Wolner, E. Endothelial cell lining of bioprosthetic heart valve material. J Card Surg 7(1):79-84, 1992.

6. Leukauf, C. Szeles, C. Salaymeh, L. Grimm, M. Grabenwöger, M. Losert, U. Moritz, A. Wolner, E. In vitro and in vivo endothelialization of glutaraldehyde treated bovine pericardium. J Heart Valve Dis 2(2):230-235, 1993.

AUTHOR´S ADDRESS

Univ.Doz.Dr. Werner Girsch

Orthopädisches Spital Speising

Speisingerstr. 109

A-1134 Vienna, Austria

Tel +43 1 80182 509

Fax +43 1 80182 285

eMail werner.girsch@univie.ac.at