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Ann Thorac Surg 1995;60:1862-1863
© 1995 The Society of Thoracic Surgeons

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Correspondence

Optimizing Cardiomyoplasty Results: Importance of Muscle Contraction Timing

Division of Cardiac Surgery, Civic Hospital, Brescia, Italy
Departments of Anaesthesiology and Cardiology, Academic Hospital, Maastricht, the Netherlands

To the Editor:

We read with great interest the article by Dr Helou and colleagues [1]. They should be congratulated for having reported such a crucial issue as muscle stimulation timing in cardiomyoplasty. Synchronization between the sensed cardiac electrical activity and the muscle activation is essential for optimizing postoperative cardiomyoplasty results.

Doctor Helou and colleagues described three modes of tuning the muscle stimulation timing: namely, the fixed-time mode, the valve-synchronized mode, and the flow-optimized mode. Nonetheless, we believe that only echocardiographic monitoring during programming of the stimulation parameters, that is, a hemodynamic-optimized mode, should be recommended and performed. Indeed, the fixed-time mode would not be related to any control of hemodynamic efficacy, potentially eliciting incorrect timing of muscle contraction in cardiac systole (either too early or too late). The valve-synchronized mode avoids the negative effect of early muscle activation and mitral regurgitation, but may not correspond to the more effective or optimal muscle support (which could be in late systole).

In our initial clinical series, we documented the fact that varying the onset of muscle contraction during cardiac systole leads to significant changes in terms of hemodynamic response [2]. These changes ranged surprisingly from marked deterioration of baseline hemodynamics (reduced ejection fraction, appearance or worsening of mitral regurgitation, compromise of the diastolic filling of the following beat, and so forth) to significant improvement in the same patient. Therefore, careful observation of progressive hemodynamic changes by varying the delay between cardiac sensing and triggered muscle contraction allowed us to properly select the most effective timing for muscle support and to confirm the relevance of tailoring such a timing by echocardiographic monitoring.

Grubb and collegues [3] clearly showed the clinical impact of inappropriate synchronization in patients submitted to cardiomyoplasty and the value of echocardiographic monitoring for correcting wrapped muscle/heart interaction. The importance of tailoring muscle stimulation parameters in each patient by echocardiographic monitoring to achieve optimal clinical results and to avoid detrimental effects has been previously reported by other authors [4] but a general agreement on the optimal management of the biomechanical assistance is surprisingly still being debated.

Hemodynamic analysis of cardiomyoplasty patients by means of a pressure/volume relation [5] distinctly showed the wide range of results when the burst stimulation timing was simply varied. Beat-to-beat analysis documented beneficial effects of assisted circulation by wrapped skeletal muscle because, at the individual best setting of muscle activation, stroke volume and left ventricular ejection rate were increased during assisted beats. But, of note, impaired cardiac performance was observed in some patients with incorrect programming of stimulation parameters. Short or too delayed intervals between sensed R wave and skeletal muscle activation were shown to be detrimental to the hemodynamic response. Moreover, in this study burst duration and pulse amplitude appeared to be additional major determinants of hemodynamic response after cardiomyoplasty.

Another important issue in these patients, as described by Grubb and associates, is the appearance of conduction defects after cardiomyoplasty, which makes mandatory a new appraisal of the time of muscle contraction to optimize the changed setting of heart/muscle interaction.

Finally, the effects of long-term muscle activity on contraction timing should not be underestimated. Indeed, structural adaptations (muscle lipomatosis and fibrosis) may significantly affect the mechanical properties of the transposed muscle graft leading to a prolongation of muscle contraction time with potential interference with the following diastolic phase [6, 7]. It is likely that, as time passes, muscle contraction time has to be shortened for muscle contraction/relaxation time to be included in the supported cardiac systole and negative effects on the coming diastolic filling to be avoided.

In conclusion, we believe that the optimization of stimulation parameters plays a crucial role in cardiomyoplasty results. Hemodynamic monitoring while varying the burst delay ensures the programming of correct coupling between cardiac activity and muscle support, prevents suboptimal use, and ultimately allows adjustment of the cardiac cycle to the ongoing changes of muscle performance due to the long-term structural changes.

References

1. Helou J, Misawa Y, Stewart JA, Colson M, Chiu RC-J. Optimizing ``delay period'' for burst stimulation in dynamic cardiomyoplasty. Ann Thorac Surg 1995;59:74–7.[Abstract/Free Full Text]
2. Lorusso R, Sandrelli L, Maisano F, et al. Echo-Doppler assessment to optimize wrapped skeletal muscle activation time following cardiomyoplasty procedure. Eur Heart J 1991;13(Suppl):230.
3. Grubb NR, Campanella C, Sutherland GR, Fox KAA. Optimizing muscle synchronization after dynamic cardiomyoplasty. Eur J Cardiothorac Surg 1995;9:45–9.[Abstract]
4. Almada H, Molteni L, Ferreira R, et al. The value of echo-Doppler in cardiomyoplasty procedures. J Cardiac Surg 1991;6:113–8.[Medline]
5. Schreuder JJ, Van der Veen FH, van der Velde ET, et al. Beat-to-beat analysis of left ventricular pressure/volume relation and stroke volume by conductance catheter and aortic modelflow in cardiomyoplasty patients. Circulation 1995;91:2010–7.[Abstract/Free Full Text]
6. Lucas CMHB, van der Veen FH, Cheriex EC, et al. Long term follow-up (12 to 35 weeks) after dynamic cardiomyoplasty. J Am Coll Cardiol 1993;22:758–67.[Abstract]
7. Kalil-Filho R, Bocchi E, Weiss RG, et al. Magnetic resonance imaging evaluation of chronic changes in latissimus dorsi cardiomyoplasty. Circulation 1994;90(Suppl 2):102–6.

This Article Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Personal Folders Download to citation manager Author home page(s): Roberto Lorusso Ottavio Alfieri Permission Requests Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Lorusso, R. Articles by Schreuder, J. Search for Related Content PubMed PubMed Citation Articles by Lorusso, R. Articles by Schreuder, J.