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Eur J Cardiothorac Surg 2006;30:816-817
© 2006 Elsevier Science NL

Letters to the Editor

Ventricular myocardial band concept and ventricular resynchronization device therapy: crossing the roads?

Clinic for Cardiac Surgery, Institute for Cardiovascular Diseases, UC Clinical Center of Serbia, 11000 Belgrade, Serbia and Montenegro

Received 29 July 2006; accepted 28 August 2006.

^_* Tel.: +381 11 3615 795; fax: +381 11 3615 795. (Email: velid{at}sezampro.yu). (URL: http://www.ctsnet.org/home/dvelimirovic).

Key Words: Helical myocardial ventricular bend • Cardiac resynchronization therapy

I read the article by Tomioka et al. [1] with great interest, eager to see how intensely the new integrative knowledge of the heart structure and function might urge future reconciliation of some exceeded concepts about electrical, mechanical, and energetic events in human heart [2].

Contrary to evident contribution of the ventricular myocardial band (VMB) concept in developing the new strategy in failing heart surgery, there was no real proof in obtaining progress in clinical electrophysiology. Classical teaching describes ventricular excitation as the product of two temporally overlapping functions: endocardial activation and transmural activation. Endocardial activation is guided by the anatomic distribution and physiology of the Hiss-Purkinje system, which depolarized most of the endocardial surfaces of both ventricles, within several milliseconds with activation fronts that move from endocardium to epicardium. Also, it was shown that ‘the anatomical conduction paths lie axially along the direction of muscular bands of the ventricle’ and hypothesis of radial conduction of activation from endocardium to epicardium was questioned [3]. Taccardi et al. [3] has shown, by multisite mapping of electrical activation within ventricular wall, that the spread of activation fronts follows complex spiral pathways, rather than direct linear ones.

Renewed interest in the mechanism of spread of activation seems appropriate at the time when electrophysiologists are pushing the frontiers of understanding and treating the arrhythmias and defining the conditions and benefits of biventricular pacing in certain patients with severe myocardial dysfunction and intraventricular conduction abnormality. Stimulated electric impulse produces radial conductance that is much faster than normal axial excitation to cause regular sequential heart contraction. Radial direction of electrically stimulated excitation, which was founded by nearly all pacing studies, is quite opposite to axial course of conduction in physiologically guided excitation of normal myocardium. The significant differences in direction of evoked and natural electrical impulses and depolarization through the heart call for some fundamental changes in electrophysiologic-mechanical consideration. The question that arises from these statements is as follows: How can we improve the myocardial function in the patients with severe myocardial dysfunction and intra/interventricular conduction delay, by using biventricular pacing aimed at reducing electrical asynchrony? Or rather: How can radial (abnormal) spread of evoked myocardial activation produce physiological sequential myocardial contraction in pump failing heart?

Leclercq et al. [4] concluded that improved mechanical synchrony and function do not require electrical synchrony. Mechanical desynchronization rather than electrical dispersion seems to be the more relevant measure [4]. The controversy in assessment of different pacing modalities on cardiac contractility in failing heart is greatly due to our lack of understanding on how pacing affects cardiac mechanism [5]. At present, it is not possible to identify patients who will respond better to left ventricular pacing alone, compared with biventricular pacing or neither and it is not clear how to identify optimal pacing site [4].

If anatomy means function, VMB concept of heart structure has to be starting hypothesis which should be widely tested. Mapping techniques in combination with sophisticated imaging system seem a promising methodology that could be the answer to problems of electro mechanical sequential activation of the normal and failing heart [4].

Remarkable results of Tomioka experimental studies, using original methodology, will stimulate further research in order to evaluate real benefit of resynchronization biventricular pacing therapy in failing human heart.

References

1. Tomioka H, Liakopoulos JO, Buckberg DG, Hristov N, Tan Z, Trummer G. The effect of ventricular sequential contraction on helical heart during pacing: high septal pacing versus biventricular pacing. Eur J Cardiothorac Surg 2006;29(Suppl. 1):S198-S206.[Abstract/Free Full Text]
2. Torrent Guasp F, Kocica MJ, Corno AF, Komeda M, Carreras-Cosa F, Flotats A, Cossin-Aguillar J, Wen H. Toward new understanding of the heart structure and function. Eur J Cardiothorac Surg 2005;27:191-203.[Abstract/Free Full Text]
3. Taccardi B, Lux LR, Ershler PR, MacLeod RS, Vyhmeister Y. Effects of myocardial fiber direction on 3-D shape of excitation wave fronts and associated potential distribution in ventricular walls. Circulation 1992;896:752.
4. Leclercq C, Faris O, Tunin R, Johnson J, Kato R, Evas F, Spinelli J, Halperin H, McVeigh E, Kass D. Systolic improvement and mechanical resynchronization does not require electrical synchrony in the dilated failing heart with left bundle-branch block. Circulation 2002;106:1760-1775.[Abstract/Free Full Text]
5. Wyman TB, Hunter CW, Prinzen WF, McVeigh RE. Mapping propagation of mechanical activation in the paced heart with MRI tagging. Am J Physiol Heart Circ Physiol 1999;276:H881-H891.[Abstract/Free Full Text]

This article has been cited by other articles:

				G. Buckberg Reply to Velimirovic: Helical myocardial ventricular myocardial band; cardiac resynchronization therapy Eur. J. Cardiothorac. Surg., November 1, 2006; 30(5): 817 - 818. [Full Text] [PDF]

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map 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): Dusan B. Velimirovic Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Velimirovic, D. B. Search for Related Content PubMed PubMed Citation Articles by Velimirovic, D. B. Related Collections Cardiac - physiology Cardiac - other Electrophysiology - arrhythmias