Copyright © 2004 by the European Society of Cardiology.
Letter to the Editor
Direct epicardial mapping predicts the recovery of left ventricular dysfunction in chronic ischaemic myocardium: Reply
Department of Cardiology and Angiology, Hospital of the University of Münster, Albert-Schweitzer-Str. 33, D-48129 Münster, Germany Tel.: +49-251-83-47830; fax: +49-251-83-47864
E-mail address: vahlhaus{at}uni-muenster.de
We greatly appreciate the comments by Dr. Achrafi. He underlines not only the importance of the detection of viability in chronic ischaemic and dysfunctional myocardium but also elaborates on the various methods used to identify such tissue. Whereas most of the arguments are well taken and discuss the present status, there are some specific points we would like to address.
It was stated by Kornowski that the NOGA system may not be able to detect viability accurately due to a relatively large intermediate zone between 6 and 10 mV. Kornowski called this intermediate zone the `grey zone'.1 We did not find such a grey zone in our study but we only cited Kornowski's statement, since his observation was the background for the hypothesis of our study. Since infarct development starts in the sub-endocardial layer, viable myocardium is more likely detectable from the epicardium. Therefore, we tried to decrease the extent of the expected grey zone with overlap by using the epicardial instead of the endocardial approach which has been introduced recently as stated by Dr. Achrafi. In this context, the NOGA system is indeed useful to correlate local contraction with electrical signal characteristics. In our study, pre-operative data on segmental LV-function were correlated to intra-operative epicardial mapping, resulting in comparable correlations. In the meantime, Perin et al.2 tried to detect viable myocardium in humans using endocardial NOGA-mapping. Most interestingly, using one of the most appropriate endpoints of myocardial viability, i.e., the transmural extent of myocardial infarction (delayed enhanced MRI)2 or functional recovery,3 both, endocardial2 and epicardial mapping3 revealed excellent diagnostic accuracy in detecting viable myocardium. The extent of the grey zone was lower in both studies2,3 than previously reported.1
Bipolar voltage does not correspond to electrical reserve (which, in our opinion, is a poorly defined parameter) but is related to the recovery of segmental myocardial dysfunction. Dysfunctional and ischaemic myocardium with the potential to recover after reperfusion is characterised by preserved endocardial2 and epicardial3 electrical activity. The concept of electrocardiographic detection of viability is based on the phenomenon called `electromechanical mis-match'.4 Presently, neither electromechanical mapping, nor direct epicardial mapping have been established as standard techniques and serve for research purposes. Neither randomised comparative studies, nor expert consensus on this issue are to be expected in the near future. Therefore, the level of evidence is far too low to recommend electromechanical mapping for this purpose.
Our study was performed in 34 patients that were admitted for elective CABG. The decision for surgery was made before enrolment and was not in the least influenced by the protocol. In our study, direct epicardial mapping was performed in a minimum of time (having long-standing experience in intra-operative mapping of arrhythmias) without any harm to any patient. Due to the residual risk, and due to the fact that data are acquired too late for clinical decision, direct epicardial mapping will not become a clinical feasible method. But electrical mapping in general (endocardial mapping and/or body surface potential mapping with generation of inverse solution) may have the potential to replace or complement gold standard methods such as radionuclide techniques, low-dose dobutamine echocardiography, or contrast enhanced magnetic resonance imaging in future. Using geometrical information from computer tomography, epicardial electrograms can already be reconstructed on the heart's surface from body surface electrocardiograms.5 Before investigating whether such non-invasive electrocardiographic imaging is able to detect viable myocardium as a first step, the diagnostic accuracy of epicardial mapping in detecting viability had to be tested as we did in our study.3
References
- Kornowski R. Left ventricular electromechanical mapping for determination of myocardial function and viability. J. Am. Coll. Cardiol. 2002;40:1075.
[Free Full Text] - Perin EC, Silva GV, Sarmento-Leite R et al. Assessing myocardial viability and Infarct transmurality with left ventricular electromechanical mapping in patients with stable coronary artery disease: validation by delayed-enhancement magnetic resonance imaging. Circulation. 2002;106:957–961.
[Abstract/Free Full Text] - Vahlhaus C, Bruns HJ, Stypmann J et al. Direct epicardial mapping predicts the recovery of left ventricular dysfunction in chronic ischaemic myocardium. Eur. Heart J. 2004;25:151–157.
[Abstract/Free Full Text] - Bruns HJ, Janssen F, Schäfers M et al. Signal characteristics of multichannel epicardial electrograms in chronic ischaemic and scarred myocardium: electromechanical mismatch indicates viability in regions of myocardial dysfunction. Basic Res. Cardiol. 2001;96:98–105.[CrossRef][ISI][Medline]
- Ramanathan C, Ghanem RN, Jia P et al. Noninvasive electrocardiographic imaging for cardiac electrophysiology and arrhythmia. Nat. Med. 2004;10:422–428.[CrossRef][ISI][Medline]
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