1.  Introduction

Evidence-based medicine (EBM) has been defined as ‘the process of systematically finding, appraising and using contemporaneous research findings as the basis for clinical decisions’ [Rosenberg and Donald, 1995]. Sackett [1998] has defined four stages in the evidence-based approach: (1) The formulation of answerable questions; (2) The search for the best evidence; (3) Critical appraisal of the evidence; (4) The decision to apply the conclusions to patients’ healthcare. These principles have been used to re-evaluate the electrocardiographic diagnostics of left ventricular hypertrophy (LVH) based on voltage criteria [Bacharova, 2003], and it has been concluded that: ad (1) we are asking an unanswerable question; ad (2) we are focused only on the increased QRS amplitude, and this is considered to be an evidence; ad (3) the evaluation of validity and importance of evidence is subject of old habits and inertia in thinking and argumentation, ad (4) the majority of results – the so-called false negative results are not used for clinical decision making. The aim of this contribution was to provide an alternative view on the ECG diagnostics of LVH, with a special focus on so-called false negative results.

2.  The Alternative Approach

Our alternative approach [Bacharova et al, 1989; Bacharova, 1985; Bacharova, 1998; Bacharova and Kyselovic, 2001] is based on the following principles:

1.      The question, which is answerable by the means of ECG, is: ‘How strong is the generator of the cardiac electric field’, or more focused: “How strong is the left ventricle as a source of cardiac electric field in relation to its size?” instead of ‘How big is the left ventricle’? (Figure 1).

2.      The so-called false negative results, e.g. the findings of QRS amplitude within normal limits in hypertrophied left ventricles of increased size/mass, are TRUE results, they are results of an objective diagnostic method, the more that they are the dominant findings in clinical practice.

3.      The difference between the expected voltage related to the increased LVM, and the actually recorded voltage, is named a "relative voltage deficit". This term indicates that the recorded QRS amplitude in an individual patient with increased left ventricular mass is lower than expected. And, contrary to the term "false negative result", which implicitly neglects the results of ECG evaluation by earmarking them as "false", it imposes the need for further diagnostic clarification. We assume that the relative voltage deficit is conditioned by changed active and passive electrical properties of the hypertrophied myocardium as compared to healthy tissue, or in terms of the spatial angle theory, by changes in non-spatial determinants.

Figure 1. A schematical presentation of the alternative attitude to so-called false negative ECG results in LVH diagnostics: The voltage is measured in two electrical sources of different size (N – normal, healthy myocardium; H – hypertrophied, pathologically changed myocardium). The voltmeters show the same voltage. These results are TRUE. It is the different electrical quality of myocardium which makes the difference.

4.      For the quantification of the relative voltage deficit we used a new parameter: a ratio of QRS voltage to left ventricular size. This ratio was named the specific potential of myocardium (SP). Using the left ventricular size as a denominator, the voltage is indexed to a unit of myocardium and the influence of left ventricular size on the voltage magnitude is taken into account. The SP value can be understood as a potential contribution of one unit of myocardial tissue of the left ventricle to the total cardioelectric field. In terms of solid-angle theory it can be considered as a summary parameter of non-spatial determinants.

5.      The relative voltage deficit changes during the time with respect to the hypertrophic remodeling of myocardium. These changes are not linear during the progress of LVH and they are not proportional to the increase of LVM.

6.      The relative voltage deficit can be modified by other associated cardiac pathology and/or by therapy.

7.      The recognition and quantification of the relative voltage deficit as a deviation from normal have diagnostic and prognostic value/importance.

It was shown, that the EBM approach is a powerful tool for re-evaluation of old hypotheses in the context of the contemporary knowledge, a tool for generating new ideas and directions for research. In the case of LVH, the EBM approach has contributed to developing an alternative view on the utilization of voltage criteria and of so-called false negative ECG results in LVH diagnostics.

Acknowledgements

This study was supported, in part, by the grant 1/0507/03 from The Science Grant Agency (VEGA), Slovak Republic.

References

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