I. INTRODUCTION

  1. Justification
  2. Philosophical background
  3. After 10 years

1 Justification

"In the industrially developed countries, sudden cardiac death is the leading cause of death. It was recognized at the dawn of recorded history and even depicted in Egyptian relief sculpture from the tomb of a noble of the Sixth dynasty approximately 4,500 years ago. Sudden cardiac death has left no age untouched. Sparing neither saint nor sinner, it has burdened man with a sense of uncertainty and fragility. The enormity of this problem demands attention."
"The medical profession has sensed the issue but has largely ignored sudden death as a problem amenable to solution. This indifference has not been the result of a lack of interest or concern but a reflection of the belief that sudden cardiac death was the inevitable culmination of coronary atherosclerosis. Because sudden death was unpredictable and afflicted the apparently healthy subject outside the hospital, the physician considered it an act of fate before which he was largely helpless. The advent of the coronary care unit has promoted a reassessment of this complex problem. It has become clear that sudden death is not the inexorable culmination of advanced coronary atherosclerosis but instead is the result of ventricular fibrillation and therefore is readily reversible. If ventricular fibrillation were only the consequence of severe coronary atherosclerosis, once reversed it would promptly recur. However, patients treated for ventricular fibrillation seldom have recurring episodes, and they usually recover and survive for long periods. The new concept that ventricular fibrillation is an electrical accident suggests that its cause is not anatomic and thereby contributes to the growing interest in redefining the basis for sudden death and developing methods for its containment."
In these two quotations from the review of Lown (Lown 1979) the reasons for studying ventricular fibrillation have been excellently formulated. The importance of sudden cardiac death - caused by ventricular fibrillation - for our society is further stressed by the following authors (Kannel 1982), (Newman 1982) and (Rossi 1982). In 1887 McWilliam (McWilliam 1887) mentioned the resemblance of the electrical activity of the heart during ventricular fibrillation to the electrical activity of the brain under certain circumstances, an observation stressed more by Van der Tweel in 1963. (Van der Tweel 1963) The success of signal analysis in neurology (Storm van Leeuwen 1976) plus the tradition in the department of cardiology of mathematical analysis of the heartrhythm during atrial- and ventricular fibrillation (Scher 1976), (Scher 1976a), (Meijler 1968), (Meijler 1981), (Bootsma 1970) and (Strackee 1971) led to the decision to investigate ventricular fibrillation by applying signal analysis to the electrical activity of the heart during fibrillation. Moreover, the stress in the last sentence quoted on the fact that ventricular fibrillation is an electrical accident, is an a posteriori justification for analyzing ventricular fibrillation in healthy dogs by means of signal analytical methods.

The fact that the results of the analysis led to model studies, which threw new light on the signal analysis, and the fact that in the same way single channel analysis and multichannel analysis influenced each other, cause a two-dimensional arrangement of the chapters in this thesis, as indicated in the (summary) table. The "experimental", "theoretical" and "synthetical" chapters (vertical) may be read more or less independently, just as the "local", "global" and "conclusion" chapters (horizontal). The mathematical appendices contain the formulas used for the computations, but most of them are not necessary for understanding the results.

2 Philosophical background

This paragraph contains a somewhat philosophical justification for the way this study was done. This part is not necessary in order to understand how the analysis was done, but maybe elucidates why it was done. Although a variety of causes of ventricular fibrillation is known - e.g. acute myocardial infarction or ischaemic heart disease, myocardial diseases, electrocution, drugs (digitalis, catecholamines, antidepressants), electrolyte abnormalities (high serum potassium) - Lown (Lown 1979) seems to assume that ventricular fibrillation is one syndrome and not just a name for a group of unrelated electrical phenomena in the heart. In order to avoid the pittfall of an author describing an other phenomenon than his readers assume, (like the controversy between C.J.Rothberger/H.Winterberg and Th.Lewis in the beginning of this century, (de Boer 1923)), first of all the definition of ventricular fibrillation used in this investigation will be given: "Fibrillation: Irregular, disorganized electrical activity of atria or ventricles. In atrial fibrillation P waves are absent and the baseline consists of irregular waveforms which continuously change in shape, duration, amplitude and direction. In the absence of advanced or complete AV block, the resulting ventricular response is totally irregular (random). In ventricular fibrillation QRS and T waves can no longer be identified. The recorded deflections continuously change in shape, duration, magnitude and direction."
This definition of the WHO/ISFC Task Force (WHO 1978) clearly is an electrocardiographic definition, so the description of atrial fibrillation differs from that of ventricular fibrillation simply because the appearance of these two syndromes on the ECG is different, not because they are necessarily due to a different mechanism.

Many authors have assumed that the bizar ECG implies random behaviour of the myocardial fibers, (Cranefield 1973): "ventricular fibrillation is a condition of random, incoordinated contraction of the fibers of the ventricle, caused by a random and chaotic spread of electrical activity."

Such a condition could produce an ECG as defined above, but more likely no discernable electrical activity at all. On the other hand a condition of local coordination instead of the normal global coordination can also produce an irregular ECG. If one would start to investigate ventricular fibrillation from a definition like that of Cranefield and find some degree of coordination, then one could conclude that no ventricular fibrillation had been investigated. In other words, the definition should not already contain the answer one is looking for. In the course of this study a lot of methodological problems - like the one just sketched - concerning the distinction between data and theories have risen. The basic philosophy underlying the research for this thesis has been formulated very well by Suppe (Suppe 1972). The so called "received view" on the structure of scientific theories has been described by him as: "Scientific theories are developed to explain or predict events which can be observed; however, for reasons of simplicity, scope and economy, such theories typically must employ theoretical entities or constructs in providing these explanations or predictions; these theoretical constructs are not directly observable. Accordingly, in any theoretical explanation or prediction one finds two sorts of sentences:

  1. various premises the truth of which is nonproblematic in virtue of their being confirmed by direct observation;
  2. various laws the truth of which is problematic since they cannot be confirmed by direct observation.
And the observational-theoretical distinction is needed to keep distinct the different statuses of these two kinds of sentence."

The problem with this widely accepted view is that the collection of data for the theories is in many cases already heavily dependent upon a large body of theories, so the simple direct observable facts maybe do not exist. In physical theories however one does not deal with particular phenomena but abstracted, idealized replicas and these theories describe the behaviour of physical systems, not phenomena. In other words: the whole body of theories used by an investigator determines what phenomena will be considered facts and how the data will be collected.

3 After 10 years

Suppe was cited as his article is easier available to the medical profession than more philosophical books, but I was strongly influenced by "standard" texts about philosophy of science (Woodger 1952), (Popper 1965), (Nagel 1971), (Hospers 1967), (Edwards & Pap 1967), (Koningsveld 1980), , (Nauta 1974),(Harré 1981) and (Commins & Linscott 1954). (The sequence indicates an order both in time of reading and in influence.)
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