[Value of measurement of the HV interval in His bundle electrocardiography in the evaluation of fascicular blocks].
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High frequency electrocardiograms were studied in 19 patients with chronic neumopathies, pulmonary arterial hypertension and respiratory failure in the great majority. Studies were made of: a) the significance of conduction disorders in the right ventricle either at the fasciculary branch or within the mass of the ventricle with regard to the time of appearance and the length of the intrinsicoid deflection and its components. b) The duration of the electrical sistole of each ventricle in relation with hyperatrophy that results in sistolic over loading. c) An attempt was made to correlate the number of high frequency deflections (discontinuity of activity) with the prognosis.
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Endocardial electrocardiograms permit the analysis of auricular depolarization and contribute to the study of ventricular activation. Direct recording of auriculograms from the right atrium and indirect recording of the left auriculograms through the coronary sinus and pulmonary artery, show the different auricular activation pathways in common atrial flutter, atrial tachycardia and in case of retrograde atrial depolarization (via the AV node, septal or parietal accessory pathway). His bundle electrograms obtained via the femoral vein or, less easy, via the brachial vein, has introduced an essential mark in the analysis of intracardiac activation enabling us to precisely locate lesions of the AV conduction system, making easier differential diagnosis between aberrant ventricular conduction and ventricular ectopic rhythms and contributing to the study of ventricular preexcitation. Endocavitary stimulation at increasing rate and by the single extrastimulus technique is the complement of intracardiac electrocardiography in evaluating sinus node function, conduction times and refractory periods at different levels, electrophysiological properties of accessory pathways and studies of the antiarrhythmic drugs. Programmed stimulation allows the recognition of reentry as the mechanism of many tachyarrhythmias. The recording of monophasic action potential by the suction--electrode technique is another step in the intracavitary electrophysiological investigation.
The interest towards intraventricular conduction defects started some 10 yr after the introduction of the string galvanometer by Einthoven. As early as 1910, it was known that conduction blockade could occur along either branch of the intraventricular conducting pathway. It took some 20 yr to identify properly the electrocardiographic manifestations of right and left bundle branch blocks. A further 30 yr were needed to obtain a sound correlation between these functional disorders and the presence of anatomical lesions. The more recent introduction of the concept of left hemiblocks further improved our understanding of intraventricular conduction defects. The latter concept is based on the hypothesis of the anatomical and functional bifascicularity of the left bundle branch, a hypothesis which cannot be accepted without some reservations. Later developments indicated that left hemiblocks associated with right bundle branch block represent manifestations of bilateral conduction disturbances (incomplete bilateral bundle branch block). Such an association may constitute a forerunner of complete atrioventricular block, or an indicator of the possibility of sudden death. Whether these complications occur frequently or unfrequently in the setting of incomplete bilateral bundle branch block remains an unsettled question.
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2 patients with symptoms of paroxysmal AV block showed widening, splitting, slurring and decreasing amplitude of the His potential. Concomitantly, this was followed by different patterns of bundle branch block. In one of the patients it was obvious that a left bundle branch block was related to a Wenckebach phenomenon in the His bundle, and in the other patient different bundle branch block patterns were related to the occurrence of the intra-His bundle conduction delay. It is suggested that the present electrophysiological findings reflect asynchronous conduction in the His bundle causing a critical conduction delay in parts of the bundle branches leading to bundle branch block.
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It was established that the presence of Samoilov-Wenckebach's periods and prolongation of the H--V interval at low frequency of the imposed rhythm as well as periods of asystolia of more than 1,200 msec are most typical for these patients. An attempt was made to determine the type of cardiac stimulation indicated for such patients from the character of the disorders of rhythm observed in them and the initial frequency of their own cardiac contractions.
The overdrive pacing method is widely used now in clinical practice for prevention and treatment of severe ventricular disorders of the cardiac rhythm. The mechanisms of arrhythmia suppression by means of this stimulation is analysed. Indications are determined for the choice of the site of stimulation and optimal impulce frequency in ischemic heart disease, and overdosage with digitalis drugs, as well as in myocardiopathy.
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A case is described where the basic sinus rhythms is associated with an advanced degree of left anterior hemiblock. The rhythm is complicated by atrial extrasystoles, associated with a lesser degree of left anterior hemiblock. This paradox of 'supernormality' is explained on a critical interplay of differential refractoriness within the divisions of the left bundle-branch.