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AHA/ACCF/HRS recommendations for the standardization and interpretation of the electrocardiogram: part III: intraventricular conduction disturbances: a scientific statement from the American Heart Association Electrocardiography and Arrhythmias Committee, Council on Clinical Cardiology; the American College of Cardiology Foundation; and the Heart Rhythm Society. Endorsed by the International Society for Computerized Electrocardiology.

Propagation of excitation in the heart involves action potential (AP) generation by cardiac cells and its propagation in the multicellular tissue. AP conduction is the outcome of complex interactions between cellular electrical activity, electrical cell-to-cell communication, and the cardiac tissue structure. As shown in this review, strong interactions occur among these determinants of electrical impulse propagation. A special form of conduction that underlies many cardiac arrhythmias involves circulating excitation. In this situation, the curvature of the propagating excitation wavefront and the interaction of the wavefront with the repolarization tail of the preceding wave are additional important determinants of impulse propagation. This review attempts to synthesize results from computer simulations and experimental preparations to define mechanisms and biophysical principles that govern normal and abnormal conduction in the heart.

Basic Mechanisms of Cardiac Impulse Propagation and Associated Arrhythmias

Background Cardiac mapping is essential for understanding the mechanisms of arrhythmias and for directing curative procedures. A major limitation of the current methods is the inability to accurately relate local electrograms to their spatial orientation. The objective of this study was to present and test the accuracy of a new method for nonfluoroscopic, catheter-based, endocardial mapping. Methods and Results The method is based on using a new locatable catheter connected to an endocardial mapping and navigating system. The system uses magnetic technology to accurately determine the location and orientation of the catheter and simultaneously records the local electrogram from its tip. By sampling a plurality of endocardial sites, the system reconstructs the three-dimensional geometry of the chamber, with the electrophysiological information color-coded and superimposed on the anatomy. The accuracy of the system was tested in both in vitro and in vivo studies and was found to be highly reproducible (SD, ...

A Novel Method for Nonfluoroscopic Catheter-Based Electroanatomical Mapping of the Heart In Vitro and In Vivo Accuracy Results

http://www.infarkt.ru/d/38025/d/recommendations_for_interpretation_of_the_ecg_4.pdf

AHA/ACCF/HRS Recommendations for the Standardization and Interpretation of the Electrocardiogram

The isolated left atrium of the rabbit, which showed no spontaneous activity, was electrically driven for 20 beats with a cycle length of 500 msec. Tachycardia could be repeatedly initiated by the application of a single adequately timed stimulus shortly after the refractory period of the last basic beat. After the termination of the tachycardia, either spontaneously or artificially by a properly timed stimulus, this procedure was repeated. The number of beats of these tachycardias varied from just one (coupled extrasystole) to many hundreds. Surface electrograms were recorded at about 300 different sites. From the moments of activation of these sites, the spread of activation during regular driving and during the premature beat and the subsequent tachycardia could be determined. In contrast to the radial spread of the activation during basic rhythm, the impulse of the premature beat was propagated in a circular pathway. This circus movement was maintained during tachycardia. These results show that even in a small area of atrial muscle containing no anatomical obstacle the impulse can be entrapped in a circus movement. This circus movement was the underlying mechanism of the arrhythmia.

Circus Movement in Rabbit Atrial Muscle as a Mechanism of Tachycardia

To obtain information concerning the time course and instantaneous distribution of the excitatory process of the normal human heart, studies were made on isolated human hearts from seven individuals who died from various cerebral conditions, but who had no history of cardiac disease. Measurements were made from as many as 870 intramural terminals. In the isolated human hearts three endocardial areas were synchronously excited 0 to 5 msec after the start of the left ventricular activity potential. These areas increased rapidly in size during the next 5 to 10 msec and became confluent in 15 to 20 msec. The left ventricular areas first excited were (1) high on the anterior paraseptal wall just below the attachment of the mitral valve; (2) central on the left surface of the interventricular septum and (3) posterior paraseptal about one third of the distance from apex to base. The last part of the left ventricle to be activated usually was the posterobasal area. Endocardial activation of the right ventricle wa...

Total Excitation of the Isolated Human Heart

Supraventricular tachycardia in an isolated rabbit heart preparation was repeatedly initiated and terminated by carefully timed atrial premature beats. Transmembrane action potentials of AV nodal cells were recorded simultaneously by a "brush electrode" consisting of 10 microelectrodes. Surface electrograms of atrium and His bundle were also recorded. The moments of activation of 54 different AV nodal cells, both during regular driving of the atrium and during tachycardia were ascertained. Premature atrial beats introduced during tachycardia would either "reset" the tachycardia or terminate it. The sequence of activation of the AV nodal cells when initiating tachycardia, during tachycardia itself, and when premature beats were interpolated during tachycardia warrant the conclusion that a circus movement in the AV node, based on functional longitudinal dissociation of the upper AV node, was the underlying mechanism of the arrhythmia.

Circus Movement within the AV Node as a Basis for Supraventricular Tachycardia as Shown by Multiple Microelectrode Recording in the Isolated Rabbit Heart

Interruption of anterior fibers of the left bundle branch system together with right bundle branch block was accomplished experimentally in canine and primate hearts. In both species the electrocardiographic effects included a major alteration of the mean electrical axis to a superior and anterior direction. Epicardial excitation was markedly delayed anteriorly, causing widening of the QRS complex in standard electrocardiographic leads. Normal outward intramural spread of excitation in anterior regions of the left ventricle was reversed after left anterior arborization block alone. After addition of right bundle branch block, intramural spread of excitation was again directed outwardly but was markedly delayed in endocardial onset. Electrical effects of these blocks could be "corrected" individually or in combination by introducing synchronized electrical stimuli distal to each lesion. A scheme is proposed by which various forms of intraventricular conduction disturbance can be defined in terms of block of one or more divisions of a three-pronged system of rapid ventricular excitation.

Left anterior arborization block combined with right bundle branch block in canine and primate hearts. An electrocardiographic study.

The pattern of atrioventricular (AV) nodal activation in isolated rabbit hearts was studied by recording transmembrane action potentials in about 200 AV nodal fibers per heart. A brush electrode consisting of ten microelectrodes was used. Both antegrade and retrograde spread of excitation were mapped: retrograde conduction was not an exact mirror image of antegrade conduction. The major input during antegrade conduction was from the crista terminalis, but the major output during retrograde conduction was through the interatrial septum. Some parts of the AV node were excited without directly participating in either antegrade or retrograde transmission of the impulse. Simultaneous pacing of the atrium and the His bundle generated antegrade and retrograde wave fronts which collided at different levels of the AV node. In this way, cells which transmitted the impulse in both directions were distinguished from those which did not (dead-end pathways). Two types of dead-end pathways were found: type A probably consisted of superficial atrial fibers terminating in the base of the tricuspid valve and type B branched off from cells in the middle node. The shape of the action potential of AV nodal cells strongly depended on the direction of propagation. In some parts of the AV node, the amplitude of the action potential was larger during antegrade activation than it was during retrograde activation; in other parts, the amplitude was smaller during antegrade conduction. The largest amplitudes occurred when wave fronts collided.

Spread of Excitation in the Atrioventricular Node of Isolated Rabbit Hearts Studied by Multiple Microelectrode Recording

Right ventricular hypertrophy (RVH) of mild, moderate, or severe degree was produced in six dogs following systolic overload of the right ventricle by surgical banding of the pulmonary trunk. Activation of the myocardium and specialized conducting tissue of the right ventricle was studied using intramural multi-electrodes or an exploring electrode, first with the heart in situ and then with the heart in a modified Langendorff perfusion circuit. Normal epicardial and intramural activation patterns were found in RVH, and the prolonged excitation time was found to be due to the increased muscle mass. No delay in activation was found in any part of the specialized conducting tissue of the right ventricle. Late activated Purkinje fibres were found in the outflow tract of the right ventricle in the dogs with hypertrophy and in a control series of normal dogs.

The present electrocardiographic criteria for complete and incomplete right bundle branch block (RBBB) are based on widening of the QRS coniplex and the rSR pattern. This type of change can occur also in RVH. Because it has been shown here that no delay occurs in the specialized conducting system of the right ventricle in RVH secondary to systolic loading, the application of criteria to electrocardiograms that also fulfil the criteria for RVH may be misleading. It is suggested that in such cases the diagnosis of a conduction disturbance must also depend upon other methods, and that the terms 'incomplete' and 'complete' RBBB should be handled with care in this context.

Gerrit E. Freud

Papers

Total Excitation of the Isolated Human Heart

Circus Movement within the AV Node as a Basis for Supraventricular Tachycardia as Shown by Multiple Microelectrode Recording in the Isolated Rabbit Heart

Left anterior arborization block combined with right bundle branch block in canine and primate hearts. An electrocardiographic study.

Spread of Excitation in the Atrioventricular Node of Isolated Rabbit Hearts Studied by Multiple Microelectrode Recording

Activation of the hypertrophic right ventricle in the dog.