Relationship of Ventricular Excitability Characteristics to Ventricular Arrhythmias in Dogs

Abstract

The relationship of the form of ventricular anodal strength-interval curves to the types of arrhythmias induced by trains of low-intensity stimuli was studied in 16 dogs. Strength-interval curves were determined after basic atrial driven beats and after induced premature ventricular depolarizations. The test stimuli for these determinations were 2-msec anodal square waves delivered in 1-msec decrements during the first half of the cardiac cycle and in 10-msec decrements during the last half of the cycle. At each time step, the stimulus intensity was increased in 5-µamp steps until a ventricular response occurred or a level of 1.2 mamp was reached. Three types of strength-interval curves were observed. Each form of the strength-interval curve was associated with a specific type of arrhythmia induced by a train of 50-Hz, 2-msec anodal stimuli of minimum threshold intensity which was applied for periods of up to several minutes. When the minimum threshold in the strength-interval curve following the basic driven beat was lower than the minimum threshold following the induced premature ventricular depolarization, the train of stimuli induced stable ventricular bigeminy. Accelerating ventricular tachycardia followed by ventricular fibrillation resulted if there were deep dips in the strength-interval curves following both the basic driven beats and the premature ventricular depolarizations. When the strength-interval curves following both the basic driven beats and the premature ventricular depolarizations smoothly approached diastolic levels without deep dips or supernormal periods, the train of stimuli caused either occasional premature ventricular depolarizations with long coupling intervals or slow ventricular tachycardia. These relationships may participate in the initiation and the maintenance of arrhythmias.

Na+ channel distribution and electrophysiological heterogeneities in guinea pig ventricular wall

“…In the present study, both epicardial and endocardial strength-interval curves have been found to exhibit a smooth hyperbolic shape with no dips on the steep descending portion of the curve (Fig. 2), suggesting that no supernormal excitability phase, an attribute of anodal break-excitation (20,33,45), was yielded by bipolar stimulations.…”

“…Previous studies have demonstrated close correlation between diastolic excitability threshold and VF threshold values (15,29,33,36,62), suggesting that increased tissue excitability may facilitate VF induction. The LV was found to be most susceptible to electrically induced VF at those intervals of the cardiac cycle at which the ventricular capture threshold is the lowest (15,33,36).…”

“…The LV was found to be most susceptible to electrically induced VF at those intervals of the cardiac cycle at which the ventricular capture threshold is the lowest (15,33,36). Furthermore, there is evidence to suggest that factors [e.g., ischemia, hyperkalemia, or infusion of aprindine (class 1b antiarrhythmic agent)] that influence excitability threshold in canine ventricular muscle may cause similar changes in VF threshold (29,62).…”

Reentrant ventricular arrhythmias in the late myocardial infarction period in the dog. 13. Correlation of activation and refractory maps.

“…Choosing too low a suprathreshold current results in the choice of an interval that would change significantly with only slight changes in current. Because there is no final conclusion about which electrical parameters best describe the refractoriness properties of the cells during in vivo conduction, twice diastolic threshold was used in the present study, and has been used routinely in other electrophysiological studies (Denes et al, 1974;Harumi et al, 1974;Levites et al, 1975). Allessie et al (1978) determined in isolated atrial strips that a refractoriness gradient of 11-16 msec was sufficient to cause conduction block.…”

The effect of procaine amide on components of excitability in long mammalian cardiac Purkinje fibers.

“…'"'In the past, cardiac excitability has been assessed primarily in the whole animal, and the index investigated has been the "threshold" current sufficient to elicit a response in studies on either strength-duration requirements or multiple response thresholds. 8 ' 9 Conflicting results appear in the literature, with some studies showing procaine amide (PA) to decrease excitability in a variety of species, 10 " 12 whereas one failed to show any significant effect. 13 Although in these studies there are many differences in experimental technique, part of the variability in the results may be attributed to the fact that the "current threshold" is determined by a complex set of passive and active membrane properties.…”