Vulnerability of the mildly ischemic ventricle to cathodal, anodal, and bipolar stimulation.

Abstract

SUMMARY We studied the difference between myocardial vulnerability to arrhythmias caused by cathodal, anodal, and bipolar stimulation in 29 dogs with partial right coronary artery ocdusion. We used 2-msec duration stimuli of up to 8 mA to determine the ventricular vulnerable periods, their relationship to the refractory periods, and the fibrillation or multiple response thresholds for unipolar anodal and cathodal stimulation after two premature ventricular contractions. The vulnerable period for arrhythmias began at the end of the respective refractory periods and terminated at a specific time within the cardiac cycle. Within this period the arrhythmia and excitation thresholds were equal. Because shorter refractory periods were obtained with anodal stimulation than cathodal, the vulnerable periods for anodal stimulation were longer. This indicated that the vulnerable periods for bipolar stimulation also would be longer than for unipolar cathodal stimulation since bipolar and anodal refractory periods are equal when the cathode and anode are of similar surface area. Results from seven of the experiments showed that a dual focus of excitation, which can only occur with bipolar stimulation, did not make the ventricle more vulnerable to arrhythmias than did unifocal stimulation. These results indicate that the difference between the arrhythmia vulnerability to unipolar cathodal, anodal, and bipolar stimulation is dependent on the relationship between their excitability characteristics, i.e., their strength-interval curves.THE EXISTENCE of a brief period in the ventricular cycle during which electrical stimulation can induce arrhythmias such as ventricular fibrillation was demonstrated in animals by Wiggers and Wegria, 1 and often has been verified. -3The extensive clinical use of cardiac stimulation has made the circumstances under which such electrical stimulation may cause an arrhythmia of importance. Although most investigations indicate that the minimum energy required to precipitate ventricular fibrillation in the normal myocardium exceeds that delivered by a clinical cardiac pacemaker, there have been clinical reports of ventricular fibrillation and tachycardia associated with a pacemaker stimulus falling in the "vulnerable period" of the cardiac cycle. This suggests the presence of pathophysiological and pharmacological factors that lower the threshold to arrhythmias such as myocardial ischemia, sympathetic activity, and premature ventricular beats. 4~6Aside from these factors, the effects of electrode and stimulus characteristics on myocardial vulnerability are not yet well understood.A recent analysis of cases of ventricular fibrillation and tachycardia attributed to pacemaker stimuli found that most such arrhythmias arose in patients undergoing bipolar rather than unipolar cathodal stimulation. 7 In our own review of the literature, 8 we found 26 cases in which the initiation of ventricular fibrillation or tachycardia (defined as at least a run of 3 premature ventricular contractions) was illustrated. In ...

Ventricular Tachyarrhythmia Initiation in a Canine Model of Recent Myocardial Infarction. Comparison of Unipolar Cathodal, Anodal and Bipolar Stimulation

“…In contrast, it was possible to initiate both ventricular tachy cardia and fibrillation readily using pro grammed pacing with unipolar cathodal, anodal and bipolar stimulation in dogs with a recent myocardial infarction (table II, III). In comparison, both Merx et al [26] and Mehra et al [27] could only induce ventricu lar fibrillation or multiple ventricular re sponses in their acute ischemic animal mod els in the course of evaluating the role of pac ing mode in tachyarrhythmia initiation. It is noteworthy that in the present infarction model the incidence of ventricular tachycar dia and fibrillation episodes was similar (ta ble II).…”

Vulnerability of the right ventricle to cathodal, anodal, and bipolar stimulation at double diastolic threshold strength

“…The anodal stimulation accelerates the rate of recovery and therefore the duration of the absolute refractory period is shortened (9). On the other hand, the beginning of the relative refractory period is the same with both stimulation techniques: anodal and cathodal.…”

“…The difference in vulnerability for unipolar cathodal and anodal stimulation is a result of certain characteristics of cardiac excitability (3,9,16). The anodal stimulation accelerates the rate of recovery and therefore the duration of the absolute refractory period is shortened (9).…”

“…On the other hand, the beginning of the relative refractory period is the same with both stimulation techniques: anodal and cathodal. The total duration of the relative refractory period will be longer with anodal stimulation and offers an explanation for the increased vulnerability induced by this stimulation technique (9). The bipolar excitation threshold at any time during the cardiac cycle is a composite of both anodal and cathodal thresholds (3,9,11,16).…”

Performance of Dedicated Versus Integrated Bipolar Defibrillator Leads with CRT‐Defibrillators: Results from a Prospective Multicenter Study

“…Ventricular refractoriness is shorter for anodal versus cathodal stimulation, particularly early after lead placement, and is associated with an increase in the vulnerable period for arrhythmias in the setting of anodal stimulation. [7][8][9] Additionally, anodal stimulation can make it difficult to determine LV pacing thresholds, occasionally resulting in an overestimation of the true LV pacing threshold and programming of unnecessarily high LV pacing outputs. On the other hand, anodal stimulation has been reported in some cases to have a beneficial effect on LV synchrony and LV systolic performance during biventricular pacing.…”