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The Ventricular Excitability‐Interval Relationship in Early Diastole in Humans: The Influence of the Electrode Configuration During Bipolar Stimulation
Author(s) -
TOIVONEN LAURI K.,
KADISH ALAN H.,
KOU WILLIAM H.,
MORADY FRED
Publication year - 1990
Publication title -
pacing and clinical electrophysiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.686
H-Index - 101
eISSN - 1540-8159
pISSN - 0147-8389
DOI - 10.1111/j.1540-8159.1990.tb02124.x
Subject(s) - medicine , stimulation , cardiology , diastole , interval (graph theory) , electrode , blood pressure , combinatorics , chemistry , mathematics
The purpose of this study was to determine the relationship between ventricular excitability and the extrasfimulus (S 2 ) coupling interval in early diastole in humans. The influence of the electrode configuration during bipolar stimulation was examined. Ventricular strength‐interval curves were constructed using an eight beat drive train at a cycle length of 600 msec, 2‐msec decrements in the S 2 coupling interval, and 0.2‐mA increments in the current intensity of S 2 at each coupling interval. A transient dip in the excitation threshold was observed in early diastole during bipolar pacing when the distal electrode was the anode in six of 17 patients (35%). In contrast, this type of dip was not observed when the distal electrode was the cathode. The excitation threshold at the trough of the dip ranged from 1.0 to 2.2 mA. Unipolar strength‐interval curves indicated that a dip occurred with anodal but not cathodal pacing. We postulated that the dip might interfere with the accurate determination of the ventricular effective refractory period by resulting in transient loss of ventricular capture during decremental scanning of diastole with S 2 . A gap in ventricular capture was produced in all six patients who demonstrated a dip in the bipolar strength‐interval curve by selecting an S 2 current intensity that fell within the dip. In conclusion, the bipolar strength‐interval curve may display an early diastolic dip in the excitation threshold, depending on the electrode configuration. During determination of the ventricular effective refractory period, if the stimulus intensity falls within the range of current intensities encompassed by the dip, a transient early diastolic gap in ventricular capture will be observed as diastole is scanned with S 2 . If this type of gap is not recognized, the ventricular effective refractory period may be overestimated.