Author + information
- Received November 18, 1985
- Revision received April 2, 1986
- Accepted April 16, 1986
- Published online September 1, 1986.
- ↵*Address for reprints: L. Brent Mitchell, MD, Division of Cardiology, Foothills General Hospital, 1403-29th Street N.W., Calgary, Alberta, Canada T2N 2T9.
Closely coupled extrastimuli are frequently necessary to induce ventricular tachycardia at electrophysiologic study. Although induction usually requires propagated extra-stimuli, systematic evaluations of minimal coupling intervals have focused on nonpropagated measures (effective refractory periods) rather than on propagated measures (functional refractory periods). The effects of procedural factors on ventricular functional refractory periods were examined in 10 patients. Like the effective refractory period, the functional refractory period shortens with rapid pacing cycle lengths (281 ± 12 ms at a cycle length of 600 ms; 260 ± 15 ms at a cycle length of 400 ms) and with multiple extrastimuli (279 ± 16 ms with one extrastimulus; 214 ± 16 ms with two extra-stimuli). The effects of multiple extrastimuli exceed those of shortening pacing cycle length. Unlike the effective refractory period, the functional refractory period is affected by recording site (increasing as the distance from the pacing site increases) but is not affected by increasing the stimulus intensity above twice diastolic threshold (282 ± 14 ms at 2 times threshold; 282 ± 13 ms at 16 times threshold) or by increasing the pulse width above 2 ms (282 ± 13 ms at a pulse width of 2 ms; 282 ± 14 ms at a pulse width of 5 ms).
The effect of varying stimulus intensity on ventricular tachycardia induction was examined in a second group of 11 patients with documented, spontaneous ventricular tachycardia. No change in ventricular tachycardia in-ducibility accompanied changes in stimulus intensity from 2 to 10 times threshold. These data support the use of a stimulus intensity of twice threshold and a pulse width of 2 ms for clinical ventricular tachycardia induction studies with progressive potency provided first by shortening pacing cycle length and then by multiple extra-stimuli.
- Received November 18, 1985.
- Revision received April 2, 1986.
- Accepted April 16, 1986.
- American College of Cardiology Foundation