Author + information
- Received December 26, 1990
- Revision received April 2, 1991
- Accepted May 13, 1991
- Published online November 15, 1991.
- Peng-Sheng Chen, MD, FACC∗,
- Gregory K. Feld, MD, FACC,
- Morton M. Mower, MD, FACC and
- Barry B. Peters, MD
- ↵∗Address for reprints: Peng-Shcng Chen, MD, 8411, Division of Cardiology, Department of Medicine, University of California, San Diego Medical Center, 225 Dickison Street, San Diego, California 92103-8411.
To test the relation between the defibrillation threshold and the upper limit of vulnerability, the shock strength associated with 50% probability of successful defibrillalion (DFT50) and that associated with 50% probability of reaching the upper limit of vulnerability (ULV50) were determined in 20 open chest dogs with use of the delayed up-down method, with pacing drive cycle lengths of 150 to 500 ms and either single 6-ms shocks (10 dogs) or 12-ms biphasic shocks (10 dogs) given at the mid-upslope, peak and mid-downslope of the T wave of electrocardiographc lead II. The shocks were given by means of a patch-patch configuration on the anterior and posterior surfaces of the heart, which was paced from a stimulating electrode attached to the left ventricular apex.
Analysis of variance showed no statistically significant differences in ULV50as determined with different pacing cycle lengths. For monophasic shocks, DFT50(331 ± 66 V or 5.8 ± 2.7 J) was not significantly different from ULV50determined at the midupslope of the T wave (318 ± 64 V or 5 ± 2 J). The correlation coefficients between the two values were 0.74 (p = 0.014) for voltage and 0.67 (p = 0.034) for energy. In contrast, DFT50was significantly higher than ULV50as determined at the peak of the T wave (219 ± 43 V or 2.3 ± 1 J) and mid-downslope of the T wave (200 ± 38 V or 1.9 ± 0.9 J). In three dogs, ventricular fibrillation could not be induced at the mid-downslope of the T wave with any baseline pacing (S1) cycle length.
For biphasic shocks, DFT50(285 ± 53 V or 4 ± 1.5 J) was not significantly different from ULV50as determined at the mid-upslope of the T wave (293 ± 54 V or 3.9 ± 1.2 J). The correlation coefficients between the two values were 0.90 (p < 0.001) for voltage and 0.82 (p = 0.004) for energy. In contrast, DFT50was significantly higher than ULV50determined at the peak of the T wave (208 ± 31 V or 1.9 ± 0.5 J) and mid-downslope of the T wave (180 ± 16 V or 1.7 ± 0.8 J). In six dogs, ventricular fibrillation could not be induced at the mid-downslope of the T wave with any S1cycle length.
It is concluded that with either monophasic or biphasic shocks, DFT50can be accurately estimated by ULV50as determined at the mid-upslope of the T wave. Altering the baseline pacing cycle length does not affect this relation.
☆ This work was done during the tenure of a Clinician Scientist Award (88 414) from the American Heart Association, Dallas, Texas and was supported in part by a Merit Review from the Department of Veterans Affairs, Washington, D.C., and grants from the Whitaker Foundation, Mechaniesburg, Pennsylvania and Cardiac Pacemakers Inc., St. Paul, Minnesota.
- Received December 26, 1990.
- Revision received April 2, 1991.
- Accepted May 13, 1991.