Programming of implantable cardioverter-defibrillators on the basis of the upper limit of vulnerability.
BACKGROUND
A patient-specific measure of defibrillation efficacy that requires a minimum number of ventricular fibrillation (VF) episodes would be valuable for programming implantable cardioverter-defibrillators (ICDs). The upper limit of vulnerability (ULV) is the weakest shock strength at or above which VF is not induced when a stimulus is delivered during the vulnerable phase of the cardiac cycle. It correlates with the defibrillation threshold (DFT) and can be determined with a single episode of VF. The objective of this study was to test the hypothesis that ICDs programmed on the basis of the ULV convert spontaneous ICD-detected VF reliably.


RESULTS
We studied 100 consecutive patients at ICD implantation and during follow-up of 20 +/- 7 months. At implantation, the ULV and DFT were determined, and the ICD system was tested at a shock strength equal to the ULV + 3 J. During follow-up, the strength of the first shock was programmed to the ULV + 5 J for arrhythmias detected in the VF zone (cycle length < 292 +/- 17 ms). We reviewed stored detection intervals and electrograms from spontaneous episodes of ICD-detected VF to determine the success rate for appropriate first shocks. The programmed first-shock strength was 17.5 +/- 5.2 J. During follow-up, there were 120 appropriate first shocks in 37 patients. The arrhythmia was rapid monomorphic ventricular tachycardia (VT) in 70% of episodes (31 patients), VF in 11% (13 patients), polymorphic VT in 1%, and unclassified in 17% (15 patients). The first shock was successful in 119 of 120 episodes (99%; 95% CI, 93% to 100%). One unclassified episode required two shocks. No patient had syncope associated with an ICD shock or arrhythmic death.


CONCLUSIONS
ICD shocks can be programmed on the basis of the ULV, a measurement made in regular rhythm, without a direct measure of defibrillation efficacy.
Swerdlow
C D
CD
Division of Cardiology, Cedars-Sinai Medical Center, Los Angeles, Calif, USA. swerdlow@ucla.edu
Peter
C T
CT
Kass
R M
RM
Gang
E S
ES
Mandel
W J
WJ
Hwang
C
C
Martin
D J
DJ
Chen
P S
PS
D000368:Aged; D017147:Defibrillators, Implantable; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D012984:Software; D017180:Tachycardia, Ventricular / Q000503:physiopathology / Q000628:therapy*; D014693:Ventricular Fibrillation / Q000503:physiopathology / Q000628:therapy*