The Significance of Paced Electrogram Fractionation in Hypertrophic Cardiomyopathy
Authors: Saumarez R. C. , Slade A. K. B. , Grace A. A. , Sadoul N. , Camm A. J. , McKenna W. J. 
Published: June 2012

Background
Increased duration of paced right ventricular (RV) electrograms in hypertrophic cardiomyopathy has been shown in 37 patients to correlate with the risk of ventricular fibrillation (VF). The changes in electrogram duration with pacing stimulus prematurity discriminated patients into three groups: VF survivors, an intermediate group with either nonsustained ventricular tachycardia (NSVT) on ambulatory monitoring or a family history of sudden death (FHSD), and those with none of these risk factors (noRF) for sudden death (SD). The consistency of these original groups has been tested prospectively in a further 64 patients.

Methods and Results
Of 64 patients with hypertrophic cardiomyopathy, 3 had documented VF, 1 had witnessed SD and is assumed to have had VF, 25 had NSVT, 21 had FHSD, and 14 had noRF. Nineteen patients had syncope. They were studied by pacing one RV site with a decremental sequence and recording high-pass filtered electrograms from three other RV sites. The delay of each fractionated potential in the electrogram was determined relative to a pacing stimulus of increasing prematurity. These measurements were repeated by pacing each ventricular site in turn. The electrograms were characterized by two parameters: the extrastimulus coupling interval (S
1
S
2
) at which delay increased by more than 0.75 ms/20 ms decrease in S
1
S
2
interval and the change in electrogram duration between an S
1
S
2
of 350 ms and ventricular effective refractory period. The 4 VF patients had a mean increase in electrogram duration of 16.1 ms and an increase in delay at a mean S
1
S
2
of 368 ms. Three VF patients were within the original VF group, while only 6 of 60 non-VF patients were within this group, discriminating between VF patients and the remainder (
P
<.007). The 14 noRF patients had a mean change in electrogram duration of 4.5 ms and an increase in delay at a mean S
1
S
2
of 301 ms. Eleven patients were within the original noRF group, and only 8 of the remaining 50 patients also were within the noRF group, discriminating between the noRF patients and the remainder (
P
<.0005). Most of the NSVT and FHSD patients were between the original VF and noRF groups, with 5 of 25 NSVT and 1 of 31 FHSD patients in the original VF group. There was no relation between syncope and electrophysiological characteristics. Programmed electrical stimulation (PES) was performed in the first 15 patients of this study. Of the total 52 patients from the original and current studies, PES identified 2 out of 6 VF patients, and there was no correlation between VF inducibility and intraventricular conduction delay.

Conclusions
These data are consistent with the original VF and noRF groups. Most patients with FHSD or NSVT were between these groups. Pooled data from the original and current groups (n=101) allow definition of a new VF group, which includes all patients with VF (n=9), 8 of 30 patients with VT, and 3 of 31 patients with FHSD. This new group may be used as a criterion for implantable cardioverter-defibrillator implantation in a prospective trial of the technique for the prediction of SD.