Methods
A derivation cohort of consecutive patients, in whom OTVA ablation was
performed at our centre, were retrospectively identified. Patients were
included if there was an unambiguous SOO, in whom ectopy was
successfully suppressed with radiofrequency (RF) ablation at a single
site, with no recurrence during a 30 minute post-ablation waiting period
as well as at least 90% reduction in ectopy burden on follow up 3 month
Holter monitor. Patients with multiple ventricular arrhythmias were
excluded.
For each patient, a single pre-ablation 24-hour ambulatory ECG was
retrospectively analysed. Where possible, recordings performed prior to
the introduction of anti-arrhythmic drugs (AAD) were selected. For every
complete one-hour recording, the ventricular ectopic (VE) total was
calculated. Variability in VE across the 24 hour period was assessed
using the coefficient of variation (CoV) = standard deviation divided by
the mean. Total number of bigeminy/trigeminy episodes and the
variability (CoV) of this was also calculated. Percentage ectopic
burden, mean heart rate and presence of sustained VT were also analysed.
Patients with left and right sided SOO were compared and ROC curve
analysis used to determine the optimal predictive parameter values.
Circadian patterns in variability were analysed by comparing each
patient’s total VE CoV between four quartiles of the day (00:00-06:00,
06:00-12:00, 12:00-18:00 and 18:00-00:00).
Parameters which were found to accurately predict SOO were then applied
prospectively to a validation cohort of consecutive patients undergoing
their first OTVA ablation. A single 24-hour ambulatory ECG, prior to AAD
therapy where possible, was chosen for the primary analysis.
In order to assess inter-Holter reproducibility of the newly derived
parameters, a supplementary analysis on any additional ambulatory ECGs
was also performed on patients in whom multiple ambulatory monitors had
been performed prior to ablation.
The predictive value of the derived parameters in determining SOO was
calculated and compared to two well established morphological ECG-based
algorithms shown to have the highest accuracy in a recent prospective
analysis (5); transitional zone index (TZI) and
V2S/V3R index (6,7).
TZI is defined as the precordial chest lead at which R wave transition
is observed in the VE minus the equivalent lead for a sinus beat, with a
TZI > 0 predicting a right sided SOO. The
V2S/V3R index is calculated by dividing
the ectopic S-wave amplitude in V2 by the ectopic R-wave amplitude in
V3, with a value > 1.5 also predicting a right sided SOO.