Further Evidence on How to Measure Local Repolarization Time Using Intracardiac Unipolar Electrograms in the Intact Human Heart.

November 2019 1 There are currently 2 methodologies for measuring local repolarization time (RT) from the unipolar electrogram (UEG). The standard method (or Wyatt method1), where RT is measured on the upslope of both upright and inverted T waves, is widely used, has a solid theoretical background, correlates with the effective refractory period (ERP) in patients,2 and has been validated in animal studies.2,3 An alternative method in which RT is also taken on the upslope of inverted T waves, but on the downslope of upright T waves, has been suggested to provide better correlation to RT derived from monophasic action potentials in human hearts,4 which has made it the method of choice in several recent human studies.5 Although the Wyatt method is supported by solid evidence and more widely used, further data from the intact human heart are, therefore, needed to bring closure to the controversy. This is increasingly relevant as advances in cardiac mapping are rapidly providing access to more and more human data. Importantly, no direct comparison between these two methods and the ERP—the most robust measure of refractoriness—has ever been conducted. In this first retrospective comparative study, the local ERP was more accurately measured with the Wyatt than the alternative method. Eleven patients (47±12 years of age; 6 women) with structurally normal hearts and normal ECG underwent electrophysiology studies for supraventricular tachycardia ablation conducted under minimal conscious sedation. The study was approved by the local ethics committee and all patients gave informed consent. Programmed electrical stimulation was performed via the distal electrodes of Decapolar catheters, with electrode spacing equal to 2-5-2 mm, at a pulse width of 2 ms, and stimulus strength of twice the diastolic threshold. Pacing was delivered from the RV apex (n=10), left ventricular base (n=10), and coronary sinus (left ventricular epicardial base, n=4). Following steady state pacing at 600 ms for 3 minutes, S1S2 restitution protocols were performed from at least 2 of these 3 sites. Eight drive trains at 600 ms were followed by an extra stimulus at coupling interval S1S2 decrementing from 1000 to 400 ms in 50 ms steps, from 400 to 300 ms in 20 ms steps and from 300 to ERP in 5 ms steps. The S2 stimulus was then decremented in 1 ms steps from 10 ms above the point of loss of capture to define the ERP (Figure [A]). UEGs were recorded with a Bard EP system with sampling frequency equal to 2 KHz and band pass filtered at 0.05 to 500 Hz using the Wilson Central terminal as reference. UEGs were subsequently low-pass filtered off-line at 80 and 25 Hz for activation and repolarization measurements, respectively. Activation-recovery intervals (ARIs)—a surrogate for action potential duration—were measured as RT minus actitation time. As upright T waves occur adjacent to the pacing site but become inverted at sites more distant to it, analysis for upright T waves used ARI measured from the electrode adjacent to the pacing site where ERP was being determined, whereas analysis for inverted T waves used ARI measured from the RESEARCH LETTER