Early assessment of biophysical parameters predicts lesion formation during RF energy delivery in vitro.

BACKGROUND: There is no currently available technology to accurately predict ablation lesion size within seconds of onset of delivery of radiofrequency (RF) energy. METHODS: Changes in several biophysical characteristics of cardiac tissue in vitro within 5-15 seconds of the onset of RF energy were evaluated to predict lesion formation at 120 seconds. RF energy was applied with a 50% duty cycle to measure heating and cooling behavior of the electrode temperature sensor. Changes in impedance, phase angle, and the resulting resistance and capacitance, power, and electrode temperature variation during RF ablation were analyzed. RESULTS: A combination of electrical-based parameters measured online as early as 5, 10, and 15 seconds after onset of RF energy in vitro was found to explain 63, 75, and 76% of variability (R(2) ) of lesion volume. These correlations were better than any single parameter, particularly impedance and target temperature. CONCLUSIONS: A combination of electrical-based parameters provides better correlation with lesion formation than a single parameter and may be useful to predict lesion size during RF ablation in vivo. These parameters appear to represent changes in the tissue during heating.

Testing of a new T-wave subtraction algorithm as an aid to localizing ectopic atrial beats.

BACKGROUND: Identifying the timing and morphology of an ectopic P wave from the surface electrogram can aid in the diagnosis and localization of atrial arrhythmias. Given the relatively short coupling interval of atrial ectopic beats, the P wave is often obscured by the larger amplitude QRS-T wave complex. A method to uncover such "buried" P waves using a standard 12-lead surface ECG would be clinically useful and could potentially be a noninvasive guide to catheter ablation of focal atrial tachycardia. METHODS: We developed an automated computerized program (BARD DUO LAB SYSTEM trade mark ) designed to subtract the QRS-T wave complex from the surface electrogram and uncover a previously obscured P wave. The purpose of the present study was to validate this program. The surface ECG from 21 patients undergoing atrial pacing during electrophysiologic study (group I) and 10 patients with atrial tachycardia (group II) were analyzed and the derived P-wave morphology assessed using correlation waveform analysis (CWA) and visual grading by three reviewers. RESULTS: The algorithm successfully uncovered the P wave in each surface ECG. For the 21 patients in group I, average CWA comparing the derived P wave with the previous paced P wave was 83%. Average CWA for group II was 82%. Visual grading of the match between derived P waves and paced P waves revealed a 21/21 match in group I patients and a 12/12 match in 9/10 of group II patients. CONCLUSIONS: An ectopic atrial P wave obscured by a coincident QRS-T wave complex can be accurately uncovered using this new algorithm. Addition of this technique to existing methods may improve the diagnosis of atrial arrhythmias and aid in the localization and ablation of ectopic atrial foci.