Detection of late potentials by adaptive filtering.

Recent studies have shown small deflections in the terminal portion of the QRS complex in postmyocardial infarction (MI) patients with episodes of potentially dangerous ventricular arrhythmias. These very small deflections, termed late potentials, are difficult to observe in ECGs acquired with electrodes on the chest surface owing to myoelectric noise from underlying muscle and other environmental noise. Most research into enhancement of late potentials has focused on signal averaging. Our interest is in a mathematical signal-processing technique called time sequenced adaptive filtering. In ECG signals processed with adaptive filtering, late potentials are discernable in individual beats. This processing technique may also allow visualization of late potentials in signals from patients with intraventricular conduction delays. Preliminary studies used 12 normal subjects and 5 patients scheduled for electrophysiology studies (EPs), with histories of cardiopulmonary arrest, symptoms of unexplained syncope, or documented malignant ventricular arrhythmias. Three of the five patients studied by EPs had inducible sustained ventricular tachycardia. Subsequently, when ECG signals were obtained from surface electrodes and process by adaptive filtering, these same three patients had prolonged QRS durations (greater than 120 ms) with occurrence of additional low voltage activity (greater than or equal to 5-10 mV) in the terminal portion of the QRS. Two of these patients had bundle branch blocks as determined by a 12-lead ECG. The remaining patients and the control subjects had normal QRS durations with no additional activity. Two subjects in the control group had some activity in the terminal portion of the QRS without prolongation of QRS duration.(ABSTRACT TRUNCATED AT 250 WORDS)