[Detection of late potentials on the signal averaged body surface ECG using X, Y, Z and anterior chest leads].

We developed the system of high-frequency analysis of the signal-averaged body surface ECG to detect low amplitude signals in the terminal portion of the QRS. Thirty-five patients four or more weeks after transmural myocardial infarction (MI) and 30 normal volunteers were studied. All patients were in normal sinus rhythm and did not have bundle branch block. Body surface ECG recording using bipolar X, Y, and Z leads was performed in a shielded room. One lead served as the reference. The three-channel amplifier was a commercially-available ECG system. The common mode rejection ratio was 120 dB. The signal from each lead was amplified and passed through an analogue filter (NF FV 624) with a low-cut frequency of 100 Hz and a high-cut frequency of 300 Hz. Then AD conversion was performed with 12-bit accuracy, 1024 samples/sec. The filtered signals for the three leads were displayed separately for each channel and were combined into a vector magnitude, square root of X2+Y2+Z2. The percent ratio of the root mean square voltage in the last 40 msec of the QRS complex to that of the total filtered QRS (%RMS40) and the duration of the filtered QRS were automatically calculated. These parameters obtained from the three groups were compared. Signal-averaged, non-filtered and filtered body surface ECGs were recorded using 25 (5 x 5 array) anterior chest unipolar leads in 20 normal volunteers and in patients with late potential. The departure index was calculated as the voltage differences between the mean value (M) in normal persons and the value in patients (Xi) with MI using the formula (Xi-M/SDi) at intervals every four msec. The departure maps, capable of identifying the location of the MI, were made from the departure index at four msec intervals; then the late potential (LP) area maps were superimposed on the departure maps. To determine the late potential, we used the filtered ECG of X, Y, and Z leads and quantitative values (%RMS 40) obtained from a vector magnitude incorporated in these three leads. Six MI patients, four anterior and two inferior, with the late potential had low amplitude signals at the end of the filtered QRS complex. The %RMS 40 was 6.8 +/- 2.9% (p less than 0.001) in MI patients with the late potential, 2.8 +/- 8.5% (p less than 0.01) in MI patients without the late potential, and 37 +/- 11% in normal subjects.(ABSTRACT TRUNCATED AT 400 WORDS)