Clinical evaluation of an improved high resolution ECG cart for recording the His bundle electrogram non-invasively

The Marquette high resolution MCA-1 ECG cart can record the His bundle electrogram non-invasively at the bedside. The second generation MAC-1 has several unique features and technical advances which may now make the technique clinically applicable. In addition to amplification and signal averaging, an adjustable input filtration system excludes beats which are unacceptably "noisy" compared to a 4 beat template. Thus, extremely "clean" signals are presented for processing by the average allowing resolution of very low amplitude signals. Clear unequivocal His bundle recordings were obtainable in 25 of 55 patients (45%). A correlation coefficient of +.97 was obtained between invasive and non-invasive HV intervals. The 55% failure rate was attributed to prolonged atrial activity in 31%, short PR in 9%, and technically unsatisfactory recordings with excessive or overwhelming noise which did not allow appreciable signal resolution in 15%.