His-Purkinje waveforms on externally recorded averaged unfiltered electrocardiograms

Electrocardiographic signal recorded in right unipolar leads (2V1, 3V1, V1) was amplified (up to 500,000 times) averaged (256 or 512 cardiac cycles) and finally digitally filtered, in order to record His-Purkinje (HP) activity. A group of 41 patients with sinus rhythm and PR intervals ranging between 100 and 250 ms was repeatedly investigated. Distinct and highly reproducible waveforms located in the PR segment, attributable to HP activity, were recorded on the averaged unfiltered traces in 14 patients (34%). Waveforms, with an amplitude ranging between 4 and 80 microV, were positive in 13 patients and negative in one. In one patient, with atrial tachycardia with 2:1 atrioventricular block, two positive successive deflections suggested the possibility of recording the proximal and distal His activity. Externally recorded averaged unfiltered traces could be useful for the investigation of HP activity in a relatively large proportion of patients.