Noninvasive real time observation of His bundle activity

While seeking a particular lead combination that would demonstrate the His bundle impulse noninvasively, an esophageal lead system was found that shows a clear cut positive going ramp in the final 40 msec of the P-R segment. Using a dual beam oscilloscope in a totally shielded true hi-fi system, tracings showed this ramp occurs immediately before the QRS of chest leads. With its timing, polarity and electrode placement it appears that it can only arise from His bundle (nodobundle) activity. Tracings are presented which show how electromagnetic interference obscures this and other P-R interval signals illustrating the need for true hi-fi conditions in ECG research