EDITOR'S NOTE: The development of invasive electro-physiological techniques has altered our approach to the diagnosis and management of cardiac dysrhythmias. The careful scrutiny of surface electrocardiographic tracings and deduction of potential mechanisms has become a bit of a "lost art" that is not nurtured in contemporary training programs. We present such an analysis of a rhythm disturbance, accompanied by "ladder diagrams" to illustrate the proposed mechanism of the dysrhythmia. Students of classic analytical texts by Katz and Pick(l) and Pick and Langendorf(2) will recognize the format of the presentation.

A QRS duration of 0.12 seconds with a RBBB type pattern in V1 and an upright QRS in Lead 2 during the tachycardia (while there is a left anterior hemiblock present during sinus rhythm), indicates there is a good possibility that the tachycardia focus is in the left ventricle in the area of the left anterior division. Since the tachycardia is probably ventricular and since the episodes of tachycardia are not initiated by a retrograde P wave, P waves 1, 2, 4, 5, 7, and 9 probably result from very prolonged retrograde conduction occurring at the end of expiration, with its associated increase in vagal tone, as judged from the fact that the "depression" of the tip of the QRS of the tachycardia occurring just after this maximum RP interval and just before the subsequent retrograde block occurs at the nadir of the respiratory cycle. P wave 6, like P waves 3 and 8, is probably a sinus escape beat occurring because of failure of the retrograde conduction in the immediately preceding QRS as a result of the RW phenomenon. The marked difference of QRS complexes 5, 7, and 9 as compared to the other tachycardia QRS's is probably not due to reciprocal fusion, but more likely due to respiratory variation alone as QRS 1, 2, and 4, their counterparts in Lead 2, show only minimal change and as there is also no evidence elsewhere in the ECG of reciprocal rhythm. A-V dissociation is ruled out because the retrograde P waves stop when the ventricular tachycardia stops.

James J. Purcell, M.D.

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REFERENCES
1. Katz LN, Pick A. Clinical Electrocardiography. I. The Arrhythmias. Lea and Febiger, Philadelphia,1956.
2. Pick A, Langendorf R. Interpretation of Complex Arrhythmias. Lea and Febiger, Philadelphia,1979.