Author + information
- Received January 31, 1992
- Revision received April 15, 1992
- Accepted June 5, 1992
- Published online November 15, 1992.
- Shane K. Kimber, MD1,
- Eugene Downar, MD, FACC∗,3,
- Louise Harris, MB, FACC2,
- Galina Langer, MD,
- Lynda L. Mickleborough, MD, FACC,
- Stephane Masse, MS,
- Elias Sevaptsidis, DCS and
- Thomas C.K. Chen, MD
- ↵∗Address for correspondence: Eugene Downar, MD, Toronto General Hospital, 12 Eaton North — 224A, 200 Elizabeth Street, Toronto, Ontario M5G 2C4, Canada.
Objectives. The aim of this study was to examine, with multichannel direct cardiac mapping techniques, the mechanisms of spontaneous shift of the QRS configuration in the surface electrocardiogram during episodes of ventricular tachycardia.
Background. Ventricular tachycardias demonstrating a spontaneous shift in their surface electrocardiographic (ECG) features are occasionally encountered. It is not known whether such changes in configuration are primarily due to a significant change in the tachycardia site of origin or represent alterations in patterns of endocardial and epicardial activation. Knowledge of these features would be helpful, particularly when ablative therapy is considered for the arrhythmias.
Methods. During map-directed cardiac surgery, episodes of ventricular tachycardia were mapped from 224 epicardial and endocardial sites. Episodes of pleomorphic tachycardia were identified and isochronal maps of endocardial and epicardial activation were constructed from representative beats before and after the change in configuration.
Results. From 52 consecutive patients who underwent detailed intraoperative mapping, 9 patients with pleomorphic ventricular tachycardia were identified in whom 14 episodes of spontaneous shift occurred. An analysis of the epicardial activation patterns revealed that the sites of earliest epirardial breakthrough showed significant alteration at the time of QRS shift in all occurrences. In 10 of these shift episodes, however, the sites of tachycardia origin, located on the endocardial surface, remained closely adjacent (<2 cm apart). Although these sites of origin remained relatively constant, significant alterations in the patterns of endocardial activation were seen in most episodes. These included changes in the direction of propagation of the wave front of activation and shifts between monoregional and figure eight patterns of activation.
Conclusions. In most episodes of pleomorphic ventricular tachycardia, the arrhythmia site of origin remains relatively constant. However, patterns of epicardial activation do undergo significant change and appear to be the major determinant of the QRS configuration on the surface ECG.
↵1 Dr. Kimber is a recipient of a research fellowship from the Heart and Stroke Foundation of Canada, Ottawa, Ontario.
↵3 Dr. Downar is a recipient of a Career Investigator Award of the Heart and Stroke Foundation of Ontario.
↵2 Dr. Harris is a recipient of a scholarship from the Heart and Stroke Foundation of Canada, Ottawa, Ontario.
☆ This work was supported by grants from the Heart and Stroke Foundation of Ontario, Toronto.
- Received January 31, 1992.
- Revision received April 15, 1992.
- Accepted June 5, 1992.