Objectives: The relationships that exist between endocardial and surface electrocardiogram (ECG) activity in patients with AFl have not been satisfactorily delineated. The aim of the study was to determine the relationships that exist between the atrial endocardial activity and the surface ECG in patients with atrial flutter (AFl).
Methods: In 40 patients with AFl, a 64-electrode basket catheter (BC) was deployed in the right atrium (RA). A decapolar catheter was inserted into the coronary sinus (CS) to record from the left atrium. The temporal relationship between endocardial and surface ECG activity was determined by means of electronic calipers.
Results: In counterclockwise AFl, the activation of the lateral wall of RA coincided with the positive deflections in lead I, V1 and V6 and the upstroke component in inferior leads. Plateau duration in lead III (121 +/- 27 ms) correlated strongly with isthmus conduction time (117 +/- 23 ms) (r = 0.91). Septal and left atrial conduction coincided with negative components in lead I, inferior leads and V6 and positive deflections in leads aVL and V1. In clockwise AFl, the F wave was notched in all ECG leads. The first component resulted from the activation of the septum and posterior wall of the RA. The second component was coincident with activity recorded in CS electrograms. The interval between the two deflections (60 +/- 18 ms) correlated strongly with interatrial conduction time (57 +/- 19 ms) (r = 0.84). Interatrial conduction interval was prolonged during AFl as compared to sinus rhythm (60 +/- 18 ms vs 43 +/- 13 ms, p = 0.04). Activation of the lateral wall of RA coincided with the negative components in lead I, inferior leads and V6.
Conclusions: The electrical activity in surface ECG closely correlates with conduction in specific parts of the atria. Polarity of the F wave in an ECG lead is determined by a resultant of opposing activities from the lateral wall of the RA and the left atrium.