Introduction: Typical flutter is due to reentry around caval veins and terminal crest. In patients with typical flutter, reversed (clockwise) reentry can be induced. We studied mechanisms of typical and reversed flutter induction.
Methods and results: Thirteen patients (11 men) underwent 16 radiofrequency (RF) ablation procedures for typical (12) or reversed flutter (1). High right atrium (RA) stimulation included 1 to 3 extrastimuli over cycle lengths 600 to 250 msec, and burst. We recorded simultaneously from three levels of septal and anterior RA. RF was delivered to the inferior vena cava-tricuspid isthmus (CTI). Of 25 inductions, 4 were a result of single, 9 double, and 11 triple extrastimuli, and 1 burst. Clinical basal flutter was induced (7 typical, 1 reversed). After RF, typical flutter was reinduced in 9 cases and reversed flutter in 7, with only typical flutter seen clinically. All flutters were interrupted by ablation or catheter pressure on the CTI. Typical flutter began by low RA septal activation block, preceded by repetitive responses in 12 instances, atypical flutter in 1, and directly from stimuli in 4. Reversed flutter started in 8 instances by low RA block of a stimulated front descending the anterior wall and in 1 by repetitive responses.
Conclusion: Septal activation block was the usual mechanism of typical flutter induction by RA extrastimuli. Facilitation of reversed flutter after RF application is probably due to a new area of block in the CTI. Flutter induction without intermediate rhythms confirms the presence of block at the terminal crest at baseline.