Isthmus Block During Atrial Flutter Ablation. Introduction: Complete bidirectional cavotricuspid isthmus block is the endpoint for ablation of typical atrial flutter. The purpose of this study was to determine whether the extent of prolongation of the transisthmus interval after ablation predicts complete bidirectional block. Methods and Results: Fifty‐seven consecutive patients underwent 60 ablation procedures for isthmus‐dependent atrial flutter. The clockwise and counterclockwise transisthmus intervals were determined before and after ablation during pacing from the low lateral right atrium and the coronary sinus. Bidirectional block was achieved with ablation in 55 (96%) of 57 patients. The transisthmus intervals before ablation and after complete transisthmus block were 100.3 ± 21.1 msec and 195.8 ± 30.1 msec , respectively, in the clockwise direction ( P < 0.0001 ), and 98.2 ± 24.7 msec and 185.7 ± 33.9 msec , respectively, in the counterclockwise direction ( P < 0.0001 ). An increase in the transisthmus interval by ≥ 50% in both directions after ablation predicted complete bidirectional block with 100% sensitivity and 80% specificity. The positive and negative predictive values were 89% and 100%, respectively. The diagnostic accuracy of ≥ 50% prolongation in the a transisthmus interval was 92%. Conclusion: Prolongation of the transisthmus interval by ≥ 50% in the clockwise and counte clockwise directions is associated with a high degree of diagnostic accuracy and an excellent negative predictive value in determining complete bidirectional transisthmus block. This may be a useful and simple adjunctive criterion for assessment of complete transisthmus conduction block.
Although pulmonary vein arrhythmogenicity plays a critical role in initiation and perpetuation of atrial fibrillation (AF) particularly in patients with paroxysmal AF, mechanisms beyond the pulmonary and other thoracic veins appear to be critical in perpetuation of AF. Among these mechanisms are the multiple wavelet hypothesis, autonomic modulation, and high frequency sources (rotors). In this chapter the role of frequency of mapping to eliminate high frequency sources is discussed in detail based on experimental data and clinical studies.
Verapamil and Ibutilide. Introduction: Early recurrence of atrial fibrillation (AF) after cardioversion may be related to shortening of the atrial effective refractory period (ERP). This study compared the effects of verapamil and ibutilide on AF cycle length (AFCL), atrial ERP, and susceptibility to recurrent AF. Methods and Results: In 33 adults, the atrial ERP was measured at basic drive CLs of 350 and 500 msec before and after a brief episode of pacing‐induced AF. During AF, verapamil, ibutilide, or saline was infused in 11 patients each. Shortening of the post‐AF atrial ERP was attenuated by verapamil and prevented by ibutilide. AFCL shortened by 32 ± 21 msec in the verapamil group ( P < 0.01 ), prolonged by 44 ± 14 msec in the ibutilide group ( P < 0.001 ), and did not change in the control group. AF converted to sinus rhythm within 10 minutes less often after verapamil (0%) than after ibutilide (82%) or than in the control group (73%). Post‐AF, AF lasting > 10 minutes was induced more often in the verapamil group than in the ibutilide group ( 26% vs 0%; P = 0.01 ). Another 10 patients received verapamil or ibutilide in the absence of AF. Atrial ERP was unchanged after verapamil and prolonged after ibutilide. Conclusion: Verapamil shortens AFCL and impedes the conversion of induced AF, whereas ibutilide prolongs AFCL and does not impede the early conversion of induced AF. Ibutilide is more effective than verapamil in preventing post‐AF shortening of the atrial ERP and reducing the susceptibility toward reinduction of AF.
Cardiac Memory. Introduction : “Cardiac memory” (primary T wave change) is thought to occur after 15 minutes to several hours of right ventricular (RV) pacing. The two components of the temporal change in repolarization are memory and accumulation. The purpose of this study was to examine quantitatively the effect of short periods of ventricular pacing on the human cardiac action potential, using monophasic action potential (MAP) recordings. Methods and Results : Thirty‐one patients (ages 43 ± 14 years) with structurally normal hearts undergoing a clinically indicated electrophysiologic procedure were enrolled. Catheters were placed in the right atrium (RA) and RV, and a MAP catheter was positioned at the RV septum. APD 90 was calculated from digitized MAP recordings. MAP morphology comparisons were performed using the root mean square (RMS) of the difference between complexes. All pacing was at 500‐msec cycle length. There were four pacing protocols: (1) RA pacing was performed for approximately 15 minutes to evaluate temporal stability of the MAP recordings (5 pts); (2) to evaluate the memory phenomenon, four successive 1‐minute episodes of RV pacing were interspersed with 2 minutes of RA pacing (5 pts); (3) the accumulation phenomenon was evaluated by assessing the effects of 1, 5, 10, and 15 minutes of RV pacing on the MAP during RA pacing (16 pts); and (4) 20 minutes of RV pacing was followed by 10 minutes of RA pacing to correlate visually apparent T wave changes with changes in MAP recordings (5 pts). In the control patients, no changes in APD 90 or RMS analysis were noted during 14.9 ± 1.4 minutes of RA pacing. In the second protocol, RMS of the difference between the baseline MAP complexes and the signal average of the first 50 beats following each of four 1‐minute RV pacing trains demonstrated progressively greater differences in morphology after successive episodes of RV pacing. In protocol 3, RMS analysis identified a progressively greater difference between the baseline MAP recording and the average of the first 50 beats after 1,5, 10, and 15 minutes of RV pacing. In protocol 4, visually apparent changes in T waves occurred in parallel with the RMS of the difference between the baseline MAP recordings and the average of the first 50 beats after 20 minutes of RV pacing. Similar changes also were demonstrated by APD 90 analysis. Conclusion : This study is the first to demonstrate that episodes of abnormal ventricular activation as short as 1 minute in duration may exert lingering effects on the repolarization process once normal ventricular activation resumes.
Complex fractionated atrial electrograms (CFAEs) may play a role in the genesis of atrial fibrillation (AF). One type of CFAE is continuous electrical activity (CEA). The prevalence and characteristics of CEA in patients with paroxysmal and persistent AF are unclear.In 44 patients (age = 59 +/- 8 years) with paroxysmal (25) or persistent (19) AF, bipolar electrograms were systematically recorded for > or =5 seconds at 24 left atrial (LA) sites, including 8 antral sites, and 2 sites within the coronary sinus (CS). CEA was defined as continuous depolarization for >1 second with no isoelectric interval. CEA was recorded at the LA septum (79%), antrum (66%), posterior (68%) and anterior walls (67%), roof (66%), base of the LA appendage (61%), inferior wall (61%), posterior mitral annulus (48%), CS (41%), and in the LA appendage (14%). Antral CEA was equally prevalent in patients with paroxysmal (63%) and persistent AF (70%, P = 0.12). In patients with paroxysmal AF, the prevalence of CEA was similar among antral and nonantral LA sites, except for the LA appendage. However, in patients with persistent AF, CEA was more prevalent at the nonantral (80%) than antral sites (70%, P = 0.03). CEA at nonantral sites except the CS was more prevalent in persistent than in paroxysmal AF (80% vs 57%, P < 0.001). The mean duration of intermittent episodes of CEA was longer in persistent than in paroxysmal AF (P < 0.001).The higher prevalence and duration of CEA at nonantral sites in persistent than in paroxysmal AF is consistent with a greater contribution of LA reentrant mechanisms in persistent AF. However, the high prevalence of CEA at nonantral sites in paroxysmal atrial fibrillation (PAF) suggests that CEA alone is a nonspecific marker of appropriate target sites for ablation of AF. The characteristics of CEA that most accurately identify drivers of AF remain to be determined.
