CLINICAL STUDY: ELECTROPHYSIOLOGY
Variable electrocardiographic characteristics of isthmus-dependent atrial flutter
Paul Milliez, MD ,
Allison W. Richardson, MD*, ,
Ogundu Obioha-Ngwu, MD*,,
Peter J. Zimetbaum, MD, FACC*,,
Panos Papageorgiou, MD, FACC, PhD*, and
Mark E. Josephson, MD, FACC*,*
* Harvard-Thorndike Electrophysiology Institute, Cardiovascular Division, Beth Israel Deaconess Medical Center, Boston, Massachusetts, USA
Harvard Medical School, Boston, Massachusetts, USA
Dr. Milliez is currently affiliated with the Lariboisiere University Hospital, Paris, France
Manuscript received August 21, 2001;
revised manuscript received June 5, 2002,
accepted June 12, 2002.
* Reprint requests and correspondence: Dr. Mark E. Josephson, Cardiovascular Division, Harvard-Thorndike Electrophysiology Institute, Beth Israel Deaconess Medical Center, 185 Pilgrim Road, Boston, Massachusetts 02215, USA
mjoseph2{at}caregroup.harvard.edu
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Abstract
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OBJECTIVES: The purpose of this study was to characterize variations in flutter-wave (F-wave) morphology among patients with clockwise isthmus-dependent (CWID) and counterclockwise isthmus-dependent (CCWID) right atrial flutter (AFL) and to attempt to correlate F-wave morphology with echocardiographic data and clinical patient characteristics.
BACKGROUND: Variations in F-wave morphology on surface electrocardiogram (ECG) during CCWID and CWID flutter have been reported but never systematically characterized.
METHODS: Over a four-year period, 139 patients with AFL on ECG underwent electrophysiologic study and echocardiography at our institution. Electrocardiographic data, intracardiac recordings, echocardiographic data, and patient characteristics were reviewed retrospectively.
RESULTS: Of 156 AFLs evaluated, 130 were CCWID, 26 were CWID. Three types of CCWID flutter were observed: type 1 had purely negative F-waves inferiorly, types 2 and 3 had F-waves inferiorly with small (type 2) or broad (type 3) positive terminal deflections; CCWID flutter types 2 and 3 were associated with higher incidence of left atrial (LA) enlargement, heart disease, and atrial fibrillation (Afib) than type 1. Two types of CWID flutter were observed: type 1 had notched positive F-waves with a distinct isoelectric segment inferiorly. Type 2 had broader F-waves inferiorly with positive and negative components and a short isoelectric segment.
CONCLUSIONS: Variable ECG patterns for CCWID and CWID AFL exist. A positive component of the F-wave in the inferior leads during CCWID flutter is associated with an increased likelihood of heart disease, Afib, and LA enlargement.
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Abbreviations and Acronyms
| | Afib | | atrial fibrillation | | AFL | | atrial flutter | | ALRA | | anterolateral right atrium | | CCWID | | counterclockwise isthmus-dependent | | CL | | cycle length | | CS | | coronary sinus | | CWID | | clockwise isthmus-dependent | | ECG | | electrocardiogram/electrocardiographic | | EPS | | electrophysiologic study | | F-wave | | flutter wave | | LA | | left atrial | | left atrium | | RA | | right atrial | | right atrium |
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Right atrial flutters (AFLs) involving the cavotricuspid isthmus have been well-described and are the most common macroreentrant atrial arrhythmias (1–8). The tricuspid annulus forms the anterior border of the circuit in such "isthmus-dependent" flutter (9). Reentry may occur in a clockwise or counterclockwise direction around the annulus (as seen from a left anterior oblique perspective). "Typical" flutter wave (F-wave) morphologies on 12-lead electrocardiogram (ECG) have been described for both counterclockwise isthmus-dependent (CCWID) and clockwise isthmus-dependent (CWID) AFL: CCWID F-waves are described as having a "sawtooth" pattern with predominantly negative deflections in the inferior leads (II, III, aVF) and in lead V6 and positive deflections in lead V1 (10,11), while CWID F-waves are described as positive inferiorly and in V6, and negative in lead V1 (11–13). Variations in F-wave morphology among CCWID and CWID flutters have been described (14,15); however, they have never been systematically categorized. We sought to define distinct ECG patterns of CCWID and CWID AFL and to attempt to correlate these patterns with echocardiographic data and clinical patient characteristics.
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Methods
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Study population.
The study population was derived from 152 consecutive patients referred to our institution between April 1996 and November 2000 for treatment of presumed AFL who underwent both echocardiography and electrophysiologic study (EPS). In each case transthoracic or transesophageal echocardiography was performed within the three months preceeding EPS. Twelve patients were excluded from analysis because flutter was determined not to be isthmus-dependent during EPS. One patient with CCWID flutter was excluded because one-to-one atrio-ventricular conduction made F-wave characterization on ECG impossible. The remaining 139 patients form the basis of this report. Patients were predominantly men (74%). Underlying heart disease was present in 52% of patients, hypertension in 26%, and prior atrial fibrillation (Afib) in 48%. Baseline clinical features are summarized in Table 1.
EPS
Informed written consent was obtained from all patients. Patients were studied in the post-absorptive state, lightly sedated by fentanyl and midazolam. Catheters were introduced via the femoral veins and were placed in the anterolateral right atrium (ALRA), coronary sinus (CS), His bundle region, and at the right ventricular apex. The ALRA catheter was a 10-pole or 20-pole catheter positioned anterior to the crista terminalis with the tip in the lateral cavotricuspid isthmus. When AFL was not present at baseline, it was induced by rapid atrial pacing or atrial extrastimuli from the CS or ALRA. In all cases isthmus-dependence was proven by demonstration of concealed entrainment while pacing from the cavotricuspid isthmus during flutter with a post-pacing interval within 20 ms of the flutter cycle length (CL). Atrial flutter was classified as counterclockwise or clockwise based on activation sequence recorded in the ALRA, proximal to distal activation being consistent with counterclockwise flutter, distal to proximal activation consistent with clockwise flutter. Electroanatomic mapping of the right atrium (RA) was also performed during flutter in 40 patients (CARTO, Biosense-Webster). Ablation was performed in the region of the cavotricuspid isthmus and was considered successful when flutter terminated and was not reinitiated and/or when bidirectional block was demonstrated. Studies were recorded on optical disk using standard digital recording systems (Prucka Engineering [Houston, Texas] and Bard Electrophysiology [Lowell, Massachusetts]).
Definitions
For the purposes of this study, isthmus-dependent flutter was defined as right AFL traversing the cavotricuspid isthmus, demonstrated by entrainment from the cavotricuspid isthmus as described above. Left atrial (LA) enlargement by transthoracic echocardiogram was defined as LA dimension >4 cm in the long-axis view and/or >5.2 cm in the four-chamber view. Enlargement of the LA was qualitatively judged by the operator in the small number of patients who had transesophageal echocardiograms, because there are no widely accepted criteria for its measurement.
ECG analysis
All patients had a 12-lead ECG performed during CCWID and/or CWID flutter while in the electrophysiology laboratory. Electrocardiograms were recorded at a standard paper speed of 25 mm/s and a gain of 10 mm/mV. When 2:1 atrio-ventricular conduction was present at baseline, carotid sinus massage or intravenous adenosine was used to unmask the F-wave. Flutter-wave morphology in each lead was evaluated. The "isoelectric" interval between F-waves was defined as that interval with a slope of <30° in relation to the horizontal plane. Monophasic F-waves were termed "F+" or "F–" depending on polarity. Biphasic F-waves were classified based on their initial and terminal components. The major component was termed "F" and the minor component "f" with "+" or "–" assigned to each component based on polarity. When positive and negative components of the F-wave were equivalent, the F-wave was termed isoelectric. Notching of the F-wave was denoted by "n" (Fig. 1). Once all ECGs were analyzed, they were categorized as CCWID or CWID based on F-wave morphology in leads II, III, aVF, V1, and V6. Flutters with a significant negative F-wave component inferiorly and in V6, and with a predominantly positive F-wave in V1 were categorized CCWID, and flutters with a significant positive F-wave component inferiorly and in V6, and an isoelectric or predominantly negative F-wave in V1 were categorized CWID. It was apparent that CCWID flutters could be further categorized into three groups and CWID flutters further categorized into two groups based on F-wave morphology in the inferior leads, V1, and V6. Leads I, aVR, aVL, and V2 to V5 were not found to be useful in differentiating flutters. All ECGs were reviewed independently by two reviewers (P.M., O.O.). Disagreement between these reviewers occurred in fewer than 10% of cases, usually because the ECG did not match a particular group in all five leads. In such cases a third independent reviewer was involved (M.E.J.), and the ECG was assigned to the category that it fit most closely, usually based on the F-wave morphology in two of three inferior leads. Reviewers were blinded as to patient characteristics, echocardiographic, and EPS data. After all ECGs were assigned to a group, EPS data were reviewed to confirm correct assignment of flutters as CCWID or CWID.
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Figure 1 Sample F-wave morphologies: F– = negative F-wave; F+(n) = notched positive F-wave; F–/f+ = biphasic predominantly negative F-wave with a small terminal positive component; f–/F+ = biphasic predominantly positive F-wave with a small initial negative component; F+/f– = biphasic predominantly positive F-wave with a small terminal negative component; I = biphasic, isoelectric F-wave with approximately equal positivity and negativity.
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Statistics
Continuous variables are presented as mean ± SD. Comparisons of categorical variables were performed using the Fisher exact test, comparisons of continuous variables using the Student t test. A two-tailed p value <0.05 was considered statistically significant.
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Results
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Of the 139 patients, 17 had both CCWID and CWID flutter, 113 had only CCWID flutter, and nine had only CWID flutter; thus, 156 flutters were analyzed. Baseline patient characteristics, echocardiographic data, and flutter CL were not significantly different between CCWID and CWID flutters. Analysis of the ECGs revealed that differentiation between CWID and CCWID flutter could be made based on F-wave morphology in leads II, III, aVF, V1, and V6 in 100% of cases (confirmed by review of intracardiac tracings). Counterclockwise isthmus-dependent flutters could then be assigned to three basic groups based on F-wave morphology in these leads: 1) F– inferiorly and V6, F+ in V1; 2) F–/f+ inferiorly, F– or F–/f+ in V6, and F+ in V1; 3) f–/F+ inferiorly and V6, F+/f– in V1 (Fig. 2). Of 130 CCWID flutters, 35 (27%) were categorized as type 1, 20 (15%) as type 2, and 75 (58%) as type 3. Group 1 patients were younger than group 2 and 3 patients (58 ± 15 vs. 68 ± 11, 67 ± 13, p < 0.01) and significantly less likely to have underlying heart disease (6% vs. 60%, 71%, p < 0.01) and LA enlargement (0% vs. 87%, 100%, p < 0.01). Group 3 patients were significantly more likely to have prior Afib than group 1 patients (64% vs. 14%, p < 0.01). Flutter CLs were longer in group 3 (257 ± 35 ms) than group 1 (244 ± 34 ms, p = 0.06) and group 2 (234 ± 29 ms, p < 0.01). There was a trend towards higher antiarrhythmic use in group 3 than in group 1 (Table 2). There were no significant differences in atrial activation patterns recorded between CCWID flutter groups. CARTO maps of the RA (35 patients) were also not significantly different between groups.
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Figure 2 Morphologic variations of counterclockwise isthmus-dependent atrial flutter on 12-lead surface electrocardiogram: (A) Type 1: F– in II, III, aVF, and V6; F+ in V1. (B) Type 2: F–/f+ in II, III, aVF; F– or F–/f+ in V6, F+ in V1. (C) Type 3: f–/F+ in II, III, aVF, and V6; F+/f– in V1. Abbreviations as in Figure 1.
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Clockwise isthmus-dependent flutters could be assigned to two basic groups based on F-wave morphology in leads II, III, aVF, V1, and V6: 1) F+(n) or F+ inferiorly and V6, F– in V1 with a relatively narrow F-wave and a distinct isoelectric segment; 2) f–/F+(n) or F+(n) inferiorly and V6, isolectric in V1, with a very broad F-wave and no distinct isoelectric segment (Fig. 3). Of 26 patients with CWID flutter, 13 (50%) were categorized as type 1 and 13 as type 2. There were no significant differences in CL, patient or echocardiographic characteristics, atrial activation patterns recorded, or RA CARTO maps (5 patients) between CWID flutters in groups 1 and 2 (Table 3). Of patients with both CCWID and CWID flutter, 14/17 (82%) had type 3 CCWID flutter, and patients were divided evenly between CWID flutter types 1 (8 patients) and 2 (9 patients). Thus, there was no clear relation between flutter morphology during CCWID flutter and morphology during CWID flutter, although the number of patients who qualified for this analysis was small. Thirteen CWID flutters had CL within 5 ms of CCWID flutter CL in the same patient, and the remaining four were within 20 ms.
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Figure 3 Morphologic variations of clockwise isthmus-dependent atrial flutter on 12-lead surface electrocardiogram: (A) Type 1: F+(n) or F+ in II, III, aVF, and V6; F– in V1, narrow F-wave/distinct isoelectric segment. (B) Type 2: f–/F+9(n) or F+(n) inferiorly and V6, isoelectric in V1, with a broad F-wave and no distinct isoelectric segment. Abbreviations as in Figure 1.
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discussion
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We sought to characterize variations in F-wave morphology by retrospectively reviewing ECGs of 156 flutters in 139 patients who underwent both EPS and echocardiography at our institution. Variations in F-wave morphology in both CCWID and CWID flutter have been reported previously (14,15) but have not been systematically described. We found that differentiation between CWID and CCWID flutter could be made consistently based on the ECG using criteria suggested by previous authors (14–16). Counterclockwise isthmus-dependent flutters were further categorized into three groups and CWID flutters into two groups based on F-wave morphology.
CCWID flutter.
Counterclockwise isthmus-dependent flutter group 1 had purely negative F-waves inferiorly. Patients in this group were younger with less heart disease and Afib than the remainder of patients with CCWID flutter. Patients with AFL are at risk for stroke, although less so than patients with Afib (17,18). It is possible that the group 1 F-wave morphology will identify a group of patients with CCWID flutter at relatively low risk for stroke, although more data will be required. Counterclockwise isthmus-dependent groups 2 and 3 had terminal positivity of the F-wave in the inferior leads, which formed a minor F-wave component in group 2 and the major component in group 3. Left atrium enlargement was very prevalent in groups 2 and 3 (98%) and was not present in any patient in CCWID group 1. This correlation raises the possibility that terminal F-wave positivity in the inferior leads may be due to activation of an abnormal LA. Several authors have attempted to correlate RA and/or CS activation during flutter with the surface ECG (14,15,19). These authors have found the negative portion of the F-wave in the inferior leads to be synchronous with septal and CS activation, while the upstroke of the negative F-wave and terminal positivity correspond with lateral RA activation. In a dog model of AFL, however, F-wave polarity on ECG was found to correlate primarily with LA activation sequence (20). We postulate that, in the presence of LA disease or enlargement, LA activation may be prolonged, allowing it to occur, in part, over Bachmann’s bundle. Coronary sinus activation in CCWID flutter is typically proximal to distal (21); however, this does not exclude partial activation of the LA over Bachmann’s bundle. Systematic LA mapping during CCWID flutter in humans will be necessary to determine how the pattern of LA activation affects F-wave morphology. We found that group 3 CCWID flutters had longer CLs than group 2 and group 1 flutters. This reason for this is unclear. There was a trend toward a higher rate of antiarrhythmic use in group 3 than in group 1, which might have contributed to longer CLs.
CWID flutter
We categorized CWID flutters into two groups based on F-wave morphology and found no significant differences between patients in these groups in regard to age, frequency of underlying heart disease, hypertension, prior Afib, LA enlargement, antiarrhythmic use, or flutter CL. In part, this may have been due to the small number of CWID flutters evaluated. Other authors have found that in clockwise flutter, activation of the lateral RA corresponds with the initial negative F-wave inferiorly or may be nearly electrocardiographically silent; septal activation corresponds with the initial upstroke of the positive F-wave inferiorly, and CS activation with the notch and second component of the F-wave (14,15,19). Interatrial conduction time was closely correlated with the interval between these two components (19). We have shown previously that, while CS activation is almost always proximal to distal during CCWID flutter, it is usually fused during CWID flutter in the same patients (with the CS catheter tip at one o’clock on the mitral annulus in the left anterior oblique view), suggesting that Bachmann’s bundle contributes significantly to interatrial activation during CWID flutter (21). In the current study we found that, while LA enlargement, heart disease, and Afib correlated with F-wave morphology in CCWID flutter, there was no such correlation with F-wave morphology in CWID flutter. In addition, there was no correlation between F-wave morphology during CWID flutter and CCWID flutter in patients who were mapped during both. This suggests that different factors contribute to CWID and CCWID F-wave morphology. It is possible that LA abnormality does not play a major role in determining F-wave morphology in CWID flutter because significant activation over Bachmann’s bundle almost always occurs. Again, a systematic evaluation of left and RA activation using advanced mapping techniques during CWID and CCWID flutter will be necessary in order to determine how interatrial conduction and LA activation patterns affect flutter morphology.
Study limitations
This study is limited in that it is a retrospective study in which correlations were made between F-wave morphology and patient characteristics such as LA enlargement and underlying heart disease without evaluation of LA activation pattern and without detailed evaluation of RA activation in most cases. Without such information it is impossible to determine the mechanism of variation in F-wave morphology or to fully understand the significance of correlations found. In addition, the study is limited in that classification of flutters depended on identification of an "isoelectric" segment during ECG analysis. As CCWID and CWID flutter are continuous circuits, it might be argued that there is no true isoelectric period; however, there was minimal disagreement between ECG reviewers regarding flutter classification.
Conclusions
In this study we demonstrated that F-wave morphology in the inferior leads V1 and V6 can reliably be used to differentiate CCWID from CWID flutter, although, if only the inferior leads are examined, CCWID and CWID flutters can sometimes be difficult to distinguish. We found that flutters can be further categorized into the morphologic subgroups described above, and that a terminal positive component of the F-wave in CCWID flutter seems to identify a patient population with a relatively high likelihood of heart disease and LA enlargement.
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Footnotes
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Dr. Milliez was supported by the "Federation Francaise de Cardiologie" and by Guidant France, Medtronic France, and St. Jude Medical France. Dr. Richardson was supported by a grant from the North American Society of Electrophysiology and Pacing.
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Abstract
Methods