Results
Among 110 consecutive patients screened, 98 met entry criteria and were included in the study. Of 45 patients with documented atrial flutter, 4 were excluded - 1 due to atypical flutter on ECG, and 3 due to lack of electroanatomic mapping. Forty-one AFL patients were therefore included in the analysis. Sixty-five control patients were recruited: 43 with a clinical diagnosis of AVNRT, 14 with AVRT, 2 with ischaemic VT, 6 patients with monomorphic PVCs and one diagnostic study for undocumented symptoms of palpitations. Fifty-seven control patients were eligible for the analysis after applying exclusion criteria.
Patient characteristics are summarized in Table 1. Demographic differences included significant age and sex differences between groups. AFL patients were older, with a higher proportion of male patients. This is related to the high prevalence of AVNRT (42) and AVRT (14) in the control group. AFL patients had a greater proportion of ischaemic heart disease, hypertension, valvular disease and obstructive sleep apnoea. This was reflected in the greater use of cardiac medication in the AFL group. Echo characteristics differed, with greater LA and RA volumes in the AFL group. AFL patients more often presented with reduced LVEF.
Correlation of RACT and demographic variables are illustrated in Table 3. RACT was significantly longer in AFL patients compared with the control group (132.6±17.3 vs 99.1±11.6 p<0.001) (Table 1). There was no significant interaction of sex and RACT values (Table 2). There was no significant association of RACT with age (Pearson correlation 0.41). On multivariate analysis RACT was independently associated with atrial flutter diagnosis (OR 1.6 (1.1 – 2.4) p = 0.03). A RACT value of 115.5ms had a sensitivity of 92.7% and specificity of 93.0% for diagnosis of atrial flutter (AUC 0.96). Increasing the cut off value to 130ms reduced sensitivity to 60.1% and increased specificity to 100% (Figures 2 and 3).
Mean follow-up was 401.9 days (±239.9). There were no recurrences of atrial flutter, and one recurrence of AVNRT during the follow-up period. Thirteen patients, all within the AFL group, developed clinical atrial fibrillation. RACT was significantly longer in patients who developed atrial fibrillation than those who did not (141.7 ± 21.0ms vs 108.8 ± 18.5ms, p <0.001). When only the AFL group was considered regarding development of AF, RACT value was higher and approached significance (141.7 ± 21.0ms vs 128.4 ± 13.7 ms, p=0.052). Among AFL patients, a RACT value of 135.5ms provided a sensitivity of 75% and specificity of 81.4% for development of AF, and AUC was 0.89. On multivariate analysis including age, BMI, LVEF, RACT, LA and RA volume, only RACT was independently associated with development of atrial fibrillation, (OR 1.1 (1.01, 1.24) p=0.024).