In patients with pre-excitation, a short PR interval and a delta wave are not always clearly seen, particularly if the pre-excitation is mild. Absent septal Q waves have been used as additional evidence suggestive of pre-excitation. The purpose of the present study was to determine the incidence of normalization of septal Q waves after successful ablation of a manifest accessory pathway in pediatric patients with normal hearts. We performed a retrospective review of electrocardiograms (ECGs) obtained before and after successful catheter ablation of a single manifest accessory pathway in patients <21 years old (84 pairs of ECGs). The ECGs obtained in patients before ablation for atrioventricular nodal re-entry tachycardia were used as controls (n = 62). The absence of Q waves in the lateral leads (V 5 to V 7 ) and inferior leads (II, III, aVF) were determined. p Values <0.05 were considered significant. Before the ablation, 72 ECGs (85%) demonstrated absent Q waves in the lateral leads, and only 17 (20%) did not show evidence of Q waves after successful ablation of the accessory pathway (p <0.001). On the inferior leads, 37 ECGs (44%) showed no evidence of Q waves before ablation compared to 24 (29%) after ablation (p <0.05). The findings on the postablation ECG were not statistically different from the findings on the ECGs of the control patients. In conclusion, Q waves in the lateral and inferior leads are often absent in patients with manifest pre-excitation. Absent septal Q waves in the lateral and inferior leads frequently normalize after successful ablation of an accessory pathway.
As described by Wolff et al in 1930, the presence of a short PR interval and bundle branch block is diagnostic of pre-excitation. The ventricular depolarization is abnormal, and the septal Q wave is often not visualized on the surface electrocardiogram (ECG). The absence of septal Q waves has been used to aid in the diagnosis of Wolff–Parkinson–White syndrome in patients in whom ventricular pre-excitation is subtle. We describe the normalization of septal Q waves after successful ablation of accessory pathways.
Methods
After institutional review board approval, a retrospective review of the electrophysiology database was performed. Patients with manifest pre-excitation who were <21 years old and had undergone successful ablation of an accessory pathway from 2003 to 2006 were included in the present analysis. Patients with congenital heart disease and those with multiple accessory pathways were excluded.
The ECGs obtained in patients with normal cardiac anatomy undergoing ablation for atrioventricular nodal re-entrant tachycardia during the same period were used as controls. These patients had no evidence of accessory pathways noted during their electrophysiologic study.
The 12-lead ECGs obtained before and after ablation were blindly analyzed by a single observer. The PR and QRS intervals (shortest PR interval in any lead, longest QRS interval in any lead), the QRS axis (normal axis 0° to 90°), and the presence of Q waves in the inferior (II, III, and aVF) and lateral (V 5 to V 7 ) leads were recorded. Q waves were defined as any negative deflection clearly visible on the surface ECG.
Electrophysiologic measurements were recorded, including the AH and HV intervals, accessory pathway and AVN effective refractory periods, cycle length showing 1:1 conduction by the pathway during burst atrial pacing, and Wenckebach’s cycle length. The absence of accessory pathway conduction after a successful ablation was documented by the presence of decremental AVN conduction and the presence of AV block in sinus rhythm during administration of adenosine in patients in whom the pathway was not found to be sensitive to adenosine during preablation testing.
The chi-square test was used for categorical variables, and the paired t test for continuous variables. p Values <0.05 were considered statistically significant.
Results
A total of 84 patients met the inclusion criteria. The mean age of the group was 13.5 ± 3.3 years (range 5.9 to 20.4). Of the 84 patients, 39 were female (45%). The patients’ mean weight was 55 ± 19 kg (range 22 to 100). Of the 84 accessory pathways, 42 were left sided, 29 were septal, and 13 were right sided. All accessory pathways were atrioventricular pathways.
The findings are summarized in Table 1 . The ECGs demonstrated absent Q waves in the lateral (p <0.001) and inferior (p <0.05) leads more frequently before than after ablation. Of the 12 patients (15%) with Q waves present in the lateral leads before ablation, 8 had pathways in the left lateral and posterolateral location and 4 in different areas of the heart (p = NS).
| Before Ablation (n = 84) | After Ablation (n = 84) | p Value 1 | Control (n = 62) | p Value 2 | |
|---|---|---|---|---|---|
| Absent Q in lateral leads | 72 (85%) | 17 (20%) | <0.001 | 12 (19%) | NS |
| Absent Q in inferior leads | 37 (44%) | 24 (29%) | <0.05 | 15 (24%) | NS |
| Abnormal axis | 34 (40%) | 9 (11%) | <0.001 | 3 (5%) | NS |
| PR interval (ms) | 83 ± 20 | 115 ± 19 | <0.001 | 119 ± 21 | NS |
| QRS interval (ms) | 123 ± 22 | 91 ± 13 | <0.001 | 92 ± 10 | NS |
The frontal QRS axis also changed after ablation ( Figure 1 ); 34 ECGs (40%) had an abnormal QRS axis (31 with a left axis and 3 with a right axis) before ablation. Only 9 (11%) had an abnormal QRS axis after ablation (p <0.001). Of the 34 patients with an abnormal QRS axis, 24 (71%) had had accessory pathways in a posterior location (p <0.001).
As seen in Table 1 , the average shortest PR interval in the ECG before ablation was significantly shorter than after ablation (p <0.001). Similarly, the average widest QRS duration before ablation was significantly longer than after ablation (p <0.001).
The intracardiac electrophysiologic measurements before ablation are summarized in Table 2 . Only the HV interval was significantly longer in patients with Q waves present in the lateral leads before ablation when comparing with ECG of patients without septal Q waves (p <0.01).
