S/QRS ratio in lead I: A surface electrocardiographic finding associated with need for permanent pacemaker in
Behzad B Pavri1, Jack Goodman1, Eitan Frankel1
1Division of Cardiology, Department of Medicine, Thomas Jefferson University Hospital, Philadelphia, Pennsylvania.
Background:
Right bundle branch block (RBBB) pattern does not imply normal left bundle branch conduction but may simply indicate a more diseased right bundle branch. In lead I, initial rapid QRS forces represent left ventricular depolarization and the terminal S wave represents slower right ventricular depolarization. We postulated that slurring of initial forces with resulting narrowing of the S-wave duration and a smaller S/QRS ratio may be associated with a need for a permanent pacemaker (PPM).
Objective:
This study aimed to assess the S/QRS ratio in lead I as an electrocardiogram measurement associated with a need for PPM.
Methods:
We measured the PR interval, QRS axis, QRS duration (QRSd), S-wave duration in lead I, and S/QRS ratio in 2 groups of patients, all with RBBB: (1) controls, patients who did not require PPM, and (2) cases, patients who received PPM for alternating bundle branch block, Mobitz 2/complete heart block, or bifascicular block with abrupt syncope. Immediate preimplant and oldest available electrocardiograms that showed RBBB were analyzed.
Results:
A total of 218 patients with RBBB were included. For controls (n = 109), over a follow-up of 90.16 months (range 4.5-347), QRSd increased from 145.2 to 146.7 ms (P = .67), and the S/QRS ratio decreased from 0.59 to 0.57 (P = .02). For cases (n = 109), over follow-up of 89.22 months (range 2.21-262.75), QRSd increased from 139.9 to 147.6 ms (P < .001), and the S/QRS ratio decreased from 0.52 to 0.43 (P < .001). On multivariable analyses, an S/QRS ratio of < 0.56 was associated with a need for PPM (odds ratio 6.87, confidence interval 3.87-12.67, P < .001).
Conclusion:
In patients with RBBB, narrowing of the S wave in lead I with an S/QRS ratio of < 0.56 is associated with increased need for PPM, even after adjusting for QRSd.
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