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Benefits of Cardiac Resynchronization Therapy in an Asynchronous Heart Failure Model Induced by Left Bundle Branch Ablation and Rapid Pacing
Published on: December 11, 2017
Peak QRS/T ratio and the spatial ventricular gradient differentiate acute vs chronic left bundle branch block after
Jonathan W Waks1, Marie-France Poulin1, Patricia Tung1
1Division of Cardiovascular Medicine, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts.
Background:
Differentiating chronic from acute left bundle branch block (LBBB) is useful in various cardiac disorders. Peak QRS/T ratio, a measure of cardiac memory, can differentiate chronic from acute LBBB with high sensitivity and specificity, but its utility in post-transcatheter aortic valve replacement (TAVR) patients with LBBB is unclear.
Objective:
This study aimed to validate the QRS/T ratio for differentiating chronic/acute LBBB in post-TAVR patients and assess whether the spatial ventricular gradient (SVG), which integrates 3-dimensional depolarization/repolarization throughout the cardiac cycle, could also distinguish chronic from acute LBBB.
Methods:
This was a post hoc analysis of a prospective, observational, single-center TAVR study. After TAVR, patients were classified as acute (new <24 hours) or chronic/preexisting LBBB. Electrocardiograms were transformed into vectorcardiograms, and peak QRS/T ratio and SVG were calculated. Sensitivity, specificity, and area under the receiver-operating curve (AUROC) assessed how QRS/T ratio and SVG differentiated chronic from acute LBBB.
Results:
Of 409 patients, 21 had preexisting, and 53 had acute/new LBBB. Patients with chronic LBBB had a higher peak QRS/T ratio than patients with acute LBBB (median 3.8 vs 2.2; P < .0001). 3-dimensional SVG vectors significantly differed between chronic and acute LBBB (joint P < .0001), due to differences in the anterior/posterior (Z) direction, (SVGz): median 43.4 vs -14.2 mV·ms, P < .0001, for chronic vs acute LBBB, respectively. A peak QRS/T ratio of ≥2.7 and an SVGz of ≥15 mV·ms had 100% sensitivity, 98.1% specificity, and an AUROC of 0.991 for chronic LBBB. Over long-term follow-up, patients transitioned from acute to chronic LBBB vectorcardiographic phenotype.
Conclusion:
Peak QRS/T ratio and SVG differentiate chronic from acute LBBB in post-TAVR patients with 100% sensitivity, 98% specificity, and an AUROC of 0.99.
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