A groundbreaking study recently published in JAMA Cardiology has introduced a new criterion for diagnosing Left Bundle Branch Block (LBBB), a heart condition that can lead to irregular heart rhythms and heart failure. This research was spearheaded by a team of medical professionals from the University of Chicago Pritzker School of Medicine.
The Shortcomings of Existing Criteria
The current diagnostic criteria for LBBB are largely based on animal experiments or mathematical models of cardiac tissue conduction. These methods, however, have been found to potentially misclassify patients, leading to inappropriate treatment decisions. For example, patients may be referred for cardiac resynchronization therapy (CRT) or conduction system pacing (CSP) based on an inaccurate diagnosis. This highlights the urgent need for improved criteria that can more accurately guide referral decisions and the choice of device for cardiac resynchronization therapy.
Introducing the New Criterion
The researchers set out to develop a straightforward new criterion for LBBB, drawing on electrophysiological studies of human patients. This criterion was then validated in an independent population. The study involved patients who underwent an electrophysiological study from March 2016 through November 2019. The validation cohort was assembled by retrospectively reviewing medical records of patients who underwent transcatheter aortic valve replacement (TAVR) from October 2015 through May 2022.
The team discovered that late notches in the QRS complexes of lateral leads were associated with complete conduction block (CCB). They suggested that a time to notch longer than 75 milliseconds in lead I is a simple ECG criterion that, when used alongside standard LBBB criteria, may enhance specificity for identifying patients with LBBB from conduction block. This could potentially improve patient selection for cardiac resynchronization or conduction system pacing.
or midpoint of a slur. If multiple notches or slurs are present in the QRS
complex, the latest one is used. The measurement shown demonstrates a time
to notch of approximately 90 milliseconds in lead I.
Validating the New Criterion
The new criterion was validated on an independent dataset comprising patients who acutely developed periprocedural LBBB during TAVR implant. The sensitivity of the new criterion remained high in this cohort. Interestingly, in a small subset of patients with prior intraventricular conduction delay (IVCD), the criterion demonstrated perfect accuracy in distinguishing IVCD from LBBB.
Clinical Implications of the Study
The results of this study carry significant clinical implications for patient selection for cardiac resynchronization. Previous research has shown that wide QRS in patients with intact Purkinje activation (IPA) cannot be corrected with CSP and patients may not respond clinically; thus, they should be given a traditional biventricular CRT system if cardiac resynchronization is attempted. The new criterion proposed in this study offers a simple yet specific assessment to assist in procedural planning.
In conclusion, this study proposes a simple new surface ECG criterion for LBBB based on direct electrophysiological observations in human patients. The new criterion significantly improved specificity in the derivation cohort, with better testing performance than the Strauss criteria. This work may have implications in choosing patients for CRT and CSP.
