Accuracy of left ventricular mechanical dyssynchrony indices for mechanical characteristics of left bundle branch block using cardiovascular magnetic resonance feature tracking

Aims More than 90% of patients with left bundle branch block (LBBB) and reduced left ventricular (LV) ejection fraction have LV dyssynchrony and a high probability of response to cardiac resynchronization therapy (CRT). A subgroup of patients with non-specific intraventricular conduction delay (IVCD) have a LBBB-like LV activation pattern when studied using invasive mapping and advanced echocardiographic techniques. These patients also frequently benefit from CRT but these patients have proven difficult to identify using ECG criteria. Cardiovascular magnetic resonance (CMR) imaging indices of dyssynchrony may identify patients with IVCD who may benefit from CRT but their relative accuracies for identification of LV dyssynchrony remains unknown. We compared the LV dyssynchrony classification accuracy of two commonly available CMR indices in a study population of patients with severely reduced LV ejection fraction and no scar, and either LBBB or normal conduction (normal QRS duration and axis, controls). Methods and results In LBBB (n=44) and controls (n=36), using CMR feature tracking circumferential strain, dyssynchrony was quantified as the circumferential uniformity ratio estimate (CURE) and the systolic stretch index (SSI). Deidentified CMR image-data were made publicly available. Both CURE and SSI quantified more severe dyssynchrony in LBBB compared to controls (p<0.001 for both). SSI more frequently discriminated LBBB and normal conduction LV activation patterns than CURE (area under the receiver operating characteristics curve [95% confidence interval] 0.98 [0.95-1.00] for SSI vs 0.77 [0.66-0.86] for CURE, p<0.001). Conclusions SSI is superior to CURE for discriminating synchronous and dyssynchronous LV activation and should be further studied in the setting of non-LBBB conduction abnormalities. ### Competing Interest Statement EH is the founder of the company Medviso AB which develops medical image analysis software. RN has received research grants from Philips Volcano and Biotronik. RJK is a consultant for Abiomed. BDA has received research grants from Boston Scientific and Abbott, and consultation fees from Abbott, Medtronic, Biotronik, and Biosense Webster. MU is principal investigator on a research and development agreement regarding cardiovascular magnetic resonance between Siemens and Karolinska University Hospital. The remaining authors have nothing to disclose that is relevant to the contents of this paper. ### Funding Statement This work was funded in part by grants to MU from New South Wales Health, Heart Research Australia, University of Sydney, Swedish Research Council, Swedish Heart and Lung Foundation, Stockholm County Council, and Karolinska Institutet. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: IRB of Duke University Medical Center gave ethical approval for this work. IRB of University of Pittsburgh Medical Center gave ethical approval for this work Swedish Ethical Review Authority gave ethical approval for this work. I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable. Yes The datasets generated and/or analyzed during the current study, as well as code needed to reproduce all aspects of the current study, are available in the Figshare repository, . The most recent version of the analysis code is available in the Github repository, . * ### Abbreviations AUC : Area under the curve BMI : Body Mass Index BSA : Body Surface Area CI : Confidence Interval CMR : Cardiovascular Magnetic Resonance CRT : Cardiac Resynchronization Therapy CURE : Circumferential Uniformity Ratio Estimate ECG : Electrocardiography HF : Heart Failure LBBB : Left Bundle Branch Block LGE : Late Gadolinium Enhancement LV : Left ventricular LVEDV : Left Ventricular End-Diastolic Volume LVEDVI : Left Ventricular End-Diastolic Volume Index LVEF : Left Ventricular Ejection Fraction LVM : Left Ventricular Mass LVMI : Left Ventricular Mass Index OR : Odds Ratio RBBB : Right Bundle Branch Block ROC : Receiver Operating Characteristics SPS : Systolic Pre-Stretch SRS : Septal Rebound Stretch SSI : Systolic Stretch Index