RV Imaging and Computer Simulation for Electromechanical Substrate in ARVC
What are the right ventricular (RV) strain patterns and corresponding pathophysiology across the subclinical, electrical, and structural stages of arrhythmogenic right ventricular cardiomyopathy (ARVC)?
Echocardiograms from 84 patients with proven ARVC desmosomal mutations were retrospectively classified in three types by two experienced observers based on RV longitudinal deformation pattern at the basal lateral segment on an apical four-chamber view: type I (normal deformation), type II (delayed onset of shortening, reduced peak systolic strain, present post-systolic shortening), and type III (little to no peak systolic strain, more prominent post-systolic strain, and often systolic stretching). Deformational echocardiographic findings were related to ARVC stage (subclinical, electrical, and structural). Computer simulations were performed to evaluate the contributions of delayed activation, mechanical hypocontractility, and increased mechanical stiffness on echocardiographic findings.
While 96% of controls had a type I (normal pattern), this was only seen in 14% of mutation carriers. Type II occurred in 42% and type III in 44%. Approximately half of patients in the subclinical stage of ARVC had type II pattern (48%), with the remaining having normal type I pattern. In the electrical stage, type II was seen in 67% of patients. In the structural stage, type III pattern was seen in 69% of patients. In computer simulations, type II pattern was explained by reduced contractility (40% of normal) and increased stiffness (200% of normal). Type III pattern was explained by more dramatic reduction of contractility (30% of normal) and increased stiffness (800% of normal). Delayed contractility did not account for echocardiographic deformation patterns.
RV deformational findings on echocardiography differed across stages of ARVC in a characteristic fashion. These changes could be explained by changes in RV contractility and stiffness, but could not be explained by conduction delay.
This study adds to the growing data supporting the use of deformational (strain) imaging of the RV in ARVC. In addition to showing that echocardiographic findings may have a role in defining whether patients are progressing from the subclinical to the electrical or the electrical to the structural stages of ARVC, this study demonstrates that these findings are related to underlying mechanical rather than electrical abnormalities in the RV. These data contradict prior basic science work suggesting that electrical conduction abnormalities precede mechanical abnormalities and account for the findings in the electrical stage of ARVC. These data also suggest that mechanical abnormalities are present relatively early and may be important even in the “electrical” stage of the disease. Importantly, this study utilized expert interpretation of strain curves rather than simply evaluating peak systolic strain as a single number, an approach which is likely to have greater clinical value. Although very promising, further research is required to evaluate if this approach leads to better risk stratification and clinical staging.
Clinical Topics: Arrhythmias and Clinical EP, Congenital Heart Disease and Pediatric Cardiology, Heart Failure and Cardiomyopathies, Noninvasive Imaging, Implantable Devices, Genetic Arrhythmic Conditions, SCD/Ventricular Arrhythmias, Atrial Fibrillation/Supraventricular Arrhythmias, Congenital Heart Disease, CHD and Pediatrics and Arrhythmias, CHD and Pediatrics and Imaging, Acute Heart Failure, Echocardiography/Ultrasound
Keywords: Arrhythmias, Cardiac, Arrhythmogenic Right Ventricular Dysplasia, Computer Simulation, Desmosomes, Diagnostic Imaging, Echocardiography, Heart Defects, Congenital, Heart Failure, Mutation, Systole
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