Abstract
AimsTo identify key structural and electrophysiological features explaining distinct electrocardiogram (ECG) phenotypes in hypertrophic cardiomyopathy (HCM).Methods and resultsHuman heart–torso anatomical models were constructed from cardiac magnetic resonance (CMR) images of HCM patients, representative of ECG phenotypes identified previously. High performance computing simulations using bidomain models were conducted to dissect key features explaining the ECG phenotypes with increased HCM Risk-SCD scores, namely Group 1A, characterized by normal QRS but inverted T waves laterally and coexistence of apical and septal hypertrophy; and Group 3 with marked QRS abnormalities (deep and wide S waves laterally) and septal hypertrophy. Hypertrophic cardiomyopathy abnormalities characterized from CMR, such as hypertrophy, tissue microstructure alterations, abnormal conduction system, and ionic remodelling, were selectively included to assess their influence on ECG morphology. Electrocardiogram abnormalities could not be explained by increased wall thickness nor by local conduction abnormalities associated with fibre disarray or fibrosis. Inverted T wave with normal QRS (Group 1A) was obtained with increased apico-basal repolarization gradient caused by ionic remodelling in septum and apex. Lateral QRS abnormalities (Group 3) were only recovered with abnormal Purkinje-myocardium coupling.ConclusionTwo ECG-based HCM phenotypes are explained by distinct mechanisms: ionic remodelling and action potential prolongation in hypertrophied apical and septal areas lead to T wave inversion with normal QRS complexes, whereas abnormal Purkinje-myocardial coupling causes abnormal QRS morphology in V4–V6. These findings have potential implications for patients’ management as they point towards different arrhythmia mechanisms in different phenotypes.
Highlights
Hypertrophic cardiomyopathy (HCM) has remained a challenge due to the extreme heterogeneity in its clinical course
Effect of cardiac anatomy on the electrocardiogram phenotypes in hypertrophic cardiomyopathy The anatomical effects of cardiac shape, hypertrophy distribution, and extent on the ECG were investigated by patient-specific geometries derived from cardiac magnetic resonance (CMR) images (Figure 2)
Hypertrophic cardiomyopathy patients with inverted T wave and normal QRS (Group 1A) were affected by apico-basal repolarization gradients caused by ionic remodelling in septal and apical hypertrophy regions
Summary
Hypertrophic cardiomyopathy (HCM) has remained a challenge due to the extreme heterogeneity in its clinical course. Most patients are asymptomatic, HCM is a major cause of sudden cardiac death (SCD) in young people due to ventricular arrhythmias. These life-threatening arrhythmias are effectively aborted by implantable cardioverter-defibrillators (ICDs) and the focus of risk stratification is to target high-risk patients with an ICD. The greatest deviation from a normal ECG occurred in two of the four ECG phenotypes: Group 1A and Group 3.5 Patients in Group 1A had normal QRS morphology, inverted T waves laterally, increased HCM Risk-SCD scores, and coexisting septal and apical hypertrophy. Patients in Group 3 had QRS abnormalities with deep wide S waves laterally and septal hypertrophy. The structural and electrophysiological sources of these different ECG phenotypes in HCM remain unclear and complex, as they may include hypertrophy, fibre disarray, fibrosis, ionic remodelling, as well as Purkinje abnormalities.[6,7,8] A better understanding of the electrophysiological and structural basis of the HCM phenotypes may help to improve personalized patient management, as the mechanisms underlying arrhythmic risk may differ
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