Improved Diagnostic Criteria for Apical Hypertrophic Cardiomyopathy
- Based on a cohort of 104 apical hypertrophic cardiomyopathy patients and controls, the upper limit of normal for maximal left ventricular apical wall thickness, indexed to body surface area, is 5.2-5.6 mm/m2 (unindexed equivalent 11 mm).
- Using this indexed threshold improves diagnostic accuracy for apical hypertrophic cardiomyopathy to 92%, as compared with 69% based on the conventional unindexed threshold of ≥15 mm.
What is the appropriate wall thickness threshold on cardiac magnetic resonance (CMR) for diagnosing apical hypertrophic cardiomyopathy (ApHCM)?
From the UK Biobank, 4,118 healthy subjects ≥45 years of age who underwent CMR were identified to establish reference ranges for apical maximal wall thickness (MWT) indexed to body surface area (BSA) and apical: basal MWT wall thickness ratio. A second group of healthy volunteers was recruited to evaluate generalization to a wider age range. A study population of 104 adults with ApHCM, managed in two British tertiary care centers, was recruited. Notable exclusion criteria were conventional contraindications to CMR and permanent pacemakers/defibrillators. ApHCM was defined based on conventional criteria: MWT ≥15 mm at end-diastole, electrocardiographic (ECG) findings, apical cavity obliteration, and/or apical aneurysm. Subjects with relative ApHCM had characteristic imaging and ECG findings but had MWT <15 mm. The upper limit of normal (ULN) was defined as mean + 3 standard deviations based on the UK Biobank data.
In the UK Biobank cohort, MWT had only a negligible association with age. The association between MWT and sex was not clinically significant after accounting for BSA. Therefore, the tested diagnostic criterion accounted only for BSA. ULN for indexed apical wall thickness was 5.2-5.6 mm/m2 (unindexed equivalent 11 mm). Mean apical: basal MWT ratios were 0.77 in healthy subjects, 1.31 in overt ApHCM subjects, and 1 in relative ApHCM subjects. Based on the indexed MWT diagnostic threshold, 99% of overt ApHCM and 78% of relative ApHCM patients were correctly identified. The indexed threshold improved overall diagnostic accuracy for ApHCM to 92%, as compared with 69% based on the conventional unindexed threshold of ≥15 mm.
Using a BSA-indexed reference standard for maximal apical wall thickness improves diagnostic accuracy for ApHCM, as compared with the conventional unindexed standard.
In real-world settings, ApHCM may be underdiagnosed, especially when patients do not undergo comprehensive evaluation including ECG and contrast-enhanced echocardiography. Patients with ApHCM may present with characteristic ECG findings, such as deep T-wave inversions, but not demonstrate overt apical hypertrophy on initial imaging evaluation. If clinical suspicion for ApHCM exists, CMR and long-term clinical follow-up are crucial. The diagnostic criteria presented in this manuscript can improve detection of ApHCM in smaller individuals, including women.
Keywords: Electrocardiography, Cardiomyopathy, Hypertrophic, Magnetic Resonance Imaging
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