Inferior Hypertrophic Cardiomyopathy: An Unusual and Insidious Site

Abstract

Hypertrophic cardiomyopathy is a heart muscle disease, characterized by increased left ventricular wall thickness that is not explained only by abnormal loading conditions. Hypertrophy preferentially involves the interventricular septum in the basal segments of the left ventricle, but often extends to the lateral wall, posterior septum, and apex of the left ventricle. A substantially isolated inferior wall hypertrophy is quite rare and diagnostically insidious. We present a clinical case in which diagnosis and therapeutic management were decisively guided by cardiac magnetic resonance.

INTRODUCTION

hypertrophic cardiomyopathy (HCM) is defined by an increase in left ventricular (LV) wall thickness (≥15 mm) that is not only explained by abnormal loading conditions. Epidemiologically, the prevalence ranges from 0.02% to 0.23%, with an annual incidence of 0.3–0.5/100,000. Approximately 60% of HCM cases are caused by the mutations in genes encoding cardiac sarcomere proteins; an additional 5%–10% are caused by other genetic disorders with metabolic and neuromuscular involvement.[1]

Hypertrophy preferentially involves the interventricular septum in the basal segments of the left ventricle but often extends to the lateral wall, the posterior septum, and the LV apex.[2] Isolated lateral and inferoseptal hypertrophy are considered rarer variants,[3] while a substantially pure or dominant inferior form is entirely sporadic. The diversity of morphological expression in HCM is due to racial and genetic factors, as well as the differences in phenotypic expression. Hypertrophy of atypical segments may go undetected on transthoracic echocardiography (TTE) and can be difficult to differentiate from an intracardiac mass, necessitating advanced diagnostic tools such as cardiac magnetic resonance (CMR).[4]

CMR is a noninvasive method, independent of the acoustic window and offers the advantage of myocardial tissue characterization.[5] Late gadolinium enhancement (LGE) reveals fibrosis in 65% of patients, typically with a patchy mid-wall distribution within hypertrophic areas and localized at the anterior and posterior right ventricular insertion points (junctions). Usually, nonhypertrophic segments do not exhibit fibrosis except in advanced stages of the disease, where diffuse extension associated with wall thinning is frequently observed.[6]

In this article, we report a highly unusual case of isolated inferior HCM. The definitive diagnosis was established using CMR, performed and evaluated at our facility within an integrated, multidisciplinary team of dedicated cardiologists and radiologists.[7]

CASE REPORT

The patient was a 64-year-old obese Caucasian female with no family history of heart disease or sudden cardiac death (SCD) and no known history of hypertension. In 2011, she underwent coronary angiography following an episode of prolonged chest pain with inferolateral electrocardiographic (ECG) abnormalities and negative troponin, which showed no evidence of coronary artery disease. No significant findings were reported on echocardiography during that hospitalization at another hospital.

The patient remained substantially well for the next 13 years until presenting to our emergency department for palpitations and lipothymia. The ECG showed wide-complex (120 ms) tachycardia at 240 bpm, an axis of approximately −150°, and a Right Bundle Branch Block morphology, likely of ventricular origin. Amiodarone infusion was ineffective and a subsequent drop in blood pressure led to hemodynamic instability. Electrical cardioversion (100-joule biphasic shock) was performed, restoring sinus rhythm without ventricular repolarization disturbances suggestive of an acute ischemic event or overload. Meanwhile, troponin levels showed a significant increase.

Bedside echocardiography in the Intensive Care Unit documented a left ventricle of normal diameter, hypo-akinetic in the basal-mid inferior wall, with mildly depressed global contractility. Subsequent coronary angiography through the right radial artery showed no evidence of significant obstructive lesions.

The patient underwent CMR, which unexpectedly revealed isolated findings in the basal-mid inferior wall of the left ventricle: Marked hypertrophy (wall thickness of 18 mm), hypo-akinesia with a slight reduction in global contractility, subendocardial contrast enhancement delay during the perfusion study, substantially transmural signal hyperintensity on LGE for fibrosis assessment [Figure 1], increased T1 mapping values (1098 ms vs. <994 ms in the remaining myocardium).

Figure 1.

Late gadolinium enhancement cardiac magnetic resonance imaging (short-axis view on the right and two-chamber long-axis view on the left): Extensive fibrosis (black arrow) corresponding to the markedly hypertrophic myocardium in the inferior wall

Examination was conclusive for HCM localized to the basal-mid inferior wall of the left ventricle.

The close correspondence between the markedly hypertrophic segment and the area of fibrosis, the irregular distribution and texture of the fibrosis and the limited perfusion defect (only subendocardial) together with the negative outcome of coronary angiography excluded the ischemic genesis of the fibrosis despite a coronary distribution (right coronary).

Another echocardiogram was performed at our Cardiology Department’s Echocardiography Laboratory using more sophisticated equipment: With a targeted examination, guided by the CMR data, the hypertrophy of the basal-mid inferior wall was appreciated [Figure 2], with a segmental Global Longitudinal Strain value of − 5% (−13% overall) [Figure 3].

Figure 2.

Echocardiographic image: Two-chamber view showing a modestly thickened inferior wall, with measurements underestimated compared to the cardiac magnetic resonance findings

Figure 3.

Echocardiographic image, myocardial strain analysis (global longitudinal strain): Less negative values corresponding to the inferior wall

During hospitalization, the patient experienced only one nonsustained ventricular tachycardia of four complexes, along with isolated and paired ventricular premature contractions. Consequently, an Implantable Cardioverter-Defibrillator was implanted for the secondary prevention of SCD, as per the 2023 ESC Guidelines on Cardiomyopathies (Class I, Level of Evidence B). Therefore, HCM risk score was not calculated.

The patient was discharged on ACE-inhibitor, beta-blocker (metoprolol), and mineralocorticoid receptor antagonist therapy. Genetic analysis via NGS sequencing of HCM-associated genes showed no pathogenic variants. Screening echocardiograms of the patient’s children were unremarkable.

DISCUSSION

This case of HCM is unique due to the atypical and focal location. It suggests that in ambiguous or nonspecific clinical presentations (arrhythmic, ischemic, or heart failure-related), it is plausible to investigate the rare possibility of an isolated, unusually located HCM. Such cases may be missed during routine or even detailed echocardiographic exams due to the inherent sub-optimal visualization of certain segments, such as the inferior wall, leading to potential underestimation of wall thickness.

In this scenario, CMR is central; by overcoming the physical limitations of echocardiography, it allows for the accurate quantitative assessment of all segments and provides decisive information regarding tissue characterization and perfusion. In this case, CMR identified focal wall thickening missed or underestimated by TTE, detected fibrosis (which carries prognostic significance), and explained the likely cause of the prior ischemic event through the evidence of a perfusion deficit.

HCM is frequently associated with myocardial ischemia due to coronary microvascular dysfunction, even in the presence of normal coronary arteries, which can lead to symptoms like chest pain. This occurs because the thickened heart muscle increases oxygen demand and compromises blood flow through small arteries. Ischemia in HCM contributes to complications such as ventricular arrhythmias, progressive LV remodeling, and is a risk factor for SCD.[8] Although distinguishing morphological subtypes of HCM has historically offered limited benefits for individualized management strategies, diagnosing unusually located HCM allows for proper patient stratification, to institute appropriate therapeutic measures, schedule serial surveillance, and extend investigations to descendants and collateral relatives, as is standard for any morphological subtype of HCM. Regarding the absence of pathogenic variants, it should be noted that the percentage of cases with a reliable genetic diagnosis where a causative Mendelian genetic variant has been identified is relatively low, approximately 40%.[9]

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Conflicts of interest

There are no conflicts of interest.

Funding Statement

Nil.