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Number 16-MG-Utility of Cardiac MRI in diagnosing HCM in obese patients
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“Utility of Cardiac MRI in diagnosing HCM in obese patients”   

 

Authors

Dan Laney

Arun Nagabandi MD

Gyanendra K Sharma  MD.

Jayanth H. Keshavamurthy MD.

James Rawson MD.

 

Institute: Medical College of Georgia at Augusta University, Division of Cardiology and Department of Radiology, Augusta, GA, USA.

 

Clinical History

A 45-year-old African American female with a medical history significant for obesity, HTN, and obstructive sleep apnea presented with recurrent, brief episodes of anginal chest pain associated with shortness of breath with exertion. Patient endorsed occasional lower extremity swelling and palpitations but denied any history of orthopnea, paroxysmal nocturnal dyspnea, or syncopal episodes. She denied any family history of sudden cardiac death or premature coronary artery disease. She quit smoking cigarettes 8 years ago and endorsed drinking alcohol occasionally, however she denied any history of illicit drug use. Physical exam, vital signs, and routine laboratory tests including troponins and BNP were unremarkable. Electrocardiogram performed in the emergency department was normal, showing no abnormalities including no signs of ischemia or hypertrophy (Figure 1).

 

 

Figure 1: EKG showing normal sinus rhythm and no other prominent findings

Previous cardiac workup for similar symptoms included negative left heart catheterization 5 years ago and negative nuclear stress test 3 years ago. A 14-day holter monitor to address her history of palpitations showed a single, short run of atrial tachycardia, but was otherwise negative. A recent echocardiogram showed a ejection fraction (EF) of 74%, severe septal hypertrophy in addition to mild concentric LVH (Figure 2). The maximum gradient obtained was 11 mmHg. No systolic anterior motion (SAM) or turbulence of LVOT was appreciated on echocardiogram. Cardiac gated CTA showed a calcium score of zero without coronary artery stenoses or myocardial bridging as well as concentric LVH without pulmonary embolism or thoracic aortic dissection (Figure 3).

 

 

Figure 2: Echocardiography showing basal septal hypertrophy (septal thickness ~ 18mm)

 

 

Figure 3: 4 chamber view on Cardiac CTA in diastole

Cardiac MRI Findings

Cardiac MRI was performed after Cardiology noted that LVH appreciated on previous studies was disproportionate to patient’s history of hypertension. Cardiac MRI showed a mildly hyperdynamic left ventricle, with mildly increased myocardial mass index, mitral regurgitation and moderate left atrial enlargement. Systolic acceleration in the LVOT was present without SAM of mitral valve complex. (Figure 5). Post contrast Cardiac MRI (MDE- Multihance Delayed Enhancement) demonstrated patchy delayed myocardial enhancement in the mid-myocardium in a non-ischemic pattern involving the mid septum and anterior wall (Figures 6-9). These finding are phenotypically consistent with a diagnosis of hypertrophic cardiomyopathy.

 

 

Figure 4: Short axis at base of heart.        Figure 5: Systolic acceleration at LVOT             



 

Figure 6: MDE short axis                    Figure 7: MDE 2 chamber view             

 

 

Figure 8: MDE 3 chamber view                             Figure 9: MDE 4 chamber view

 

Conclusion

As demonstrated by our patient, electrocardiography, echocardiography, nuclear imaging and CTA are insufficient in screening for HCM especially in obese individuals. In obese patients, such as the one presented, voltage criteria on electrocardiogram consistent with LVH can be missed. Echocardiography is similarly insufficient, as our patient’s echocardiogram was interpreted as demonstrating concentric LVH with some asymmetric septal hypertrophy. Cardiac CTA was also read as showing concentric LVH. Nuclear medicine imaging, while used in workup of this patient in the form of  Gated SPECT, provided little additional information and is simply not optimal for diagnosis of HCM per se.  Conversely, Cardiac MRI, provided imaging sufficient to be read as HCM. Cardiac MRI provided superior resolution and reduced intra and interobserver variations compared with other modalities as well as characteristic delayed enhancement pattern within the myocardium. This allowed for more accurate assessment and subsequent recognition of HCM while also decreasing the patient’s radiation exposure,  making Cardiac MRI as the best screening tool for HCM in young, obese individuals with asymmetric LVH that is disproportionate to patient’s history of HTN.

Recognition that Cardiac MRI is the best imaging modality with which to screen for HCM is significant because HCM is a common, heritable cause of sudden cardiac death in young individuals that can be difficult to diagnose, especially in the obese, leading to grave consequences. Because we were able to recognize HCM by cardiac MRI, our patient will be referred to a geneticist for diagnostic confirmation with genotyping. If the results of genetic analysis also confirm HCM, the patient’s family members will be screened for the disease as well given the heritable nature of the disease and their genetic predispositions to having HCM. Ultimately, by using Cardiac MRI to screen for HCM in young, obese individuals with LVH disproportionate to patient’s history of HTN, both the patient and the patient’s family members can be offered medical management to avoid sudden cardiac death.

 

Perspective:

HCM is characterized by LVH with predominant septal thickening exceeding 15mm during diastole, leading to LVOT obstruction and SAM of the mitral valve in 25% of cases [1]. Studies estimate that HCM, an autosomal dominant disease, has a worldwide prevalence of 0.2% or roughly 1:500 individuals, which, given the relative rarity of presentation, means that many people with the disease go undiagnosed [2].  While recognition of HCM in younger individuals, especially those younger than 35 year old, is primarily important because of the concern for sudden cardiac death resulting from ventricular tachyarrhythmias, this is not the only course of the disease. HCM can also result in progressive heart failure characterized by exertional dyspnea as well as atrial fibrillation resulting in heart failure and increased risk of embolic stroke [2]. The current standard for definitive diagnosis is genetic testing as the following genes have been shown to cause HCM: myosin binding protein C, beta myosin heavy chain, Troponin I, Troponin T, actin, alpha tropomyosin, regulatory light chain, and essential light chain [2]. Cardiac MRI is a similarly powerful tool in screening for HCM because it allows for easy recognition of the phenotypic expression of the disorder, confident differentiation between HCM and other cardiac disorders and myopathies, and potential recognition of the subset of patients at risk of sudden cardiac death [3,4].

 

References:

1. Franco A, Javidi S, Ruehm SG. Delayed Myocardial Enhancement in Cardiac Magnetic Resonance Imaging. J Radiol Case Rep. 2015;9 (6): 6-18.  

 

2. Gersh BJ, Maron BJ, Bonow RO et-al. 2011 ACCF/AHA Guideline for the Diagnosis and Treatment of Hypertrophic Cardiomyopathy: a report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines. Developed in collaboration with the American Association for Thoracic Surgery, American Society of Echocardiography, American Society of Nuclear Cardiology, Heart Failure Society of America, Heart Rhythm Society, Society for Cardiovascular Angiography and Interventions, and Society of Thoracic Surgeons. J. Am. Coll. Cardiol. 2011;58 (25): e212-60.  

 

3.Hansen MW, Merchant N. MRI of hypertrophic cardiomyopathy: part I, MRI appearances. AJR Am J Roentgenol. 2007;189 (6): 1335-43.


4.Hansen MW, Merchant N. MRI of hypertrophic cardiomyopathy:part 2, differential diagnosis, risk stratification, and posttreatment MRI appearances. AJR 2007; 189:1344–1352.

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