AssessmentsCardiomyopathies: Clinical practice
USMLE® Step 1 style questions USMLE
USMLE® Step 2 style questions USMLE
A 65-year-old patient comes to the office because of increased shortness of breath for 3 months. His symptoms are particularly bad at night. Medical history includes long-standing hypertension and alcoholism. Examination shows a displaced apex beat and normal breath sounds. Cardiac auscultation shows an S3 gallop and a pan-systolic murmur radiating to the axilla. The chest X-ray is shown below. Which of the following is the most likely diagnosis?
Content Reviewers:Rishi Desai, MD, MPH
When cardiomyopathy develops as a way to compensate for some other underlying disease, like hypertension or valve diseases, it’s called secondary cardiomyopathy, but when it develops all by itself it’s called primary cardiomyopathy.
Now, there are three main types of cardiomyopathy. The most common type is dilated cardiomyopathy, that’s where all four chambers of the heart dilate, or get bigger, and the heart walls become thin and lose contractility.
Next up is hypertrophic cardiomyopathy and that’s where the walls get thick, heavy, and hypercontractile.
The muscles and size of the ventricles, though, stay about the same size and only get slightly enlarged.
Restrictive cardiomyopathy may be idiopathic or secondary to a disorder that either deposits harmful substances, like iron or amyloid, in the heart tissue, or there’s fibrosis caused by immune cells or radiation.
Individuals may also develop acute symptoms like presyncope or syncope, which is a sudden loss of consciousness usually lasting a few seconds. These individuals are at an increased risk of myocardial infarction.
And because cardiomyopathies affect the cardiac muscle as well as the pacemaker cells that run through the cardiac muscle - they can lead to arrhythmias like atrial fibrillation, ventricular ectopic beats, ventricular tachycardia or fibrillation, and atrioventricular block.
On auscultation, hypertrophic cardiomyopathy causes a crescendo-decrescendo murmur between S1 and S2, so during systole, where it gets louder as blood first rushes out, and then softer.
The S3 heart sound is the result of blood rushing and slamming into the dilated ventricular wall during diastole; while the S4 heart sound is due to decreased ventricular compliance.
Then comes the ECG, which is usually abnormal in a variety of different ways because there’s significant remodeling of the cardiac muscle in all of the cardiomyopathies.
Identification of the cardiomyopathy type relies primarily upon echocardiographic evaluation, which makes it possible to measure the thickness of the wall, dimensions of the cavities and the pericardial space, as well as the left ventricular function expressed by the ejection fraction.
In dilated cardiomyopathy, the echocardiogram generally shows left ventricle dilation, with an end-diastolic dimension higher than 112% of the predicted value (after correcting for age and body surface area).
Additionally, individuals have a normal or decreased wall thickness, and an ejection fraction below 45%.
Hypertrophic cardiomyopathy is characterized by increased ventricular wall thickness or mass, and the left ventricular volume may be normal or reduced.
The normal cardiac wall thickness for women is up to 11mm and for men is up to 12mm. Between 12 and 15mm there’s a grey area, which isn’t classified as hypertrophic cardiomyopathy, unless a family member is affected as well.
But any individual with a cardiac wall thickness over 15 mm is diagnosed with hypertrophic cardiomyopathy.
Finally, in restrictive cardiomyopathy, the heart’s shape tends to be normal, so it’s characterized by non-dilated ventricles with impaired ventricular filling, but generally there’s a normal ejection fraction - so between 55 and 70%.
Hypertrophy is typically absent, although infiltrative and storage diseases may cause an increase in left ventricular wall thickness.