Kardiomiopati

01Pathophysiology

Dilated Cardiomyopathy (DCM)

DCM is the most common form of cardiomyopathy and the leading indication for heart transplantation. The core defect is progressive destruction or dysfunction of myocytes, which leads to eccentric hypertrophy: the ventricle dilates to compensate for reduced contractile force. As the chamber expands, wall stress increases according to the Law of Laplace ($\text{Wall Stress}=\frac{P\times r}{2h}\backslash text\{Wall\; Stress\}\; =\; \backslash frac\{P\; \backslash times\; r\}\{2h\}$), creating a vicious cycle where dilation raises wall stress, which worsens contractile efficiency, which triggers further dilation.

The most tested etiologies include viral myocarditis (Coxsackie B virus is the classic association), chronic alcohol use (direct toxic effect on myocytes), peripartum cardiomyopathy (last trimester through 5 months postpartum), doxorubicin (anthracycline chemotherapy causing dose-dependent irreversible damage), and Chagas disease (Trypanosoma cruzi, tested in patients from Central and South America). The downstream physiology is that of systolic heart failure: the heart cannot generate adequate forward output, leading to pulmonary congestion (dyspnea, orthopnea) and systemic venous congestion (peripheral edema, hepatomegaly). The S3 gallop you hear on exam reflects rapid passive filling into a volume-overloaded, floppy ventricle.

Stasis of blood in a poorly contracting, dilated chamber also predisposes to mural thrombus formation, which can embolize and cause stroke. This is why you will see questions about anticoagulation in DCM patients, particularly those with very low ejection fractions.

Hypertrophic Cardiomyopathy (HCM)

HCM is the most common cause of sudden cardiac death in young athletes. This sentence alone accounts for a large percentage of how this disease is tested. The inheritance pattern is autosomal dominant with variable penetrance. The most commonly tested mutation is in the beta-myosin heavy chain gene on chromosome 14.

The pathology is asymmetric septal hypertrophy, where the interventricular septum grows disproportionately thick compared to the free wall. This thickened septum narrows the left ventricular outflow tract (LVOT). During systole, high-velocity blood flowing through the narrowed LVOT creates a Venturi effect that pulls the anterior leaflet of the mitral valve toward the septum. This phenomenon is called systolic anterior motion (SAM), and it is both the hallmark echocardiographic finding and the mechanism behind the dynamic outflow obstruction.

Understanding the physiology of the obstruction is essential for answering management questions. Anything that decreases left ventricular volume (dehydration, Valsalva maneuver, standing up suddenly, exercise, vasodilators) worsens the obstruction because the septum and mitral leaflet are brought closer together. Conversely, anything that increases left ventricular volume (squatting, leg elevation, IV fluids) or increases afterload (phenylephrine) separates these structures and reduces obstruction. This is the single most tested concept in HCM.

The murmur is a harsh, crescendo-decrescendo systolic murmur best heard at the left lower sternal border. It is the only common murmur that increases with Valsalva (most murmurs decrease). On ECG, you may see LVH with deep, narrow Q waves in the lateral and inferior leads, which represent septal depolarization and are sometimes called "dagger Q waves."

The mechanism of sudden death is a ventricular arrhythmia (ventricular tachycardia or fibrillation) triggered by the disorganized myocyte architecture ("myocardial disarray") within the hypertrophied septum. This is why competitive sports are prohibited and ICD placement is considered in high-risk patients.

Restrictive Cardiomyopathy (RCM)

RCM is the least common of the three. The ventricle has normal (or near-normal) systolic function but is abnormally stiff, impairing diastolic filling. The heart can squeeze but cannot relax properly. This means the ejection fraction is preserved, but filling pressures are elevated.

The stiffness is caused by infiltration or fibrosis of the myocardium. Amyloidosis is the most commonly tested etiology: misfolded proteins deposit in the myocardial interstitium, making the walls rigid. On echocardiography, amyloid deposits produce a characteristic "sparkling" or "granular" appearance of the myocardium. On tissue biopsy, amyloid stains with Congo red and shows apple-green birefringence under polarized light, a classic buzzword.

Other important causes include sarcoidosis (non-caseating granulomas infiltrating the myocardium, which can also cause conduction abnormalities and arrhythmias), hemochromatosis (iron deposition, classically presenting with the triad of cirrhosis, diabetes, and skin hyperpigmentation), and radiation therapy (fibrosis from prior chest radiation, often years after treatment for lymphoma or breast cancer).

Because the stiff ventricle cannot accommodate venous return, patients develop elevated right-sided filling pressures early. This is why ascites, peripheral edema, and JVD often dominate the presentation before pulmonary symptoms become severe. The Kussmaul sign (paradoxical rise in JVP during inspiration, when it should normally fall) reflects the inability of the stiff right ventricle to accept the increased venous return that inspiration generates. This sign is also seen in constrictive pericarditis, which is the main differential.

02Classification and Clinical Manifestation

Classification by Pathophysiology

Clinical Manifestation by Subtype

Additional Cardiomyopathy Subtypes Tested in Vignettes

03Diagnostic Workup

Echocardiography is the best initial test for all cardiomyopathies. When a vignette describes a patient with heart failure symptoms and asks "what is the next step?", the answer is nearly always echocardiography. It provides the ejection fraction, chamber dimensions, wall thickness, valvular function, and diastolic parameters in one noninvasive study. This single test often clinches the diagnosis:

For DCM, echo reveals a globally dilated, hypokinetic LV with an EF typically below 40%. All four chambers are enlarged. You may see functional mitral regurgitation caused by annular dilation. The CXR will show cardiomegaly (cardiothoracic ratio > 0.5) and signs of pulmonary edema. BNP or NT-proBNP will be elevated and is useful for distinguishing cardiac from pulmonary causes of dyspnea. If the etiology is unclear and you need to confirm a diagnosis like myocarditis or infiltrative disease, endomyocardial biopsy is the gold standard, but it is rarely performed in practice and is only the answer when the vignette presents an unclear etiology that biopsy would resolve.

For HCM, echo shows the hallmark findings: septal wall thickness greater than 15 mm (or a septal-to-free-wall ratio greater than 1.3:1), a small LV cavity, and SAM of the mitral valve. Doppler will demonstrate a dynamic LVOT gradient that increases with provocative maneuvers. Cardiac MRI is increasingly recognized as the most accurate imaging modality because it precisely quantifies the degree of hypertrophy and can identify areas of myocardial fibrosis using late gadolinium enhancement, which correlates with arrhythmia risk. Genetic testing is used for family screening once a proband is identified, not for primary diagnosis. All first-degree relatives should be screened with echocardiography and potentially genetic testing.

For RCM, echo shows normal ventricular cavity size with biatrial enlargement and prominent diastolic dysfunction (elevated E/e' ratio). In amyloidosis, you see thickened ventricular walls with the characteristic "sparkling" appearance and often a small pericardial effusion. The findings may overlap with constrictive pericarditis (see Differential section below). Endomyocardial biopsy is the gold standard for confirming the etiology because it directly visualizes the infiltrate. For amyloidosis, biopsy shows Congo red-positive deposits with apple-green birefringence. A less invasive approach for AL amyloidosis includes serum free light chains and serum/urine protein electrophoresis. For transthyretin (ATTR) amyloidosis, technetium-99m pyrophosphate (Tc-99m PYP) nuclear scintigraphy is highly accurate and can sometimes obviate biopsy.

One important distinction to know: cardiac catheterization with simultaneous right and left heart pressure measurement can help differentiate RCM from constrictive pericarditis when imaging is inconclusive. In RCM, the LV and RV diastolic pressures are discordant (LV > RV by more than 5 mmHg) because the stiff myocardium affects the thicker left ventricle more. In constrictive pericarditis, pressures are equalized across all chambers because the rigid pericardium encases both ventricles equally.

04Management and Treatment

DCM: The management mirrors guideline-directed medical therapy for heart failure with reduced ejection fraction (HFrEF). The "four pillars" of HFrEF therapy tested on exams are: (1) ACEi/ARB/ARNI, (2) beta-blocker, (3) aldosterone antagonist, and (4) SGLT2 inhibitor. Each of these has mortality benefit. Diuretics (furosemide) relieve congestion but do not improve survival. The key sequencing point: do not start beta-blockers in a patient who is acutely decompensated. Stabilize with diuretics first, then initiate and titrate beta-blockers once euvolemic. If EF remains below 35% despite 3 to 6 months of optimal therapy, an ICD is indicated for primary prevention of sudden cardiac death. If the patient also has a wide QRS (especially LBBB with QRS > 150 ms), cardiac resynchronization therapy (CRT) provides additional benefit.

A frequently tested scenario involves peripartum cardiomyopathy: the vignette describes a woman in the third trimester or early postpartum period with new-onset heart failure. ACE inhibitors and ARBs are absolutely contraindicated during pregnancy because of fetal renal agenesis, oligohydramnios, and other developmental defects. The "next best step" in a pregnant patient with heart failure is hydralazine plus isosorbide dinitrate for afterload reduction, along with diuretics and beta-blockers (labetalol or carvedilol are preferred). Once the patient has delivered, you can transition to standard ACEi/ARB therapy.

HCM: The treatment logic is entirely different from DCM and is a common source of errors. The goal is to reduce the dynamic LVOT obstruction by keeping the ventricle full and slowing the heart rate. Beta-blockers achieve this by (1) slowing heart rate, which prolongs diastolic filling time, and (2) reducing contractility, which decreases the force pushing the anterior mitral leaflet toward the septum. Verapamil is the second-line agent and works similarly through negative inotropy and negative chronotropy. Disopyramide is a class IA antiarrhythmic with strong negative inotropic properties and is added when beta-blockers or verapamil alone are insufficient.

The "avoid" list for HCM is heavily tested. Digoxin increases contractility and worsens obstruction. Dihydropyridine calcium channel blockers (nifedipine, amlodipine) cause vasodilation and reflex tachycardia, both of which worsen obstruction. Nitrates and ACE inhibitors reduce preload and afterload, respectively, shrinking the ventricular cavity and worsening obstruction. Dehydration and strenuous exercise have the same effect through reduced preload.

For sudden death prevention, ICD implantation is the only therapy proven to prevent mortality. The standard risk factors tested include: family history of sudden cardiac death, syncope of unexplained etiology, LV wall thickness over 30 mm, nonsustained ventricular tachycardia on Holter, and abnormal blood pressure response during exercise testing.

RCM: Management is the most limited because no therapy reverses the diastolic stiffness itself. Treatment focuses on the underlying disease. The single most testable management point is that digoxin should be avoided in cardiac amyloidosis because amyloid fibrils bind digoxin with high affinity, increasing the free drug concentration and causing toxicity even at standard doses. Diuretics must be used cautiously because these patients depend on elevated filling pressures to maintain cardiac output; aggressive volume removal leads to severe hypotension.

05Differential Diagnosis and Distractors

06Traps and High-Yield Pearls

The most common trap with cardiomyopathy questions is applying DCM management principles to HCM. Many students reflexively choose an ACE inhibitor or digoxin for any patient with heart failure symptoms, but in HCM, these agents worsen the outflow obstruction and can be fatal. The exam tests whether you can recognize that HCM is a fundamentally different physiology: the problem is not a weak pump (systolic failure) but a mechanical obstruction made worse by anything that reduces chamber size. If a vignette describes a young athlete with syncope, a systolic murmur that increases with Valsalva, and an echo showing asymmetric septal hypertrophy, the correct answer will never be an ACEi, a nitrate, or digoxin.

A second common error involves confusing restrictive cardiomyopathy with constrictive pericarditis. Both present nearly identically with diastolic failure, elevated JVP, and Kussmaul sign. The vignette will contain one distinguishing detail. Look for pericardial calcification or a history of prior cardiac surgery, radiation, or tuberculosis, which point toward constriction. Look for amyloidosis features (nephrotic syndrome, macroglossia, periorbital purpura), hemochromatosis clues (bronze skin, diabetes, cirrhosis), or sarcoidosis hints (bilateral hilar lymphadenopathy, erythema nodosum) to identify a restrictive process.

A third tested concept is the murmur behavior in HCM. Most systolic murmurs decrease with Valsalva because the reduced venous return lowers the volume of blood crossing the valve. HCM is the critical exception: Valsalva reduces LV volume, worsening obstruction, making the murmur louder. The only other murmur that increases with Valsalva is the click/murmur of mitral valve prolapse (the click moves earlier and the murmur lengthens). If a question asks what happens to a murmur with a given maneuver, HCM and MVP are the two diagnoses to consider when the answer is "louder" or "more prominent."

Finally, always remember that Takotsubo cardiomyopathy is a diagnosis of exclusion. The vignette will describe what looks like an acute MI (chest pain, ST elevation, troponin bump) but the catheterization reveals clean coronary arteries. The classic patient is a postmenopausal woman who recently experienced a severe emotional shock (death of a loved one, natural disaster, surprise party). The apical ballooning pattern on ventriculography or echo is the confirmatory finding, and the condition is generally reversible.

The core competency being tested across all cardiomyopathy questions is your ability to classify the type of cardiomyopathy based on the clinical and echocardiographic phenotype and then apply the correct, type-appropriate management rather than defaulting to a one-size-fits-all heart failure approach.