Cardiomyopathies

The NHLBI puts the shared idea simply: the types "differ based on their cause and how they affect the heart’s structure and function," and "All types weaken the heart muscle." Some are permanent and some are temporary — "Certain types are temporary and get better with time." A person can even have more than one at once.

Dilated cardiomyopathy (DCM) is the big, thin, weak ventricle. It is enlargement and dilation of one or both ventricles with impaired contractility, "defined as a left ventricular ejection fraction (LVEF) less than 40%." By definition these patients have systolic dysfunction, whether or not heart-failure symptoms have appeared yet — and many have "a long latent period where they are clinically asymptomatic."

Hypertrophic cardiomyopathy (HCM) is the thick, stiff, over-squeezing ventricle. It is an inherited sarcomere disease and "the most common inherited cardiomyopathy." The wall thickens — most often the interventricular septum — to 15 mm or more in adults, and the ejection fraction is often elevated (above 65%). The problem is not squeezing; it is filling, and sometimes an outflow tract that closes itself off.

Restrictive cardiomyopathy (RCM) is the rigid ventricle. It is diastolic dysfunction "in a non-dilated ventricle" — the walls are not thickened by hypertrophy but stiffened, usually by something infiltrating between the muscle cells (amyloid is the commonest cause in developed countries). It is the least common of the three, about 5% of cardiomyopathies, and carries the worst prognosis of them all.

The dilated heart gets bigger to keep up, and bigger makes it worse. Myocardial remodeling increases both end-systolic and end-diastolic volumes; as the ventricles dilate, the mitral and tricuspid valves stop closing properly, which "further lowers the ejection fraction and increases the ventricular wall stress." The body’s rescue systems join in: heart rate and vascular tone rise, the renin–angiotensin–aldosterone system switches on, catecholamines climb and natriuretic peptides rise. "Eventually these compensatory mechanisms become overwhelmed and the heart fails." This is the same neurohormonal loop the Heart Failure page draws — which is exactly why DCM is treated with the heart-failure drugs.

Its natural history is predictable. Continued enlargement brings conduction-system disease, ventricular arrhythmias, thromboembolism and heart failure. "The earlier these patients are identified and treated, the better the prognosis." The outlook is poor — StatPearls records that "Almost 50% of patients are dead within 5 years."

Most DCM has no identifiable cause. When a cause is found it is a list worth knowing because several are reversible or preventable: viral myocarditis, Chagas and Lyme disease, ischemic disease, hypertension, anthracycline chemotherapy, alcohol, HIV, peripartum cardiomyopathy and infiltrative disease.

Five mechanisms make HCM symptomatic — dynamic left ventricular outflow tract obstruction (LVOTO), mitral regurgitation, diastolic dysfunction, myocardial ischemia and autonomic dysfunction. The one that explains the bedside is the first.

How the outflow tract closes. The thickened septum narrows the outflow tract, and during systole the front mitral leaflet is pulled forward into it — systolic anterior motion (SAM). The narrower the cavity, the sooner septum and leaflet meet. That makes the obstruction dynamic: "The gradient can also be provoked by changes in preload and afterload." Anything that shrinks the ventricle — dehydration, standing, straining, vasodilators — worsens obstruction, and "Volume depletion decreases stroke volume and worsens the LVOT gradient. This can lead to hypotension, lightheadedness, and syncope." A gradient of 30 mm Hg or more is hemodynamically significant; 50 mm Hg or more is the threshold for surgical or percutaneous intervention, primarily if symptomatic.

Stiffness and ischemia without blocked coronaries. Hypertrophy, disordered myocytes and fibrosis stiffen the wall, so relaxation is impaired and pressures rise in the left ventricle and atrium. Thick muscle, abnormal small arterioles and poor flow reserve create a supply–demand mismatch that scars the muscle — chest pain in HCM does not require coronary disease.

Why atrial fibrillation hits HCM so hard. AF is the commonest arrhythmia in HCM (about 25% of patients), and the stiff ventricle depends on the atrium to finish filling — "up to 35% of left ventricular filling depends on left atrial contraction." Lose the atrial kick and output falls, sometimes to hypotension.

The sudden-death rhythm. Nonsustained ventricular tachycardia appears in 20% to 30% of patients, and ventricular tachycardia degenerating into ventricular fibrillation is the most common cause of sudden cardiac death. In the United States HCM is "the most common identifiable cause of sudden cardiac death in healthy people younger than 35, including well-trained athletes."

Restrictive: the heart that needs its high pressures. Most RCM comes from infiltration of abnormal substances between myocytes, storage of abnormal metabolic products, or fibrosis — amyloidosis first, then sarcoidosis, hemochromatosis, storage diseases and endomyocardial fibrosis; drugs such as anthracyclines are among the other causes. Because the rigid ventricle only fills against high pressure, diuretics "must be monitored closely to prevent excessive diuresis as patients with RCM rely on high filling pressures to maintain cardiac output." The picture is right-sided congestion — jugular venous distension, ascites, leg edema — often with atrial fibrillation.

Takotsubo: stunned by catecholamines. A nonischemic cardiomyopathy that "predominantly affects postmenopausal women," with transient regional systolic dysfunction and no significant coronary disease. The leading explanation is catecholamine excess (plasma levels two- to three-fold elevated) causing microvascular spasm, stunning or direct injury; estrogen normally protects, which is why postmenopausal women react with exaggerated vasoconstriction and sympathetic activation. In about 80% of cases the apex balloons while the base over-contracts — the shape of the Japanese octopus trap that gives the condition its name. Emotional triggers are found in about 27.7% of patients and physical stressors in about 36%; no clear trigger in about 28.5%; happy events can do it too.

It is not benign. About 10% develop cardiogenic shock, mortality was 4.1% in the International Takotsubo Registry, and "cardiogenic shock and death rates are comparable to those of patients with acute coronary syndrome." The heart usually recovers — NHLBI says in 3 to 4 weeks with medicine — but about 5% have a second event.

Peripartum: heart failure around childbirth. PPCM is heart failure from left ventricular systolic dysfunction with an ejection fraction below 45%, developing toward the end of pregnancy or after delivery with no other cause. One proposed mechanism is prolactin cleaved into a toxic 16-kDa fragment that damages cardiac vessels; about 15% to 20% of cases carry dilated-cardiomyopathy gene variants. Timing matters for the nurse: about 19% are found in the final month of pregnancy and about 75% within the first month postpartum — 45% of those in the first week after delivery.