Cardiomyopathies, Valve Disease and Structural Defects

Pathophysiology and Management of Cardiomyopathies

Dilated cardiomyopathy is characterized by ventricular dilation, impaired systolic contraction, and an ejection fraction typically below forty percent. When assessing an unstable patient, the critical care nurse may detect an S3 gallop and a displaced point of maximal impulse. As left-sided filling pressures rise, pulmonary artery occlusion pressure becomes elevated. Ventricular remodeling can also pull the internal architecture out of alignment; dilating the mitral annulus and displacing the papillary muscles frequently leads to functional mitral regurgitation. When prescribed under provider orders, carefully titrated vasodilators can reduce afterload and improve forward stroke volume, though the nurse must vigilantly monitor blood pressure and systemic perfusion for profound hypotension.

Hypertrophic cardiomyopathy presents a starkly different physiological challenge. It involves left ventricular hypertrophy, often asymmetric septal hypertrophy, resulting in impaired diastolic filling while the ejection fraction is usually preserved or elevated. In hypertrophic obstructive cardiomyopathy, dynamic left ventricular outflow tract obstruction worsens when preload decreases, afterload decreases, or contractility increases. Think of the outflow tract like a narrow garden hose: reducing the water flowing in, dropping the backpressure, or squeezing the walls harder causes the passage to narrow even further. Consequently, positive inotropes and medications that substantially reduce preload or afterload worsen the obstruction and precipitate hypotension.

Physical assessment of hypertrophic obstructive cardiomyopathy demonstrates dynamic murmur changes. The systolic murmur intensifies during maneuvers that reduce ventricular volume, such as the Valsalva maneuver or standing, and softens with maneuvers that increase ventricular volume, such as squatting or passive leg raises. For symptomatic obstructive disease, beta-blockers serve as the general first-line therapy. Non-dihydropyridine calcium channel blockers represent acceptable alternatives when appropriate, requiring continuous nursing monitoring for hypotension and conduction abnormalities.

Stress, or Takotsubo, cardiomyopathy produces transient left ventricular systolic dysfunction, often characterized by apical ballooning. Although commonly thought of as a response to acute stress, a distinct physical or emotional trigger may be entirely absent, and coexisting coronary artery disease does not exclude the condition. Stress cardiomyopathy frequently mimics acute coronary syndrome, even presenting as ST-elevation myocardial infarction, yet cardiac biomarker elevations are typically modest relative to the extensive degree of ventricular dysfunction observed. If a patient develops cardiogenic shock from stress cardiomyopathy, the critical care nurse must assess for dynamic left ventricular outflow tract obstruction, as administering positive inotropes in that scenario will worsen the obstruction and intensify hypotension.