Definitions of Hypovolemia and Cardiomyopathy
Hypovolemia
Hypovolemia is a critical decrease in intravascular volume caused by hemorrhage, inadequate fluid intake, or external fluid loss (such as diarrhea or excessive sweating), leading to diminished venous return (preload), decreased ventricular filling, reduced stroke volume, and ultimately decreased cardiac output unless compensated by increased heart rate. 1
Pathophysiology and Clinical Context
Hypovolemic shock occurs when the volume depletion becomes severe enough to cause hemodynamic instability and tissue hypoperfusion 1
The condition results in a small, hyperdynamic, unloaded ventricle with reduced left ventricular end-diastolic area on echocardiography 1
In profound hypovolemia, the inferior vena cava diameter becomes small (<10 mm) with inspiratory collapse in spontaneously breathing patients 1
Common Causes in Clinical Practice
Hemorrhage from trauma, surgery, or gastrointestinal bleeding 1
Inadequate fluid intake during prolonged travel or illness 1
External fluid losses including traveler's diarrhea (affecting 10-40% of travelers to high-risk regions), excessive sweating in hot climates (up to 1.2 L/day fluid loss), and increased respiratory water losses during air travel (approximately 200 mL/hour) 1
Iatrogenic causes in heart failure patients from excessive diuretic therapy, fluid restriction, or RAAS inhibitor use 1
Clinical Manifestations
Fatigue, exercise intolerance, weight loss, increased heart rate 1
Muscle cramps, weakness, postural dizziness 1
Low urine volume, hypotension, lethargy, confusion 1
Abdominal pain in severe cases 1
Cardiomyopathy
Cardiomyopathy is a myocardial disorder in which the heart muscle is structurally and functionally abnormal in the absence of coronary artery disease, hypertension, valvular disease, or congenital heart disease sufficient to cause the observed myocardial abnormality. 1
Major Classification Categories
According to the American Heart Association, cardiomyopathies are classified into distinct morphological and functional phenotypes 2:
Dilated cardiomyopathy: characterized by ventricular chamber enlargement and systolic dysfunction 2, 3
Hypertrophic cardiomyopathy: notable for massive ventricular hypertrophy without obvious cause, affecting 1 in 500 of the general population, caused by more than 1,400 mutations in 11 or more genes encoding cardiac sarcomere proteins 1, 4, 3
Restrictive cardiomyopathy: demonstrates restriction to ventricular filling due to restrictive forces in the endomyocardium 2, 3
Arrhythmogenic right ventricular cardiomyopathy: primarily affects the right ventricle 2
Inflammatory cardiomyopathy: includes myocarditis and related conditions 2
Further Subdivision
Primary cardiomyopathies: genetic, nongenetic, and acquired forms 2
Secondary cardiomyopathies: myocardial involvement as part of systemic disorders such as amyloidosis, systemic sclerosis, or infiltrative diseases 2
Clinical Characteristics
Hypertrophic cardiomyopathy features impaired diastolic and systolic function, tendency for sudden death, familial propensity, and cardiac manifestations in approximately 80% of patients with myotonic dystrophy type 1 1, 2, 3
Dilated cardiomyopathy demonstrates severe systolic failure progressing to congestive heart failure, usually without familial tendency 3
Most patients with nonischemic cardiomyopathy have no identifiable causative factor (idiopathic dilated cardiomyopathy), though some cases relate to systemic disorders, cardiotoxic agents (alcohol, cocaine, anthracyclines), or myocardial inflammation 1
Important Clinical Pitfall
Hypovolemia can precipitate acute decompensation in cardiomyopathy patients, particularly in hypertrophic cardiomyopathy where volume depletion combined with catecholamine therapy can cause severe left ventricular outflow tract obstruction and hemodynamic collapse 4, 5, 6. During anesthesia or critical illness in these patients, it is essential to prevent hypovolemia and maintain adequate preload 4.