A disproportionate thickening of the interventricular septum is the hallmark of which form of cardiomyopathy?

A. Is caused by hypertrophy and hyperplasia with associated fibrosis of the intima and media: While these changes can occur in the vascular walls over time due to hypertension, they are not the primary cause of primary hypertension itself. Primary hypertension is more complex and multifactorial.

B. Underactivity of the sympathetic nervous system and the RAAS: Primary hypertension is characterized by increased activity of the sympathetic nervous system and the renin-angiotensin-aldosterone system (RAAS), not underactivity. Increased activity of these systems contributes to elevated blood pressure.

C. Is caused by complicated interactions of genetics and the environment without evidence of a specific causative agent: This statement accurately describes primary hypertension, which results from a combination of genetic predisposition and environmental factors such as diet, physical activity, and stress. There is no single identifiable cause for primary hypertension, making this the correct answer.

D. Is caused by systemic disease that raises peripheral vascular resistance and/or cardiac output: This statement pertains more to secondary hypertension, which is due to identifiable causes such as kidney disease, endocrine disorders, or other systemic diseases. Primary hypertension does not arise from a specific systemic disease but rather from multifactorial influences.

A. Septal: Septal cardiomyopathy typically refers to abnormalities in the interventricular septum and does not specifically address the rigidity and noncompliance of the myocardium that affects diastolic filling.

B. Restrictive: Restrictive cardiomyopathy is characterized by a rigid and noncompliant myocardium that impedes ventricular filling during diastole. This results in elevated pressures in the ventricles and may lead to heart failure symptoms due to poor filling capacity.

C. Infiltrative: Infiltrative cardiomyopathy involves the deposition of abnormal substances (such as amyloid or sarcoid) within the myocardial tissue, which can lead to stiffness. While this may contribute to restrictive physiology, "restrictive" is the more precise term for the condition described.

D. Hypertrophic: Hypertrophic cardiomyopathy is characterized by an abnormal thickening of the heart muscle, particularly the left ventricle. While this condition can affect diastolic filling, it is primarily due to muscle hypertrophy rather than rigidity and noncompliance of the myocardium.