Chapter 27: Disorders of Cardiac Function & Circulatory Shock

The chapter provides a comprehensive analysis of various cardiac disorders, heart failure syndromes, and circulatory shock states. Disorders of cardiac function are introduced, starting with conditions affecting the pericardium, such as acute pericarditis, pericardial effusion, and the severe compression known as cardiac tamponade. A significant portion details Coronary Artery Disease (CAD), emphasizing how coronary atherosclerosis and fixed/unstable plaques lead to an imbalance in myocardial oxygen supply and demand. This imbalance manifests as chronic ischemic heart disease (e.g., stable angina) or Acute Coronary Syndrome (ACS), which includes unstable angina (UA), NSTEMI, and STEMI, differentiated by ECG changes and the release of cardiac-specific biomarkers like troponin. Management of ACS focuses urgently on reperfusion via pharmacologic agents, percutaneous coronary intervention (PCI), or coronary artery bypass grafting (CABG). The text explores diverse Cardiomyopathies—classified as primary (genetic, mixed, acquired) or secondary—including hypertrophic cardiomyopathy (HCM), dilated cardiomyopathy (DCM), and myocarditis, which primarily cause mechanical or electrical dysfunction. Infectious and immunologic diseases like Infective Endocarditis and Rheumatic Heart Disease are covered, often resulting in lasting Valvular Heart Disease defined by hemodynamic derangements such as stenosis or regurgitation affecting blood flow, notably in the mitral and aortic valves. Heart Failure (HF) is detailed by its types (systolic vs. diastolic, right vs. left) and characterized by decreased cardiac output and congestion. Key physiological compensations like the Frank-Starling mechanism, sympathetic nervous system activation, and the renin–angiotensin–aldosterone mechanism are explored, highlighting how chronic activation eventually leads to pathological ventricular remodeling. Specialized sections discuss congenital heart defects in infants and children (like VSD and Tetralogy of Fallot) and acquired pediatric heart disease (Kawasaki disease). Finally, the chapter addresses Circulatory Shock—the failure to supply tissues with adequate oxygen—classifying it into four main types: Cardiogenic (pump failure), Hypovolemic (volume loss), Obstructive, and Distributive (excessive vasodilation, including septic, neurogenic, and anaphylactic shock). Cellular mechanisms involve a shift to anaerobic metabolism and lactic acid production, leading ultimately to severe complications like Acute Lung Injury/ARDS and Multiple Organ Dysfunction Syndrome (MODS).