Disorders of Cardiac Function: Anatomy & Physiology Study Guide

Disorders of Cardiac Function

Introduction

This study guide provides an overview of the anatomy and physiology of the heart, focusing on disorders of cardiac function. It covers the structure and function of the heart, mechanisms of heart failure, valvular disorders, and pericardial diseases, with emphasis on clinical manifestations and compensatory mechanisms.

Anatomy & Physiology Overview

Cardiac Anatomy

• Heart Chambers: The heart consists of four chambers: right atrium, right ventricle, left atrium, and left ventricle.

• Valves: The heart contains four main valves: tricuspid, pulmonary, mitral (bicuspid), and aortic valves. These ensure unidirectional blood flow.

• Chordae Tendineae and Papillary Muscles: These structures anchor the atrioventricular valves (tricuspid and mitral) and prevent prolapse during ventricular contraction.

• Myocardium: Composed of cardiac muscle cells (myocytes) containing sarcomeres with actin and myosin filaments. Intercalated discs facilitate coordinated contraction as a functional syncytium.

Cardiac Cycle

• Systole: Period of ventricular contraction and blood ejection. Includes isovolumetric contraction (all valves closed) and ventricular ejection (aortic and pulmonary valves open).

• Diastole: Period of ventricular relaxation and filling. Includes isovolumetric relaxation (all valves closed) and ventricular filling (mitral and tricuspid valves open).

• Heart Sounds: S1 (closure of AV valves), S2 (closure of semilunar valves), S3 and S4 (abnormal, associated with heart failure).

Cardiac Function

• Cardiac Output (CO): The volume of blood pumped by the heart per minute. $CO = HR \times SV$

• Normal Ranges: CO: 4-6 L/min, HR: 70-100 bpm, Ejection Fraction (EF): 55-75%

• Ejection Fraction (EF): $EF = \frac{SV}{LVEDV}$

• Preload: The degree of stretch of cardiac muscle fibers at the end of diastole (LVEDV).

• Afterload: The resistance the ventricle must overcome to eject blood.

• Contractility: The intrinsic strength of cardiac muscle contraction, independent of preload and afterload.

Heart Failure

Definition and Types

• Heart Failure (HF): A structural or functional disorder causing low cardiac output and/or congestion.

• Systolic Dysfunction (HFrEF): Heart failure with reduced ejection fraction (EF < 40%), due to impaired contractility.

• Diastolic Dysfunction (HFpEF): Heart failure with preserved ejection fraction (EF > 50%), due to impaired ventricular relaxation/filling.

• Left-sided HF: Affects pulmonary circulation, leading to pulmonary congestion.

• Right-sided HF: Affects systemic circulation, leading to peripheral edema.

Common Causes

• Hypertension

• Coronary artery disease

• Myocardial infarction

• Valvular heart disease

• Cardiomyopathy

Comparison of Systolic vs. Diastolic Dysfunction

	Systolic (HFrEF)	Diastolic (HFpEF)
Mechanism	Impaired contractility	Impaired relaxation/filling
Ejection Fraction	<40%	>50%
LVEDV	Increased	Decreased
Common Causes	Ischemic heart disease, MI	Hypertension, LV hypertrophy

Compensatory Mechanisms

• Neurohumoral Activation: Sympathetic nervous system (SNS), renin-angiotensin-aldosterone system (RAAS), and antidiuretic hormone (ADH) increase HR, contractility, and fluid retention.

• Frank-Starling Mechanism: Increased preload stretches myocardium, enhancing contractility up to a point.

• Natriuretic Peptides: ANP and BNP are released in response to volume overload, promoting natriuresis and vasodilation.

• Remodeling: Chronic overload leads to hypertrophy and changes in ventricular shape, which may worsen function.

Clinical Manifestations

• Left-sided HF: Pulmonary congestion (dyspnea, orthopnea, crackles), decreased CO (fatigue, confusion), pulmonary edema.

• Right-sided HF: Peripheral edema, ascites, jugular venous distension, hepatomegaly.

• General: Tachycardia, arrhythmias, sudden cardiac death.

Diagnosis

• BNP Levels: <100 pg/mL (HF unlikely), 100-500 pg/mL (uncertain), >500 pg/mL (HF likely)

• Echocardiography: Assesses ejection fraction, chamber size, wall motion.

• Chest X-ray: May show cardiomegaly, pulmonary edema.

Treatment

• ACE inhibitors, ARBs, beta-blockers, diuretics, aldosterone antagonists, digoxin, vasodilators.

• Therapies target preload, afterload, contractility, and neurohormonal activation.

Valvular Disorders

Types and Definitions

• Stenosis: Narrowing of valve opening, impeding forward flow.

• Regurgitation (Insufficiency): Incomplete valve closure, allowing backward flow.

• Prolapse: Valve inversion into the atrium, often with regurgitation.

Common Valvular Disorders

• Aortic Stenosis: Resistance to LV outflow, causing concentric LV hypertrophy. Symptoms: angina, syncope, heart failure, systolic murmur.

• Mitral Stenosis: Impaired LV filling, enlarged LA, pulmonary congestion, right-sided HF, diastolic murmur.

• Aortic Regurgitation: Augmented LV filling, LV dilation, signs of HF, diastolic murmur.

• Mitral Regurgitation: Associated with papillary muscle/chordae tendineae dysfunction, LA pressure increase, LV dilation, systolic murmur.

Effects and Clinical Manifestations

• Altered intracardiac blood flow, heart murmurs, ventricular remodeling, symptoms of heart failure.

Pericardial Disorders

Types

• Pericarditis: Inflammation of the pericardium, often viral in origin (e.g., coxsackievirus).

• Pericardial Effusion: Accumulation of fluid in the pericardial space; may be asymptomatic or cause tamponade.

• Cardiac Tamponade: Rapid accumulation of pericardial fluid causing compression of the heart and decreased cardiac output.

Pathophysiology and Clinical Presentation

• Acute Pericarditis: Sharp chest pain, worsens with inspiration, relieved by sitting forward, pericardial friction rub, ECG changes (ST elevation, PR depression), elevated WBC/CRP.

• Pericardial Effusion: Small effusions may be asymptomatic; large or rapidly accumulating effusions can cause tamponade (hypotension, jugular venous distension, muffled heart sounds, pulsus paradoxus).

• Cardiac Tamponade: Life-threatening; requires urgent pericardiocentesis.

Treatment

• Pericarditis: NSAIDs, colchicine, corticosteroids (if severe).

• Pericardial effusion/tamponade: Pericardiocentesis, treat underlying cause.

Summary Table: Key Cardiac Disorders

Disorder	Main Feature	Key Symptoms	Common Causes
Heart Failure (HFrEF)	Reduced EF, impaired contractility	Dyspnea, fatigue, edema	MI, hypertension
Heart Failure (HFpEF)	Preserved EF, impaired filling	Dyspnea, exercise intolerance	Hypertension, LV hypertrophy
Aortic Stenosis	LV outflow obstruction	Angina, syncope, murmur	Calcific degeneration
Mitral Regurgitation	Backflow into LA	HF symptoms, murmur	Papillary muscle dysfunction
Pericarditis	Pericardial inflammation	Chest pain, friction rub	Viral infection
Cardiac Tamponade	Compression by fluid	Hypotension, JVD, muffled heart sounds	Pericardial effusion