Disorders of Cardiac Function: Anatomy & Physiology Study Guide

Anatomy & Physiology of the Heart

Cardiac Anatomy

The heart is a muscular organ responsible for pumping blood throughout the body. Its structure and function are essential for understanding cardiac disorders.

• Chambers: The heart has four chambers: right atrium, right ventricle, left atrium, and left ventricle.

• Valves: The atrioventricular (tricuspid and mitral) and semilunar (pulmonary and aortic) valves ensure unidirectional blood flow.

• Myocardium: Composed of cardiac muscle cells containing sarcomeres with actin and myosin filaments. Calcium influx is essential for contraction.

• Intercalated discs: Specialized connections between cardiac muscle cells that facilitate rapid electrical impulse conduction, allowing the heart to contract as a coordinated unit.

Cardiac Cycle

The cardiac cycle consists of alternating periods of contraction (systole) and relaxation (diastole) that drive blood flow.

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

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

• Heart Sounds: S1 (closure of AV valves), S2 (closure of semilunar valves), S3 (rapid ventricular filling), S4 (atrial contraction).

Cardiac Function

Cardiac output (CO) is the volume of blood the heart pumps per minute and is a key indicator of cardiac function.

• Formula: $CO = HR \times SV$

• Normal Ranges:

  • CO: 4-6 L/min

  • HR (Heart Rate): 70-100 bpm

  • EF (Ejection Fraction): 55-75%

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

• Stroke Volume (SV): The amount of blood ejected by the ventricle per beat.

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

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

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

Frank-Starling Mechanism: Increased preload (LVEDV) leads to increased stroke volume due to optimal overlap of actin and myosin filaments, up to a physiological limit.

Heart Failure

Definition and Types

Heart failure is a structural or functional disorder of the heart resulting in impaired cardiac output and/or congestion.

• Systolic Dysfunction (HFrEF): Heart failure with reduced ejection fraction (EF < 40%). Impaired contractility.

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

• Left-sided Heart Failure: Affects the left ventricle; leads to pulmonary congestion.

• Right-sided Heart Failure: Affects the right ventricle; leads to systemic venous congestion.

Common Causes

• Hypertension

• Coronary artery disease

• Myocardial infarction

• Valvular heart disease

• Cardiomyopathy

Pathophysiology and Compensatory Mechanisms

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

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

• Remodeling: Chronic overload leads to ventricular hypertrophy and changes in shape (concentric or eccentric), which can worsen function.

Clinical Manifestations

• Left-sided failure: Pulmonary congestion (dyspnea, orthopnea, crackles, cough), decreased CO (fatigue, confusion, renal insufficiency).

• Right-sided failure: Systemic congestion (peripheral edema, ascites, jugular venous distension, hepatomegaly).

• Other: Arrhythmias, sudden cardiac death.

Diagnosis

• BNP Levels:

  • <100 pg/mL: Heart failure unlikely

  • 100-500 pg/mL: Indeterminate

  • >500 pg/mL: Heart failure likely

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

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

Treatment Overview

• ACE inhibitors, ARBs, beta-blockers, aldosterone antagonists

• Diuretics for fluid overload

• Inotropes (e.g., digoxin) for contractility

• Management of underlying causes (e.g., hypertension, ischemia)

Valvular Disorders

Types and Definitions

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

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

• Prolapse: Valve leaflets bulge backward, sometimes leading to regurgitation.

Common Valvular Disorders

Disorder	Pathophysiology	Clinical Features
Aortic Stenosis	LV outflow obstruction, concentric LV hypertrophy	Angina, syncope, heart failure, systolic murmur
Mitral Stenosis	Impaired LV filling, LA enlargement	Exercise intolerance, pulmonary congestion, diastolic murmur
Aortic Regurgitation	LV volume overload, dilation	Signs of heart failure, diastolic murmur
Mitral Regurgitation	Papillary muscle/chordae dysfunction, LA pressure increase	Heart failure symptoms, systolic murmur

Effects on Ventricular Remodeling

• Stenosis leads to pressure overload and concentric hypertrophy.

• Regurgitation leads to volume overload and eccentric hypertrophy.

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 if slow, but rapid accumulation can cause tamponade.

• Cardiac Tamponade: Compression of the heart due to fluid accumulation, leading to impaired filling and decreased cardiac output.

Clinical Features and Diagnosis

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

• Pericardial Effusion: May be asymptomatic or cause dyspnea, muffled heart sounds.

• Cardiac Tamponade: Hypotension, jugular venous distension, muffled heart sounds (Beck's triad), pulsus paradoxus.

Treatment

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

• Pericardial Effusion/Tamponade: Pericardiocentesis (urgent for tamponade), treat underlying cause.

Summary Table: Key Cardiac Terms

Term	Definition
Preload	Ventricular wall stretch at end-diastole (LVEDV)
Afterload	Resistance to ventricular ejection
Contractility	Intrinsic strength of contraction
Cardiac Output (CO)	Volume of blood pumped per minute
Ejection Fraction (EF)	Fraction of end-diastolic volume ejected per beat

Example: In heart failure, increased preload may initially help maintain cardiac output (Frank-Starling mechanism), but chronic overload leads to pulmonary congestion and ventricular remodeling.

Additional info: This guide expands on the provided notes with definitions, clinical context, and summary tables to support exam preparation in Anatomy & Physiology.