Pathophysiology of Cardiovascular Diseases

Epicardium

The protective outer layer of the heart muscle.

Myocardium

The middle muscular layer and the strongest part of the heart, responsible for contraction and pumping.

Endocardium

The innermost layer of the heart with a smooth lining and muscles to prevent clot formation.

Cardiomyocytes

Specialized cells that compose the heart muscle.

Pericardium

A protective layer enclosing the heart consisting of inner visceral and outer parietal layers with lubricating fluid.

Normal Heart Weight

A muscular organ weighing between $250-350\,g$.

Normal Adult Blood Volume

Approximately $5\,\text{liters}$, which passes through the heart once every minute.

Tricuspid (AV) valve

The valve that separates the right atrium from the right ventricle.

Mitral (Bicuspid) valve

The valve that separates the left atrium from the left ventricle.

Pulmonary valve

The valve that separates the right ventricle from the pulmonary artery.

Aortic valve

The valve that separates the left ventricle from the aorta.

SA node

The part of the conduction system that generates the initial electrical impulse causing the atria to contract.

Purkinje fiber

Fibers that distribute the electrical impulse throughout the ventricular muscle to cause simultaneous contraction.

Arteries

Blood vessels that distribute oxygenated blood away from the heart to the tissues.

Veins

Blood vessels that collect deoxygenated blood from the tissues and return it back to the heart.

Capillaries

The sites of gas, nutrient, and waste exchange between the blood and tissue cells.

Systemic circulation

The loop that allows oxygenated blood and nutrients to reach the rest of the body.

Pulmonary circulation

The loop that allows for the oxygenation of the blood in the lungs.

Coronary Circulation

The circulation specifically dedicated to supplying the heart organ itself.

Systolic dysfunction

A pump failure where the cardiac muscle contracts weakly and chambers cannot empty properly.

Diastolic dysfunction

A pump failure where the muscle cannot relax sufficiently to permit ventricular filling.

Obstruction to flow

Pathophysiology caused by lesions preventing valve opening or increased chamber pressure, such as systemic hypertension.

Regurgitant flow

Valve pathology that allows backward flow of blood, resulting in increased volume workload.

Shunted flow

Defects that inappropriately divert blood from one chamber or vessel to another, leading to pressure and volume overloads.

Heart Failure (HF)

A progressive condition where the heart cannot pump effectively to supply sufficient oxygen to peripheral organs for metabolic function.

Ischemic Heart Disease (IHD)

A common cause for global CVD burden and heart failure; accounted for $19.3\%$ of total deaths in the Philippines from Jan-Nov 2024.

RAAS (Renin–Angiotensin–Aldosterone System)

A neurohormonal pathway activated in heart failure that leads to sodium and water retention.

Dyspnea on exertion

A clinical manifestation of left-sided heart failure involving shortness of breath during physical activity.

Orthopnea

A symptom of left-sided heart failure where a patient has difficulty breathing while lying flat.

Paroxysmal nocturnal dyspnea

A condition in left-sided heart failure involving sudden attacks of shortness of breath at night during sleep.

Ascites

The accumulation of fluid in the abdominal cavity, often seen in right-sided heart failure.

Jugular venous distention

A sign of right-sided heart failure involving visible bulging of the neck veins.

Cardiac cachexia

Systemic muscle wasting associated with advanced heart failure.

BNP or NT-proBNP

Laboratory markers that are elevated in patients with heart failure.

Echocardiography

The gold standard imaging procedure for heart failure used to measure ejection fraction.

ACE inhibitors / ARBs

Pharmacologic treatments for heart failure intended to reduce afterload and slow cardiac remodeling.

Volume-Pressure Relationship

A basic principle where volume is always equal to pressure ($V=P$), meaning higher blood volume leads to higher blood pressure, and lower blood volume leads to lower blood pressure.

Epicardium

The protective outer layer of the heart wall.

Myocardium

The powerful, strongest middle muscular layer of the heart responsible for contraction and pumping.

Endocardium

The innermost layer of the heart with a smooth lining and smooth muscles to prevent clot formation.

Cardiomyocytes

The specialized cells that compose the heart muscle tissue.

Pericardium

A protective layer enclosing the heart consisting of inner visceral and outer parietal layers with lubricating fluid.

Tricuspid Valve

The atrioventricular (AV) valve that separates the right atrium and the right ventricle.

Mitral Valve

Also known as the Bicuspid valve, it separates the left atrium and the left ventricle.

Pulmonary Valve

The valve that separates the right ventricle and the pulmonary artery.

Aortic Valve

The valve that separates the left ventricle and the aorta.

Electrical Conduction Pathway

The built-in system that determines heartbeat timing via the following sequence: SA node $\rightarrow$ atria $\rightarrow$ AV node $\rightarrow$ bundle of His $\rightarrow$ Purkinje fibers.

Systolic Dysfunction

A failure of the pump where cardiac muscle contracts weakly and chambers cannot empty properly.

Diastolic Dysfunction

A failure of the pump where the heart muscle cannot relax sufficiently to permit ventricular filling.

Regurgitant Flow

A mechanism of pathophysiology where valve pathology allows the backward flow of blood, increasing volume workload.

Cardiac Output ($CO$)

The amount of blood ejected from the left ventricle; normally, it equals venous return.

Left-Sided Heart Failure

Heart failure commonly caused by systemic hypertension or ischemic heart disease, leading to pulmonary congestion and edema.

Right-Sided Heart Failure

Heart failure most often caused by left-sided heart failure, resulting in peripheral edema and visceral congestion.

Cardiac Remodeling

A pathophysiologic mechanism involving ventricular hypertrophy and dilation that leads to a progressive decline in cardiac function.

Echocardiography

The gold standard diagnostic tool for heart failure that measures ejection fraction and assesses ventricular function.

Cardiac Cachexia

A systemic effect of heart failure characterized by muscle wasting.

Right-to-Left Shunt

A congenital heart defect (e.g., Tetralogy of Fallot) where pulmonary circulation is bypassed, causing cyanosis.

Left-to-Right Shunt

The most common CHD (e.g., ASD, VSD, PDA) where blood flow into pulmonary circulation increases, typically without cyanosis.

Atresia

A congenital malformation characterized by the complete obstruction of a chamber, valve, or vessel.

Ischemic Heart Disease ($IHD$)

A syndrome caused by myocardial ischemia, an imbalance between cardiac blood supply and oxygen requirements.

Angina Pectoris

Exertional chest pain typically due to atherosclerotic disease causing greater than $70\%$ fixed stenosis.

Myocardial Infarction ($MI$)

The necrosis of heart muscle resulting from ischemia, often caused by acute thrombosis after plaque disruption.

Myocardial Ischemia

A condition of reduced blood flow to the heart muscle that may be reversible if blood flow is promptly restored.

Cardiac Arrhythmias

Abnormalities in heart rhythm caused by disturbances in electrical impulse generation or conduction.

Hypertensive Heart Disease ($HHD$)

Structural and functional changes in the heart, such as left ventricular hypertrophy, caused by chronic high blood pressure.

Renin

An enzyme released by the kidneys when blood pressure or sodium is low to start the RAAS cascade.

Angiotensin II

One of the strongest vasoconstrictors in the body that raises blood pressure quickly and stimulates aldosterone.

Aldosterone

A hormone that signals the kidneys to retain sodium and water, thereby increasing blood volume.

Atrial Natriuretic Peptide ($ANP$)

A hormone released by the heart when volume is high that promotes sodium and water excretion to lower blood pressure.

Atherosclerosis

A chronic inflammatory disease characterized by the buildup of lipid-rich plaques within the arterial wall.

Foam Cells

Formed during atherosclerosis when macrophages attract and ingest oxidized LDL cholesterol within the arterial wall.