Anatomy and Function of the Heart

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Questions and Answers

What are the three layers of the heart from inside to outside?

Endocardium, Myocardium, Epicardium

What proteins are part of the sarcomere in cardiac myocytes?

Myosin

Actin

Troponin and tropomyosin

All of the above (correct)

The cardiac muscle's striated appearance is due to a series of string of ________.

sarcomeres

Valves in the heart ensure bidirectional flow of blood.

False Signup and view all the answers

Match the following heart valves with their composition:

Tricuspid and Mitral valves = Leaflets Pulmonary and Aortic valves = Semilunar valves with cusps Valve structures = Fibrosa (collagen), Spongiosa (loose connective tissue), Venticularis or atrialis (elastin), Endothelial cells Signup and view all the answers

What factors predispose to the development of Infective Endocarditis (IE)?

Seeding of blood with microbes and haemodynamic disturbance occurring across deformed heart valve. Signup and view all the answers

Which valve is most commonly affected by Infective Endocarditis?

Mitral valve Signup and view all the answers

Non-bacterial non-thrombotic endocarditis is also known as Libman-Sacks endocarditis.

True Signup and view all the answers

______ valve is most commonly affected by Non-Bacterial Thrombotic Endocarditis (NBTE).

Mitral Signup and view all the answers

Match the following complications with Myocardial Infarction:

Arrhythmias and conduction defects = Possible sudden death Congestive Cardiac Failure = Extension of infarct or re-infarction Mural thrombus = Possible Embolization Myocardial wall rupture = Possible valvular insufficiency Signup and view all the answers

Which test is more specific for detecting myocardial injury compared to Creatinine Kinase (CK)-MB?

Troponins Signup and view all the answers

What are some complications of Myocardial Infarction?

Sudden cardiac death, Acute ventricular fibrillation, Myocardial rupture, Congestive heart failure, Thrombo-embolism Signup and view all the answers

Which of the following are causes of Myocarditis?

All of the above Signup and view all the answers

______ cardiomyopathy is characterized by gradual development of heart failure and dilatation of the heart.

Dilated Signup and view all the answers

Hypertrophic Cardiomyopathy is characterized by symmetrical hypertrophy of the heart muscle.

False Signup and view all the answers

Match the following heart tumors with their descriptions:

Myxoma = Most common primary tumor in adults with gelatinous mass Rhabdomyoma = Most common primary heart tumor in infants with gray-white myocardial masses Fibroma = Heart tumor composed of fibrous tissue Angiosarcoma = Primary tumor with malignant endothelial cells Signup and view all the answers

What is the definition of Congenital Heart Disease?

Structural abnormalities of the heart or great vessels present at birth Signup and view all the answers

Which aetiological factor is associated with Trisomy 21 (Downs syndrome) in Congenital Heart Disease?

Ventricular Septal Defect (VSD) Signup and view all the answers

Study Notes

The Pathology of the Heart

Normal Heart Structure and Function

Normal weight: 250-300g for females, 300-350g for males
Left ventricular (LV) thickness: 1.3-1.5cm
Right ventricular (RV) thickness: 0.3-0.5cm
Blood supply: Right and Left coronary arteries, which behave as end-arteries functionally
The heart has three layers: endocardium, myocardium, and epicardium
The main functional unit is the myocardium, composed of cardiac myocytes
Ventricular myocytes are the most specialized
The contractile unit of the myocytes is the sarcomere, composed of myosin, actin, troponin, and tropomyosin

Cardiac Muscle Striated Appearance

Due to series of sarcomeres
Myosin pulls actin towards the center of the cell, creating shortening of the functional unit, which leads to contraction
Increase in degree of shortening leads to increase in contraction
Moderate dilation of chambers leads to increase in shortening
Further dilation causes reduction in overlap of myosin and actin, leading to reduced contraction seen in heart failure

Atrial Myocytes

Smaller than ventricular myocytes
Less well-arranged
Atrial cell cytoplasm contains specific atrial granules, which store atrial natriuretic peptide, with regulatory functions such as vasodilation, natriuresis, and diuresis

Intercalated Discs

Connect cardiac myocytes, containing specialized intracellular junctions
Function in mechanical and electrical coupling
Example: gap junction

Valves

Ensure unidirectional flow of blood
Composed of Tricuspid, Pulmonary, Mitral, and Aortic valves
Tricuspid and Mitral valves have leaflets, while Pulmonary and Aortic valves have cusps
Valves are composed of fibrosa, spongiosa, ventricularis, or atrialis, and endothelial cells
Valves are repaired by interstitial cells
Other structures related to valves include chordae tendinae and papillary muscles
Valves can suffer from prolapse, calcification, and fibrosis

Conduction System

SA (Sino-Atrial) pacemaker node: located between right atrial appendages and superior vena cava
AV (Atrio-Ventricular) node: located in the right atrium, along the atrial septum
Bundle of His: located in the right atrium, extending to the summit of the ventricular septum
Right and Left Bundle branches: extend to different ventricles
SA node beats at a rate of 60-100/minute
Beat is moderated by the AV node and regulated by the autonomic nervous system

Coronary Arteries

Originate from ostia beneath the aortic valves
Left coronary arteries: Left Anterior Descending (LAD), Left Circumflex (LCx)
Right Coronary Artery (RCA)
Right Coronary Artery is dominant in most cases, supplying the posterior 1/3 of the cardiac septum

Aging and the Heart

Heart undergoes atrophy with age
Accumulation of age pigment, lipofuscin, which is brown in color
Brown atrophy is seen in cachexia and cancer

Congestive Cardiac Failure

Heart is unable to maintain an output sufficient for the metabolic requirements of the tissues and organs
Can appear as the end stage of many forms of chronic heart disease
Causes:
- Loss of cardiac myocytes
- Impaired contractility
- Mechanical cardiac overload
- Impaired filling of the chambers

Left-Sided Heart Failure

Causes:
- Ischaemic heart disease
- Systemic hypertension
- Rheumatic heart disease
- Myocardial diseases

Organ Changes

Lungs:
- Increased hydrostatic pressure
- Pulmonary oedema and congestion
- Heart failure cells
- Brown induration of the lungs
Kidneys:
- Stimulation of the renin-angiotensin system
- Salt and water retention
- Acute tubular necrosis
- Pre-renal azotaemia
Brain:
- Cerebral hypoperfusion
- Hypoxic symptoms (e.g. irritability, stupor, and coma)

Right-Sided Heart Failure

Causes:
- Cor pulmonale
- Tricuspid and Pulmonary valve lesions
- Congenital heart disease associated with left-to-right shunt
- Left heart failure
Organ Changes:
- Liver:
  - Congestive hepatomegaly
  - Central haemorrhagic necrosis
  - Nutmeg appearance
  - Cardiac sclerosis
  - Cardiac cirrhosis
- Spleen:
  - Congestive splenomegaly
  - Siderofibrotic nodules (Ghandy-Gamna bodies)
- Subcutaneous tissue:
  - Pitting pedal oedema
  - Anasarca
- Body cavities:
  - Pleural, pericardial, and peritoneal effusion

Hypertensive Heart Disease

Definition: Response of the heart to increased demands induced by systemic or pulmonary hypertension
Systemic hypertensive heart disease:
- LVH (usually concentric) in the absence of other vascular pathology
- History of hypertension
Causes of Hypertension:
- Essential hypertension (90-95%)
- Secondary hypertension (5-10%)
- Renal diseases
- Endocrine diseases
- Vascular diseases
- Neurogenic diseases
Pathogenesis:
- Increased pressure overload → myocardial hypertrophy
- Cardiomegaly and LV thickness

Rheumatic Heart Disease

Definition: Not directly caused by the organism, but by antibodies to streptococci that cross-react with tissues of the heart, kidneys, etc.
Commoner in blacks, and in warmer climates
Develops in 50-75% of childhood cases
35% of adults
Organ Changes:
- Pericardium:
  - Fibrinous or sero-fibrinous exudate
  - Bread and butter pericarditis
- Myocardium:
  - Aschoff bodies (foci of fibrinoid necrosis surrounded by lymphocytes, macrophages, and plasma cells)
  - Death may occur in acute RF from CCF
- Valves:
  - Acute valvulitis: hyperaemia, oedema, and thickening of the valves
  - Chronic valvulitis: progressive scarring and deformity of the valve leaflets
  - McCallum's plaque (fibrous plaques on the subendocardium of the left atrium)
Extra-cardiac lesions:
- Subcutaneous nodules
- Polyarthritis (migratory)
- Pleural and pericardial effusions
- CNS: Sydenham's chorea (characterized by rapid, irregular, and purposeless movements)

Infective Endocarditis

Definition: Invasion of the heart valve or the mural endocardium by infective agents
Two forms:
- Acute (fatal, fulminant infection)
- Subacute (smouldering, indolent illness)
Epidemiology and pathogenesis:
- Congenital heart disease
- Valvular defects
- Rheumatic heart disease
- Prosthetic valve
- Immunosuppression
- Diabetes mellitus
- Chronic alcoholics
- Intravenous drug abuse
- Commoner in males above 50 years
Bacteriology:
- Streptococcus viridans (50%)
- Staphylococcus aureus (20%)
- Streptococcus pneumonia
- HACEK group (Haemophilus, Actinobacillus, Cardiobacterium, Eikenella, Kingella)
Pathology:
- Vegetations on the heart valve
- Fibrinous, granular, or ulcerative lesions
- Heart failure
- Embolization
- Immune complex disease
- Osteomyelitis### Sudden Death
Sudden death occurs within an hour of symptom onset
Associated with severe coronary atherosclerosis (>75% lumina narrowing)
Complications include thrombus or plaque hemorrhage or rupture
Mechanism is usually an arrhythmia
Aortic dissection can also cause sudden collapse

Complications of MI

Ischaemic cardiomyopathy: severe atherosclerosis of all major arteries, inadequate vascular supply, myocyte loss, fibrosis, decreased compliance, compensatory hyperplasia, and hypertrophy
Common complications: cardiac arrhythmias (75-95%), sudden death (20%), cardiogenic shock (10-15%), left ventricular aneurysm, and mural thrombosis (15-40%)
Uncommon complications: myocardial rupture, papillary muscle rupture, re-infarction, infarct extension, post-infarction pericarditis, and Dressler's syndrome

Factors Determining Infarct Size

Size of the myocardial bed at risk and its metabolic/oxygen needs
Duration of obstruction
Coronary artery anatomy, dominance, and collaterals
Site of coronary artery obstruction
Severity of obstruction
Rate at which obstruction developed

Laboratory Diagnosis of MI

None of the available tests are specific or sensitive
Tests must be correlated with clinical symptoms, ECG, and angiography
Timing is crucial

Creatinine Kinase

Total creatinine is from both skeletal and cardiac origin; non-specific
MB, MM, and BB fractions
MM: cardiac and skeletal, with isoenzymes
MB: specific for cardiac, 2% is skeletal
BB: found in brain, bowel, and bladder, not measured routinely
CK-MB is measured every 2-4 hours for 9-12 hours after patient is first seen

Troponins

Troponins I and T are structural components of cardiac muscle and released into blood with myocardial injury
Very specific, more than CK-MB
Begins to rise within 3-12 hours, remains elevated for 5-9 days for troponin I and up to 2 weeks for troponin T
Difficult to diagnose re-infarction because of the prolonged elevation
Troponin T is not very specific, as it can appear with skeletal myopathies or renal failure

Myoglobins

Myoglobin is a protein found in skeletal and cardiac muscle
Elevated before CK-MB, but not specific
Lactate dehydrogenase (LDH) begins to rise in 12-24 hours, peaks in 2-3 days, and dissipates in 5-14 days
LDH isoenzymes are more specific

Prevention of MI

Control of hypertension and diabetes
Drug and dietary treatment of hypercholesterolemia
Dietary reduction of plasma cholesterol and LDL
Reduction of fat intake
Avoidance of obesity
Moderation of salt intake
Cessation of smoking
Exercise

Cardiomyopathies

Dilated cardiomyopathy: characterised by gradual development of heart failure associated with 4-chamber hypertrophy and dilatation of the heart
Hypertrophic cardiomyopathy: characterised by heavy hypercontracting heart, asymmetrical septal hypertrophy, and AD in 50% of cases
Restrictive cardiomyopathy: characterised by endomyocardial fibrosis, Loeffler's endocarditis, and endocardial fibroelastosis

Myocarditis

Aetiology: infections, immune-mediated reactions, and toxins
Morphology: acute phase, enlarged, flabby heart, cut surface shows mottling of ventricular wall, microhaemorrhages
Histology depends on the causative agent

Cardiac Tumours

Primary tumours are rare, metastatic tumours are common (5% of patients dying of cancer)
Primary tumours in descending order of frequency: myxoma, fibroma, lipoma, papillary fibroelastoma, rhabdomyoma, and angiosarcoma
Myxoma: most common primary tumour in adults, 90% occur in the atria, single tumour, 1-10cm in diameter, sessile or pedunculated, gelatinous mass

Congenital Heart Disease

Definition: structural abnormalities of the heart or great vessels present at birth
Incidence: 6-8 per 1000 live births
Aetiology: mostly unknown, associated with chromosomal abnormalities, environmental factors, and maternal infection

Classification of CHD

Acyanotic with shunt (Lt to Rt shunt): PDA, VSD, ASD
Cyanotic (Rt to Lt shunt): tetralogy of Fallot, late cyanotic VSD (Eisenmenger complex), transposition of great vessels, total anomalous pulmonary venous connection, persistent truncus arteriosus, tricuspid atresia
Acyanotic (no shunt): coarctation of the aorta, aortic stenosis and atresia, pulmonary stenosis and atresia

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Description

Test your knowledge of the heart's structure and function, including its layers, sarcomere proteins, and valve composition. Learn about the factors that lead to Infective Endocarditis.