Heart Pathology

• Heart


  • Remarkably efficient, durable, and reliable pump
  • Distributes more than 6,000 L of blood daily
  • Beats 30-40 million times a year
  • Provides tissues with vital nutrients and facilitates waste excretion
• Heart weight


  0.4-0.5% of the body weight (250 to 320g in females, 300-360g in males)
• Right ventricular wall thickness

  0.3-0.5 cm

  
• Left ventricular wall thickness

  1.3-1.5 cm

  
• Increase in weight or thickness

  Indicates hypertrophy
• Enlarged chamber size


  Implies dilation
• Increase in weight or size or both

  Resulting from hypertrophy or dilation is called cardiomegaly
• Major epicardial coronary arteries

  • Left Anterior Descending (LAD)
  • Left Circumflex (LCX)
  • Right Coronary Artery

  
• Divisions of LAD


  Called diagonal branches
• Divisions of LCX


  Called marginal branches
• Conduction system


  • Frequency of electrical impulses is sensitive to neural inputs, extrinsic adrenergic agents, hypoxia, potassium concentration
• Components of the conduction system

  • Sinoatrial Node (SA) pacemaker
  • Atrioventricular Node (AV)
  • Bundle of His
  • Right and left bundle branches
  • Purkinje network
• Congenital heart diseases


  Abnormalities of the heart or great vessels that are present at birth

  
• Most congenital heart diseases arise from faulty embryogenesis during gestational weeks 3 through 8, when major CVS structures form and begin

  
• Significant heart malformations are common among premature infants and stillborn

  
• Defects that affect individual chambers or discrete regions of the heart are often compatible with maturation and life

  
• Types of congenital heart defects

  • Septation defects (ASD/VSD)
  • Unilateral obstructions
  • Outflow tract anomalies

  
• Causes of congenital heart diseases

  • Sporadic genetic abnormalities
  • Single gene mutations
  • Small chromosomal losses
  • Additions or deletions of whole chromosomes (Trisomy 21 or Down Syndrome)
  • Congenital rubella infection
  • Teratogens
  • Gestational DM
  • Folate supplementation
  • Maternal age

  
• Major categories of clinical features of congenital heart diseases

  • Malformations that causes Left-to-right shunts
  • Malformations that causes Right-to-left shunts
  • Malformations that causes Obstructions

  
• Shunt


  An abnormal communication between chambers or blood vessels, these permit blood flow down pressure gradients from the left (systemic) to right (pulmonary) side or vice versa
• Right-to-left shunting


  Can cause hypoxemia and cyanosis because pulmonary circulation is bypassed and poorly oxygenated blood enters the systemic circulation

  
• Right-to-left shunting


  Can also cause paradoxical embolism by allowing emboli to enter the systemic circulation
• Cyanosis


  Severe, long-standing cyanosis causes distal blunting and enlargement (clubbing) of the fingertips and the toes (called hypertrophic osteoarthropathy), as well as polycythemia
• Common causes of right-to-left shunts

  • Tetralogy of Fallot
  • Transposition of Great Arteries
  • Persistent Truncus Arteriosus
  • Tricuspid Atresia
  • Total anomalous pulmonary venous connection

  
• Left-to-right shunts


  Increase pulmonary blood flow, but are not initially associated with cyanosis

  
• Left-to-right shunts


  Chronically elevate both volume and pressure in the pulmonary circulation
• Pulmonary arteries


  Respond by undergoing medial hypertrophy and vasoconstriction

  
• Prolonged vasoconstriction


  Stimulates the development of irreversible obstructive intimal lesions
• Right ventricle


  May also undergo hypertrophy
• Eisenmenger Syndrome


  When the original right-to-left becomes left-to-right, introducing poorly oxygenated blood to the circulation
• Pulmonary hypertension


  Marks irreversibility of congenital heart disease lesions

  
• Obstructive congenital heart diseases

  Occur when there is narrowing of cardiac chambers, valves, or blood vessels

  
• Atresia


  Complete obstruction
• In Tetralogy of Fallot, both obstruction and shunt is present
• Atrial septal defect (ASD)


  Abnormal, fixed openings in the atrial septum caused by incomplete tissue formation that allows communication of blood between the left and right atrium

  
• ASD should not be confused with patent foramen ovale (POF) which represents the failure to close of a foramen
• ASD blood flow


  RA → RV → PA → Lungs → PV → LA –(ASD)→ RA

  
• Right ventricular hypertrophy (RVH)


  Happens because of the excess blood volume dumped into the right side of the heart

  
• Patent foramen ovale


  Closes permanently in 80% of the population by 2 years of age
• Patent foramen ovale


  In the remaining 20%, the unsealed flap can open if right-sided pressures become elevated