Cardiac Physiology and Anatomy Overview

Cardiac Physiology Overview

• The heart has 4 chambers: 2 atria and 2 ventricles
• It has 4 valves: mitral, tricuspid, aortic, and pulmonary
• The heart's function is based on a coordinated system called a functional syncytium
• Cardiac muscle cells are stimulated as a unit.
• The main energy source for cardiac muscle is fat, not glucose
• Blood flow is mainly during diastole, rather than systole

Anatomy of the Heart

• The diagram identifies key heart structures: superior vena cava, inferior vena cava, right atrium, right ventricle, left atrium, left ventricle, right pulmonary arteries, pulmonary trunk, left pulmonary arteries, pulmonary veins, aorta, brachiocephalic artery, left common carotid artery, left subclavian artery, atrioventricular (tricuspid) valve, mitral valve (bicuspid), chordae tendineae, papillary muscles, pulmonary trunk, pulmonary arteries, atrioventricular valves, semilunar valves

Cardiac Cycle

• The normal heart rate is approximately 75 beats per minute
• Each beat is one cardiac cycle. A full cycle takes about 0.8 seconds
• Cardiac phases breakdown:
  • Atrial systole (0.1 seconds)
  • Ventricular systole (0.3 seconds)
  • Atrial diastole (0.7 seconds) & ventricular diastole (0.3 seconds)
• Systole is the contraction phase, ejecting blood from the ventricles- Normal systolic pressure is 120 mmHg.
• Diastole is the relaxation phase, refilling the chambers- Diastolic pressure is 80 mmHg.
• The atria contract to fill the ventricles, providing 30% of ventricular filling
• 70% of ventricular filling occurs passively

Ventricular Systole

• When ventricles contract, mitral & tricuspid valves close
• This creates the first heart sound (S1)
• Ventricular contraction continues opening aortic and pulmonary valves to eject blood
• About 70 ml of blood are ejected per ventricle (stroke volume)

Atrial and Ventricular Diastole

• Atrial diastole: blood enters the atria (venous return)
• Ventricular diastole: ventricles relax, aortic & pulmonary valves close causing the second heart sound (S2)

Heart Sounds

• Lubb: first heart sound; occurs during ventricular contraction; caused by the closing of the mitral and tricuspid valves
• Dub: second heart sound; occurs during ventricular contraction; caused by the closing of the aortic and pulmonary valves
• A murmur is an abnormal heart sound

Heart Sound Locations

• Aortic area
• Tricuspid area
• Pulmonary area
• Mitral area

Electrocardiogram (ECG)

• Records electrical activity of the heart
• Electrodes are used for recording
• Leads connect two electrodes, often used to give an electrical picture of the heart
• ECG recording: uni-polar (one active electrode), bi-polar (two active electrodes), inactive electrode commonly placed on the right leg

ECG Leads

• Unipolar:
  • Limb leads: aVR, aVL, aVF (recorded by 3 electrodes on the limbs)
• Bipolar:
  • Limb leads: I, II, III(recorded by 3 leads on the limbs).
• Chest Leads (V1-V6): six electrodes placed on the chest (positions have location specifics)

ECG Components

• P wave: atrial depolarization
• QRS complex: ventricular depolarization
• T wave: ventricular repolarization
• Intervals:
  • PR interval (0.12-0.2 seconds): time from SA node activation to ventricular depolarization
  • QRS interval (< 0.1 seconds): time for ventricular depolarization
  • QT interval (0.43 seconds): duration of ventricular depolarization and repolarization