CVS

• Cardiac Cycle


  Regular, Repeated, Sequential, Synchronous events in the heart

  
• Heart


  • 4 chambers: 2 atria, 2 ventricles
  • 2 syncytia: Atrial & Ventricular
  • 4 valves: 2 Atrio-Ventricular, 2 Semilunar

  
• Heart as a Pump

  • Atrial Syncytium: Atria contract & relax simultaneously
  • Ventricular Syncytium: Ventricles contract & relax simultaneously
  • Right heart deals with deoxygenated blood at low pressures
  • Left heart deals with oxygenated blood at high pressures
  • Contraction (Systole): ↑ Pressure → opening of valve in front and closing of valve behind → Ejection or emptying of the chamber → ↓ of volume
  • Relaxation (Diastole): ↓ Pressure → opening of valve behind and closing of valve in front → Filling of the chamber → ↑ of volume
  • Normally: Filling = Emptying

  
• Heart Rate & Cardiac Cycle

  • If HR = 75 bpm, cardiac cycle is 0.8 sec
  • Systole ≈ 0.4 of cardiac cycle
  • If HR = 225 bpm, cardiac cycle is 0.26 sec, Systole ≈ 0.65 of cardiac cycle, Diastole only about 0.09 sec
  • Frank Starling Mechanism: Force of contraction is directly proportional to the initial length of the cardiac muscle fibre i.e. LV end diastolic volume, within physiological limits

  
• Fundamental Rule: Atrial & Ventricular systole cannot occur at the same time

  
• Events During Cardiac Cycle

  • Electrical: ECG
  • Mechanical: Contraction (Systole), Relaxation (Diastole)
  • Physical: Opening & Closing of Valves
  • Chemical
  • Thermal

  
• Ventricular Systole


  • Isovolumic/Isometric contraction: All valves are closed, Rapid rise in pressure, No change in volume
  • Rapid Ejection: Lasts 0.1 sec, 50 ml blood ejected
  • Slow Ejection: Over 0.15 sec, 20 ml blood ejected

  
• Ventricular Diastole


  • Isovolumetric/Isometric relaxation: Pressure falls steeply, No change in volume
  • Early rapid passive filling: Volume increases by 50 ml
  • Slow filling/Diastasis: Volume increases by 10 ml
  • Last active filling: Atria contract to push 10 ml into ventricles

  
• Atrial Events


  • Atrial Systole: Immediately after atrial depolarization, increases pressure in atria, increases ventricular volume by 10 ml, produces S4
  • Atrial Diastole: First 300 ms only atria fill, next 400 ms both atria and ventricles fill

  
• Pressure and Volume Changes are inversely related during the Cardiac Cycle

  
• Stroke Volume


  Volume of blood pumped by each ventricle per beat ≈ 70 ml

  
• Ejection Fraction


  Index of LV function, >60% normal, 45-55% mild heart failure, 30-45% moderate heart failure, <30% severe heart failure

  
• Cardiac Output


  Volume of blood pumped by each ventricle per minute ≈ 5-6 L

  
• Venous Return = Stroke Volume
• Cardiac Pressure Volume Loop shows the inverse relationship between pressure and volume during the cardiac cycle

  
• Aortic Blood Flow, ECG, Heart Sounds, and JVP are all synchronized with the Cardiac Cycle

  
• Heart sounds


  Essential in cardiovascular system examination
• Heart sounds identification


  • Depends on position best heard
  • Intensity
  • Timing
  • Pitch
  • Radiation
  • Changes with respiration & position

  
• Additional heart sounds


  • Murmurs
  • Pericardial rub
  • Pericardial knock
• Physiological splitting of second heart sound


  1. Expiration: Aortic & pulmonary valves close simultaneously, second heart sound is single

  2. Inspiration: Pulmonary valve closes after aortic valve, augmented inflow into right ventricle leads to delayed closure of pulmonary valve, second heart sound is split
• S1 (First heart sound)


  Caused by closure of atrioventricular valves
• S2 (Second heart sound)


  Caused by closure of semilunar valves
• A (Aortic component of S2)


  Caused by closure of aortic valve
• P (Pulmonary component of S2)


  Caused by closure of pulmonary valve
• Examination of arterial pulse is essential in cardiovascular system examination

  
• Peripheral arterial pulses


  • Temporal artery
  • External maxillary artery
  • Carotid artery
  • Brachial artery
  • Radial artery
  • Femoral artery
  • Popliteal artery
  • Posterior tibial artery
  • Dorsalis pedis artery
• Characteristics of arterial pulse examined

  • Rate (normal/tachycardia/bradycardia)
  • Rhythm (regular/irregular)
  • Character (normal/abnormal)
  • Volume (low/normal/large)
  • Radio (radial/radiofemoral delay)

  
• Pulse deficit


  Heart rate - Pulse rate, when heart beats but no pulse felt due to small stroke volume
• Abnormal arterial pulse characters

  • Pulsus parvus (small weak pulse)
  • Collapsing/water hammer (rapid upstroke, rapid descent - aortic regurgitation)
  • Bisferiens (slow rising, collapsing - aortic stenosis with/without regurgitation, hypertrophic cardiomyopathy)
  • Dicrotic (two waves - dilated cardiomyopathy)
  • Pulsus alternans (alternate strong and weak beats)
  • Pulsus bigeminus (premature ventricular contraction follows a regular beat)

  
• Pulsus paradoxus


  Inspiration causes decrease in pulse amplitude, normal decrease is 5-10 mmHg, accentuation indicates pericardial tamponade, status asthmaticus, SVC obstruction

  
• Examination of jugular venous pressure is essential in cardiovascular system examination

  
• Jugular venous pressure


  Reflects phasic pressure changes in the right atrium, provides indirect measure of central venous pressure, approximately 8 cm water or 7 cm blood or 5.88 or ≈ 6 mmHg

  
• Measurement of jugular venous pressure

  1. Position patient semi-recumbent at 45°

  2. Turn head slightly to left

  3. Assess vertical distance between sternal angle and top of pulsation point of internal jugular vein

  4. JVP = 5 cm (distance from centre of right atrium to sternal angle) + measured distance

  
• Waves in jugular venous pulse

  • X - atrial relaxation and descent of tricuspid valve into right ventricle during ventricular systole
  • Y - filling of ventricle after tricuspid opening
  • a - atrial wave
  • c - carotid or ventricular wave: bulging of tricuspid valve into right atrium during isovolumetric contraction
  • v - venous filling of right atrium

  
• Jugular venous pressure


  Indicates adequacy of circulating volume, contractile state of the myocardium

  
• Differences between arterial and venous pulse

  • Carotid artery pulse: no effect on earlobes, finger pressure, abdominal pressure
  • Jugular venous pulse: moves earlobes outwards, more prominent with finger pressure, more prominent with abdominal pressure, varies with respiration and posture