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  1. 1. Cardiac Physiology Review
  2. 2. Cardiac Cycle • The heart is 2 pumps that work together – right (pulmonary) and left (systemic) half • Repetitive, sequential contraction (systole) and relaxation (diastole) of heart chambers
  3. 3. Cardiac Cycle • Blood moves through circulatory system from areas of higher  lower pressure – Contraction of heart produces the pressure
  4. 4. Cardiac Physiology The Cardiac Cycle – Diastole Relaxation/filling phase Coronary arteries fill – Systole Ejection fraction Normally, 2/3 of ventricular volume is ejected
  5. 5. Bledsoe/Porter/Cherry, Essentials of Paramedic Care, Second Edition Update Diastole
  6. 6. Bledsoe/Porter/Cherry, Essentials of Paramedic Care, Second Edition Update Systole
  7. 7. Cardiac Physiology • Stroke volume Amount of blood ejected in 1 cycle Dependent on Preload Cardiac contractility Afterload
  8. 8. Preload • Affected by venous blood pressure and the rate of venous return • Related to the ventricular end- diastolic volume (EDV) – a higher EDV implies a higher preload • Amount of stretch to RV/LV due to end diastolic pressures
  9. 9. Contractility • Intrinsic ability of the heart to contract independent of preload and afterload • Contractility is synonymous with inotropy
  10. 10. Afterload • Maximum tension of the myocardium mass at end of systole – Tension or stress developed in the wall of the left ventricle during ejection (systole) • Dilated LV has a higher afterload • Conversely, a hypertrophied LV has a lower afterload
  11. 11. Starling’s Law The more the myocardial muscle is stretched, the greater its force of contraction will be The more diastolic volume, the greater the cardiac output.
  12. 12. Cardiac Output Volume of blood that the heart pumps in 1 minute Stroke volume (mL) x heart rate (bpm) = cardiac output (mL/min) SV x HR = CO
  13. 13. Endocrine Role Gail Walraven, Basic Arrhythmias, Seventh Edition ©2011 by Pearson Education, Inc., Upper Saddle River, NJ
  14. 14. The Heart is an Endocrine Organ • Hormones are secreted by the heart in response to hemodynamic stress • Effects Diuresis (loss of water), natriuresis (loss of sodium), and vasodilation • These hormones are referred to as natriuretic peptides: Atrial natriuretic peptide (ANP) Brain natriuretic peptide (BNP)
  15. 15. Natriuretic peptides • Atrial natriuretic peptide (ANP) Released by atrial muscle cells in response to atrial distension and sympathetic stimulation Counters renin-angiotensin-aldosterone system • Brain natriuretic peptide (BNP) Secreted principally by the ventricles of the heart in response to excessive stretching of myocytes Results in decreased central venous pressure (CVP), cardiac output, and blood pressure BNP levels are elevated in congestive heart failure
  16. 16. Nervous System Control Gail Walraven, Basic Arrhythmias, Seventh Edition ©2011 by Pearson Education, Inc., Upper Saddle River, NJ
  17. 17. Nervous System Control Electrolytes Sympathetic Parasympathetic Autonomic Control of the Heart – Chronotropy • Rate – Inotropy • Contractility – Dromotropy • Conductivity
  18. 18. Autonomic Nervous System
  19. 19. Cardiac Plexus • Formed by the cardiac nerves derived from the cervical ganglia of the sympathetic trunk & the cardiac branches of the vagus & laryngeal nerves
  20. 20. Function of the Heart & Control of Heartbeat •Contracts spontaneously • does not need nervous stimulation to contract • Motor nerves that supply the human heart modulate HR • Sympathetic motor impulses ↑ HR • T3-T4 •GO UP TO THE NECK, AND COME BACK DOWN TO THE HEART •Parasympathetic motor impulses ↓ HR •VAGUS NERVE (X)
  21. 21. Electrolytes!
  22. 22. Sodium & Potassium Sodium (Na+) Plays a major role in depolarizing Greater concentration outside cell Must be actively pumped in Sodium-Potassium Pump = active transport **requires ENERGY** Triggered by depolarization propagation Potassium (K+) Influences repolarization Greater concentration inside cells
  23. 23. The Sodium Potassium Pump
  24. 24. • Depolarization caused Ca++ to enter cell and enables transmitter molecule to be released – Which excites neighboring cells
  25. 25. Electrolytes Chloride (Cl–) Transmission of impulses (wave of depolarization)
  26. 26. Magnesium (Mg2+) Intracellular magnesium is correlated with intracellular K+ essential for nucleic acids, enzyme function (esp. synthesis of ATP)
  27. 27. Cardiac Muscle 3
  28. 28. Characteristics of Cardiac Muscle 1. Cardiac muscle = intermediate • between skeletal & smooth muscle • Excitatory and conductive fibers 2. Cardiac muscle = uninucleate
  29. 29. Intercalated discs When one cell becomes excited, the action potential spreads rapidly across the entire group of cells Syncytium Work together
  30. 30. Synctia The heart has two syncytia: – Atrial syncytium Contracts from superior to inferior – Ventricular syncytium Contracts from inferior to superior The only way an impulse can be conducted from the atria to the ventricles is through the atrioventricular (AV) bundle.
  31. 31. Cardiac Muscle 1000X intercalated disc striations short branching cells; intercalated discs at cell junctions nucleus
  32. 32. Initiation of Electrical Flow • Polarization – “Ready” state • Depolarization – “Discharge” state • Repolarization – “Recovery” state
  33. 33. Depolarization of Cardiocytes • Resting Potential Inside of the cell is more negatively charged than the outside • Action Potential Influx of sodium changes the membrane polarity
  34. 34. Repolarization • Cell membrane remains permeable to sodium for only a fraction of a second • Sodium actively pumped outside the cell • Returns to polarized state
  35. 35. Properties of Conduction System 1. Excitability 2. Conductivity • Dromotropy 3. Automaticity 4. Contractility • Inotropy
  36. 36. Bledsoe et al., Paramedic Care: Principles & Practice, Volume 3: Medical Emergencies, 3rd Ed. © 2009 by Pearson Education, Inc. Upper Saddle River, NJ
  37. 37. 3 A-V bundle path shown with blue 1 2 3 A-V bundle path shown with blue arrows
  38. 38. Conduction System Each component of the conductive system has its own intrinsic rate of self-excitation – SA node = 60–100 bpm – AV node = 40–60 bpm – Purkinje system (Ventricles) = 20–40 bpm • What happens if SA node stops firing???
  39. 39. Pacemaker site with the fastest rate will generally control the heart
  40. 40. Irritability • A site along the conduction pathway becomes irritable and speeds up • Overrides higher pacemaking sites for control of the heart
  41. 41. Escape Mechanism • The normal pacemaker slows down or fails • Lower pacing site assumes pacemaking responsibility – This is how you get escape beats, junctional and ventricular rhythms