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ECG BASICS & PHYSIOLOGY OF HEART

ECG BASICS & PHYSIOLOGY OF HEART. Heart is a pumping organ. How heart keeps pumping?. 1.special structure of cardiac muscle syncytial nature both resting membrane potential & action potential are different form skeletal muscle 2.auto rhythmicity of heart. Action potential of heart muscle.

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ECG BASICS & PHYSIOLOGY OF HEART

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  1. ECG BASICS&PHYSIOLOGYOFHEART

  2. Heart is a pumping organ

  3. How heart keeps pumping? 1.special structure of cardiac muscle • syncytial nature • both resting membrane potential & action potential are different form skeletal muscle 2.auto rhythmicity of heart

  4. Action potential of heart muscle

  5. Factors affecting action potential • 1 K+ concentration • 2 Ca++ concentration • 3Na+ concentration • 4 temperature

  6. Excitation contraction coupling

  7. Excitation contraction coupling

  8. Duration of contraction • Atria 0.2sec • Ventricle 0.3 sec • Normally contraction time is 40% of cardiac cycle. When heart rate increases 3 times it is 65% of cardiac cycle. • Relaxation decreases • Ventricular filling decreases

  9. Cardiac cycle

  10. Atrial systole

  11. IMC

  12. ejection phase

  13. IMR

  14. Heart sounds

  15. Regulation of pumping • 1Frank Starling mechanism • 2 autonomic innervation • Within physiological limit heart pumps all the blood that comes to it without allowing excessive pooling of blood in the veins

  16. Parasympathetic innervation

  17. Effects of autonomic stimulation • Chronotropic effect • Dromotropic effect • Bathmotropic effect • Inotropic effect

  18. Effects of autonomic stimulation • Sympathetic stimulation: HR can go upto 250 bpm in young individual. • Parasympathetic stimulation: HR can go down to zero. Although vagal escape follows. • Both Sympathetic and parasympathetic system maintain a low level firing at resting condition.

  19. Energy considerations • Source: oxidative respiration • FA- biggest source • glucose/ lactate also used • Energy efficiency max 20-25%, rest is converted to heat (HF: 5-10% ) • Expenditure increases when ventricles are dialated BP is elevated Energy expenditure is measured by oxygen comsumption

  20. Special conductive system

  21. Rate of discharge • SA node 70-80 bpm • AVnode 40-60 bpm • AV bundle 15-40 bpm

  22. Autorhythmicity of SA node

  23. Autorhythmicity of SA node

  24. Autorhythmicity of SA node

  25. Autorhythmicity of SA node

  26. Autorhythmicity of SA node

  27. Special conductive system • Nodal delay • .09sec AV node • .04 sec penetrating portion • Additional .03 sec internodal pathway

  28. Ectopic pacemaker • Heart block • Stokes Adams syndrome

  29. ECG

  30. Heart muscle wraps around heart like a double spiral with a fibrous septa between the spiral layers.

  31. Flow of current

  32. leads

  33. Other leads • Chest leads 6 in no. • + pole connected to chest, -ve to all 3 limbs • Infrequently 7th & 8th chest leads & esophageal leads used. • aVR- Rt +ve • aVF- Lt leg +ve • aVL- Lt arm +ve • Recording of V1 V2 upside down as it is more closer to base rather than apex

  34. Axis of leads

  35. Vector • Instantaneous mean vector: At any given instance the total amount of current flowing in the heart is represented in magnitude and direction by the vector. Current flows from DEPOLARISED to POLARISED area i.e. NEGATIVE to POSITIVE

  36. Vector analysis • Closer the angle higher is the component • +ve vector: reading above the baseline • - ve vector: reading below the baseline

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