![Mechanical Events of the
Cardiac Cycle
1. Ventricular Filling Period [ventricular diastole,
atrial systole]
2. Isovolumetric Contraction Period [ventricular
systole]
3. Ventricular Ejection Period [ventricular
systole]
4. Isovolumetric Relaxation Period [ventricular
diastole, atrial diastole]](https://image.slidesharecdn.com/ecgcompletelecture-240204125716-3aff92d9/85/ECG-complete-lecture-notes-along-with-interpretation-3-320.jpg)
ECG complete lecture notes along with interpretation
- 1. Electrocardiogram (ECG) Dr. Suva Nath BHMS, MSc.(Medical Physiology), MHA, PhD(Medicine) Consultant Physician & Faculty of Medical Sciences
- 2. Cardiac Cycle Cardiac Cycle: the electrical, pressure and volume changes that occur in a functional heart between successive heart beats. •Phase of the cardiac cycle when myocardium is relaxed is termed diastole. •Phase of the cardiac cycle when the myocardium contracts is termed systole. • Atrial systole: when atria contract. • Ventricular systole: when ventricles contract.
- 3. Mechanical Events of the Cardiac Cycle 1. Ventricular Filling Period [ventricular diastole, atrial systole] 2. Isovolumetric Contraction Period [ventricular systole] 3. Ventricular Ejection Period [ventricular systole] 4. Isovolumetric Relaxation Period [ventricular diastole, atrial diastole]
- 5. Cardiac Cycle • Electrical changes in heart tissue cause mechanical changes, i.e. muscle contraction. • Thus, changes in electrical membrane potential of specific parts of the heart tissue represent mechanical events in specific areas of the heart tissue.
- 6. Electrocardiography • Two common abbreviations for electrocardiogram: EKG and ECG. • EKG comes from German language where cardiogram is written as kardiogram. • The ECG records the electrical activity of the heart. • Mechanical activity of the heart is sensed by echocardiography.
- 7. Electrocardiography ECG - electrocardiogram • graphic recording of electrical events • established electrode pattern results in specific tracing pattern • electrical pattern reveals blood supply problems
- 8. Electrophysiology • If an electrode is placed so that wave of depolarization spreads toward the recording electrode, the ECG records a positive (upward) deflection. • If wave of depolarization spreads away from recording electrode, a negative (downward) deflection occurs.
- 12. Electrophysiology • When myocardial muscle is completely polarized or depolarized, the ECG will not record any electrical potential but rather a flat line, isoelectric line. • After depolarization, myocardial cells undergo repolarization to return to electrical state at rest.
- 13. Electrical Events of the Cardiac Cycle •Sinoatrial (SA) node is the normal pacemaker of heart and is located in right atrium. •Depolarization spreads from SA node across atria and results in the P wave. •Three tracts within atria conduct depolarization to atrioventricular (AV) node. • Conduction slows in AV node to allow atria to empty blood into ventricles before vent. systole. •Bundle of His connects AV to bundle branches. •Purkinje fibers are terminal bundle branches.
- 15. ECG Time & Voltage • ECG machines can run at 50 or 25 mm/sec. • Major grid lines are 5 mm apart; at standard 25 mm/s, 5 mm corresponds to .20 seconds. • Minor lines are 1 mm apart; at standard 25 mm/s, 1 mm corresponds to 0.04 seconds. • Voltage is measured on vertical axis. • Standard calibration is 0.1 mV per mm of deflection.
- 17. Electrocardiogram •Normal P wave has amplitude of ≤ 0.25 mV •Q wave is first downward deflection after P wave; signals start of ventricular depolarization •R wave is positive deflection after Q wave •S wave is negative deflection preceded by Q or R waves •T wave follows QRS
- 19. ECG Limb Leads
- 20. ECG Augmented Limb Leads
- 23. 12-Lead ECG •Limb lead II shows large R amplitude because left ventricle current vector lies parallel with electrode placement. •Chest lead V1 has large S wave because left ventricle current vector is directed away from electrode.
- 24. Interpretation of ECG: Rate First measurement to calculate is heart rate. PQRST waves represent one complete cardiac cycle. 1. At standard paper speed, divide 1500 by distance between R to R waves. 2. Find R wave on heavy line. Count off 300, 150, 100, 75, 60 for each following line. Where next R lands is quick estimate. 3. Multiply number of cycles in 6 second marks by 10.
- 25. Interpretation of ECG: Rate
- 26. Interpretation of ECG: Rhythm •Normal heart rhythm has consistent R-R interval. •Mild variations due to breathing also normal.
- 27. Interpretation of ECG: Rhythm Normal Sinus Rhythm • Rate: 60-100 b/min • Rhythm: regular • P waves: upright in leads I, II, aVF • PR interval: < .20 s • QRS: < .10 s Sinus Bradycardia • Rate: < 60 bpm • Rhythm: regular Sinus Tachycardia • Rate: > 100 bpm
- 29. AV Conduction Disturbances oAtrioventricular conduction disturbances refer to blockage of electrical impulse at AV node. o1st degree P waves result in delayed QRS. o2nd degree some but not all P waves have QRS.
- 30. Arrhythmias Arrhythmia: an irregular heartbeat. • Sinus arrhythmia- P wave precedes @ QRS but RR interval varies. • Premature Atrial Contraction (PAC) • Premature Ventricular Contraction (PVC)
- 31. Arrhythmias
- 32. Myocardial Ischemia ST segment depression. • Hallmark of myocardial ischemia. • Reduction of oxygen-rich blood supply alters normal cellular action causing ST segment displacement ≥ 1 mm below line. • Upsloping, horizontal, downsloping