Cardiac Physiology Lecture 13 PDF

Cardiac Physiology 2  Electrocardiogram Points to consider about ECG: 1. ECG is the record of cardiac impulse that reach the body surface, not a direct recording of actual electrical activity of the heart. 2. ECG is a complex recording of the overall cardiac...

Cardiac Physiology 2  Electrocardiogram Points to consider about ECG: 1. ECG is the record of cardiac impulse that reach the body surface, not a direct recording of actual electrical activity of the heart. 2. ECG is a complex recording of the overall cardiac activity during depolarization and repolarization. 3. The recording represents comparisons in voltage detected by electrodes at two points on skin, not actual potential.  Limb leads Lead I: Right arm to aVR: right arm left arm aVL: left arm Lead II: Right arm to left leg Lead III: Left arm to left leg aVF: left leg Ground electrode 1 2 6 3 4 5  Electrocardiogram Different parts of the ECG record can be correlated to specific cardiac event: The P wave represent atrial depolarization. The QRS complex represents ventricular depolarization. The T wave represents ventricular repolarization.  Ventricular depolarization R Ventricular repolarization Atrial Depolarization T P P Q S PR ST TP interval AV nodal Ventricular Ventricular Relaxation delay Contraction NORMAL RATE AND RHYTHM ABNORMALITIES IN RATE Tachycardia ABNORMALITIES IN RHYTHM Extrasystole (premature beat) Ventricular fibrillation Complete heart block CARDIAC MYOPATHIES Myocardial infarction Cardiac Cycle  Beginning just after a ventricular contraction Semilunar valves closed AV valves opened Diastole: Passive ventricular filling. The AV valves open and blood flows into the relaxed ventricles, accounting for most of the ventricular filling.  Semilunar valves closed AV valves opened Diastole: Active ventricular filling. The atria contract and complete ventricular filling.  Semilunar valves closed AV valves closed Systole: Period of isovolumic contraction. Ventricular contraction causes the AV valves to close, which is the beginning of ventricular systole. The semilunar valves were closed in the previous diastole and remain closed during this period.  Semilunar valves opened AV valves closed Systole: Period of ejection. Continued ventricular contraction pushes blood out of the ventricles, causing the semilunar valves to open.  Semilunar valves closed AV valves closed Diastole: Period of isovolumic relaxation. Blood flowing back toward the relaxed ventricles causes the semilunar valves to close, which is the beginning of ventricular diastole. Note that the AV valves closed, also.  Semilunar valves closed AV valves closed Semilunar Diastole: Period of valves closed isovolumic relaxation. AV valves opened Diastole: Passive ventricular filling. Laminar flow (does not create any sound) Turbulent flow (can be heard) http://www.wiley.com/college/jenkins/0470227583 /animations/ch19/index_19_07_01.html