ECG Practical PDF

Electrocardiogram Practical Prof D Fisher CVS practical 2 1 ECG Basics The ECG represents the sum of the action potentials of millions of cardiomyocytes 2 Action Potenti...

Electrocardiogram Practical Prof D Fisher CVS practical 2 1 ECG Basics The ECG represents the sum of the action potentials of millions of cardiomyocytes 2 Action Potential: Myocyte 3 Conducting System of Heart Bachmann’s Bundle Internodal fibers 4 The different ECG waves 5 Depolarization and Repolarization at the Ventricles 6  An ECG (electrocardiogram) records the electrical activity of your heart at rest. It provides information about your heart rate and rhythm, and shows if there is enlargement of the heart due to high blood pressure (hypertension) or evidence of a previous heart attack (myocardial infarction). The resting ECG is different from a stress or exercise ECG or cardiac imaging test. You may need an ECG test if you have risk factors for heart disease such as high blood pressure, or symptoms such as NB!!! Note there is a difference between the palpitations or chest pain. electrical activity of the heart and its mechanical activity!! 7  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. 8  Semilunar valves closed AV valves opened Diastole: Active ventricular filling. The atria contract and complete ventricular filling. 9  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. 10  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. 11  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. 12  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. 13 14 The ECG electrodes The ten electrodes are: The four extremity electrodes: LA - left arm RA - right arm N - neutral, on the right leg (= electrical earth, or point zero, to which the electrical current is measured) F - foot, on the left leg It makes no difference whether the electrodes are attached proximal or distal on the extremities. However, it is best to be uniform in this. (eg. do not attach an electrode on the left shoulder and one on the right wrist). The six chest electrodes: V1 - placed in the 4th intercostal space, right of the sternum V2 - placed in the 4th intercostal space, left of the sternum V3 - placed between V2 and V4 V4 - placed 5th intercostal space in the nipple line. Official recommendations are to place V4 under the breast in women. V5 - placed between V4 and V6 V6 - placed in the midaxillary line on the same height as V4 (horizontal line from V4, so not necessarily in the 5th intercostal space) 15  The Bipolar Leads: The 3 channel ECG uses 3 or 4 ECG electrodes. These basic leads yield enough information for rhythm- Lead 1 monitoring. For determination of ST elevation, these basic leads are inadequate as there is no lead that gives (ST) information about the anterior wall. ST changes registered during 3-4 channel ECG monitoring should prompt acquisition of a 12 lead ECG. Lead 2 Lead 3 The extremity leads are: I from the right to the left arm II from the right arm to the left leg III from the left arm to the left leg 16 Practical: Connecting the electrodes to a volunteer 17  Some Heart Rhythm Problems Conduction deficits Resulting problems due to damage to conducting pathways disturbing normal rhythm of the heart If SA node or intermodal pathways are damaged the AV node assumes command Heart beats at slower rate Heart block Any damage to the AV node that partially or totally releases the ventricles from the control of the SA node The ventricles then begin to beat at their own rate, which is much slower, some or all of the time 18 (a) Normal sinus rhythm. (b) Junctional rhythm. The SA node is nonfunctional, P waves are absent, and heart is paced by the AV node at 40 - 60 beats/min. (c) Second-degree heart block. (d) Ventricular fibrillation. These Some P waves are not conducted chaotic, grossly irregular ECG through the AV node; hence more deflections are seen in acute P than QRS waves are seen. In heart attack and electrical shock. this tracing, the ratio of P waves to QRS waves is mostly 2:1. 19 Figure 18.18 Arrhythmia due to cardiac disease normal Atrial flutter Atrial fibrillation Ventricular tachycardia ventricular fibrillation 20 Follow the instructions of these exercises: 1. ECG and pulse in a resting volunteer. You will record the ECG and the volume pulse, analyze the signals and observe their relationships. 2. The pulse. You will identify and discuss similarities and differences in the pulses of the different participants. Please watch the video demonstration for attaching the leads to a patient. 21