ELECTROCARDIOGRAM (E.C.G)
E.C.G.
A recording of the electrical activity of the heart is called electrocardiogram (ECG). The instrument used to record the electrical activity of heart is called as electrocardiograph. IMPORTANCE The ECG gives important information concerning the spread of excitation to the different parts of the heart. It is important for the diagnosis of cases of abnormal cardiac arrhythmias and myocardial damage.
P Wave 1. Small, upward wave 2. Duration is 0.1 seconds. 3. It arises due to depolarization of trial tissue. 4. Travel of impulse from SA node to atrial muscle. Q Wave 1. Duration is 0.04 second. 2. Negative deflection 3. Denotes travel of impulse to mid part of interventricular septum. R Wave 1. Prominent positive deflection. 2. Represents the onset of ventricular systole. S Wave 1. Negative deflection that follows the R Wave. 2. Denotes the spread of impulse to basal part of ventricles. T Wave 1. Positive deflection and rounded 2. Denotes ventricular repolarization. 3. End of T wave coincides with closure of ventricular valves. U Wave 1. Due to slow repolarization of papillary muscles. 2. Positive deflection, small round wave. PR INTERVAL 1. Duration: 0.13 to 0.16seconds. 2. Denotes atrial depolarization plus conduction time of Bundle of His. 3. If duration > 0.2 seconds, then it means there is delayed conduction in B UNDLE OF HIS. 4. If duration 0.12 seconds, indicates heart block.
ST INTERVAL 1. Duration: 0.32 seconds. 2. Represents ventricular repolarization. QT INTERVAL 1. Duration: 0.40 to 0.43 sec. 2. Interval between start of Q wave to end of T Wave. 3. Represents ventricular depolarization and ventricular repolarization.
ABNORMAL ECG
CLASSIFIED INTO FOLLOWING TYPES: 1. HEART BLOCK. Disturbance in the normal transmission of the impulses anywhere from sinoatrial node to bundle branches. Cause: coronary artery disease. Types: 1. Sinoatrial Nodal Block No generation of impulse from SA Node. And other pacemaker from the atrium generates the impulse 2. Atrioventricular Nodal Block Disturbance in conduction of impulse between atria and ventricles. Two types: a) Incomplete heart block: Partial disturbance of conduction between atria and ventricles. Two types: i . First degree: All the atrial impulses reach the ventricles. PR interval is > 0.2 seconds. Atrial rate: ventricular rate:: 1:1.
ii. Second degree: All the atrial impulses are not conducted to ventricles. It can be of a) 2:1 Heart block Atrial rate: ventricular rate:: 2:1. b) 3:1 Heart block Atrial rate: ventricular rate:: 3:1. Wenchebach phenomenon: gradual lengthening of PR interval until 1 ventricular Beat is dropped. 2. Complete heart block: No transmission of impulse from atria to ventricles. Ventricle starts generating impulse but at a slower rate (45 heartbeats /minute.) BUNDLE BRANCH BLOCK Disturbance in conduction of impulse in any branch of bundle of his. QRS COMPLEX> 0.12 second. Normal heart rate ARRYTHMIAS Heart beat originating any where from the heart. Two types: 1. Atrial arrythmia 2. Ventricular arrythmia
MYOCARDIAL INFARCTION Irreversible damage to the myocardium due to decreased blood supply to the heart. ECG Findings 1. Elevation of ST Segment 2. T Wave inversion
Multiple Choice Questions: 1. a) b) c) d) Main source of energy to the heart is Free fatty acid Proteins Glucose Peptides
2. Opening of semilunar valve occurs during a) Atrial systole b) Start of Ventricular systole c) End of ventricular systole d) Ventricular diastole
3. One of the following statements is wrong a) RA systole precedes LA systole b) Contraction of RV starts after that of LV c) Isovolumetric ventricular relaxation begins after closure of semilunar valves d) Opening of Semilunar valves results in second heart sound
4. In complete heart block of following is true a) QRS complex is narrow b) No passage of impulse from atria to ventricles c) PR interval is prolonged d) SA node activity is normal 5. P wave of ECG occurs at a) Beginning of ventricular systole b) Beginning of atrial systole c) After Q wave d) Normally it is inverted, round
6. One of the following is Incorrect a) Normally QRS interval 0.08 – 0.12 sec b) Normal PR interval is 0.13 – 0.16 sec
c) QRS complex indicates ventricular depolarization d) P wave indicates ventricular depolarization