CVS revision note part 2 -ECG
- Body is a volume conductor (offers little resistance to spread of electrical impulse )
- Fluctuations of electrical potentials of myocardial cells can be recorded extracellular using electrodes
- When the sum of theses fluctuations recorded on a moving strip of paper, throughout the cardiac cycle, It is called Electrocardiogram
- ECG can be recorded using unipolar or bipolar electrodes
- Net flow of current is from upper right to lower left side of the body
Normal ECG
- P wave - atrial depolarization
- QRS complex ( < 0.12 S) - ventricular depolarization and Atrial repolarization
- T wave - ventricular repolarization
- PR Interval (< 0.2 s ) - from onset of wave to onset of QRS complex
- QT Interval - beginning of QRS complex to end of T wave.
-Ventricular depolarization and repolarization
Sinus rhythm
Sinus arrhythmia
Normal phenomenon in healthy young individuals, breathing at normal rate. Heart rate increase in inspiration and decrease in expiration.
Sinus tachycardia (heart rate more than 100 beats per minute)
Sinus bradycardia (heart rate less than 60 beats per minute)
Sinus rhythm
- Occurs in normal heart
- Each heart beat originate in SA node
- Heart rate vary between 60 – 100 beats per minute
- P wave appear at regular intervals
Sinus arrhythmia
Normal phenomenon in healthy young individuals, breathing at normal rate. Heart rate increase in inspiration and decrease in expiration.
Sinus tachycardia (heart rate more than 100 beats per minute)
- Emotion
- Exercise
- Fever
- Anemia
- Hyperthyroidism
Sinus bradycardia (heart rate less than 60 beats per minute)
- Trained athletes
- Increased intra cranial pressure
- Hypothyroidism
- SA node anomalies
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