Question

What are the physiologic and pharmacologic effects on EKG?

Answer 1

Electrocardiogram (ECG or EKG) is a graphic record of electrical activity of the heart, obtained by the help of electrodes placed on body surface. Electrocardiograph is the instrument used to record the ECG.

Cardiac impulse arises in the sinoatrial node and spreads to both atria and the atrioventricular node. There is a delay of 0.13 seconds in the atrioventricular node. The impulse then goes to the right and left bundle branches and through the purkinje fibers is distributed to the whole cardiac muscles.

Principles of ECG

Electrical activity is recorded when part of muscle fiber is depolarized or repolarized.
No electrical activity is recorded when the muscle fiber is fully depolarized or repolarized.

Class I Antiarrhythmics: Sodium Channel Blockers
- Block the influx of sodium into cardiac cell during depolarization; affect phase 0 of action potential

Cause: Some can cause prolonged QT interval

Class II Antiarrhythmics: Beta Blockers
- Block the sympathetic nervous system's beta receptors; affect phase 4 of the action potential

Cause: Prolonged PR interval, slow heart rate