ECG/EKG

what are cardiac muscles

branching, intercalated discs with gap junctions, involuntary, striated, single nucleus per cell

what is an ECG/EKG

• recording of electrical activity of cardiac muscle

• uses

  • study of cardiac function

  • identify disorders of myocardium and conduction system

• detects electrical currents between (-) charged depolarized cells and (+) charged depolarized cells

what are mechanical vs. electrical events

• mechanical

  • contract and relax

  • what we infer

• electrical

  • depolarization and depolarization

  • what we measure

what is a P wave

• small upward deflection on the ECG

• represents atrial depolarization

  • spreads from SA node through contractile fibers in both atria

what is the QRS complex

• has three parts

  • starts with downward deflection

  • followed by large, upright, triangular wave

  • ends as a downward wave

• represents rapid ventricular depolarization

  • action potential through contractile fibers

what is a T wave

• dome-shaped upward deflection

• indicates ventricular repolarization

• occurs as ventricles are starting to relax

• smaller and wider than QRS complex

  • repolarization occurs more slowly than depolarization

what is the cycle of an ECG

1. depolarization of atrial contractile fibers produces P wave

2. atrial systole (contraction)

3. depolarization of ventricular contractile fibers produces QRS complex

4. ventricular systole (contraction)

5. repolarization of ventricular contractile fibers produces T wave

6. ventricular diastole (relaxation)