ECG Part II

Rate-measure of frequency of occurrence of cardiac cycles(b/m) < 60 beats/min is a bradycardia beats/min is normal >100 beats/min is a tachycardia

Rhythm Sinus-normal cardiac rhythm originating via impulse formation in the sinoatrial or sinus node Defined by p wave axis that is positive in the inferior leads Morphology is the same Cadence is regular NOT A P BEFORE EVERY QRS

Axis-direction of ECG waveform in the frontal plane measured in degrees Normal-frontal plane is directed leftward between -30 degrees and +90 degrees Leads I and AVF should both be positive Lead 1 is upright and AVF is negatively deflected (towards head) left axis deviation Lead 1 is negative and AVF is negative, indeterminate axis

Intervals-PR PR sec Time required for impulse to travel from the atrial myocardium(SA node) to ventricular myocardium Reflects conduction through the AV node

Intervals-QRS Depends on the lead Normally it is from the beginning of the Q wave to the end of the S wave sec

Intervals- QTc Reflects duration of activation and recovery of the ventricular myocardium Varies inversly with heart rate QTc = QT (vent rate – 60) Normal range is <.450 sec R-R interval and divide in half

Tachycardia's Wide vs. Narrow

ATRIAL FIBRILATION

Bundle Branch Blocks

Myocardial Ischemia Increase in myocardial demand due to decrease in blood flow, not cessation of flow Only changes seen are in repolarization, st-t changes away from involved segment of myocardium

Myocardial Infarction Results due to cessation of blood flow, or a decrease in demand, therefore causing primary changes in QRS complexes with changes in the ST segments This results in elevation of the J point