ECG Part II

Rate-measure of frequency of occurrence of cardiac cycles(b/m) < 60 beats/min is a bradycardia 60-100 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- 0.10-0.220 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 0.07-0.120 sec

Intervals- QTc

Reflects duration of activation and recovery of the ventricular myocardium

Varies inversly with heart rate QTc = QT + 1.75(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