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