The Basics of Reading ECGs  
Reading the tracing:

electrical impulse of atrial depolarization
the first downward stroke of the QRS- often absent
upward deflection of the QRS- ventricular depol.

downward deflection of the QRS-ventricular depol.
repolarization of the ventricles
summation of ventricular depolarization
click here for discussion
   
 
Analyzing the Rate Locate an R-wave which falls on a dark line on the ECG paper. If the peak falls on each dark vertical line on a strip, that would indicate a rate of 300 beats per minute. If the R-R interval matched every other dark vertical line it would be 300/2 or 150. If every third line, 100; every fourth line 75 and every fifth line 60, etc.

At the top of each ECG strip is a series of marks or dots. The distance between dots represents 3 seconds. Count the number of R-peaks between three dots (6 seconds) and multiply by 10 to get heart rate. This is especially useful when the rate is very slow or irregular.

Analyzing the Rhythm:

1. Is the QRS complex rhythm regular or irregular?

2. What is the P-wave/QRS complex relationship? Is there a P-wave prior to each QRS complex? consider AV blocks If the P-waves are absent, is the atrial rhythm fibrillation or flutter?

3. Are the complexes narrow or wide? consider conduction issues

3. If the P-waves are related to the QRS complex, is the P-R interval fixed? Is there a progressive increase in the P-R intervals with a decrease in the R-R intervals? consider AV blocks

4. Are there any premature events? A narrow QRS complex is of supraventricular origin. A widened QRS complex may be ventricular or supraventricular with aberrancy in etiology.