This is a good teaching strip on many levels. At the BASIC level, we see a strip that clearly meets all the criteria for sinus tachycardia: a regular rhythm over 100/min. with P waves that look normal and all look alike. The rate is 110 per minute. The PR interval is just at the upper limits of normal at .20 second, or 200 ms. The QRS complex is within normal limits, but slightly wide at .10 seconds.
This strip is good for teaching rate determination by several different methods. It is helpful that QRS complexes 1, 5, and 10 fall on the dark lines of the paper.
This is a Lead II rhythm strip, and it is helpful to show students that not ALL Lead II strips produce an upright QRS complex. Of course, correct lead placement should be confirmed. In this particular case, the patient had suffered an anterior - septal wall M.I., and has a left anterior hemiblock, also called left anterior fascicular block. This shifts the frontal plane axis to the left, causing Lead II to have a negative QRS. Axis can't be accurately determined from one lead, but axis shift explains the negative QRS in this strip.