This strip shows a junctional rhythm at a rate of 110 beats per minute. The QRS complexes are slightly wide at .10 seconds (100 ms), and they are within the parameters for supraventricular rhythm. The term, "junctional tachycardia" could be used, also, but this is not likely a "reentrant" junctional tachycardia, which would be fast, regular, and have a sudden onset. That type of junctional tachycardia is a PSVT.   In this strip, we can see the underlying sinus rhythm in P waves that appear to pop up randomly.  However, if you march out the P waves, you will find that they are regular, at a rate of about 90 per minute.  The junctional rhythm has overrun the sinus rhythm.  Most of the P waves cannot conduct due to where they have landed - in the refractory period of the QRS.  The exception might be the P wave after the fifth QRS.  The sixth QRS might be conducted from that P wave.

When accelerated junctional rhythm is encountered, you should suspect DIGITALIS TOXICITY - the classic dysrhythmia associated with digitalis toxicity is accelerated junctional rhythm. Other causes in adults could be beta-agonist drugs such as adrenalin, cardiac infection, ischemia, or surgery.
 

This patient was diagnosed by the rescue crew as having atrial fibrillation, based on the fact that they thought the rhythm was irregular, and they could not see P waves.  They also noted a wavy baseline, and considered it to be fibrillatory waves.  In reality, the underlying rhythm is regular, with some PACs (regularly irregular). The P waves are small and hard to see in the baseline artifact.  We have marked the P waves in Lead I with small dots.  

It pays to look at multiple leads, reduce artifact as much as possible, and look at the strip for evidence of an underlying rhythm.  

It is not shown here, but the ECG machine is often able to show that the P waves are present by giving a PR interval and P wave axis in the diagnostics.

This rhythm strip shows normal sinus rhythm, slightly on the fast side of normal at 95 bpm.  The baseline undulates up and down with the movements of the patient's chest as she breathes.  One way to correct this problem on a monitor strip is to move the limb electrodes away from the chest and onto the limbs.

We try to remember to include some good old "Normal Sinus Rhythm" strips from time to time.  Teachers often have large collections of strange and unusual strips that their colleagues have saved for them.  But, then they find themselves resorting to electronic rhythm generators for samples of "normal".  Here is a strip from a healthy, 23-year-old woman showing NSR.  The rate is 65 bpm, QRS duration 76 ms, PRI 136 ms, QTc 410.  There are no abnormal ST segments or T wave changes.  There are very slight rate changes from beat to beat, and the P waves appear to change morphology a bit.  This can be due to the patient's breathing movements, and we would not delve too deeply into this in light of the fact that this is an ECG from an asymptomatic young ECG student.  Absolute precision would come from an generator, but rarely from a human being. This is a good strip to teach rate and interval determination.