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.

This strip shows an underlying sinus bradycardia with a rate less than 40/min.  There is one "premature" beat, which can be considered to be ectopic, because it interrupts an otherwise regular rhythm.  The interesting thing is that the premature beat is not terribly early - it is about 740 ms from the previous beat.  If all the beats were spaced like this, the heart rate would be about 84/min.  There is probably an element of "escape" here, in that the ectopic beat is able to express itself due to the slow rate.  A faster sinus rate would override this ectopic focus.  So, we could view this early beat as a help, rather than a problem.  The most important consideration here is to address the cause of the bradycardia, and treat appropriately. 

This is an example of a junctional rhythm that is slower than what is considered "intrinsic rate" for the junction.  The rate is around 30 bpm.  We know this is a "supraventricular" rhythm because of the narrow QRS.  Junctional beats travel to the ventricles via the bundle branches, which provides very fast conduction, resulting in a narrow QRS complex.  The P waves can be seen at the end of each QRS.  They are upside-down in this Lead II rhythm strip, indicating retrograde conduction from the junctional pacemaker to the atria.

Clinically, the important thing when we encounter such a slow rate is to evaluate the patient's response to the rate.  If the patient is hypoperfused (pale, decreased level of consciousness, low BP), we need to act to increase the rate, regardless of the cause of the bradycardia.

This series of ECG rhythm strips shows a paroxysmal supraventricular tachycardia successfully treated with adenosine.  The patient was complaining of a rapid heart rate and palpitations, but was hemodynamically stable.  It is not known whether any parasympathetic stimulation, such as a Valsalva maneuver or carotid sinus massage, was used initially.   

The first rhythm strip shows a PSVT, presumably AV nodal reentrant tachycardia, at a rate of about 215 per minute.  (We originally indicated a rate of 240 per minute, but this was a typo). Using the simplist method of determining rate, the six-second method, we see 21, but almost 22, QRS complexes in six seconds. Differential diagnosis would include sinus tachycardia, but this rate is too fast for sinus tach, especially in a resting patient.  Also, sinus tach would slow down as the patient is rested or made more comfortable, and this rate did not vary.  Also, when confronted with a supraventricular tachycardia, one should also consider atrial flutter and atrial fibrillation.  This is somewhat slow for atrial flutter with 1:1 conduction, and that rhythm is much more rare than AVNRT. It is too regular for atrial fibrillation.  So, we are left with the probable diagnosis of paroxysmal supraventricular tachycardia.  The “paroxysmal” part is presumed since AVNRT has an abrupt onset, and the patient’s symptoms started suddenly. 

The second rhythm strip shows what happened after adenosine was administered.  The patient received first a 6 mg dose, rapid IV push.  When that was not effective, he received 12 mg rapid IV push.  The rhythm strip is typical of the first minute or so after adenosine administration.  Adenosine can cause transient AV blocks, escape rhythms, and ectopic irritability.  The half-life of adenosine is only 6 seconds, so the dysrhythmias and uncomfortable symptoms are short-lived.  In this strip, we see frequent PVCs and runs of V tach.