Nice, clear example of ventricular bigeminy with an underlying sinus rhythm. We do not know from this strip if the sinus rhythm is a bradycardia at a rate of about 42 per minute, or if the underlying sinus rhythm is actually at a rate of 85 per minute, with every other sinus beat inhibited by the occurance of a PVC. In the first possibility, the ventricular beats would be considered "escape" beats, positively contributing to the patient's heart rate. In the second instance, the rather late-occurring PVCs would cause the heart to be refractory, preventing the sinus P wave from conducting it's impulse to the ventricles. Sometimes, we can see signs of the sinus P wave "hiding" in the PVC, but in this case, if P waves exist, they fall almost exactly in the middle of the ventricular beats' QRS complex, making them invisible. A good strategy would be to watch the strip continuously for some time, hoping to catch the conduction of two sinus beats in a row, solving the dilemma.
Here is a nice example of sinus tachycardia taken from a 2-year-old in the post-anesthesia care unit after a short GI endoscopic procedure. Would you call this NSR, since it is from a child? The pre-op heart rate in this child was 120/min.
For your more advanced students, remind them that, in adults especially, a heart rate close to 150/min. should cause them to examine the ECG in several leads, looking for the presence of atrial flutter with 2:1 conduction. Another important teaching point, most ADULTS with sinus tach at 150/min. would manifest an obvious reason for the rapid heart rate (dehydration, pain, anxiety, shock, etc.) Challenge your basic students to come up with as many causes for sinus tach as they can.
TODAY, we are starting a new feature on the ECG GURU. ECG BASICS will provide rhythm strips and 12-leads for your beginner or refresher students. It can be discouraging to the entry-level student to see only intermediate or advanced material and not understand it. We must remember to start at the most elementary concepts, and then build on them, just as we do with any other subject. Even more advanced students sometimes benefit from a return to the "basics". In this weekly feature, you will find downloadable content that is, like all ECG Guru content, FREE for use in an educational context. Please let us know in the "Comments" section below what ECGs, rhythm strips, or illustrations you would like to see featured in this new area.
Today's strip: Sinus bradycardia with first-degree AV block. The rate is in the 30's and slowing, and the PR interval is .26 seconds.
