This is a rhythm strip from a NIPS procedure (non-invasive programmed stimulaltion), which is a programming test for an implantable cardioverter defibrillator (ICD). The test is done under light anesthesia, similar to that used for colonoscopy. In this example, the patient is in normal sinus rhythm at the beginning of the procedure. The pacemaker technician overdrives the patient's rate to observe the pacing function, then a stimulus is delivered to cause ventricular fibrillation (V Fib). Initially, the ventricular rhythm is somewhat organized and coarse (V flutter), but it will rapidly deteriorate if not corrected. Before it deteriorates, the ICD delivers a shock, and the patient's rhythm is restored. In this example, bi-ventricular pacing was conducted for a few minutes before the patient resumed NSR. The patient is then recovered from the anesthesia and discharged home.
For your students, this is a good example of the relative safety of shocking the well-perfused heart. Although it is possible to put the heart into an intractable V Fib with this test, the ICD usually is able to convert the potentially lethal rhythm easily. It is a good reminder that we need to perfuse the heart well before performing defibrillation on a person with unwitnessed cardiac arrest.