Second degree type II (Mobitz II) on the ECG for nurses & nursing students
Second degree AV blocks can be further categorized as Type I or Type II.
Following normal sinus impulse generation, the electrical impulse must travel through the atria to the AV node. Whereas second degree type I AV blocks are commonly a result of AV node “fatigability”, type II blocks are more commonly associated with issues relating to the His-purkinje system below the AV node, rarely occurring independent of structural heart disease or fibrosis of the heart.
On the ECG we should first notice that the R to R interval is irregular. Next, we should quickly attempt to locate P waves. Once we’ve located the P waves, evaluate the PR interval. If the PR interval is constant for each P wave that leads to a ventricular depolarization waveform (QRS), we’re looking at a second-degree type II AV block. This ECG presentation is a result of the sporadic non-conduction of P waves to the ventricles which occurs without discernible warning.
An exception to this would be the 2:1 AV block in which every other P wave results in a ventricular depolarization. In this case, there is insufficient information to tell if the PR interval is prolonging prior to the dropped QRS complex so we simply state presence of 2:1 AV block (below).
Patients may be asymptomatic or may present with symptoms ranging from lightheadedness to syncope or worse. If you encounter this rhythm, assess your patient and notify the provider. Mobitz II AV blocks have the potential to progress to complete heart blocks and death if unrecognized and left untreated.
Drew, B.J., Califf, R.M., Funk, M., Kaufman, E.S., Krucoff, M., Laks, M.M., Macfarlane, P.W., Sommargren, P., Swiryn, S., & Van Hare, G.F. (2004). Practice Standards for Electrocardiographic Monitoring in Hospital Settings. Circulation. 110(17), 2721-2746. doi: 10.1161/01.CIR.0000145144.56673.59
Katz, A. M. (2011). Arrhythmias. In F. DeStefano (Ed.), Physiology of the heart. (pp. 432-487). Lippincott, Williams, & Wilkins.
Zheng, T. (2021). Electrocardiography and cardiac rhythm. In E. M. Perpetua & P. A. Keegan (Eds.), Cardiac nursing: The red reference book for cardiac nurses (pp. 289-359). Wolters Kluwer.
