Atrioventricular Blocks (AV blocks) - ECG Diagnosis Summary First Degree AV Block • The P wave is normal in morphology. • PR interval greater than 0.20 sec that remains constant. • The QRS is normal in duration or wide if there is an existing bundle branch block. Second Degree AV Block Type I aka Mobitz I / Wenckebach • Normal P waves. • The PRI progressively lengthens until a P wave is not followed by a QRS. • As the PRI lengthens, there is shortening of the RR interval. • The RR interval containing the dropped P wave is less than 2x of the shortest RR interval. • The PRI (may be normal or prolonged) of the first conducted P wave is shorter than the last conducted PRI. • The largest increment in the PRI is usually on the second conducted P wave. • There is "group-beating" on the ECG. Second degree AV Block type II (aka Mobitz II) • There is constant PR interval (normal or prolonged) before a P wave is dropped. • The QRS is usually widened because the location of the block is often infranodal. • The QRS complex maybe narrow indicating a more proximal location of the block (AV node). High-grade AV Block aka Advanced AV Block • During sinus rhythm, when 2 or more P waves are not conducted the term given is advanced or high-grade AV block. • The QRS may be wide or narrow. • This is a clinically concerning variant of Mobitz II and often implies advanced conduction disease and may progress to complete heart block. Third Degree AV Block aka Complete Heart Block • In sinus rhythm with complete AV block, the PP and RR intervals are regular but the P wave has no relationship with the R wave. • The PR interval varies because there is really no P and QRS relationship. • The ventricular rate is usually 40-60 bpm and narrow when it is driven by a junctional pacemaker (AV node). • The QRS is wide and less the 40 bpm when an infra-Hisian pacemaker takes over. Paroxysmal AV Block aka Ventricular Standstill • Abrupt and persistent AV block ( multiple P waves with no QRS) in the presence of otherwise normal AV conduction. • May be initiated by a conducted or blocked PAC or PVC, acceleration or slowing of sinus rhythm. • Once the block is initiated, the block will persist until terminated by an escape, usually ventricular, with a predictable relationship of the escape to the following P wave. #atrioventricular #blocks #AVBlock #cardiology #ekg #ecg #diagnosis #electrocardiogram #classification #summary
