The correct interpretation includes marked sinus bradycardia with a second-degree atrioventricular (AV) block (Mobitz I) and occasional junctional escape, left-axis deviation, and evidence of an inferior MI. Poor R-wave progression is also noted in the precordial leads.
Marked sinus bradycardia is seen in the first three and the last four P waves of the rhythm strip. The P-P intervals have a rate of 50 beats/min—different than the overall rate of the QRS complex (remember, “sinus” is synonymous with “P wave”!). The rate of the QRS complex (38 beats/min) is slower than the atrial rate, signifying a block of some sort.
Second-degree AV block is evident from the lengthening PR interval in the first two P-QRS complexes, followed by a P wave with no associated QRS complex. Although the fourth QRS complex in the rhythm strip is narrow and similar in appearance to the others, it’s too far from the previous P wave to have been conducted from the atrium—indicating a junctional escape beat arising from the AV node. (The rhythm returns to second-degree AV block for the remainder of the beats seen on the ECG.)
Left-axis deviation is signified by the R axis of –78° (lower than the normal limit of –30°). The Q waves in leads II, III, and aVF indicate a prior inferior MI. Finally, poor R-wave progression is seen in the precordial leads, with no significant transition between leads V1 and V6.
Although second-degree AV block is not an indication for permanent pacing, symptomatic bradycardia that persists despite medical management is. Because this patient was symptomatic while taking an AV nodal blocking agent (metoprolol), a permanent pacemaker was recommended.