Question 12

R_0028

+ Describe the main findings in R-0028 which is an ECG from a 29 year old man with a fractured forearm

The key features in this ECG are:

  • The P waves are inverted in the inferior leads and upright in Lead aVR
  • The P wave is adjacent to the QRS complex (i.e. the PR interval is short). This is seen well in the inferior leads and in Lead aVL
  • The rhythm appears regular, the QRS complexes are normal and the ventricular rate is about 56 beats per minute

The inverted P waves and the short PR interval indicate an atrial pacemaker near the atrioventricular node (AVN), with the atrial being depolarized in a retrograde direction i.e. AVN → SAN (sinoatrial node) direction rather than the normal SAN → AVN direction. Because this pacemaker is near the junction of the atria and the atrioventricular node the resulting heart beats are called junctional or nodal beats. When there are more than three consecutive junctional beats a junctional or nodal rhythm is said to be present

There are two types of junctional rhythm:

  • Junctional escape rhythm: This is a "back up" or escape rhythm that develops where the normal SAN pacemaker slows excessively or fails to discharge. The junctional site becomes the cardiac pacemaker, producing a sequence of 3 or more junctional escape beats at a rate of 40 - 60 beats per minute. There may be AV dissociation, or (as in this case) the atria are activated retrogradely from the junctional focus.
  • Accelerated junctional rhythm: This is not an escape rhythm but is due to a junctional pacemaker that discharges at a rate of 60 - 100 beats per minute. If the rate of the junctional pacemaker is greater than 100 beats per minute the rhythm is called a junctional tachycardia

Final Diagnosis: Junctional escape rhythm with a heart rate of about 56 beats per minute. Normal QRS morphology and axis