The Patient:    Paramedics were summoned to the home of a 74-year-old woman who had a complaint of shortness of breath.  She was found sitting, alert and oriented, with labored respirations at 30/min. She stated that the shortness of breath came on suddenly. She denied any cardiac or pulmonary medical history, and said she took no medications. The patient was ambulatory.  Her skin was cool and moist.  Her SpO2 on room air was 85%, improving to 90% on oxygen via 15 lpm non-rebreather mask.  Her lungs sounded clear.

When the patient was moved to the transport vehicle, she suddenly became nonverbal, with a leftward gaze. Her pupils were noted to be unequal and non-reactive (we do not know which was larger).  Her BP was 67/43.

During transport, her heart rate declined into the 20’s and became apneic and pulseless.  Recorded BP was 46/25. CPR was done until and after arrival at the hospital, where efforts to resuscitate were halted after some time.

This is an example of a junctional rhythm that is slower than what is considered "intrinsic rate" for the junction.  The rate is around 30 bpm.  We know this is a "supraventricular" rhythm because of the narrow QRS.  Junctional beats travel to the ventricles via the bundle branches, which provides very fast conduction, resulting in a narrow QRS complex.  The P waves can be seen at the end of each QRS.  They are upside-down in this Lead II rhythm strip, indicating retrograde conduction from the junctional pacemaker to the atria.

Clinically, the important thing when we encounter such a slow rate is to evaluate the patient's response to the rate.  If the patient is hypoperfused (pale, decreased level of consciousness, low BP), we need to act to increase the rate, regardless of the cause of the bradycardia.

This rhythm strip illustrates a junctional escape rhythm.  The sinus rhythm has slowed or stopped, and the junctional tissue has taken over as the pacemaker of the heart.  The "junction" is loosely defined as the area between the AV node and the Bundle of His.  The intrinsic rate of the pacemaking tissue in this area is 40 - 60 beats per minute.  This slow rate is usually overridden by the sinus node, and the junction is not allowed to express itself as a pacemaker.  Should the sinus node fail or fall below the junctional rate, the junction "escapes" and takes control of the heart.  The QRS complex in junctional rhythm will normally be narrow, because the impulse follows the bundle branches down through the ventricles in a normal fashion, resulting in quick and normal ventricular depolarization.  If the QRS complex is wide in a junctional rhythm, there is another, separate cause, such as bundle branch block.

 If the junctional impulse is able to penetrate the AV node and depolarlize the atria, the P wave will be deflected downward in Leads II, III, and aVF, as the impulse is travelling in a retrograde direction (backward).  The P wave could end up slightly before the QRS, during the QRS, or after the QRS. In this strip, the P waves are seen after the QRS complexes.

This is quite an interesting ECG, and the ECG Guru would love to hear what you think about it.  What we do know is that it is a wide-complex bradycardia in a patient for whom we have no clinical data, except that she is a 51 year old female.  The rhythm is probably junctional, as no P waves are seen and the rhythm is regular.  The rate of 63 per minute would be consistent with that. Interestingly, no disassociated sinus P waves are seen.  All slow wide-complex rhythms should be evaluated for idioventricular origin, or AIVR.  The QRS in V1 shows an atypical right bundle branch block pattern.  We usually look for rSR', or "bunny ears",  but  this ECG shows an upright R wave with a smaller, slurred r wave before it.  What makes this look like RBBB is the prominent wide little S wave in V6 and in Lead I.  We question the R wave progression, too.  Do you think it is possible that the electrodes for V2 and V3 are switched?  The axis is leftward, causing Lead II to be nearly biphasic - it represents a synthesis of what is seen in Leads I and III.  This is enough left axis shift to diagnose a left anterior fascicular block (with RBBB = bifascicular block). 

This is a great ECG, and we can't wait to hear from all you ECG Gurus out there. Maybe we will need to adjust our diagnosis after we hear from you.