The Patient:    This ECG was taken from an elderly woman. Unfortunately, we do not know any details about the case.  That acknowledged, there are many interesting aspects to this ECG.

The ECG:  The first thing we notice is the severe bradycardia – almost certain to be symptomatic.  The rate is 32 bpm and the rhythm is regular.  There are no P waves.  This is a junctional rhythm, slightly slower than expected from junctional escape.

The QRS shows the presence of right bundle branch block.  Each QRS on the ECG starts as a narrow complex, but then adds an “extra” wave onto the end – the delay caused by the right ventricle depolarizing late.  The terminal delay is very noticeable in V1 as an R’ wave, and in Leads I and V6 as a small, wide s wave.  There is right axis deviation, so the diagnosis of bifascicular block (RBBB and left posterior fascicular block) can be made.

V2 through V6 show fragmentation of the QRS complexes and a loss of voltage and R wave progression.  This points to anterior wall M.I. We can’t know the age of the M.I. without clinical correlation, but the ST segments in those leads are very flat, with uniformly symmetrical inverted T waves all the way to V6.  All of these signs indicate recent injury.  An anterior M.I. can cause the bifascicular block we are seeing, since the bundle branches begin in the septum.

The Patient   This ECG was recorded from an 86-year-old man who was weak, pale, and diaphoretic. He was hypotensive, with a BP of 88/54.  He denied chest pain or shortness of breath.

The ECG   The 12-lead ECG shows a bradycardia at about 60 beats per minute and regular.  The QRS complexes are narrow, at a little less than .08 seconds (800 ms).  The P waves are negative in Leads II, III, and aVF and positive in aVR.  This is an indication that the P waves are traveling in a “retrograde” fashion – backward. The origin of the P waves has to be the AV junction or the lower atria for this to happen.  The PR interval is on the short side of normal at about .12 seconds (120 ms), possibly even less.  This is common in junctional rhythm, as the impulse starts at the AV junction, and travels back through the atria and forward through the ventricles at the same time.

There are no premature beats, and the ST segments are not elevated or depressed. There are no T wave inversions, except for aVR, where it is normal.

Assessment    One cause of junctional rhythm is sinus brady.  That is, the sinus node begins firing so slowly that the junctional pacemaker “escapes”, and takes control of the heart.  When the sinus node speeds up, it may once again take over the heart’s rhythm from the junction.  The fastest pacemaker controls the heart. A junctional rhythm may escape when the sinus node fails or there is a complete AV block in the AV node area.

Patient Outcome    This patient was diagnosed with orthostatic hypotension, bronchitis, and urinary tract infection. He was treated in the hospital and cleared by a cardiologist for discharge two days later.

Our thanks to Michael Francis and Chris Burden for donating this ECG.

This Lead II rhythm strip shows a regular rhythm with narrow QRS complexes and retrograde P waves.  The strip was taken from a nine-year-old girl.  The rate is about 110 per minute and the PR interval is .12 seconds (120 ms).

When retrograde conduction is seen in the atria, it is often assumed that the rhythm is originating in the junction.  When a junctional pacemaker is initiating the rhythm, the atria and ventricles are depolarized almost simultaneously.  This can produce a P wave in front of the QRS with a short PR interval, during the QRS, or after the QRS.  Sometimes, in junctional rhythm, a block prevents the impulse from entering the atria, producing NO P wave.  Junctional rhythms are usually slow "escape" rhythms, but can be accelerated or tachycardic.

The fact that this rate is 110 / minute and the PR interval is normal at .12 seconds, we should consider that this rhythm could also be from an ectopic pacemaker low in the atria.  From this low starting point, the impulse will travel backward, in a "retrograde" fashion, through the atria, producing a negatively-deflected P wave in Lead II.

We do not have clinical data on this patient, and so do not know what possible causes of arrhythmia might be present, and what the expected rate should be in this situation.  

We do not have a patient history for this ECG, other than that it was an 81-year-old woman with chest pain.  The classic signs of acute ST-elevation inferior wall M.I. are there:  ST segment elevations in Leads II, III, and aVF.  There are the expected reciprocal ST depressions in Leads I and aVL.   The ST depression in V2 suggests posterior wall injury, and would normally be seen in V1 as well, unless something else is causing ST elevation in V1 at the same time.  That "something" would be right ventricular injury, and it can be confirmed by performing a V4Rt (or full set of right-sided V leads).  The slight elevation in V3 and V4 don't seem to "fit" with the IWMI - one might expect V5 and V6 to have ST elevation, reflecting injury in the low lateral wall.  We don't have the cath lab results, so we do not have an explanation for this (lead placement issues, perhaps?).

The rhythm here is interesting, but not unexpected with IWMI.  The rhythm is junctional, as reflected by the regular, narrow QRS complexes at a rate of about 54/min.  IWMI often causes blocks of the AV node, which has the same blood supply as the inferior wall in most people.  Even though there appear to be some "PR intervals", they are not consistent, and also do not meet the criteria for second-degree AVB Type I, so we are left with an interpretation of complete heart block.  The P waves here are also inconsistent.  They are regular at times, then disappear.  The SA node can be affected in IWMI also, and develop rate irregularities and exit blocks.  The IMPORTANT thing to consider is how the patient is handling the rate.  If this rate is not causing perfusion problems, that is - the patient has enough rate to maintain her blood pressure and level of consciousness, the rate is not harmful, and the junctional rhythm is not harmful.  In fact, one could argue that this junctional rhythm is more beneficial to the injured heart than a faster sinus rate would be.