The patient:  This ECG was obtained from a 91-year-old woman who was complaining of weakness.  Unfortunately, we have no other information. 

The ECG:  This ECG has something for your basic students, and even more for the more advanced learners.  The first thing  that anyone should notice is the slow rate.  The ventricular rate is around 35 bpm, and regular.  If the patient is showing signs of poor perfusion, we would stop here and prepare to increase the rate with a temporary pacemaker (transvenous or transcutaneous). Why is the rate so slow?  There is no P wave in front of each QRS, so this is not sinus bradycardia.  Rather, we see P waves at a rate of approximately 100 bpm, wit a very regular rhythm.  Beginners should “march out” the P waves with calipers or by marking a straight edge piece of paper.  There are 15 P waves on this ECG – some are buried within QRS complexes (QRS #3) or T waves (QRS #4).

 Because there are two distinct, regular rhythms, but they do not track with one another, we know this is possibly third-degree AV block (complete heart block).  Another clue is that there are no steady, repetitive PR intervals, which means there is no relationship between the atrial rhythm and the ventricular rhythm.

 For more advanced learners, it is helpful to try to identify the origin of the escape rhythm.  If it is junctional, the AV block is above the junction.  If the escape is ventricular, the AV block is below the junction.  A junctional rhythm is usually between 40 – 60 bpm, with a narrow QRS.  Ventricular escape rhythms are usually less than 40 bpm and with wide QRS complexes.   This ECG will be a little challenging on this front, because the rhythm has some characteristics of junctional rhythm and of ventricular rhythm.

If you are an ECG instructor, you probably carefully choose ECGs to illustrate the topic you are teaching. One of the reasons for the existence of the ECG Guru website is our desire to provide lots of such illustrations for you to choose from.

Sometimes, though, an ECG does not clearly illustrate one specific dysrhythmia well, because the interpretation of the ECG depends on so many other factors.  In order to get it “right”, we would need to know information about the patient’s history, presentation, lab results, or previous ECGs. We might need to see the ECG done immediately before or after the one we are looking at.  Some ECG findings must ultimately be confirmed by an electrophysiology study before we can know for sure what is going on.

For those of us who are “ECG nerds”, it can be fun to debate our opinions and even more fun to hear from wiser, more advanced practitioners about their interpretations.

My belief, as a clinical instructor, is that we must teach strategies for treating the patient who has a “controversial” ECG that take into account the level of the practitioner, the care setting, and the patient’s hemodynamic status.  In some settings, it might be absolutely forbidden for a first-responder to cardiovert atrial fibrillation, for example.  But atrial fib is routinely cardioverted under controlled conditions in hospitals.  The general rule followed by emergency providers that “all wide-complex tachycardias are v tach until proven otherwise” has no doubt prevented deaths in situations where care providers did not agree on the origin of the tachycardia.

The ECG:    We do not have much patient information to go with this ECG, just that it is from a 71-year-old woman who developed severe hypotension and lost consciousness, but was revived with transcutaneous pacing.   Here is what we do know about this ECG:

·        There are regular P waves, at a rate of about 39 bpm (sinus bradycardia).

This ECG was recorded from a 75-year-old man with substernal chest pain and diaphoresis.  It shows a pretty classic picture of acute inferior wall M.I. The second ECG is a repeat tracing with the V4 wire moved to the V4 Right position, and it is positive for right ventricular M.I.  The patient was found to have a 100% occlusion of the right coronary artery, which was opened and stented in the cath lab.

There are several other examples of IWMI with RVMI in our archives, so we will confine this commentary to the ECG signs that make these tracings so typical of right coronary artery occlusion. Once you are familiar with the typical pattern of IWMI / RVMI, it is easy to see, even when the ST elevation is subtle (as this one certainly is NOT).

Signs of IWMI in these ECGs are: 

·         ST elevation in inferior leads II, III and aVF.

·         Reciprocal ST depression in leads I and aVL. 

Signs of RVMI in these ECGs are:

·         ST elevation in V4 right.

·         ST elevation in V1 without ST elevation in V2.

This ECG shows a second-degree AV block, Mobitz Type II.  It is also called “high grade AV block” because there is a 3:1 ratio of P waves to QRS complexes and a resulting slow rate.

Right bundle branch block and left anterior fascicular block are also present, as is common with Type II blocks.  The underlying rhythm is sinus.  Second-degree AVB, Type II, usually represents an intermittent tri-fascicular block:  often right bundle branch block and left anterior fascicular block (hemiblock) are present, and the left posterior fascicle develops an intermittent block.  During times of tri-fascicular block, the P waves are not conducted.  When the posterior fascicle is conducting, a QRS occurs.

A differential diagnosis for this ECG is complete heart block with ventricular escape rhythm.  A longer strip would be needed to see the P waves eventually dissociate from the QRSs, if they are going to do so.  Clinically, there is really little difference in the treatment of a high-grade "second degree" block and a "third degree" block. Both are treated with emergency support of the slow rate, as needed, and then a permanent implanted pacemaker.

It is notable that, in this case, the interpretation given by the machine is completely incorrect, even including the intervals.  This is not common, but does occur.  The machine's interpretation should be considered, but not followed blindly.