Wednesday, March 4, 2020

A 40-something with chest pain. Is this inferior MI?

This was sent by a Saleh Hatem, an avid reader of the blog.

The patient presented with chest pain:
ECG #1: There is a narrow complex tachycardia.
Is there inferior ST Elevation?

Here was my interpretation:

What appears to be ST Elevation in inferior leads is really a P-wave that is contiguous with the QRS. (The next bump over is a T-wave that looks like a P-wave!).

Since the P-wave is not inverted, it is NOT retrograde, and therefore it is a native sinus beat.  This sinus beat does conduct, but there is severely prolonged PR interval (severe first degree AV block), with a PR interval of over 400 ms.

So: Sinus tachycardia with severe first degree AV block.

Here is what he wrote:

Her serial trop was negative.  

Later ECGs confirmed your interpretation, Dr. Smith.  Thanks.

The reader later sent these same followup ECGs:

ECG #2: The sinus rate has slowed and now the P-wave is hidden in the T-wave.

ECG #3: The sinus rate has slowed even more and now the P-wave comes after the T-wave, with a PR interval of just under 400 ms.

MY Comment by KEN GRAUER, MD (3/1/2020):
This is an insightful case succinctly explained by Dr. Smith. For the purpose of academic discussion — I will expand on a number of important points.
  • For clarity — I have reproduced and labeled the ECG in this case in Figure-1. (Please NOTEI wrote my comment before the reader sent in the 2 follow-up tracings in this case = ECGs #2 and #3).

Figure-1: The ECG sent to Dr. Smith by a reader. The patient presented with chest pain. Presumably, this is her initial ECG obtained in the ED (See text).

MTHOUGHTS: Despite my best efforts to straighten this tracing — it is both angled and folded, and this distorts measurement of intervals.
  • Cell phone pictures of ECGs have become an invaluable tool for quick delivery of acute tracings to others for timely expert consultation. That said — it is important to remember that folding and angling of a tracing will distort ECG grid lines. Inability to reliably measure intervals because of this distortion may greatly impair accurate interpretation of complex arrhythmias. For Example — In Figure-1, the reason my caliper measurement of the PR interval varies is not because the PR interval is increasing — but because this tracing is slanted!
  • As per Dr. Smith — the underlying rhythm in Figure-1 is sinus tachycardia, with marked prolongation of the PR interval (I measure a PR interval ~2 large boxes in duration = 0.40 second). I’ve marked a number of P waves with RED arrows — whereas the T wave in the long lead II rhythm strip is highlighted by a BLUE arrow.
  • As per Dr. Smith — the polarity of each P wave is what tells us that P waves (RED arrows) are conducting forward with a very long PR interval, rather than backward in retrograde fashion. Thus, P waves are upright in each of the 3 inferior leads (RED arrows) — and negative in right-sided leads aVR and V1 (GREEN arrows), as is commonly seen with forward-conducting sinus P waves.
  • I believe the R-R interval in Figure-1 is constant — although this is not easy to determine because of the aforementioned distortion of the ECG grid. The reason I KNOW that the PR interval is not increasing in this tracing — is that the distance from each P wave in the long lead II rhythm strip — to the preceding QRS complex (ie, the QRS complex behind it) remains the same.
  • The rate of the sinus tachycardia in Figure-1 is extremely fast = about 130/minute! So, my 1st, 2nd and 3rd questions about this patient would be WHY is her heart rate so fast?

Finally — We should ask, WHY is the PR interval so long?
  • Most of the time with sinus tachycardia the PR interval decreases. We are not privilege to any information about this female patient beyond that she presented with chest pain — and was found to have negative serial troponins. I can’t remember the last time I saw a tracing with sinus tachycardia this fast — and a PR interval this long. Therefore — I’d LOVE to know more about the clinical history and follow-up in this case.
  • PEARL — I found a short-and-sweet Review regarding 1st-Degree AV Block by Oldroyd and Makaryus (CLICK HERE). Among the Common Causes of 1st-Degree AV Block listed in this brief Review (to which I added some + suggestion from Dr. Jerry Jones in Comments below) are: iincreased vagal tone (especially common in younger individuals with athletic training); ii) Fibrotic changes of the cardiac conduction system (especially in older patients); iii) Coronary artery disease (including Acute MI); iv) Inflammation/infection (presumably myocarditis; rheumatic fever; endocarditis; etc.); v) Infiltrative disease; vi) Lyme disease with carditis; andvii) Neuromuscular disorders.
  • P.S. We are told that "later ECGs confirm the impression that the rhythm is sinus tachycardia with 1st-degree AV block". I'd LOVE to see those later ECGs. Was this patient in sinus tach with a very long 1st-degree block — or — Was the rhythm in Figure-1 really ATach (Atrial Tachycardia), in which the PR interval can be short or long depending on where the atopic atrial activity originates?

  • FOLLOW-UP Note (3/4/2020): My wish was granted! After I posted the above comment — the reader sent us ECGs #2 and #3, which were the follow-up tracings in this case (See the end of Dr. Smith discussion above). As per Dr. Smith — as the heart rate slowed down, confirmation that the PR interval was indeed unchanging (ie, ~0.40 second) became evident — which proves the diagnosis of 1st-Degree AV Block (and rules out Mobitz I with a long Wenckebach cycle; and also rules out Atrial Tachycardia as a possibility). This leaves to be determined: i) Why the patient presented in such a rapid Sinus Tach (ie, ~130/minute); and, ii) Why this patient has such a markedly prolonged PR interval. Our THANKS to Dr. Smith and the reader for presentation of this case!


  1. Steve and Ken...

    Last year I spoke at an AAEM assembly in Las Vegas on this very topic. First degree AV block is not very common in people under the age of 50 (around 1.6%), so whenever you see a 1st degree AV block in someone in the "under-50" age group, you MUST ask yourself "Why?" Of course, you DID exactly that!

    1st degree AV block is not always a benign finding in that it may be a harbinger of something quite serious. Always consider Lyme carditis: it often presents as a 1st degree AV block, but up to 50% (depending on which article you read) of Lyme disease patients presenting with 1st degree block will go on to develop 3rd degree AV block - sometimes very precipitously!

    Another problem to consider is an aortic para-valvular abscess that is impinging on the His bundle as a result of infective endocarditis. The patient's history and exam usually allow the physician to hone in on that diagnosis fairly quickly.

    I've always maintained that among the most frustrating and difficult dysrhythmias I've ever had to diagnose, a simple sinus tachycardia with a 1st degree AV block can be among the worst. This one wasn't - fortunately - but they CAN result in a real conundrum at times.

    1. THANKS so much for your comments Jerry. Following your suggestion — I just now credited YOU with addition of Lyme carditis (under my PEARL above) among entities to consider when one sees 1st degree AV block. P.S. KEY to solving the diagnostic conundrum you mention is additional monitoring (ideally either before or after the rhythm in question) — which unfortunately we are not privilege to in this case. As I said in my P.S. — I’d LOVE to see those later ECGs that are alluded to … THANKS as always for your comments!

  2. Thanks all for invaluable discussion..I have sent later ECGs to Dr.Smith to be included in this post..

    1. @ Dr. Alhatem — THANK YOU so much for sending us the follow-up tracings in this case! ( = ECGs #2 and #3). I have added a Follow-Up Note to My Comment above regarding these last 2 tracings — which as you said confirms the diagnosis of sinus tachycardia with marked 1st-degree AV block — :)

  3. I am from Brazil and I Love this site. Everyday i am here. Kkk

    I want make a question. Is there AV dissociation in this case?

    1. Obrigado pelo seu coment├írio Felipe! (Thanks for your comment!). No — there is no AV dissociation here — because the PR interval remains the same throughout the entire tracing in ECG #1 (which is a little hard to see, because the tracing is slanted). That the PR interval remains constant throughout is proven in the 2 follow-up ECGs (ECGs #2 and 3) — so the rhythm is 1st degree AV block (ie, each P waves DOES conduct, albeit with a very long PR interval). When there is AV dissociation — the PR interval will not remain the same throughout — because some of the P waves will not be conducting the impulse through to the ventricles — :)


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