Monday, April 24, 2023

ECG Blog #376 — A 15yo with Fever ...

The 12-lead ECG and long lead rhythm strip in Figure-1 — was obtained from a previously healthy 15-year old male, who presented with fever and diarrhea. He was hemodynamically stable. No chest pain.
  • How would YOU interpret the ECG in Figure-1?
  • What is the cardiac rhythm?
  • What do you suspect as the clinical diagnosis?

Figure-1: The initial ECG in today’s case — obtained from a 15-year old male with fever and diarrhea. What is the rhythm? What is the clinical diagnosis?

NOTE: In the interest of optimizing clinical relevancy and time efficiency for arriving at the diagnosis — I highlight in step-by-step fashion my approach to today’s case.

MY Thoughts on the Initial ECG in Today’s Case:
For cases in which the patient is hemodynamically stable — I generally like to begin by assessing the rhythm in the long lead II rhythm strip at the bottom of the tracing. After assuring myself that no immediate action is needed to treat the rhythm — I’ll often take a quick glance at the 12-lead ECG. Doing so in Figure-1 — it should be obvious that in addition to the irregular rhythm — that many of the leads in the 12-lead tracing show ST elevation or depression.
  • PEARL #1: Common things are common. In a previously healthy adolescent (who is 15 years old in today's case) — the presentation of an acute febrile illness that is without a complaint of chest pain, is highly unlikely to be due to an acute MI. As a result — as soon as I saw the irregular rhythm and both ST elevation and depression on the 12-lead ECG — I immediately suspected acute myocarditis as the most probable cause of this abnormal ECG.

Assessing the Rhythm:
I favor use of the Ps, Qs, 3R Approach for assessing the cardiac rhythm (See ECG Blog #185). To emphasize — Use of a systematic approach to rhythm interpretation should not slow you down. For example — in no more than 10 seconds of reviewing the long lead II rhythm strip in today’s case — I was able to deduce the following:
  • A certain number of P waves are present (RED arrows in Figure-2).
  • The QRS complex is narrow — so the rhythm is supraventricular.
  • The ventricular rhythm in Figure-2 is not Regular. Instead — there is a regular irregularity (ie, groupbeating) — in the form of bigeminal rhythm with alternating shorter-then-longer R-R intervals.
  • At least some of the P waves in today’s rhythm are Related to neighboring QRS complexes. We know this — because many of the PR intervals repeat. Thus, in Figure-2 — We see that the PR interval before each QRS that ends a shorter cycle is the same! (ie, The PR intervals before beats #2, 4, 6, 8, 10 and 12 are all = 0.24 second such that this tells us that each of these P waves is being conducted, albeit with 1st-degree AV block).
  • We also know that while some P waves in Figure-2 are conducting — other P waves are not conducting (which we know because the RED arrow P waves that appear just before the onset of beats #5, 7 and 9 have a PR interval that is too short to conduct)
  • Since the QRS complex nearest to these P waves that are not conducting (ie, the QRS complex of beats #5,7,9) — is narrow and looks very much like the QRS of sinus-conducted beats #2,4,6,8,10 and 12 — we can presume that beats #5,7,9 are junctional beats. And because the AV Nodal escape rate in children and adolescents may be faster than in adults (ie, 50-to-80/minute — instead of 40-to-60/minute) — beats #5,7 and 9 may represent junctional escape beats.

  • Finally — The underlying atrial rhythm in Figure-2 is probably regular. IF this is indeed the case — then there will be more P waves than QRS complexes, which means that some form of 2nd-degree AV block is likely to be present. And, the finding of group beating — in association with a regular atrial rhythm — with a number of PR intervals that repeat — should strongly suggest Wenckebach conduction.

  • To Emphasize: We have not yet proved the above assumptions. That said — keeping in mind how “Common things are common” — and — following the Ps, Qs, 3R systematic approach to rhythm interpretation — allows us within seconds to suspect the most likely clinical and rhythm diagnosis in today's case.

Figure-2: The long lead II rhythm strip that appeared below the 12-lead ECG that was shown in Figure-1. RED arrows highlight that a certain number of P waves are definitely present. Is the underlying atrial rhythm regular?

HOW to Prove Our Assumptions:
The KEY step in proving our assumptions — is to establish that the underlying atrial rhythm in Figure-2 is indeed regular. This is EASY to do with the use of calipers.
  • Set your calipers to the P-P interval suggested by any 2 consecutive P waves in Figure-2 that we can definitely identify. This could be the P-P interval defined between the 3rd and 4th RED arrows in Figure-2 — between the 5th and 6th RED arrows — or between the 7th and 8th RED arrows.
  • Realizing that slight variation in the P-P interval is common (known as sinus arrhythmia) — the PINK arrows in Figure-3 suggest the probable location of underlying sinus P waves. In support that sinus P waves are probably hiding under each of these PINK arrows — is the presence in Figure-3 of a small “hump” or notch in each of these locations (when compared to the appearance of normal ST-T waves or QRS complexes in this rhythm strip)

  • PEARL #2: Using calipers to “walk out” the P-P interval we selected makes it fast and easy to find the probable location (under the PINK arrows) of these regularly-occurring sinus P waves.

Figure-3: Using calipers makes it EASY to “walk out” the probable location of sinus P waves hiding under each of the PINK arrows. Note that a small “hump” or notch lies under each PINK arrow (compared to the normal appearance of ST-T waves and QRS complexes without PINK arrows). 

PEARL #3: The reason it is so helpful to identify an underlying regular atrial rhythm (as we have done in Figure-3) — is that doing so rules out other causes of group beating, such as PACs (including blocked PACs) and sinus pauses (as is commonly seen with Sick Sinus Syndrome).
  • KEY Point: One of the KEY criteria for recognizing AV blocks — is that the atrial rhythm should be regular (or at least almost regular — as the P-P interval may vary slightly if there is sinus arrhythmia). In contrast — P waves that clearly occur too early or too late to be consistent with a sinus rhythm, are much less likely to be due to an AV block.

Putting IAll Together: We’ve established that today’s rhythm is supraventricular with “group beating” — and with an underlying regular sinus rhythm. Some P waves conduct — but others do not. There are more P waves (ie, colored arrows in Figure-3) than QRS complexes — so, some form of 2nd-degree AV block appears to be present, although we've not yet established the precise mechanism.
  • As emphasized in ECG Blog #326 (and as I review in the ADDENDUM below— Mobitz I, 2nd-Degree AV Block (ie, AV Wenckebach) — is by far (!) the most common form of 2nd-degree AV block, especially when there is consistent group beating as we see in Figure-3.
  • There are many different forms of AV Wenckebach — some of which do not show obvious progressive PR interval prolongation until a beat is dropped. For example — It is common to see junctional escape beats with AV Wenckebach (See ECG Blog #63 for illustration of this phenomenon).
  • The QRS complex is narrow (The QRS is typically narrow with Mobitz I — whereas it is almost always wide when Mobitz II is present).
  • The PR interval is increased for those P waves that do conduct (which is commonly seen with Mobitz I — much more so than with Mobitz II).
  • We do not see consecutively conducted P waves with a constant PR interval anywhere on today's tracing (as is required for there to be the Mobitz II form of AV block)

  • BOTTOM Line: With regard to the rhythm in today's case — I knew within seconds that some form of AV Wenckebach was almost certain to be present (especially in view of the clinical scenario, that strongly suggested acute myocarditis as the underlying etiology).


Taking Another LOOK at Today's 12-Lead ECG:
As emphasized above in Pearl #1 — Common things are common. ECG abnormalities in a previously healthy adolescent, who presents with an acute febrile illness — is unlikely to be due to an acute MI (all the more so in today's case — in which this 15-year old did not even have chest pain). For clarity — I've reproduced the initial tracing from today's case in Figure-4. I see the following:
  • Regarding the Rhythm: Group beating is present in a bigeminal pattern, with regular sinus P waves (as described in detail above). This is almost certain to represent some form of AV Wenckebach.

  • Regarding Intervals: Conducted beats manifest a prolonged PR interval — the QRS is narrow everywhere — the QTc may be slightly prolonged.
  • There is a vertical frontal plane axis (ie, the QRS is nearly isoelectric in lead I — if not slightly negative).
  • There is no chamber enlargement.

Q-R-S-T Changes:
  • Q Waves — are seen intermittently in leads I,aVL; and in V1,V2 (ie, a tiny initial r wave is seen for some beats in these leads). 
  • R Wave Progression — is appropriate, with transition (where the R wave becomes taller than the S wave is deep) occurring at a normal location between leads V3-to-V4.

  • ST-T Wave Changes — There is coved ST elevation in high-lateral leads I and aVL — as well as in lead V2 (and to a much lesser extent in lead V1). There is marked ST depression in each of the inferior leads. There is also ST depression in leads V2-thru-V4 (downsloping in lead V3) — with terminal T wave positivity in these leads.

BOTTOM Line: The ECG in Figure-4 is markedly abnormal. In addition to probable Mobitz I, 2nd-degree AV block — multiple leads show either ST elevation or ST depression that is not characteristic of any specific anatomic area for acute coronary occlusion (especially given the presence of AV Wenckebach, but in the absence of acute inferior ST elevation).
  • As emphasized above — the History in today's case is most consistent with acute myocarditis — because the patient is an adolescent with an acute febrile illness, but no chest pain. 

  • PEARL #4: The ECG findings of acute myocarditis are highly variable. Virtually anything can be seen, depending on the specific etiology of the myocarditis, and the severity of illness. That said — One often sees Q waves and ST-T wave abnormalities that may be marked (with or without any of a variety of cardiac arrhythmias) — but which occur in a distribution that typically does not suggest a specific anatomic location. This is precisely what we see in Figure-4.
  • At other times — the ECG of a patient with acute myocarditis may look very similar to that of an acute evolving infarction. Both entities manifest troponin elevation (that may be marked) — and sometimes cardiac catheterization (or Cardiac MRI, if available) may be the only way to distinguish between these 2 entities.
  • To Emphasize: When the patient is older and presents with a history of cardiac-sounding chest pain — then acute infarction will be much more common than acute pericarditis, myocarditis, or perimyocarditis.

Follow-Up in Today's CASE:
The patient in today's case was diagnosed as having acute myocarditis. The patient did well with conservative management — and both ECG and the rhythm abnormality resolved as his clinical condition improved.

Figure-4: I've reproduced from Figure-1 the initial tracing in today's case.


Beyond-the-Core: Laddergram Illustration ...
Certain complex arrhythmias may have more than a single plausible rhythm interpretation. The fact that this occurs in today's case — is what makes interpretation of today's rhythm so challenging.
  • To Emphasize: Precise determination of the mechanism of today's arrhythmia is not needed for appropriate management. Instead — simply recognizing that some form of AV Wenckebach is likely to be present (as we describe above) — in association with an acceptable ventricular rate — is clinically sufficient, since a normal rhythm will most probably return as the patient's acute myocarditis resolves. That said — It may be insightful to review step-by-step construction of a laddergram when the mechanism of the rhythm is not immediately apparent.

Constructing the Laddergram:
  • NOTE: For more on the basics of HOW to Read (and/or Draw) Laddergrams — Please see my ECG Blog #188 —

Figure-5: I find it easiest when constructing a laddergram — to first complete the Atrial Tier (that shows atrial activity). The BLUE arrows illustrate how I drop a vertical line from the onset of each P wave.

Figure-6: It is also usually easy to fill in the Ventricular Tier — which I do by dropping vertical lines down from the onset of each QRS complex.

Figure-7: Once the Atrial and Ventricular Tiers are filled in — We can begin "solving" the laddergram. I do this by connecting those P waves that I am certain are conducting — with the QRS in the Ventricular Tier that is likely to be produced. In today's case — this will be for the P waves in front of beats #2,4,6,8,10 and 12 — because these P waves all have the same PR interval.

Figure-8: The reason today's rhythm is so challenging — is that I see 2 possible mechanisms that may explain this arrhythmia.
— — — — — — — — 
Possibility #1: We have previously established that the PR interval of the YELLOW P waves is too short to conduct. I therefore suspected that beats #1,3,5,7,9 and 11 are junctional escape beats — which I have drawn in as small RED circles within the AV Nodal Tier. This leaves me with having to explain the path within the AV Nodal Tier to be followed by the YELLOW and WHITE P waves.

Figure-9: I thought it logical to postulate that the WHITE P waves are not being conducted because of the 2nd-degree AV block. Although we know that the YELLOW P waves are also not conducted (because their PR interval is too short to conduct) — these YELLOW P waves never have a "chance" to conduct (because the junctional escape rhythm takes over before these P waves can make it to the ventricles). Whether these YELLOW P waves would conduct IF junctional beats #1,3,5,7,9 and 11 did not occur is unknown.

Figure-10: There is a 2nd Possibility for the mechanism of today's rhythm. Some patients have dual AV Nodal Pathways — each with their own conduction properties. In such cases — there may be a marked difference in the PR interval for those P waves on the rhythm strip that are conducting (depending on which AV Nodal Pathway is being used). IF dual AV nodal pathways were operative in today's case — then the BLUE arrow P waves in Figure-10 may be conducting with a very long PR interval — and — it may be that the WHITE arrow P waves are the ones that are not conducted because of this unusual pattern of Mobitz I.

As noted earlier — Complex arrhythmias may sometimes have more than a single plausible rhythm interpretation. I am not certain whether Possibility #1 or #2 is the correct explanation in today's case. That said, as noted earlier — Clinically, it does not matter!
  • Some form of AV Wenckebach is present. The overall ventricular rate is more than satisfactory (ie, the average rate is over 80/minute) — and given the diagnosis of acute myocarditis — we anticipated that the AV conduction disturbance would resolve as the patient's condition improved. It did — and the patient recovered uneventfully.


Acknowledgment: My appreciation to Chaim Katalan (Laniado Hospital, Israel) for the case and this tracing.



Related ECG Blog Posts to Today’s Case:

  • ECG Blog #205 — Reviews my Systematic Approach to 12-lead ECG Interpretation.
  • ECG Blog #185 — Review of the Ps, Qs, 3R Approach for systematic rhythm interpretation.

  • ECG Blog #188 — Reviews how to read and draw Laddergrams (with LINKS to more than 80 laddergram cases — many with step-by-step sequential illustration).

  • ECG Blog #236 — Reviews the 3 Types of 2nd-Degree AV Block.
  • ECG Blog #63 — for a case of AV block with junctional escape beats
  • ECG Blog #192 — Reviews the Causes of AV Dissociation (and emphasizes why AV Dissociation is not the same thing as Complete AV Block).
  • ECG Blog #186When to suspect Mobitz I?


ADDENDUM (4/24/2023):

One of the most problematic areas in arrhythmia interpretation is assessment of the AV Blocks. This doesn't have to be so difficult ... I review the basics in ECG Blog #186 — which are briefly summarized in the Audio Pearl below.

  • In ECG Blog #236 — my 15-minute ECG Video Pearl #52 reviews how to recognize the 2nd-Degree AV Blocks (including "high-grade" AV block).
  • Section 2F (6 pages = the "short" Answer) from my ECG-2014 Pocket Brain book provides quick written review of the AV Blocks (This is a free download).
  • Section 20 (54 pages = the "long" Answer) from my ACLS-2013-Arrhythmias Expanded Version provides detailed discussion of WHAT the AV Blocks are — and what they are not! (This is a free download).

ECG Media PEARL #4 (4:30 minutes Audio): — takes a brief look at the AV Blocks — and focuses on WHEN to suspect Mobitz I.

  • What follows below is a 7-page excerpt from my ACLS-2013 Arrhythmias (Expanded Version) book — in which I review the distinction between AV dissociation vs complete AV block.


  1. Stunning! I believe nobody can match you in Arrhythmias, Hats off to you!

  2. Your blog is a treasure... It should be saved for the next generations ... Thank you for your great help

    1. Thank you so much for the kind words! My pleasure — :)