Monday, May 23, 2022

ECG Blog #307 — No Symptoms, But a Slow Rate

The ECG in Figure-1 — was obtained from a man in his 40s, who was referred to the ED (Emergency Department) for a "slow rhythm". The patient was asymptomatic at the time this ECG was recorded.
  • How would YOU interpret this rhythm?
  • What are your diagnostic considerations?

Figure-1: 12-lead ECG and long lead rhythm strip recorded on an asymptomatic man in his 40s.

My Thoughts on Figure-1:
Intuitively applying the Ps, Qs, 3R Approach for assessment of the rhythm in Figure-1 (See ECG Blog #185)my initial impression of this tracing (that I made within the first ~15 seconds of seeing this ECG) — was the following:
  • There is a slow, supraventricular (narrow QRS) rhythm .
  • This rhythm is irregular.
  • There is some variation in QRS morphology (seen best in the long lead V1 rhythm strip). 
  • P waves are present — and at least some of these P waves are not conducting.
  • In a quick overall glance at this 12-lead tracing — there do not appear to be acute ST-T wave changes (at least nothing that might require prompt cath or thrombolytic treatment).

  • NOTE: The clinical goal of this quick initial look at today's tracing is meant to see IF there are any priorities that need to be immediately addressed. That said — since this patient was asymptomatic (therefore hemodynamically stable) — it is likely that he has been in this rhythm for at least some period of time — and by definition, this provides us with a moment for more careful analysis.

PEARL #1: In applying the Ps, Qs, 3R Approach — I have found the simple act of identifying all P waves to be invaluable for guiding me toward the right diagnosis.
  • Using calipers greatly facilitates identifying all of the P waves (including those partially or totally hidden within the QRS or ST-T wave of certain beats).
  • The P waves are small everywhere in Figure-1. That said — they are BEST seen in the long lead II rhythm strip. Setting calipers at the P-P interval between any 2 P waves that are clearly seen in the long lead II rhythm strip — readily allows you to "walk out" this interval throughout the rhythm strip (RED arrows in Figure-2).

PEARL #2: It is common to see slight irregularity in the P-P interval in association with slow sinus rhythms (regardless of whether or not some degree of AV block is present). Awareness of this sinus arrhythmia facilitates finding sinus P waves that may be partially hidden (ie, such as the earlier-than-expected P wave seen immediately after the QRS complex of beat #6 in Figure-2).

CHALLENGE: Look at the RED arrows in Figure-2 that highlight all sinus P waves in this rhythm strip:
  • Are any of these P waves conducted to the ventricles? IF so — Which P waves in Figure-2 appear to be conducted?
  • Are there any P waves that you know are not being conducted?

Figure-2: I've added RED arrows to highlight sinus P waves.

For clarity in Figure-3 — I've modified the colors of the arrows in the long lead rhythm strip (from Figure-2) — to highlight P waves that most probably are not conducting.
  • The 3 P waves highlighted by the YELLOW arrows in Figure-3 are definitely not conducting. The first 2 of these arrows (ie, the YELLOW arrows in front of beats #1 and #4) — highlight P waves with a PR interval that is too short to conduct.
  • The 3rd YELLOW arrow in Figure-3 highlights a P wave that occurs immediately after beat #6. We know that this P wave is also not conducting — because it clearly falls within the absolute refractory period.

  • Of the remaining 6 P waves — the 2 P waves highlighted by the PINK arrows (that occur nearly midway between beats #3-4 and between #5-6)are highly unlikely to be conducted, because this would require an exceedingly long PR interval.

  • RED arrows highlight the remaining 4 P waves. Each of these remaining 4 P waves could be conducting.

PEARL #3: Perhaps the BEST clue that a P wave is being conducted to the ventricles — is when the same PR interval is seen before several beats.
  • In Figure-3the PR interval preceding beats #2, 5 and 7 is identical. Therefore — each of the P waves in front of these beats is being conducted to the ventricles. I measure this PR interval as slightly more than 1 large box in duration (ie, ~0.22 second) — so, consistent with 1st-degree AV block.

  • QUESTION: Isn't the PR interval preceding beat #3 slightly longer than the PR interval before beat #2?

Figure-3: I've labeled the P waves in today's rhythm with 2 additional colors.

Putting It All Together:
We have essentially "solved" the arrhythmia in Figure-3:
  • The underlying rhythm is sinus bradycardia and arrhythmia (with an overall ventricular rate ~50/minute). The PR interval of sinus-conducted beats is prolonged to 0.22 second — so there is 1st-degree AV block.

  • Some form of 2nd-degree AV block is present — because the on-time P waves highlighted by PINK arrows in Figure-3 fail to conduct despite having more than adequate opportunity to do so.
  • The type of 2nd-degree AV block is Mobitz I (AV Wenckebach) — because in the one group of beats in which there are 2 consecutive P waves that do conduct, the PR interval progressively increases until a beat is dropped (ie, the PR interval before beat #3 is longer than the PR interval before beat #2 — and then the next on-time P wave highlighted by the PINK arrow after beat #3 is not conducted).
  • Other features consistent with the Mobitz I form of 2nd-degree AV block in Figure-3 include: i) Statistics = The clinical reality that over 90-95% of all 2nd-degree AV blocks are of the Mobitz I type; ii) The QRS complex is narrow (whereas it is usually wide with Mobitz II); and, iii) Sinus-conducted beats manifest 1st-degree AV block (whereas it is more likely that the PR interval of conducted beats with Mobitz II will be normal).

  • Clinically The importance of distinguishing between the Mobitz I and Mobitz II forms of 2nd-degree AV block — is that patients with Mobitz II are much more likely to need a pacemaker (See LINKS and the ADDENDUM below for more on the ECG diagnosis and clinical implications of the AV blocks).

What Then are Beats #1, 4 and 6?
We have emphasized that the P waves highlighted by YELLOW arrows in front of beats #1 and #4 have a PR interval that is too short to conduct. No P wave immediately precedes beat #6. Therefore — none of these beats are sinus-conducted.
  • Since the QRS complex of beats #1, 4 and 6 is narrow — these beats are not ventricular in etiology.
  • By the process of elimination, since beats #1,4,6 are neither sinus-conducted nor ventricular in etiology — they must be "escape" beats arising either from the AV node or from the Bundle of His. Because the R-R interval preceding beats #4 and #6 is long (ie, ~10 large boxes in duration — corresponding to an escape rate of ~30/minute) — these beats probably originate from "lower down" in the conduction system (ie, from the Bundle of His).
  • In support of a His origin for these escape beats — is the decidedly different QRS morphology of beats #1, 4 and 6 in the long lead rhythm strips. While QRS morphology of junctional escape beats may differ slightly from QRS morphology of sinus-conducted beats — there usually is not as marked of a difference in morphology as we see in Figure-3.

PEARL #4: Although it is fairly easy to tell which P waves are (and are not) being conducted to the ventricles in Figure-3 — it is sometimes quite difficult to determine this. In such cases — recognizing slight variation in QRS morphology may provide an important clue that indicates which beats represent non-conducted "escape" beats — and, knowing this may greatly facilitate diagnosis of the rhythm etiology (See ECG Blog #63 for an example of this Pearl in action)

PEARL #5: It is important to realize that there is transient AV dissociation in Figure-3. That is — None of the P waves highlighted by the YELLOW arrows are related to neighboring QRS complexes (because none of these P waves are conducted to the ventricles).
  • This serves to illustrate that AV dissociation is not the same thing as complete AV block. The fact that no less than 4 of the P waves in Figure-3 are conducted to the ventricles rules out the possibility of complete AV block (in which none of the P waves would be conducted to the ventricles).

  • For more on distinction between AV dissociation vs complete AV block — See ECG Blog #191.

The Laddergram:
For clarity — I've drawn a laddergram in Figure-4 of today's case, to illustrate the mechanism of this arrhythmia.

Figure-4: Laddergram of today's case. Mobitz I 2nd-degree AV block is diagnosed by progressive increase in the PR interval (from beat #2-to-beat #3) — until the P wave after beat #3 is blocked. Beats #1, 4 and 6 are "escape" beats. Although I drew these "escape" beats as originating from within the AV Nodal Tier — they may well originate from a lower level in the conduction system (ie, from the Bundle of His).

CASE Conclusion:
Surprisingly, the 40-ish year old man in today's case was not symptomatic at the time he presented with his initial ECG (which I've reproduced in Figure-5).
  • Presumably — the reason he came to the ED, was that someone noted a slow and irregular pulse.
Figure-5: The initial ECG in today's case. P waves are labeled with RED arrows.

WHY Did this Patient Present with Asymptomatic Mobitz I?
It is not common for patients to present with significant bradycardia and 2nd-degree AV block without any symptoms — especially in the younger adult age group of today's patient. As a result — this case presentation should raise a number of questions:
  • Was the patient truly asymptomatic? Many patients deny or ignore symptoms — so a careful history in hope of discovering clues to the rhythm etiology is essential.
  • The most likely etiology for a bradycardia with Mobitz I, 2nd-degree AV block — would seem to be a myocardial infarction that the patient was somehow unaware of. While the ECG in Figure-5 does not show obvious signs of recent or acute infarction — there are some subtle ECG findings. These include: i) A hint of ST segment coving and elevation in the 1 QRST complex that we see in lead aVL (corresponding to beat #3); and, ii) A taller-than-expected R wave appears in lead V3. These 2 findings could be consistent with recent postero-lateral infarction — though they are in no way definitive. Other leads show no more than nonspecific ST-T wave flattening.

  • Additional considerations for entities that might result in Mobitz I, 2nd-degree AV block are shown in Figure-6. If nothing in a careful history and thorough evaluation of this patient suggests any of these entities — cardiac cath should be considered, looking for underlying "silent" coronary disease that might be amenable to reperfusion.
  • If nothing "fixable" is found — a pacemaker may ultimately be needed if there is further slowing of the overall ventricular rate and/or if symptoms develop.

Figure-6: Diagnostic considerations for a patient who presents in AV block (adapted from Mangi et al — StatPearls, 2021).

Acknowledgment: My appreciation to Mubarak Al-Hatemi (from Qatar) for the case and this tracing.

For MORE on Diagnosis of ABlocks/AV Dissociation:
  • ECG Blog #185 — Reviews the Ps, Qs, 3R Approach to Rhythm Interpretation.

  • ECG Blog #188 — for Review on How to Read (and Draw) Laddergrams.

  • ECG Blog #63 — Reviews a case of Mobitz I with Junctional Escape.

  • ECG Media Pearl #4 (4:30 minutes Audio— The AV Blocks & WHEN to Suspect Mobitz I — See ECG Blog #186 —
  • ECG Media Pearl #(12:00 minutes Video ECG Blog #189 — What type of AV Block? Detailed analysis of this challenging arrhythmia (including ECG Video with step-by-step analysis of this complex laddergram).

  • ECG Media Pearl #8 (8:20 minutes Video) — ECG Blog #191 — Distinguishing between AV Dissociation vs Complete AV Block.
  • ECG Media Pearl #9 (5:40 minutes Video) — ECG Blog #192 — Reviews the 3 Causes of AV Dissociation.

  • ECG Media Pearl #19 (5:00 minutes Audio) — ECG Blog #202 — How to quickly rule out complete AV Block within seconds!
  • ECG Media Pearl #41 (4:00 minutes Audio) — ECG Blog #224 — Reviews HOW to recognize Mobitz I within seconds when there is ongoing Inferior STEMI.

ADDENDUM (5/23/2022):
This 15-minute ECG Video — Reviews the 3 Types of 2nd-Degree AV Block — plus — the hard-to-define term of "high-grade" AV block. I supplement this material with the following 2 PDF handouts.
  • 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).
  • Mobitz I ( = AV Wenckebach).
  • Mobitz II.
  • 2nd-Degree AV Block with 2:1 AV conduction.

Thursday, May 19, 2022

ECG Blog #306 — Alternating Beats

The ECG in Figure-1 — was obtained from a 60-year old woman, who presented to the ED (Emergency Department) with intermittent shortness of breath over the past week. No chest pain. The patient has a history of diabetes and hypertension.
  • How would YOU interpret the ECG in Figure-1?
  • Why are there "alternating" beats?

Figure-1: 12-lead ECG obtained from a 60-year old woman with intermittent dyspnea (but no chest pain).

NOTE: Today’s tracing is another ECG “Quick Case” ( EQC) — in that I’ll provide a more “time-efficient” account of my thought process (with goal toward expediting your interpretation within seconds rather than minutes)! Relevant links are at the bottom of the page.


MY Thoughts on the ECG in Figure-1:
The technique for recording today's ECG provides us with a continuous look at the rhythm — but the leads switch halfway through.
  • The advantage of this technique — is that it provides us with a simultaneous look at the first 9 beats in each of the 6 limb leads — and then, a simultaneous look at beats #10-thru-17 in each of the 6 chest leads.
  • The disadvantage — is that we do not get to see the rhythm strip recorded entirely from the perspective of any one lead.

Even before applying the Ps, Qs, 3R Approach for assessing the rhythm (as described in ECG Blog #185) — I was "struck" by the picture of "alternating" beats in Figure-1. By this I mean — that the shape of each QRST complex changes every-other beat. In this sense — this is a bigeminal rhythm.
  • I reviewed the concept of "Bigeminy" — and the common bigeminal rhythms in ECG Blog #243. Given the obvious widening of every-other-beat in Figure-1 — the principal diagnostic considerations would be distinction between: i) Ventricular bigeminy (in which every-other-beat is a PVC); ii) Atrial or junctional  bigeminy (in which every-other-beat is a PAC or PJC — with QRS widening resulting from either preexisting bundle branch block or aberrant conduction)vsiii) Sinus rhythm with a conduction defect such as bundle branch block occurring every-other-beat.

PEARL #1: As is so often the case — the simple act of labeling all P waves is often revealing (Figure-2).
  • RED arrows in Figure-2 show that the underlying rhythm is a regular sinus tachycardia at ~120/minute. Doesn't the PR interval look to be the same in front of each of the 17 beats on today's tracing?

PEARL #2: If the reason for the alternating beats in Figure-2 is atrial, junctional or ventricular bigeminy — then the wider beats should be "premature" (ie, PACs, PJCs and PVCs are all characterized by their early occurrence before the next expected sinus beat).
  • Therefore — the KEY to diagnosing the etiology of the rhythm in Figure-2, is to carefully measure the R-R interval from the beginning of a normally-conducted sinus beat — until the beginning of a wider sinus-conducted beat ( = the R-R interval marked "A" in both limb leads and chest leads).
  • Then compare this interval "A" — to the R-R interval marked "B", which extends from the onset of a wider sinus-conducted beat — until the next normally-conducted (narrower) beat.
  • In both limb leads and chest leads — interval "A" is precisely equal to interval "B". And since the PR interval preceding all beats in this tracing is the same — this confirms that all beats in Figure-2 are sinus-conducted with the same PR interval. The only thing changing — is that the QRS complex becomes wider every-other-beat — because all even-numbered beats in Figure-2 ( = beats #2,4,6,8,10,12,14,16) are being conducted with LBBB (Left Bundle Branch Block)

Figure-2: I have labeled all P waves from Figure-1 — and compare the R-R intervals of alternating beats (See text).

Intermittent Bundle Branch Block:
We are used to seeing conduction defects (ie, RBBB, LBBB, IVCD, hemiblocks) occur with every beat. On occasion — conduction defects may be "rate-related" (usually in association with an increase in rate — in which the QRS widens when the rate accelerates to a certain amount — and then narrows again after the rate slows down).
  • Conduction defects can also be intermittent. Usually this occurs with a "fixed" interval of time between beats that conduct normally, and wider beats that manifest the conduction defect (ie, most often showing the intermittent conduction defect  every 2nd, every 3rd, or every 4th beat). This is the situation with today's tracing — in which we see LBBB conduction every-other-beat.
  • On occasion — the intermittent conduction defect may show random alternation between normal and impaired conduction, with no "fixed" interval between narrow and wider beats (See My Comment in the June 25, 2020 post in Dr. Smith's ECG Blog).

What We Can Learn from Intermittent BBB Conduction!
Because conduction defects alter the sequence of ventricular depolarization — the sequence of ventricular repolarization will also be changed! As a result — it will always be more challenging to evaluate ST-T wave changes in association with a conduction defect (especially with LBBB — which alters the initial vector of ventricular depolarization).
  • PEARL #3: Today's tracing offers the unique opportunity to see the effect that LBBB may have in each of the 12 leads of an ECG. To facilitate visualizing this effect — I first color in BLUE the odd-numbered beats which are conducted normally (Figure-3). Doing so allows us to appreciate the even-numbered beats — which are conducted with LBBB.

  • NOTE: QRS morphology for the even-numbered beats in Figure-3 is typical for LBBB in the limb leads (ie, monophasic, all upright R wave in high-lateral leads I and aVL). The straight descent with predominant negativity for the anterior leads is typical for LBBB — although lead V6 lacks the monophasic R wave usually expected with typical LBBB.

  • PEARL #4: With LBBB — the finding of very deep S waves in one or more of the anterior leads (ie, deeper than 25-30 mm) suggests LVH. This is seen is leads V1 and V2 (which manifest S waves of 30 and 25 mm, respectively).
  • Because the left ventricle enlarges not only to the left, but also posteriorly with LVH — some patients with LBBB will not manifest an all-upright R wave until we arrive at a lead more lateral than lead V6 (ie, a lead V7 or V8). However, given how typical the morphology of even-numbered beats is for LBBB in both high-lateral and anterior leads — I'd assess the conduction defect in this tracing consistent with LBBB.

  • As discussed in ECG Blog #204 and ECG Blog #282 — ST-T waves for the even-numbered beats in Figure-3 that are conducted with LBBB morphology do not suggest acute infarction.

Figure-3: I've colored in BLUE the odd-numbered beats that manifest normal conduction. This facilitates assessment of the even-numbered beats — which manifest LBBB conduction (See text).

PEARL #5: Assessment of acute ST-T wave changes is best made by identifying the normally-conducted sinus beats in a tracing. To facilitate this assessment — I've colored in YELLOW the even-numbered beats in Figure-4, which are conducted with LBBB.
  • While true that it will at times be possible to identify acute ST-T wave changes in beats conducted with bundle branch block — I always begin by focusing on ST-T wave assessment of normally conducted beats, as it's usually much easier to spot abnormal findings in sinus-conducted beats.

  • Note in Figure-4 — that there is diffuse ST depression (ie, in almost all leads — most marked in leads V3-thru-V6) in the normally-conducted beats. This occurs in association with ST elevation in these odd-numbered beats in lead aVR.

PEARL #6: Recognition of the ECG pattern seen in Figure-4 for the normally-conducted beats — in which there is diffuse ST segment depression (usually present in at least 7-8 leads+ ST elevation in lead aVR — should immediately suggest the following Differential Diagnosis:
  • Severe Coronary Disease (due to LMain, proximal LAD, and/or severe 2- or 3-vessel disease) — which in the right clinical context may indicate ACS (Acute Coronary Syndrome).
  • Subendocardial Ischemia from another Cause (ie, sustained tachyarrhythmia; cardiac arrest; shock/profound hypotension; hypoxemia; GI bleeding; anemia; "sick patient"; etc.).
To EMPHASIZE: This pattern of diffuse Subendocardial Ischemia does not suggest acute coronary occlusion (ie, it is not the pattern of an acute MI) — but rather ischemia due to the above differential diagnosis!

Figure-4: I've colored in YeLLOW the even-numbered beats that manifest LBBB conduction. This facilitates assessment of the odd-numbered beats — which are normally conducted (See text).

FINAL Comparison:
I complete my discussion of this deceptive rhythm — by isolating in Figure-5, a direct comparison between normally-conducted beats vs beats conducted with LBBB:
  • I find it insightful to directly compare QRS and ST-T wave morphology of the normally-conducted sinus beats (ie, beats #3 and 11)vs — beats conducted with LBBB (ie, beats #4 and 12).

Figure-5: Direct comparison between normally-conducted beats vs beats conducted with LBBB.

Putting It All Together:
Today's tracing was obtained from a 60-year old woman, who presented to the ED with intermittent dyspnea (but no chest pain) over the past week. The patient had a history of diabetes and longstanding hypertension.
  • The rhythm in today's tracing is sinus tachycardia at ~120/minute. Every-other-beat is conducted with LBBB. The very deep anterior S waves in beats conducted with LBBB suggests LVH. The marked and diffuse ST depression, with ST elevation in lead aVR — suggests diffuse subendocardial ischemia.
  • As suggested above in Pearl #6 — diffuse subendocardial ischemia could be due to severe coronary diseaseor — to some other cause. The patient's age, co-morbidities (ie, diabetes, hypertension) and symptoms (dyspnea, albeit without chest pain) — clearly predispose to coronary disease. IF there is no heart failure or other potentially treatable disorder — cardiac cath may be needed to clarify the anatomy. 

Acknowledgment: My appreciation to Hafiz Abdul Mannan Shahid (from Lahore, Pakistan) for the case and this tracing.

Relevant ECG Blog Posts to Today’s Post: 

  • See ECG Blog #185 — for review of the Systematic Ps, Qs, 3R Approach to Rhythm Interpretation.
  • ECG Blog #205 — Reviews my Systematic Approach to 12-lead ECG Interpretation.

  • ECG Blog #204 — Reviews a user-friendly approach to the ECG Diagnosis of conduction defects (ie, LBBB — RBBB — IVCD).

  • ECG Blog #282 — Reviews application of modified-Smith-Sgarbossa Criteria for evaluation acute MI with LBBB (as well as ECG diagnosis of LVH with LBBB).

  • ECG Blog #271 — Reviews the ECG diagnosis of diffuse subendocardial ischemia.

  • ECG Blog #198 — An Irregular WCT (LBBB or IVCD).
  • ECG Blog #162 — LBBB with obvious STEMI.
  • ECG Blog #146 — LBBB with Acute ST-T Wave Changes.
  • ECG Blog #204 — Assessment of Sinus Rhythm and a Wide QRS (due to IVCD).

  • The January 31, 2022 post in Dr. Smith's ECG Blog — Reviews subtle signs of acute OMI in a patient with LBBB (Please see My Comment at the bottom of the page).
  • The June 25, 2020 post in Dr. Smith’s ECG Blog — in which I review a case of Sinus Rhythm with Intermittent RBBB.

Sunday, May 15, 2022

ECG Blog #305 — The Cause of Palpitations?

The ECG and long lead II rhythm strip in Figure-1 — was obtained from a previously healthy middle-aged woman, with a history of intermittent palpitations over the past few months. No syncope or chest pain. She was hemodynamically stable at the time this ECG was recorded.

  • How would YOU interpret the ECG in Figure-1?
  • What might cause this rhythm?

Figure-1: 12-lead ECG and long lead II rhythm strip recorded on a middle-aged woman with palpitations in recent months. Hemodynamically stable.

MY Thoughts on the ECG in Figure-1:
As always — I favor starting by assessing the cardiac rhythm. Applying the Ps, Qs, 3R Approach (ECG Blog #185) — to the long lead II rhythm strip at the bottom of the tracing:

  • The QRS is narrow everywhere (which we can confirm by verifying that every beat in the 12 leads above the rhythm strip has a narrow QRS).
  • The rhythm is fast and irregularly irregular. But unlike Atrial Fibrillation (AFib) — there are P waves! (Figure-2).

PEARL #1: It is sometimes difficult to distinguish between baseline artifact vs different-shaped P waves. And, sometimes both artifact and different shaped P waves (PACs) may be present:

  • This is not the case in today’s tracing! There is essentially no artifact in the baseline or within ST-T waves. As a result — What we see on this tracing is valid!
  • There is NO doubt that an upright P wave with reasonable PR interval precedes each QRS complex that follows a short pause (ie, BLUE arrows before beats #2, 6, 7, 12, 16 and 17 in Figure-2).

  • PEARL #2: The P wave in front of beat #2 in the long lead II rhythm strip deserves special mention — because it is tiny. This is the benefit of assessing the rhythm by use of simultaneously-recorded leads! A quick look straight above beat #2, at the 2nd BLUE arrows in lead I and in lead III (vertical RED lines that correspond in timing to the P wave in front of beat #2 in the long lead rhythm strip)confirms that there is a P wave in front of beat #2 in the long lead rhythm strip, albeit a P wave that looks different (smaller) than all other P waves in this long lead II (except for the equally tiny P wave in front of beat #1).

  • PEARL #3: I find the most helpful way to determine when and where P waves might be hiding (within their preceding ST-T wave) — is to figure out WHAT a “normal” ST-T wave looks like. In Figure-2 — I thought the ST-T wave of beats #1, 11 and 15 represent what a “normal” ST-T wave (ie, not altered by a PAC hidden within it) should look like. 

  • PEARL #4: The commonest cause of a pause is a blocked PAC! (See ECG Blog #14 and Blog #66). Awareness of this clinical reality has led me to always look carefully at the ST-T wave at the beginning of any relative pause in the rhythm — to see if there might be a P wave partially "buried" within that ST-T wave. And so, I thought the YELLOW arrows that occurred right after beats #6 and 16 clearly represented non-conducted atrial activity — with the notching under these arrows highlighting blocked PACs.

My Initial Impression of the Rhythm in Figure-2:
Having established that the rhythm in Figure-2 was supraventricular (narrow QRS) — and both fast and irregular — but not AFib because there clearly was atrial activity — I contemplated my differential diagnosis:
  • P wave morphology was not consistent. For example — the tiny P waves in front of beats #1 and 2 in the long lead II rhythm strip clearly looked different than the larger and rounder P waves that precede beats #7, 16 and 17. And the P wave in front of beat #12 looked taller still, as well as being more pointed. Therefore — my initial impression of this rhythm was MAT (Multifocal Atrial Tachycardia).

And then I looked again more carefully ...

Figure-2: I've labeled atrial activity from Figure-1 with BLUE arrows. I've labeled non-conducted P waves with YELLOW arrows. The vertical RED lines illustrate PEARL #2, which describes use of simultaneously-recorded leads (See text).

Regarding MAT: What Does Not "Fit" for Today's Patient:
I have previously reviewed the ECG diagnosis of MAT (See ECG Blog #199 and Blog #65).
  • MAT almost always occurs in one of 2 common predisposing settings. These 2 settings are: i) In patients with severe, often longstanding pulmonary disease; and/or, ii) In acute ill patients with multi-system disease (ie, sepsis, shock, electrolyte and/or acid base disorders). As a result — I'm hesitant to diagnose MAT in the absence of one of these 2 settings. The fact that today's patient was a previously healthy middle-aged woman is therefore against the likelihood of seeing MAT.

While labeling today's ECG for Figure-2I looked again at the long lead II rhythm strip. In Figure-3 — I've added a number of additional YELLOW arrows where the ST-T wave appears to be clearly deformed by additional non-conducting atrial activity. For many of these additional YELLOW arrows — we can see indication of partially hidden atrial activity of other simultaneously-recorded leads.
  • LOOK AGAIN at the long lead II rhythm strip in Figure-3. If you can accept the validity of the colored arrows I've added — after the first 2 P waves in each grouping — Aren't the BLUE and YELLOW arrows that follow until the pause fairly regular?

  • PEARL #5: Not all rhythms "read the textbook". While we often think of entities such as Atrial Tachycardia and MAT as "pure" rhythm etiologies — many patients do not manifest "pure" versions of these arrhythmias. I've found it best to consider entities such as ATach, MAT, wandering atrial pacemaker, and sinus rhythm with multiple PACs as ends of a "spectrum"with many patients manifesting more of a "mixture" between the spectrum end points for these various rhythm disorders.

MY "Revised" Rhythm Diagnosis:
While emphasizing that today's rhythm does not perfectly fit any of the rhythm etiologies that I mention above — I think it is closest to ATach.
  • Remember — The atrial rate with ATach is not always regular. On the contrary — ectopic atrial tachycardia is more likely to manifest a "warm-up" phase until this rhythm gets going. Perhaps the slightly longer P-P intervals at the beginning of each grouping represent such a "warm-up" phase?
  • Even with atrial impulses arising from the same site — P wave morphology may vary. Isn't it strange that the PR interval is the same for so many of the different-looking P waves in Figure-3 (ie, the P waves in front of beats #1, 2, 6, 7, 12, 13, 16 and 17). I would not expect the PR interval to remain the same for so many beats if the underlying rhythm was MAT.

  • ATach (Atrial Tachycardia) very commonly manifests Wenckebach conduction. Therefore, rather than "blocked PACs" — Perhaps the YELLOW arrows that I've drawn in Figure-3 represent non-conducted P waves from short ATach-related Wenckebach cycles?

BOTTOM LINE Regarding Today's Case:
I fully acknowledge that I do not know a definitive answer for the rhythm etiology in today's case. That said — I believe this rhythm is "clinically behaving" like an ectopic ATach in this previously healthy middle-aged woman who has intermittently been bothered by recurrent palpitations over the past few months.
  • In order is a General Evaluation of this patient — to include chest X-Ray, Echo and baseline lab work (ie, thyroid function, serum electrolytes, hematocrit).

  • Verify in this patient's History the duration of her symptoms — and determine IF she is a longterm smoker (that might predispose to MAT) — and/or if there is significant alcohol, drug, caffeine or other substance use that might predispose her to a recurrent irregular SVT.
  • IF these results did not yield clues to the etiology of today's rhythm — then empiric treatment with a medication such as a ß-blocker might be in order.

  • IF her palpitations (and this rhythm) persisted — referral to EP Cardiology would be in order.

Figure-3: The more I looked at this tracing — the more indication I saw of more atrial activity (additional BLUE and YELLOW arrows drawn in since Figure-2).


Acknowledgment: My appreciation to Arjun K Budhathoki (from Kathmandu, Nepal) for making me aware of this case and allowing me to use this tracing.


Relevant ECG Blog Posts to Today's Post:
  • ECG Blog #185 — Reviews the Ps, Qs, 3R Approach to Rhythm Interpretation.

  • ECG Blog #199 — Reviews the ECG diagnosis of MAT (including a Video Pearl on this subject).
  • ECG Blog #65 — Another example of MAT (vs Wandering Pacemaker).

  • ECG Blog #250 — Causes of a Regular SVT (including AFlutter & ATach).
  • ECG Blog #138 — ATach vs AFlutter.
  • ECG Blog #261 — Reviews a case of ATach with Wenckebach conduction.