ECG Blog #427 — To Cath this Elderly Patient?

The ECG in Figure-1 — was obtained on the scene by EMS (Emergency Medical Services). The patient was a man in his 90s, who ~1 hour earlier, noted the onset of severe CP (Chest Pain). He was hemodynamically stable — but clearly distressed with a sense of “impending doom” at the time ECG #1 was recorded.

• Despite the patient’s age — he was independent, lived alone, had good mental function — and had family support.

QUESTIONS:

• How would YOU interpret the initial ECG in Figure-1?
• Given the patient’s advanced age — Should the cath lab be activated?
• — OR — Are the QS waves in the chest leads indication of a completed infarction?
• 
  
• Extra Credit: How many beats are seen on this ECG? 

Figure-1: The initial ECG in today's case.

MY Thoughts on Today's CASE:

The format for recording today's ECG is different than that used in most medical systems that I've encountered.

• As illustrated in Figure-2 — only 7 beats are seen. For clarity — I've numbered these 7 beats in each of the 4 groups of 3 leads.
• The advantage of this type of recording system is that for these 7 beats — we get to see QRS morphology for each of these 7 beats in each of the 12 leads.
• The disadvantage of this type of recording system — is that 7 beats is a very small sample for assessing events occurring on this ECG. For example — if the 1 PVC ( = beat #5) would not have occurred until 3 beats later, then we would not have seen any PVCs on this tracing.
• 
  
• PEARL #1: My exposure over the past decade to numerous international ECG internet forums has taught me how numerous the different ECG recording formats are. It's worth routinely spending a few initial moments for verifying what recording format is used for the ECG you are about to interpret. With minimal practice — it becomes EASY to recognize the identical timing for each of the 7 beats in today's tracing — with the 5th beat always being the PVC (which confirms that this particular format only views 7 beats — but shows us QRS morphology for these 7 beats in each of the 12 leads).

Now that we have identified the recording format used for today's tracing — We can begin our systematic interpretation.

• Six of the 7 beats in today's tracing manifest a narrow QRS complex — that when measured, is irregularly irregular (ie, Although difficult to appreciate visually — caliper measurement reveals a variable R-R interval for the first 4 beats — with an obviously shorter R-R interval between beats #6 and 7).
• P waves are absent. This defines the rhythm as AFib (Atrial Fibrillation), here with a controlled ventricular response (ie, overall heart rate between ~70-to-100/minute).
• Beat #5 is a PVC (Premature Ventricular Contraction) — because it is early, not preceded by a P wave, and manifests a markedly wider and very different-looking QRS morphology in almost every lead compared to the other 6 beats.
• 
  
• The QTc looks normal.  
• There is no chamber enlargement.

Regarding Q-R-S-T Wave Changes:

• Q waves are present in leads III, aVF — with QS complexes in leads V1-thru-V5, with no more than a tiny initial r wave in lead V6.
• R Wave Progression — never occurs because of the persistence of these chest lead QS complexes.
• 
  
• Regarding ST-T Wave Changes: There is marked ST elevation, with straightening of the ST segment takeoff in leads V2-thru-V6. This J-point ST elevation attains 2-3 mm for leads V2,V3,V4 — being slightly less than this in leads V5,V6. Given that ST elevation is usually not seen in lead V1 — the 1 mm of ST elevation seen in this lead in today's tracing is abnormal.
• ST-T waves in the limb leads are also abnormal. The much broader-than-expected and "fatter"-at-their-peak T waves in leads I, II and aVL are hyperacute. There is subtle ST elevation in lead aVF — and ST-T wave flattening in lead III.
• 
  
• IMPRESSION: In this patient who presents with severe, new-onset CP — today's ECG is diagnostic of an extensive, ongoing antero-lateral STEMI.

CASE Follow-Up:

The decision was made not to activate the cath lab. Repeat ECG showed further progression of ST-T wave changes. The patient was at that point transferred for cardiac cath and PCI. Unfortunately the patient arrested before catheterization could be completed — and could not be resuscitated.

Figure-2: I've labeled today's ECG to illustrate that only 7 beats are seen. Did YOU notice the abnormal ST-T wave in the PVC? (within the BLUE rectangle in lead V3).

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COMMENT: 

• Advanced age is not a contraindication to cardiac catheterization. More important than chronologic age is functional status (This patient was living alone, fully independent, with good mental function and with family support).
• 
  
• PEARL #2: The presence of Q waves (including deep QS waves — as are seen in leads V1-thru-V5 in Figure-2) — is not necessarily an indication of completed infarction or of permanent damage. Surprisingly — even large Q waves may develop in as short a time period as 1-to-2 hours. Such Q waves may sometimes regress — and even completely resolve. Comparison with a prior ECG would be needed in order to determine the presence and extent of any previous infarction — and clinical follow-up would be needed to determine whether any new Q waves will be permanent.
• 
  
• PEARL #3: It may sometimes be difficult to distinguish between active, ongoing infarction — vs LV aneurysm that developed following a prior infarction — vs superimposed new infarction, that occurs on top of prior infarction. That said — the shape and relative disproportionality of the elevated chest lead ST-T waves in Figure-2 — compared to S wave depth in the leads being looked at, are diagnostic of an acute ongoing event until proven otherwise. The amount of J-point ST elevation with LV aneurysm is at most modest (clearly less than what we see in leads V2-thru-V5 of today's tracing) — and longstanding elevated ST segments typically do not manifest such straightening of the ST segment takeoff, as is evident in leads V2-thru-V6.

PEARL #4: Assessment of ST-T wave morphology of one or more PVCs may sometimes prove insightful for determining whether or not an acute OMI is ongoing. While clearly not needed in today's case (because assessment of the diffuse and marked chest lead ST elevation is already definitive for an acute STEMI) — on occasion, ST-T wave morphology will be diagnostic for an acute OMI only in PVCs.

• The PVC within the BLUE rectangle in lead V3 of Figure-2 — illustrates a shape of ST elevation that simply should not be there for a PVC in the absence of an acute OMI.
• An example of a case in which the diagnosis of acute OMI was made purely by assessment of ST-T wave morphology in a PVC can be found HERE (See My Comment at the bottom of this page in the October 8, 2018 post in Dr. Smith's ECG Blog). 

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Acknowledgment: My appreciation for this case that is anonymously contributed.

==================================

Related ECG Blog Posts to Today’s Case:

• ECG Blog #205 — Reviews my Systematic Approach to 12-lead ECG Interpretation.
• 
  
• ECG Blog #193 — Reviews the basics for predicting the "culprit" artery (as well as reviewing why the term "STEMI" — should be replaced by "OMI" = Occlusion-based MI).

=================================

• CLICK HERE — for my 6 new ECG Videos (on Rhythm interpretation — and on 12-lead interpretation with Case Studies for ECG diagnosis of acute OMI).
• CLICK HERE — for my 2 new ECG Podcasts (on ECG & Rhythm interpretation Errors — and — Errors in assessing for acute OMI).

=================================

• Recognizing hyperacute T waves — patterns of leads — an OMI (though not a STEMI) — See My Comment at the bottom of the page in the November 8, 2020 post on Dr. Smith's ECG Blog.
• Recognizing ECG signs of Precordial Swirl (from acute OMI of LAD Septal Perforators) — See My Comment at the bottom of the page in the March 22, 2024 post on Dr. Smith's ECG Blog. 
• 
  
• ECG Blog #294 — Reviews how to tell IF the "culprit" artery has reperfused.
• ECG Blog #230 — Reviews how to compare serial ECGs. 
• ECG Blog #115 — Shows how dramatic ST-T changes can occur in as short as an 8-minute period.
• ECG Blog #268 — Shows an example of reperfusion T waves.
• ECG Blog #400 — Reviews the concept of "dynamic" ST-T wave changes.
• 
  
• ECG Blog #337 — A "NSTEMI" that was really an ongoing OMI of uncertain duration (presenting with inferior lead reperfusion T waves).

ECG Blog #426 — Are STEMI Criteria Met?

The ECG in Figure-1 — was obtained from a 70-ish year old man with episodic CP (Chest Pain) over the previous 2-3 days, being awakened from sleep now for a more severe CP episode.

QUESTIONS:

• In view of this history — How would YOU interpret this ECG?
• Should you activate the cath lab?

Figure-1: The initial ECG in today's case.

MY Initial Thoughts on Today's CASE:

Although it is difficult from the brief history we are given, to determine the true onset of whatever might be happening — the patient's age, persistence and severity of CP are clearly cause for concern.

• Which lead(s) immediately "caught YOUR eye"?

ANSWER:

The ST-T waves in 5 leads immediately captured my attention. I have labeled these leads in Figure-2 with RED and BLUE rectangles.

• WHY did these leads capture my attention?

Figure-2: I've labeled with RED and BLUE rectangles the 5 leads that immediately "caught" my eye.

The Most Abnormal Leads in Figure-1:

When assessing a patient for a possible acute OMI — I like to begin with leads that I know are definitey abnormal.

• PEARL #1: If when assessing a patient with new CP — you see 1 or 2 leads in which you know the ST-T waves are definitely abnormal — it then becomes much easier to identify more subtle changes in neighboring leads that support your impression of an acute ongoing event.

Applying PEARL #1 to Today’s CASE:

The initial ECG in today’s case shows sinus rhythm at ~80/minute— normal intervals (PR-QRS-QTc) — normal axis — and no chamber enlargement. Although there are QS complexes in leads V1,V2 — this is not necessarily abnormal, and R wave progression is appropriate (with transition where the R wave becomes taller than the S wave is deep — occurring normally, here between leads V2-to-V3). 

• Lead III and Lead V3 (within the RED rectangles in Figure-2) — are the 2 leads in ECG #1 that I absolutely knew were abnormal.
• 
  
• The QRS complex in lead III is tiny (ie, the R wave in lead III is at most 2 mm tall). And, although the T wave in this lead is not “tall” in terms of its absolute height — this T wave in lead III is clearly disproportionate in size, with respect to its QRS complex (ie, The T wave in lead III is almost twice as tall as the R in this lead — with this T wave being “fatter”-at-its-peak and much wider-at-its-base than-it-should-be, given the dimensions of the QRS in lead III). 
• Once we recognize in this patient with new CP, that the ST-T wave in lead III is clearly hyperacute — it becomes much EASIER to recognize that the T wave in neighboring lead aVF is also disproportionately taller and “fatter”-at-its-peak than it should be, given modest height of the R wave in this lead aVF.
• 
  
• PEARL #2: It’s important to appreciate by the above principles — that even though by itself, I would not necessarily interpret the ST-T wave in neighboring lead II as “abnormal” — in the context of new CP, in which we have just identified hyperacute T waves in the other 2 inferior leads ( = leads III and aVF) — Doesn’t the T wave in this 3rd inferior lead ( = lead II) also look “fatter”-at-its-peak and wider-at-its-base than it should, especially given modest amplitude of the R wave in this lead?  
• 
  
• PEARL #3: In my experience, the EASIEST way to convince myself that ST-T wave changes in leads III and/or aVF are acute — is to LOOK FOR the “magical” mirror-image opposite relationship that almost always exists between the ST-T waves in leads III and aVL when there is acute inferior OMI (See ECG Blog #167 and Blog #184, among many other posts). 
• KEY Point: It is rare with acute inferior OMI not to see reciprocal ST-T wave changes in lead aVL. This is an important distinguishing point between inferior lead ST elevation that is normally seen with a benign repolarization variant (in which you will not see reciprocal ST-T wave changes in lead aVL) — vs with acute inferior OMI, in which you will!
• 
  
• Clearly, in Figure-1 — the ST-T wave flattening, with shallow T wave inversion that we see in lead aVL is a subtle finding (within the BLUE rectangle in aVL) — BUT — in the context of a patient with new CP and hyperacute T waves in the inferior leads — I interpreted the ST segment flattening with shallow T wave inversion in lead aVL as being consistent with a reciprocal change.

PEARL #4: Because of the common blood supply of the RCA (Right Coronary Artery) — and the LCx (Left Circumflex) artery (ie, both of these coronary arteries usually supply both the inferior and posterior walls of the left ventricle) — it is very common when you see ECG evidence of acute OMI in one of these anatomic areas, to also see it in the other anatomic area (See ECG Blog #193 — and Blog #351, among many others).

• Applying this PEARL #4 to the initial ECG in today’s case — I was hoping to find further support that the subtle ST-T wave changes in 4 of the limb leads were real — by also finding ST-T wave changes in the chest leads suggestive of acute or recent posterior OMI.
• In a patient with new CP — there should be no doubt that the ST-T wave in lead V3 in Figure-2 (within the RED rectangle in lead V3) is abnormal! Given the tiny amplitude of the QRS complex in this lead — the T wave in lead V3 is at least equally tall as the R in lead V3, with this T wave being “fatter”-at-its-peak and wider-at-its-base than it should be, given small size of this R wave.
• 
  
• PEARL #5: Normally — there should be slight ST elevation with a gently upsloping ST segment in leads V2,V3. Thus, the ST-T wave in neighboring lead V2 is also abnormal — in that the ST segment in this lead is flat without any ST elevation (ie, within the BLUE rectangle in V2).

Putting It All Together:

In view of the history of new CP — today’s initial ECG is diagnostic of an acute OMI ( = an MI with acute coronary Occlusion).

• While additional assessment can certainly be undertaken — the point to emphasize is that the ECG in Figure-1, in association with the history of new, severe CP that awakened this patient from sleep — is all that is needed to know that prompt cath with PCI should be done as soon as this is possible.
• There is no need to wait for Troponin results to come back before the patient is taken to cath. This is because even if the initial Troponin came back normal — this rules out nothing! (ie, An initial hs-Troponin may occasionally be normal with acute OMI). Therefore — there is no need to wait for Troponin results, because these results will not alter the need for prompt cath.
• Serial ECGs should of course be obtained — but, there is no need to wait for a 2nd ECG before the patient is taken to cath — since given the history of new, severe CP and hyperacute ST-T waves in multiple leads — regardless of whether a 2nd ECG looks better or worse — prompt cath is needed.
• Assuming arrangements are made for prompt cath — there will almost always be "a moment" before cath is done that a repeat ECG can be obtained, which will be helpful in assessment. But the point to emphasize, is that the decision to perform prompt cath need not wait until that 2nd ECG is done.
• As is also emphasized often in this ECG Blog — spontaneous reperfusion of the "culprit" artery is common — and, IF this occurs before a 2nd ECG is done, ST-T wave changes may "look better" (See References to related Blog posts below). But — What spontaneously opens — may just as easily spontaneously reclose — which is why even if a 2nd ECG "looks better" — prompt cath with PCI is still needed to prevent spontaneous reocclusion of the "culprit" artery at a later point.
• 
  
• Finally — this is not be called a NSTEMI (because this term would falsely imply that there has not been acute coronary occlusion — and that PCI will not be of benefit). The term "NSTEMI" has been overused, and is often applied by "default" (ie, because millimeter-based criteria for a STEMI are not seen on any of the ECGs that have been done). Instead, we know from discussion above and the pathophysiology involved, that acute coronary occlusion (ie, an OMI) is by far the most likely explanation for events in today's case.

KEY Point: All extra testing in today's case would serve to do is delay — with resultant risk of losing more myocardium that might be saved by PCI from prompt intervention. Therefore — as soon as you know there has been acute OMI — cardiac cath with PCI is indicated (without further need to "confirm" what you have already confirmed).

==================================

Acknowledgment: My appreciation to Si Cocksey (from Manchester, UK) 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 #193 — Reviews the basics for predicting the "culprit" artery (as well as reviewing why the term "STEMI" — should be replaced by "OMI" = Occlusion-based MI).

=================================

• CLICK HERE — for my 6 new ECG Videos (on Rhythm interpretation — 12-lead interpretation with Case Studies for ECG diagnosis of acute OMI).
• CLICK HERE — for my 2 new ECG Podcasts (on ECG & Rhythm interpretation Errors — and — Errors in assessing for acute OMI).

=================================

• Recognizing hyperacute T waves — patterns of leads — an OMI (though not a STEMI) — See My Comment at the bottom of the page in the November 8, 2020 post on Dr. Smith's ECG Blog.
• Recognizing ECG signs of Precordial Swirl (from acute OMI of LAD Septal Perforators) — See My Comment at the bottom of the page in the March 22, 2024 post on Dr. Smith's ECG Blog. 
• 
  
• ECG Blog #294 — Reviews how to tell IF the "culprit" artery has reperfused.
• ECG Blog #230 — Reviews how to compare serial ECGs.
• ECG Blog #115 — Shows how dramatic ST-T changes can occur in as short as an 8-minute period.
• ECG Blog #268 — Shows an example of reperfusion T waves.
• ECG Blog #400 — Reviews the concept of "dynamic" ST-T wave changes.
• 
  
• ECG Blog #337 — A "NSTEMI" that was really an ongoing OMI of uncertain duration (presenting with inferior lead reperfusion T waves).

ECG Blog #425 — Are there P Waves?

I was sent the ECG in Figure-1 — told only that the patient was 70 years old, and had a history of an ASD (Atrial Septal Defect). 

• Serum K+ was normal.
• The patient was hemodynamically stable with ECG #1.

QUESTIONS:

• How would YOU interpret the rhythm in Figure-1?
• Are there P waves?

Figure-1: The initial ECG in today's case.

MY Initial Thoughts on Today's CASE:

Knowing that today's patient has a history of an ASD (Atrial Septal Defect) — is relevant to the interpretation of today's interesting tracing!

• There are many variations of ASDs — with severity of this entity and the age at which the patient presents dependent on multiple factors. Surprisingly, patients with an ASD may present for medical attention at any age. 
• Many patients go years without significant symptoms. That said — most patients eventually do become symptomatic (Webb and Gatzoulis: Circulation 114: 1645-1653, 2006).
• 
  
• PEARL #1: Given a potentially longterm course for the patient with an ASD — it's important to appreciate that a lack of symptoms does not necessarily exclude the possibility of hemodynamically significant heart disease.
• 
  
• PEARL #2: The ECG may provide clues to the underlying severity of the ASD in a given patient — especially in the adult patient who is not overtly symptomatic. Thus, the finding of any of the following may all portend more significant underlying disease: i) Rhythm disturbances (ie, AV block; AFib/AFlutter; other atrial arrhythmias); ii) Signs of RVH and/or pulmonary hypertension (RAA, right axis, tall R and/or qR pattern in lead V1; ST-T wave changes of RV "strain"; incomplete or complete RBBB); and/or iii) LVH.
• 
  
• Given complexity of the multiple facets of ASD management during the course of a patient's lifetime — lifelong adult CHD (Congenital Heart Disease) care is recommended, as potential timing of surgical repair in adulthood is a very challenging determination to make (Cotts — Eur Heart J 43:2260-2671, 2022 — and — Lopes and Mesquite — Arq Bras Cardiol 103(6):446-448, 2014).
• 
  
• NOTE: For more on ECG recognition of RVH and/or pulmonary hypertension (re the qR pattern in lead V1) — See ECG Blog #234 and Blog #248.

Regarding the Initial ECG in Figure-1:

Realizing some technical faults with ECG #1 (slight folding and angulation of the ECG — therefore some distortion of measurements) — there appears to be a regular WCT (Wide-Complex Tachycardia) at ~135/minute, but without clear sign of sinus P waves.

• I've labeled the initial ECG in Figure-2 — to highlight the areas of uncertainty that I had in assessing this tracing. Specifically — I was not at all certain whether the BLUE arrows and question marks represented P waves with a long PR interval — or — T waves from the preceding QRS with a long QTc — or — the combination of T waves that are "fusing" with underlying atrial activity?
• 
  
• KEY Point: Given obvious QRS widening in ECG #1 — distinction between P waves vs T waves vs a combination of both is an essential determination for whether today's rhythm is likely to be supraventricular or VT (Ventricular Tachycardia).
• 
  
• PEARL #3: Knowing that today's patient has an ASD led me to suspect some form of SVT (SupraVentricular Tachycardia) instead of VT, because of how common RBBB conduction defects are in the patient with a significant ASD. And although QRS morphology in Figure-2 is somewhat unusual — the findings of QRS widening with a QR pattern in lead V1, with wide terminal S waves in lateral leads I and V6 — especially given marked fragmentation (notching) in multiple leads — could certainly be consistent with adult CHD in which the patient had a longstanding, hemodynamically significant ASD with significant underlying structural abnormality. 

Figure-2: Do the BLUE arrows and question marks represent P waves? — T waves? — and/or a fusion of T waves with underlying atrial activity?

PEARL #4: If the BLUE arrows and question marks in Figure-2 are the result of sinus P waves (that are perhaps fusing with preceding T waves) — then the PR interval would be prolonged.

• That said, as the rate of a sinus rhythm increases — the PR interval tends to shorten, probably the result of reduced basal vagal tone. Because of this, it is uncommon to see sinus tachycardia with a prolonged PR interval.
• While there are some patient who have baseline PR interval prolongation, who continue to manifest a certain amount of PR interval prolongation with sinus tachycardia — most tachycardias that seem to show a "sinus P wave" near the mid-point of the R-R interval turn out to have 2:1 AV conduction (from either ATach or AFlutter).
• As discussed in ECG Blog #227 — this principle is known as the Bix Rule, named after the Viennese cardiologist who first cautioned against "accepting" the diagnosis of "sinus tach with 1st-degree" before meticulous search for an "extra" P wave hidden within the QRS complex.
• 
  
• KEY Point: If I was able to identify 2:1 atrial activity — this would virtually confirm my suspicion that today's rhythm was some form of SVT (and not VT) — since coincidental occurrence of 2:1 atrial activity with perfectly timed simultaneous VT is extraordinarily rare.

Searching for Extra P Waves:

I illustrate in Figure-3 — how to assess the possibily of 2:1 atrial activity in today's tracing. 

• IF today's tracing was the result of an SVT with 2:1 AV conduction (from either ATach or AFlutter) — then we would expect to see evidence of an additional atrial deflection (P wave or flutter wave) at that point precisely midway between successive atrial deflections (ie, between successive RED lines in Figure-3).
• Whereas it is impossible to tell if an extra atrial deflection might be lying under the PURPLE lines in leads aVF and V3 (since the PURPLE line occurs in the middle of the QRS in these leads) — I would have expected to see some form of upright deflection under the PURPLE arrow in leads I and V2 if there was 2:1 atrial activity.
• 
  
• BOTTOM Line: While important to consider the possibility of an SVT rhythm with 2:1 AV conduction in Figure-3 — I see no evidence to support this theory.

Figure-3: How to assess for possible 2:1 atrial activity.

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Putting It All Together:

At this point in my assessment of today's rhythm — I fully acknowledge that I did not know for certain the etiology of this arrhythmia.

• I had established that today's rhythm was a regular WCT at ~135/minute — but with uncertain (if any) atrial activity. The differential diagnosis is between some form of SVT vs VT (especially since we were told that serum K+ was normal).
• Given the history of an ASD — I thought an SVT would be more likely than VT, because QRS morphology in today's rhythm looked potentially consistent with adult CHD in a patient with longstanding, underlying structural disease (ie, given the widened QR pattern in lead V1 — with wide terminal S waves in lateral leads + marked fragmentation of several QRS complexes).
• I was hoping to find evidence for 2:1 atrial activity — because if present, this would virtually confirm that today's rhythm was supraventricular. Unfortunately — my search for 2:1 atrial activity (as shown in Figure-3) was unsuccessful.
• This could have been an optimal time to try a Lewis Lead — which sometimes reveals atrial activity not evident with standard lead placement (See ECG Blog #223).
• Finding a prior tracing on today's patient could also prove insightful — especially if at a slower heart rate with sinus rhythm, the same QRS morphology is seen as appears in Figure-3. Unfortunately — no prior tracing was available at this time.
• The "good news" — is that today's patient was hemodynamically stable, which meant there was at least a moment of time to try to attain greater certainty as to the etiology of the rhythm.
• Learning more about the patient's history could be insightful.

The CASE Continues:

• The patient's medical record was found. Recent Echo showed a large Ostium Secundum ASD defect — with left-to-right shunting and huge dilatation of right-sided chambers.
• It turns out the patient had been symptomatic — with progressively increasing exertional dyspnea over the past few months.

The initial ECG was repeated — and is shown in Figure-4.

QUESTIONS:

• How would you interpret the repeat ECG shown in Figure-4?
• 
  
• Does ECG #2 clarify what the initial rhythm was?

Figure-4: ECG #2 is a repeat ECG, done later that day. 

MY Thoughts on the Repeat ECG in Figure-4:

For clarity with measurements in ECG #2 — I've drawn in 5 large boxes on the ECG grid (seen in between leads I and II in Figure-4). Note when comparing this repeat tracing with the initial ECG in today's case — that because many more beats are captured in ECG #2, that the relative size of a large box on ECG grid paper is different between these 2 tracings.

• Group beating in the form of a bigeminal rhythm (alternating shorter-then-longer R-R intervals) is present in ECG #2. This bigeminal rhythm is most easily appreciated in leads V5, V6. 
• 
  
• Sinus rhythm has been restored! (RED arrows in Figure-5 showing clearly defined P waves in this repeat ECG in multiple leads — with return to sinus rhythm defined by the presence of upright P waves with fixed PR interval in lead II).
• Every-other-beat in Figure-5 is a PAC (highlighted by YELLOW arrows that show a slight-but-real different P wave morphology for these PACs, that are clearly narrower than the RED-arrow P waves of sinus beats).

Figure-5: I've labeled the repeat ECG — which shows a bigeminal rhythm in which every-other-beat is a PAC (YELLOW arrows).

CASE Conclusion:

Comparison of the 2 ECGs in today's case allows a definitive diagnosis of the rhythm in the initial ECG to be made retrospectively. Consider Figure-6:

==========================

• Please NOTE in Figure-6: When comparing leads aVF and V6 from ECG #2 — with ECG #1 — that the relative size of a large box on ECG grid paper in my illustration is different between ECG #1 and ECG #2.

=================

• It is because the overall heart rate has slowed in ECG #2 — that we are able to see sinus P waves emerge from where they were hiding within the preceding T waves. Sinus P waves (RED arrows) are now clearly seen for even-numbered beats in leads aVF and V6 of this repeat tracing.
• We are able to see the pointed P waves of the PACs in lead aVF of ECG #2 (YELLOW arrows).
• However, in lead V6 — we are not able to clearly distinguish the P waves of PACs, because these YELLOW-arrow PACs in lead V6 "fuse" with the preceding T wave.
• Now imagine in your "mind's eye" if the rate of the atrial bigeminy rhythm in lead aVF of ECG #2 was a little bit faster. Wouldn't fusion of the RED-arrow sinus P waves in lead aVF with the T waves preceding them be expected to produce a similar picture of fused P wave and T wave, as is seen in lead aVF of ECG #1?
• 
  
• BOTTOM Line: Retrospectively — the return of sinus rhythm with atrial bigeminy in ECG #2 strongly suggests that the rhythm in ECG #1 was sinus tachycardia at ~135/minute, in which tall, pointed inferior lead P waves from this patient's longstanding ASD fused with the T waves that preceded them to produce the unusual QRS appearance in ECG #1.
• 
  
• PEARL #5: The KEY to proving that the mechanism of a tachycardia is sinus — is frequent ECG monitoring that once the cause of sinus tachycardia is treated, will result in enough slowing of the tachycardia rate to allow sinus P waves to emerge from where they were hiding in the preceding T waves. This is precisely what we see in Figure-6.

Figure-6: Comparison between today's initial ECG — and leads aVF and V6 in the repeat tracing. Slight slowing of the heart rate with return to a sinus mechanism allows sinus P waves to emerge from where they were hiding in the preceding T waves.

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ADDENDUM (4/14/2024):

Based on some questions that have arisen regarding the PR intervals in ECG #1 and ECG #2 — I've added Figure-7, that I hope will clarify my discussion.

• I fully acknowledge that the difference in size of the ECG grid in the 2 tracings that I show here is potentially confusing. Rather than digitizing both tracings (which risks introducing error inherent with digitization of fine measurements from ECGs that are not completely flat and completely straight) — I thought it better to show the original ECGs.
• 
  
• I've added PINK lines in Figure-7 to show that by my measurements — the PR interval in the initial ECG (TOP = lead II rhythm strip) measures just under 1 large box (corresponding to a PR interval = 0.18 second).
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• By my measurements — this is the same PR interval ( = 0.18 second) that I measure for the sinus beats (RED arrow P waves) in lead aVF of ECG #2.
• The PR interval for the PACs (YELLOW arrow P waves) in ECG #2 appear to have a slightly longer PR interval — but PR interval duration of PACs may vary depending on from where in the atria the PACs arise, as well as conduction velocity through the atria, which may be altered by early occurrence of these supraventricular impulses.
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• BOTTOM Line: I wish I had additional tracings. I wish I had tracings that were scanned completely flat and straight. And I wish I had record of ECG monitoring just before — and during — and just after the rhythm changes from the regular tachycardia in ECG #1 — to the bigeminal rhythm in ECG #2. Unfortunately — I lack this information. 
• That said — I thought my discussion in today's case to be a valid explanation based on the 2 tracings that I have (in which I believe that the PR interval is virtually the same for sinus-conducted beats in ECGs #1 and #2). But I fully acknowledge that other explanations may be possible.

As always — Comments from my readers are welcome! — :) 

Figure-7: In the hope of clarifying PR interval duration in ECG #1 and ECG #2 — I've written out the measurements I've made (See text).

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Acknowledgment: My appreciation to Ella Hmayer (from Tunisia) for the case and this tracing.

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Related ECG Blog Posts to Today’s Case:

• ECG Blog #185 — Reviews my System for Rhythm Interpretation, using the Ps, Qs & 3R Approach.
• ECG Blog #205 — Reviews my Systematic Approach to 12-lead ECG Interpretation.
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• ECG Blog #210 — Reviews the Every-Other-Beat (or Every-Third-Beat) Method for estimation of fast heart rates — and discusses another case of a regular WCT rhythm. 

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• CLICK HERE — for my 6 new ECG Videos (on Rhythm interpretation — 12-lead interpretation with Case Studies for ECG diagnosis of acute OMI).
• CLICK HERE — for my 2 new ECG Podcasts (on ECG & Rhythm interpretation Errors — and — Errors in assessing for acute OMI).

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• ECG Blog #220 — and ECG Blog #361 — Review of the approach to the regular WCT ( = Wide-Complex Tachycardia).
• ECG Blog #196 — Reviews another Case with a regular WCT rhythm.
• ECG Blog #263 and Blog #283 — More WCT Rhythms ...
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• ECG Blog #227 — Reviews the "Bix Rule" (Looking for 2:1 atrial activity when you see a long PR interval with a tachycardia).
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• For more on ASD in Adults — Webb and Gatzoulis: Circulation 114: 1645-1653, 2006.
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• ECG Blog #197 — Reviews the concept of Idiopathic VT, of which Fascicular VT is one of the 2 most common types. 
• ECG Blog #346 — Reviews a case of LVOT VT (a less common idiopathic form of VT).
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• ECG Blog #204 — Reviews the ECG diagnosis of the Bundle Branch Blocks (RBBB/LBBB/IVCD). 
• ECG Blog #203 — Reviews ECG diagnosis of Axis and the Hemiblocks. For review of QRS morphology with the Bifascicular Blocks (RBBB/LAHB; RBBB/LPHB) — See the Video Pearl in this blog post.
• ECG Blog #211 — WHY does Aberrant Conduction occur?
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• ECG Blog #301 — Reviews a WCT that is SupraVentricular! (with LOTS on Aberrant Conduction).
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• ECG Blog #323 — Review of Fascicular VT. 
• ECG Blog #38 and Blog #85 — Review of Fascicular VT.
• ECG Blog #278 — Another case of a regular WCT rhythm in a younger adult.
• ECG Blog #361 — A regular WCT in a middle-aged man.
• ECG Blog #35 — Review of RVOT VT. 
• ECG Blog #42 — Review of criteria for distinguishing VT vs aberrant conduction.
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• ECG Blog #422 — Reviews another case of adult Congenital Heard Disease.