ECG Blog #382 — What Does the Holter Show?

I was sent the Holter monitor tracing in Figure-1 — but without the benefit of any clinical information.

QUESTIONS:

A total of 9 QRS complexes are seen in the 2 simultaneously-recorded monitoring leads.

• How would YOU interpret the rhythm in Figure-1?
• How many P waves do you see?
• Why do the QRS complexes of beats #4 and 5 in the bottom lead look different than the other 7 beats?
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• What do you suspect as the clinical diagnosis?

Figure-1: The initial 15-second rhythm strip in today’s case.

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NOTE: The recording system used in rhythm strips from today’s post may be different from what you are accustomed to. In Figure-2 — I've labeled some of these differences — and I highlight atrial activity.

• Note in Figure-2 — in the upper right corner of this rhythm strip (within the RED rectangle) — that the recording speed is 12.5 mm/second (instead of the 25 mm/sec. speed that many of us are used to) — BUT — that the width of each large box on the ECG grid paper has been reduced by 50% (so that each small rectangular box on this ECG grid paper still represents 200 msec. = 1/5 second — as shown by the RED arrow).
• As a result — the time to record 5 of these small rectangular boxes on each rhythm strip in today’s post is still 1.0 second (with each increment of 1.0 second separated by vertical dotted GRAY lines).
• The advantage of this system of recording is that QRS amplitude of each complex is maintained — while an easier-to-read longer rhythm strip can be displayed (ie, ECG Rhythm #1 displays a full 15 seconds of today’s rhythm! — instead of the usual 6-10 second rhythm strips many of us are used to).
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• Finally — Note that each R-R interval in Figure-2 has been precisely calculated for you. For example — the R-R interval between beats #1-2 = 1820 msec. ( = 1.82 second = 9.1 little boxes, as per the GREEN arrows ==> which corresponds to a heart rate of 300 ÷ 9.1 = 33 beats/minute). 
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• PEARL #1: This computer-determined calculation allows us to instantly appreciate small changes in heart rate (ie, The R-R interval before beat #4 = 1679 msec. — which is significantly shorter than the 1820 msec. R-R interval for the first few beats in this tracing). 

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How Many P-Waves are there in ECG Rhythm #1?

The benefit of having 2 simultaneously-recorded leads in a given rhythm strip — is that this allows us to see ECG findings that may only be visibile in one of the 2 leads being monitored.

• Sinus P waves with a constant PR interval are clearly seen to precede beats #4-thru-9 (RED arrows in the upper monitoring lead in Figure-2).
• P waves in the upper lead of Figure-2 are upright, albeit small in amplitude. These P waves that precede beats #4-thru-9 — are larger and biphasic in the lower monitoring lead.
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• The QRS complexes of beats #1,2,3 are wider — and look very different in both monitoring leads in Figure-2, than the QRS morphology of sinus beats #4-thru-9. These wider beats are not preceded by sinus P waves — which suggests they are ventricular escape beats! The R-R interval that separates these ventricular beats = 1820 msec. — which corresponds to a ventricular rate of ~33/minute (which fits perfectly within the usual range of an idioventricular escape rhythm).
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• PEARL #2: The fact that the R-R interval preceding return of the 1st sinus-conducted beat ( = beat #4) is shorter ( = 1679 msec.) than the 1820 msec. R-R interval of the 3 ventricular escape beats — suggests that the reason sinus rhythm resumes beginning with beat #4, is that the rate of sinus discharge sped up sufficiently to surpass the rate of idioventricular escape!
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• PEARL #3: Note that the R-R interval varies significantly between sinus-conducted beats #4-thru-9 (ie, from 1679 msec. to 1828 msec.) — which corresponds to a variation in the rate of sinus bradycardia from 36-to-33/minute. This suggested to me from this initial rhythm strip — that additional rhythm strips from this patient's 24-hour Holter recording will probably show episodes of varying duration of ventricular escape when the rate of sinus bradycardia slows below the ventricular escape rate!
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• PEARL #4: In view of the etiology I suspected for the mechanism of explaining the rhythm change in Figure-2 — I looked closer at the lower monitoring lead for partially hidden atrial activity. Note tiny-but-real differences in QRS morphology for the first 3 beats in the lower lead (ie, a pseudo r' notch at the end of the QRS for beats #1 and 2 that is not seen at the end of beat #3 — and an extra initial positive deflection at the beginning of beat #3 that is not seen at the beginning of beats #1 and 2). This strongly suggests that sinus P waves are occurring throughout this rhythm strip — and are partially hidden under the PINK arrows!

Figure-2: I've labeled the initial rhythm strip in today’s case (See text).

Why Do Beats #4 and 5 Look Different?

Although QRS morphology for each of the sinus-conducted beats in the upper monitoring lead in Figure-2 look similar — beats #4 and 5 clearly look different than the other 7 beats in the lower monitoring lead!

• Beats #4 and 5 manifest a narrow biphasic (almost equal R wave and S wave) morphology in the lower lead. This is an intermediate morphology between the predominantly upright QRS of sinus-conducted beats #6-thru-9 — and the wider predominantly negative QRS of beats #1-thru-3, which are the ventricular escape beats.
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• PEARL #5: The most logical explanation for why the QRS complex of beats #4 and 5 in the lower monitoring lead look different and intermediate in morphology between QRS morphology of the initial 3 ventricular escape beats and the pure sinus-conducted beats that follow ( = beats #6-thru-9) — is that beats #4 and 5 must be Fusion beats! Identification of beats #4 and 5 as "fusion" beats (F) confirms a ventricular etiology for beats #1,2,3. This makes sense given that the underlying rhythm in today's case appears to be marked sinus bradycardia and arrhythmia, with a ventricular escape rhythm appearing when the SA node rate drops below 33/minute.
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• NOTE: The rhythm strip in Figure-2 is a Holter tracing — so baseline artifact undulations that we see, in addition to some variation in QRS amplitude for sinus beats #6-thru-9 is not unexpected. That said — the difference in QRS morphology between beats #4,5 vs beats #6-thru-9 in the lower lead is clearly real, and most logically explained by interpreting beats #4 and 5 as fusion beats.

What Do YOU Suspect as the Clinical Diagnosis?

As mentioned above — I had no clinical information (not even the age of this patient) at the time I was sent this initial tracing. That said — Common things are Common.

• Although there are a number of ECG findings that characterize SSS (Sick Sinus Syndrome) — by far, the most common initial rhythm of this syndrome will be sinus bradycardia and arrhythmia. There is often a long subclinical period (of up to a decade or more!) — during which sinus bradycardia and arrhythmia may be seen as the only indication of SSS, albeit not yet to a degree that produces symptoms.

PEARL #6: As I discuss in my review of SSS (See ECG Blog #342 for details) — establishing a diagnosis that sinus bradycardia indicates SSS — will depend on the following:

• Finding out the age of the patient (ie, SSS is most common in older individuals) — and learning whether the patient has been symptomatic? (ie, with syncope-presyncope, fatigue, dyspnea, chest pain?).
• Checking the rest of the Holter to see if episodes of bradycardia primarily occur at night? (since sleep apnea is a readily treatable cause of nighttime bradycardia, as well as of other arrhythmias).
• Checking all medications that the patient is taking (including herbal products). You are looking for potential rate-slowing medication — that may be the cause of bradycardia (Not to forget inquiry about beta-blocker eye drops — which are partially absorbed, and which can be an easily overlooked as an iatrogenic cause of bradycardia). 
• Ruling out other potential causes of bradycardia (ie, recent ischemia-infarction; hypothyroidism).
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• BOTTOM Line: Although many questions remain to be answered regarding clinical correlation of today's case — I immediately considered SSS as being statistically the most common cause of a rhythm like the one we see in Figure-2.

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What Else did the 24-Hour Holter Show?

I was sent a number of additional 15-second rhythm strips from this patient's 24-hour Holter Monitor. In addition — I was provided with the Holter Summary Report. Pertinent ECG findings from this summary included the following:

• An overall average heart rate for the day of monitoring of between 45-50/minute. The rate did not drop below 30/minute — and it did not exceed 100/minute. Bradycardia was not limited to nighttime hours.
• No pause beyond 2.0 second.
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• Occasional PVCs throughout the day without sustained repetitive forms.
• 2 short runs of SVT (presumably atrial tachycardia).
• Periodic transition from wide-to-narrow QRS complexes (similar to that seen in Figure-2).

Below in ECG Rhythms #2-thru-6 — are selected additional rhythm strips I received. Do these tracings support my initial impression?

ECG Rhythm #2:

ECG Rhythm #3:

ECG Rhythm 4:

ECG Rhythm #5:

 ECG Rhythm #6:

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MY Thoughts on ECG Rhythms #2-thru-6:

Overall — these additional rhythm strips support my initial impression.

ECG Rhythm #2:

Amazingly — We see no less than 7 variations in QRS morphology for the 9 beats shown in ECG Rhythm #2. For clarity in Figure-3 — I've labeled P waves in this tracing (RED arrows in Figure-3).

• I find it difficult to determine which (if any) of the 9 beats in Rhythm #2 are purely sinus-conducted.
• Although the QRS complex of beat #8 occurs earlier-than-expected and looks similar to the QRS of sinus-conducted beats in Figure-2 — this beat is biphasic in the lower monitoring lead, and we previously determined that biphasic beats #4 and 5 in the lower lead of Figure-2 were fusion beats (F).
• For this reason — I suspect beat #2 in Figure-3 is also a fusion beat (because beat #2 is also biphasic in the lower lead).
• Beats #3-thru-7 in Figure-3 represent various degrees of ventricular etiology, with-or-without some component of fusion. Note that the PR interval for beats like #3,4,5 is clearly too short for normal conduction (therefore predisposing to a certain amount of fusion). 
• Beat #9 is different — and shows us a different shape (V) for this wide beat in both the upper and lower monitoring lead (compared to the shape of previous ventricular escape beats in these 2 leads). Therefore — There appear to be at least 2 different ventricular sites for the ventricular escape rhythm!
• Finally — I put a question mark (?) above beat #1 — because I can't figure out what this beat represents (ie, Ventricular escape, possibly with fusion from perhaps yet another ventricular site?).

PEARL #7: The specific etiology of each beat in these selected tracings is not important. Instead — What counts is the "theme" of the overall rhythm disturbance in today's Holter report.

• The overall "theme" of these rhythm strips — is that there is an underlying marked sinus arrhythmia and bradycardia, with frequent escape rhythms arising from one or more ventricular sites. This results in a variety of fusion beats between sinus-conducted beats and ventricular escape rhythms.

Figure-3: I've labeled P waves (RED arrows) and selected beats in ECG Rhythm #2. Note that the PR interval is clearly too short to conduct normally for a number of beats (that therefore must represent fusion between sinus and ventricular beats).

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ECG Rhythm #3:

The overall "theme" of today's Holter monitor recording continues. For clarity in Figure-4 — I've labeled P waves in this tracing (RED arrows in Figure-4).

• None of the P waves in Figure-4 come before the QRS. Therefore — there are no sinus-conducted beats in ECG Rhythm #3. Instead — all beats in Figure-4 must be of a ventricular etiology!
• Beat #3 clearly manifests an intermediate QRS morphology (Best appreciated in the lower monitoring lead — where beat #3 is intermediate in shape to the wide positive QRS of beats #1,2,4 — and the wide negative QRS of beats #7 and 8). Therefore — Beat 4 represents a fusion beat between 2 different ventricular escape foci!
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• Negative but narrow beats #5 and 6 are also clearly intermediate in QRS morphology between the wide upright QRS of beats #1,2,4 — and the wide negative QRS of beats #7 and 8. Therefore — beats #5 and 6 also represent fusion between 2 different ventricular escape foci!

Figure-4: I've labeled ECG Rhythm #3.

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ECG Rhythms #4, 5 and 6:

The "theme" of today's Holter monitor continues with these last 3 rhythm strips.

• There is marked bradycardia throughout — with frequent ventricular escape from different ventricular foci — often for extended periods without return of sinus rhythm.

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Putting It All Together:

I have subsequently found out that the patient in today's case is a woman in her 80s — so the likelihood of Sick Sinus Syndrome increases! I previously mentioned that the Holter Summary showed the following:

• An overall average heart rate for the day of monitoring of between 45-50/minute. The rate did not drop below 30/minute — and it did not exceed 100/minute. Bradycardia was not limited to nighttime hours.
• No pause beyond 2.0 second.
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• Occasional PVCs throughout the day without sustained repetitive forms.
• 2 short runs of SVT (presumably atrial tachycardia).

Clinically — the degree of persistent marked bradycardia is worrisome, even if prolonged pauses (of >2.5-to-3.0 second) are not yet seen — and even if this patient is not yet reporting "symptomatic bradycardia".

• Failure of the heart rate to go over 100/minute during the course of a day suggests there may be chronotropic incompetence — another concerning sign of SSS.
• The short runs of SVT are consistent with possible "Tachy-Brady" Syndrome — in which many patients with SSS alternate between marked bradycardia and various tachyarrhythmias.
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• Follow-Up: Our interpretation of this Holter was passed on to the patient's primary physician. I would bet that this patient will soon receive a permanent pacemaker.

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Acknowledgment: My appreciation to Andreas Röschl (from Neumarkt, Germany) for the case and this tracing.

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ADDENDUM (June 3, 2023): 

• The Audio PEARL (2:45 minutes) below reviews the ECG findings of SSS.

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Related ECG Blog Posts to Today’s Case: 

• ECG Blog #185 — Reviews the Ps, Qs and 3R Approach to Systematic Rhythm Interpretation.
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• ECG Blog #342 — reviews the ECG diagnosis of SSS (Sick Sinus Syndrome)
• ECG Blog #256 — Reviews another case of SSS.
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• ECG Blog #128 — ECG Blog #129 — and ECG Blog #133 — for review on Fusion Beats (that also show AV dissociation).
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• ECG Blog #295 — Reviews the concept of bradycardic-induced BBB ( = Phase 4 block). This is discussed near the bottom of the page (ie, in Pearl #5 — that appears just under Figure-6).
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• The July 5, 2018 post in Dr. Smith's ECG Blog — (Please see My Comment at the bottom of the page for Review on the ECG diagnosis of Sick Sinus Syndrome).