ECG Blog #342 - This IS a 12-Lead ECG ...

The pre-hospital 12-lead ECG shown in Figure-1 — was obtained from an older woman complaining “odd heartbeat” episodes that began today. In between episodes — her heartbeat would return to normal.

• How would YOU interpret her ECG in Figure-1?
• What is the likely diagnosis? How would you confirm this?

Figure-1: The prehospital ECG of an older woman with episodes of “odd heartbeat”. (To improve visualization — I've digitized the original ECG using PMcardio).

MY Thoughts on the ECG in Figure-1:

Although there is no long lead rhythm strip in Figure-1 — this patient’s problem is obvious from the 12-lead tracing.

• The QRS is narrow for the first 6 beats in this tracing (beats #1-thru-5 in simultaneously-recorded leads I,II,III — and the 6th beat recorded in leads aVR,aVL,aVF). The rhythm for these 6 beats is fast (over 100/minute) — and irregularly irregular without P waves. This defines the rhythm for these first 6 beats as AFib (Atrial Fibrillation) with a rapid ventricular response.
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• An extended pause follows the 6th QRS complex. The duration of this pause is over 24 large boxes ( = almost 5 seconds!). Finally — a beat occurs ( = beat #7 in Figure-2).
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• Beat #7 is probably conducted — because this beat is preceded by a P wave with what looks to be a seemingly normal PR interval in lead V4 (ie, of ~0.14 second in duration). QRS morphology for the 3 leads that we see in simultaneously-recorded leads V4,V5,V6 — appears to be typical for LBBB conduction.
• Alternatively (ie, because the PR interval looks to be shorter than 0.14 second in lead V6) — it could be that a sinus P wave and a delayed ventricular escape beat both occurred at about the same time. Clinically — this patient's primary diagnosis remains the same regardless of whether beat #7 is (or is not) conducted.
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• Following beat #7 — there is another extended pause of at least 2 seconds (ie, We see ~10 large boxes without a beat) — at which point the rhythm strip ends.

IMPRESSION:

• Today's patient should be assumed to have SSS (Sick Sinus Syndrome) — until you can prove otherwise.

Figure-2: I've counted the number of large boxes between beat #6 and beat #7. As can be seen — the pause is more than 24 large boxes = nearly 5 seconds in duration! (See text).

A Closer Look at Today's Case:

The ECG in Figure-2 provides an excellent example of how a patient with SSS (= Sick Sinus Syndrome) may present.

• SSS is by far the most common reason for permanent pacemaker placement. The entity becomes increasingly common as the population ages — especially in patients over 60-70 years of age. There is often a long subclinical period (of up to a decade or more!) — during which sinus bradycardia and arrhythmia are seen — but not to a degree that produces symptoms.
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• PEARL #1: Perhaps the easiest way to remember the arrhythmias most commonly associated with SSS — is to think of what one might expect IF the SA node became “sick”. Therefore: i) The most common initial rhythm with SSS will be sinus bradycardia and arrhythmia; ii) Some months (or years) afterwards — increasingly long sinus pauses (which may ultimately lead to sinus arrest) — and various forms of SA nodal block may occur; iii) Typically, there is not just SA nodal disease — but also AV nodal disease and AV block — with resultant slowing of the AV nodal escape rate in response to increasingly long pauses or other forms of bradycardia; iv) Many patients also have a “Tachy-Brady” syndrome — in which tachyarrhythmias (most commonly rapid AFib) alternate with periods of bradycardia; and, v) Because the SA node is “sick” — the SA node recovery time is often prolonged. As a result — long pauses commonly follow episodes of tachycardia (because tachycardia episodes result in SA node suppression).
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• PEARL #2: The indication for pacemaker placement with SSS is “symptomatic bradycardia”. Thus, it is not those episodes of rapid AFib that are seen in patients with "Tachy-Brady" Syndrome that qualify — but rather severe bradycardia that causes symptoms! KEY Point: If the only way to control “tachy” episodes is with medication that then produces symptomatic bradycardia — this qualifies as indication for pacemaker placement.
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• PEARL #3: It is important to appreciate that short pauses (ie, between 1.5-2.0 second) are relatively common during ambulatory Holter monitoring. Many of these short pauses are benign. KEY Point: Pauses clearly become cause for concern once they exceed 2.0 second in duration (especially ≥2.5 second). Clear indication for pacing with SSS is generally accepted to be present once pauses attain ≥3.0 second in duration.

PEARL #4: Given the above “Basics of SSS” — diagnosis of this very common syndrome in the elderly becomes surprisingly EASY:

• Suspect SSS whenever an “older patient” presents with inappropriate bradycardia (ie, marked and persistent heart rate slowing — especially when associated with symptoms such as fatigue or syncope; frequent prolonged sinus pauses; slower-than-expected AFib, etc.).
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• Rule out common potentially "fixable" causes of inappropriate bradycardia. These include rate-slowing medication — recent ischemia/infarction — hypothyroidism — sleep apnea. If none of these potentially “fixable” causes are present — then it is almost certain that the older patient in front of you who is presenting with inappropriate bradycardia has SSS.
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• Is Pacing Indicated? — The decision of whether or not pacemaker implantation is indicated then depends on: i) Severity of the disorder — and its direct correlation with symptoms resulting from inappropriate bradycardia; and, ii) Ruling out any "potentially fixable" cause(s).

CONCLUSION to Today's Case:

Unfortunately — I do not have specific follow-up regarding the patient in today's case. That said — We can strongly suspect that a permanent pacemaker will probably be needed in this older patient with notable symptoms.

• ECG features of SSS that appear in Figure-2 include: i) "Tachy-Brady" Syndrome, with rapid AFib (for the first 6 beats in this tracing); and, ii) Post-tachycardia suppression that results in successive prolonged pauses (nearly 5 seconds in duration — followed 1 beat later by another prolonged pause).
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• KEY Point: As emphasized earlier under PEARL #4 — potentially "fixable" causes of inappropriate bradycardia need to be ruled out before we can establish the diagnosis of SSS. 
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• I suspect that beat #7 in ECG #1 is conducted. If so — then this beat is conducted with LBBB. This would be an example of a paradoxical (ie, bradycardia-induced) conduction defect — and would further suggest the likelihood of underlying heart disease.
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• Realistically — it's hard to imagine that a "fixable cause" will be found that will be able to reverse this degree of SA node suppression (with such excessive pauses). I suspect that close observation during a brief hospitalization will establish definitive need for a pacemaker.
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• P.S. (3/27/2024): Other descriptions might be used for the extended pause of nearly 5 seconds in Figure-2 — including transient ventricular standstill and/or PD-PAVB (Pause-Dependent Paroxysmal AtrioVentricular Block) — although as described in ECG Blog #419, cessation of atrial activity as well as ventricular escape is against "PD-PAVB". That said, regardless of the terminology used — the "Bottom Lines" remain the same: i) This patient almost certainly has advanced SSS; and, ii) Permanent pacing will almost certainly be needed.

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Acknowledgment: My appreciation to Evan MacIntyre (from North Carolina, USA) for the case and this tracing.

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ADDENDUM (November 3, 2022):

• 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.

ECG Blog #256 — Reviews another case of SSS (Sick Sinus Syndrome).

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).

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).