Thursday, November 3, 2022

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.

  • 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).

  • 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. Clinicallythis patient's primary diagnosis remains the same regardless of whether beat #7 is (or is not) conducted.

  • 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.

  • 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 Syndromemay 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.

  • 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).

  • 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.

  • 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.).

  • 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.

  • 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).

  • 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. 

  • 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.

  • 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.

  • 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.


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


ADDENDUM (November 3, 2022):
  • The Audio PEARL (2:45 minutes) below reviews the ECG findings of SSS.


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).


    1. Thank you for an excellent interpretation.

    2. Muchas gracias por el caso está espectacular

    3. Do you think that this EKG can suggest a sort or ischemia, even if increased demand by tachycardia
      - some ST depression in inferior leads
      - elevation of J point in aVR with straight ST
      - in aVL, marked and straight ST elevation of 1mm/ very small and fragmented QRS complex, wide T wave
      Thanks for all your posts Ken!

      1. Merci bien Gilles — and excellent point that you raise! We simply don't know. One of the common causes of what we call "diffuse subendocardial ischemia" (in which there is ST depression in lots of leads with ST elevation in aVR) is a fast supraventricular rhythm. To distinguish the ST depression that we see in this case between what is "rate-related" vs potentially ischemic would require a careful history and follow-up ECGs after control of the tachycardia — which we unfortunately don't have access to in this case. THANKS again for your comment! — :)

    4. Great Post Dr. Grauer. THank you.

      I have few questions.
      1. Is there a phase IV block on this ecg?
      2. When we have seen atrial fibrillation in the initial part of ECG, with such a prolonged block, how can we use the term sick sinus syndrome when we have not seen any sinus activity except in the last beat?

    5. THANKS for your comments! I don't think this is a Phase 4 (ie, paradoxical) BBB for beat #7 in the "usual sense" that we think of this (which typically does not follow such an extended pause. In view of my lack of follow-up (and lack of additional ECG tracings) — I suggested that there are "features" of Sick Sinus Syndrome here — and that this patient will need a pacemaker unless something "fixable" can be found — but definitive answers really are not available given the limited information that we have. That said — the very prolonged sinus pause following the SVT — after which another pause occurs are really features that are VERY typical for SSS in an older patient like the one in today's case. THANKS again for your comments — :)