Syncope and Atrial fibrillation in a Healthy 70-something Male

An otherwise healthy 70-something was sitting talking with other when he had brief sudden witnessed syncope for 20 seconds. He awoke asymptomatic.  There was no CP, SOB, abd pain, HA or any other symptom either before or after.  There was no prodrome: it was not preceded by any flushing, sweating, nausea, etc.  He immediately completely recovered.

O/w healthy.  No recent illness of any sort.

PMH: Known paroxysmal Atrial fib.  He is usually is in sinus rhythm as far as he knows, but he cannot subjectively feel atrial fibrillation, so he is never completely certain when he is in sinus or atrial fib.

His only med is rivaroxaban (Xarelto), and he is taking all doses.

He is from out of town and no previous records can be obtained.  In particular, whether he really is usually in sinus.

Here is his ECG:

Atrial Fib with a Ventricular Response of about 66.
Besides Atrial Fib, what is the potentially severe pathology here?

When there is atrial fibrillation without any AV nodal blockers, there should be a rapid ventricular response.  A patient in atrial fibrillation who is not taking AV nodal blockers and whose heart rate is not elevated has AV node disease until proven otherwise.

Hyperkalemia might do this, but the K was normal.

We admitted him for probable EP study and possible pacemaker.

I admitted the patient and called the cardiologist on call to be certain that he would consult for the inpatient team.

On reading the note the next day, the inpatient admitting team gave an assessment of "dehydration" and was about to discharge the patient.

I called Cardiology and they rapidly got in touch with the inpatient team, cancelled the discharge, and educated the inpatient team appropriately.

Later, while on telemetry, the patient had a 12 second pause (asystole).

He underwent pacemaker placement and is doing fine.

Learning Points:

1. An AV node that is not transmitting impulses from atrial fibrillation is sick, and is the likely culprit in syncope.

2. Syncope without prodrome is a significant risk factor for cardiac syncope and poor outcome.  For a complete but concise discussion of ED syncope, with annotated bibilography, see this post:

Emergency Department Syncope Workup: After H and P, ECG is the Only Test Required for Every Patient.....

3. One other consideration is this:  Patients who have intermittent atrial fib, who convert and revert, may of course convert spontaneously to sinus rhythm. An important point that I did not know, and that our fine cardiologist Mengistu Simegn informed me of, is that after conversion, the sinus node may have a very long pause before re-initiating sinus rhythm after conversion from atrial fib.  This may be another reason for pacer implantation.

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Comment by KEN GRAUER, MD (7/5/2018):

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This blog post provides an excellent example of how a patient with SSS (= Sick Sinus Syndrome) may present. I’ll supplement Dr. Smith’s commentary with some points to keep in mind about the diagnosis of SSS.

• 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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• The easy way to remember the arrhythmias most commonly associated with SSS — is to think of what one might expect if the SA node became “sick”. Thus, there is sinus bradycardia and arrhythmia — sinus pauses (which may be longlasting, ultimately leading to sinus arrest) — and SA nodal block. 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. Many patients have a “Tachy-Brady” syndrome — in which tachyarrhythmias (most commonly rapid AFib) alternate with periods of bradycardia. Because the SA node is “sick” — the SA node recovery time is often prolonged, which is why long pauses most commonly follow episodes of tachycardia (which produced SA node suppression). New slow AFib reflects a combination of these rhythm problems.
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• The indication for pacemaker placement with SSS is “symptomatic bradycardia”. Thus, it is not those episodes of rapid AFib seen in patients with Tachy-Brady that qualify. But, IF the only way to control “tachy” episodes is with medication that then makes the patient overly bradycardic — that would then qualify as indication for pacemaker placement.
• Regarding PAUSES — it is important to appreciate that pauses between 1.5-2.0 second are relatively common during ambulatory Holter monitoring. Many of these are benign. 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.
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• AFib (Atrial Fibrillation) — is the most common sustained cardiac arrhythmia. But description of a patient’s rhythm simply as, “AFib” — is incomplete. One should always qualify the ventricular response of AFib as part of this diagnosis. As per Dr. Smith — new-onset AFib is almost always accompanied by a rapid ventricular response (ie, average ventricular rate over ~120/minute). Less commonly, new AFib with be associated with a controlled ventricular response (rate between ~70-110/minute). If ever a new presentation of AFib has a slow ventricular response (ie, rate less than ~50-60/minute) — one needs to immediately look for a cause!
• Since by definition the R-R interval with AFib is constantly changing — I prefer a “Gestalt” overview when estimating the ventricular response. Thus, in this case — R-R intervals vary predominantly between 4-to-5 large boxes (Figure-1) — which suggests an average ventricular response between ~60-70/minute. As per Dr. Smith — this suggests a slower-than-expected ventricular response to AFib for this 70-year old man with witnessed syncope — especially since he is on no rate-slowing medication!

Figure-1: AFib with a relatively slow ventricular response (See text).

Given the above “Basics of SSS” — diagnosis of this very common syndrome in the elderly becomes easy:

• Suspect SSS whenever an “older patient” presents with inappropriate bradycardia (ie, frequent prolonged sinus pauses; sinus bradycardia with fatigue; slower-than-expected AFib with syncope, 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.
• The decision of whether or not pacemaker implantation is indicated then depends on severity of the disorder — and its direct correlation with symptoms. The 12-second pause this patient manifested on telemetry made that decision easy …