Syncope while on a treadmill

A 60-something ow healthy male had syncope while on treadmill.  911 was called and the patient was found by medics to be diaphoretic and hypotensive.

This strip was obtained:

Apparent Wide Complex Tachycardia at a rate of 280

What do you think?

What do you want to do?

Appropriately, the medics electrically cardioverted immediately. They did not feel they had time to sedate.

He cardioverted to a supraventricular rhythm, and a 12-lead was obtained.

He was brought to the ED.

What is the diagnosis from the above rhythm strip?

To me, it was clearly atrial flutter with 1:1 conduction.   

The rate of 280 is just right for atrial flutter.  The waves look like atrial flutter waves, NOT like a wide ventricular complex.  There are little spikes (narrow complexes) at the top of every wave -- this is the narrow QRS complex on top of a flutter wave.

But how can the AV node conduct at a rate of 280?  Why such rapid AV conduction?  Because the patient was exercising, which increases sympathetic tone, facilitating AV conduction. 

Diagnosis: Atrial flutter with 1:1 conduction, with fast AV conduction made possible by sympathetic drive of exercise

On arrival, we obtained another 12-lead:

Unremarkable

Further history: One month history of shortness of breath on exertion, denies palpitations, chest pain, orthopnea, leg swelling. Recently diagnosed with intermittent paroxysmal atrial fibrillation but no EKGs available to confirm. 

Troponins 34>33>43, likely secondary to myocardial injury from tachycardia. 

Reverted to atrial fibrillation with RVR while in the hospital 3 times and needed cardioversion.

The patient was started on amiodarone, anticoagulation, and metoprolol, and scheduled for atrial flutter ablation.

He underwent ablation in the EP Lab.

At discharge

Continue amiodarone 400 mg PO BID x2 weeks then 200 mg daily until follow-up  

Continue Toprol XL 25 mg daily. 

Continue Eliquis 5mg BID, should be continued for 3 months

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MY Comment, by KEN GRAUER, MD (9/20/2024):  

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I found the following aspects of today's case of special interest. 

• Why did Dr. Smith immediately say the rhythm was AFlutter with 1:1 AV conduction?
• Why did today's patient develop AFlutter while exercising on a treadmill?
• Is longterm endurance-training a risk factor for AFib and AFlutter?

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Why is Today's Initial Rhythm AFlutter?

The KEY to determining the initial rhythm in today's case — depends on the heart rate. To illustrate this point — I've reproduced and labeled in Figure-1, a representative portion of today's initial rhythm (showing 3 simultaneously-recorded but unlabeled monitoring leads).

• As discussed often in Dr. Smith's ECG Blog — quick determination of heart rate often provides an important clue to the etiology of certain regular SVT (SupraVentricular Tachycardia) rhythms (See My Comment in the July 19, 2023 post, among others).
• Determining heart rate is easy when the rate is not overly fast. I favor simply dividing 300 by the number of large boxes in the R-R interval. (See my ADDENDUM below if you'd like a 3-minute refresher video on this approach).
• Quick and accurate estimation of heart rate is more challenging when the rhythm is fast and regular. I favor the Every-Other (or Every-3rd or 4th) Beat Method — that I've developed to facilitate rapid and accurate rate estimation. Find a QRS complex that begins on a heavy ECG grid line. In today's tracing — I chose the 10th beat in the top lead (See the 1st vertical RED line over this beat in Figure-1). 
• Because of how fast today's initial rhythm is — I looked at the R-R interval for every-4th-beat. Note in Figure-1 — that the amount of time it takes to record 4 beats (RED numbers in the top lead) is just over 4 large boxes (BLACK numbers in this Figure). Therefore — ONE FOURTH the rate is a little slower than 300/4 ~70/minute.
• The actual rate for the rhythm in ECG #1 is therefore ~70 X 4 ~280/minute.

How Does Knowing the Heart Rate Help?

As I've emphasized in My Comment in the October 25, 2022 post — and the March 6, 2020 post — determining IF the heart rate of a regular SVT rhythm is close to 150/minute (ie, ~130-to-170/minute range) provides a clue as to the need for considering each of the 4 Common Causes of a regular SVT in your differential diagnosis (ie, Sinus Tachycardia — Reentry SVTs [ = AVNRT; AVRT] — AFlutter — and ATach).

• A regular SVT rhythm significantly faster than ~170/minute is less likely to be sinus tachycardia in an adult — and unlikely to be AFlutter with 2:1 AV conduction.
• Exceptions to the above general rule of course exist (ie, Children may have sinus tach well over 200/minute — and an occasional adult with enhanced sympathetic tone may also have surprisingly fast sinus tachycardia) — but I find it helpful to be aware of these general rate limits.

BUT — Today's initial rhythm is much faster = about 280/minute!

• Athough we only see 3 of the 12 leads in Figure-1 — the QRS complex appears to be narrow and the rhythm is regular. Although there is some undulation in the baseline — clear sign of repetitive atrial activity is not seen. Best description of today's initial rhythm is therefore that of a regular SVT rhythm at ~280/minute, without clear sign of atrial activity.
• Sinus tachycardia does not go this fast.
• The 2015 ACC/AHA/HRS Guidelines on SVT (Page et al — Circulation 133(14):e506-e574, 2016) list the usual upper rate limit for ectopic ATach and AVNRT at ~250/minute — though other sources suggest occasional rates for these rhythms (and for AVRT in patients with an accessory pathway) that may attain up to 280/minute (StatPearls, 2023).
• The above said — it is unusual to encounter a regular SVT rhythm at a rate ≥280/minute. This finding should therefore suggest strong consideration of AFlutter with 1:1 AV conduction (Ectopic ATach and reentry SVTs could be possible — but are statistically less likely when the ventricular rate is as fast as it is in today's case). 
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• To Emphasize: Clinically — It will usually not matter what the precise etiology of a regular SVT at ≥280/minute is, since immediate cardioversion will usually be indicated regardless of what the specific etiology is (especially when the patient is acutely symptomatic — as in today's case).

Figure-1: The Every-Other-Beat Method (or in today's case — the Every-4th-Beat Method) for rapid estimation of heart rate. 

Does Exercise Induce Non-Sinus Tachyarrhythmias?

The answer to this question is fascinating — albeit extending beyond the scope of this ECG Blog. But some thoughts on this issue include the following:

• The answer regarding the effect of exercise on non-sinus tachyarrythmias is — It depends ... IF the patient is an adult of a certain age, who has underlying heart disease — then a high level of exercise becomes increasingly likely to precipitate non-sinus tachyarrhythmias, including potential to induce malignant ventricular arrhythmias. The KEY to determine is therefore — Does the patient have underlying heart disease?
• Details regarding the cardiac history for the 60-something man in today's case are limited to knowing he had dyspnea on exertion of uncertain cause over the preceding month — and that he was recently diagnosed with AFib (although it is unknown if the patient was in AFib prior to his syncopal episode on the treadmill). It is also unknown if this 60-something man had been regularly exercising over time vs being sedentary.
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• At the extreme — CPVT (Catecholamine Polymorphic Ventricular Tachycardia) is a rare but important entity to recognize because of its known association with exercise-induced arrhythmias despite a structurally normal heart! (See the February 6, 2015 post in Dr. Smith's ECG Blog - and - the Case Study of polymorphic VT induced by exercise, by Hoffmayer, Scheinman et al — Heart Rhythm 19:1214-1216, 2022).

The question that arises is — What effect (positive or negative) might regular endurance training have in adults without known heart disease (and without CPVT) — on the likelihood that vigorous exercise may precipitate a non-sinus tachyarrhythmia?

• Previous doctrine had been that regular performance of appropriate level exercise (including endurance training) provided important health benefits, as well as enhancing one's sense of well being.
• That said — recent evidence suggests that longterm endurance-training exercise may increase the risk of developing AFib (and AFlutter), especially as adults age (Opondo et al — Circ: Arrhythm & Electrophys 11(5), 2018) — (Calvo et al — Br J Sports Med 46(Suppl 1):i37-i43, 2012) — (Burkhart and Gerasimon — J Osteopath Med 118(5):337-340, 2018) — (Müssigbrodt, Mandrola et al — Scan J Med & Sci in Sports, 2017).
• "Moderate" exercise seems to have a protective effect with reduced risk of AFib — whereas "excessive" exercise has been shown to significantly increase the risk of developing AFib, especially as adults age. How much exercise is "moderate" vs "excessive" — is as yet unanswered (and appears to be highly variable depending on the individual).
• A series of potential mechanisms have been proposed for this increased incidence of AFib and AFlutter in otherwise healthy adults as they age. These include — inflammation of cardiac tissue from longterm endurance training — development of structural abnormalities from "athlete's heart" (remodeling; fibrosis of the atria; atrial and/or ventricular dilation or enlargement) — the effect of longterm increased vagal tone from athletic training — the effect of frequent sympathetic stimulation from endurance exercise — frequent PACs — and potentially other as yet undiscovered mechanisms.

BOTTOM Line: As per Dr. Smith — increased sympathetic tone from active treadmill exercise presumably precipitated the tachyarrhythmia-induced syncopal episode in today's patient (in similar fashion as sustained sinus tachycardia from peak exertion induced AFib in this Case Study by Faris et al — Cureus 14(2):e22577, 2022).

• How much of an effect underlying structural heart changes may have had in predisposing the 60-something man in today's case (who recently had AFib diagnosed) — is uncertain.
• As one who taught ETT (Exercise Treadmill Testing) locally and nationally to primary care residents and clinicians — I found being there during ETT to assess exercise capacity of healthy adults for the purpose of exercise prescription to be highly insightful for recommending safe exercise limits.
• What to advise hardcore endurance athletes regarding potential longterm effects of vigorous endurance-training exercise is another story. 

ADDENDUM: In this 3-minute video — I review a quick, user-friendly and accurate method for estimating heart rates (including the Every-Other-Beat Method — for rapid estimation of heart rate when the rate is very fast).

User-friendly estimation of heart rate (including when the rate is very fast).