A young man with tachycardia. Should We Try Adenosine?

A young man presented with weakness and fever.  His pulse was 186.  An ECG was recorded:

What do you think?

There is a regular narrow complex tachycardia. Thus, it is supraventricular tachycardia.  It is important to remember that SVT includes Sinus Tachycardia!  That is why I like to call re-entrant SVT "Paroxysmal" SVT, or PSVT).   The sinus node is "supraventricular" and in young people it can beat VERY fast.  Especially when there is fever.

You must look closely for P-waves, and if you do, the P-waves are obvious (if you look at the leads most likely to reveal P-waves: leads II and V1).  In lead II, the P-wave is always upright and has the greatest amplitude because the atrium depolarizes towards the apex (lead II).  Lead V1 because it should be biphasic, up-down (the positive deflection is the right atrium and the negative deflection is the left atrium.)

So scrutinize this ECG for P-waves: lead II has an extra little bump before every QRS, and lead V1 has an up-down P-wave (the negative deflection is the easiest to see).

Other strategies for discerning sinus tach:

1. A heart rate that is not perfectly constant.  See if it changes gradually with fluids or antipyresis or just spontaneously.  Sinus tach will rarely remain exactly constant, while PSVT or flutter will always have the same re-entrant rate

2. Try Lewis Leads.  This is using the Monitor leads, not the 12-lead electrodes!

See many cases with use of Lewis Leads on this blog: 

Case continued

The providers jumped to conclusions and gave adenosine.  It only worked temporarily.  I do not have the strips.

His heart rate decreased after IV fluids and antipyretics.

He was diagnosed with strep pharyngitis.

See these Great Cases

1. Sometimes even Wide Complex Tachycardia is Sinus.  See this case in which Lewis leads were necessary to figure this out: Wide Complex Tachycardia. What is the Diagnosis?

2. A very fast narrow complex tachycardia in an Infant

3. A Relatively Narrow Complex Tachycardia at a Rate of 180.

4. See what happens when you cardiovert sinus tach:

A Relatively Narrow Complex Tachycardia at a Rate of 180.

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MY Comment, by KEN GRAUER, MD (7/17/2023):

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Please NOTE (7/19): I was given today’s ECG without knowing any history other than the question that was raised = “Should we give Adenosine?”. Dr. Smith reviews the answer and his approach above. My comments below present my approach from the perspective of one charged with overreading the ECGs of learners and clinicians of all levels of expertise.

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I was shown the ECG in Figure-1 — that I was told was obtained from a 26-year who presented to the ED with throat pain and tachycardia.

• The Question raised was: Should Adenosine be given?

Figure-1: Initial ECG in today’s case.

MY Thoughts:

Management of the rhythm in Figure-1 depends on: i) Whether the patient is hemodynamically stable; ii) The etiology of the rhythm; and, iii) What else might be going on with the patient.

• By the Ps, Qs, 3R Approach — The QRS complex in ECG #1 is narrow in all 12 leads. The rhythm is fast and regular. This defines today's rhythm as a regular SVT (SupraVentricular Tachycardia).
• 
  
• For discussion sake — I'll assume that this 26-year old is hemodynamically stable. Most of the time, previously healthy younger adults will be hemodynamically stable when they present with a regular SVT rhythm (unless other significant pathology is ongoing). Therefore — most of the time you'll be able to initiate medical management (ie, vagal maneuvers, a trial of medication) — without the need for immediate cardioversion.
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• The principal differential diagnosis of a regular SVT rhythm includes 4 entities: i) Sinus tachycardia; ii) A reentry SVT (either AVNRT if the reentry circuit is contained within the AV node — or AVRT if an accessory pathway located outside the AV node is involved); iii) Atrial Tachycardia; or, iv) Atrial Flutter with 2:1 AV conduction. Although other entities are possible (ie, junctional tachycardia, SA nodal reentry) — ready recall of this short LIST simplifies management by limiting the number of common considerations.
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• Accurate estimation of heart rate can be very helpful in expediting assessment. For example — IF the heart rate in an adult is >170minute, then both Sinus Tach and AFlutter become less likely (ie, not impossible! — but less likely). That said — IF the heart rate of a regular SVT rhythm in an adult is close to ~150/minute (ie, ~140-160/minute) — then any of the above 4 entities have to be considered in the differential diagnosis.

What is the Heart Rate in Today's SVT Rhythm?

• When the rhythm is fast and regular — the Every-Other (or Every-Third) Beat Method allows rapid and accurate rate estimation. Find a QRS complex that begins on a heavy line. In today's tracing — I chose the 2nd beat in lead I (See the 1st vertical GREEN line over this 2nd beat in Figure-2). Using the Every-Third Beat Method — the amount of time that it takes to record 3 beats (RED numbers in lead I) is just under 5 large boxes (BLUE numbers in this Figure). Therefore — ONE THIRD the rate is a little faster than 300/5 ~60-65/minute.
• The actual rate for the rhythm in ECG #1 is therefore ~60-65 X 3 ~185-190/minute. 
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• CLICK HERE — if interested in brief video review of this Every-Other-Beat Method.

Figure-2: The Every-Other-Beat Method for rapid estimation of heart rate. BLUE arrows highlight potential atrial activity in the inferior leads (See text).

Is there Atrial Activity in Today's Tracing?

When I first looked at today's rhythm — I was admittedly not at all certain about whether or not we were seeing atrial activity.

• I did see slight notching in the terminal portion of the ST-T wave in each of the 3 inferior leads (BLUE arrows in Figure-2) — but I was not initially sure if these tiny deflections truly represented sinus P waves — and — the the heart rate of ~185-190/minute for today's SVT rhythm is considerably faster that what will usually be seen for sinus tachycardia in a non-exercising adult.
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• KEY Point: Although lead II is by far the BEST lead for identifying sinus P waves — there are times when other leads may be better for showing atrial activity (Figure-3).

Figure-3: I've added RED arrows in leads I and V1 — to highlight sinus P waves that are well seen in these leads (See text).

Atrial Activity in Other Leads:

After lead II — the next best lead for identifying sinus P waves is lead V1, probably because of this chest lead electrode's proximity to the right atrium.

• PEARL: The RED arrow in Figure-3 highlights clear indication of sinus P waves in lead V1. Whereas sinus P waves in lead II should always be upright (unless there is lead misplacement or dextrocardia) — Sinus P waves in lead V1 are often negative. In my experience — the shape of the scooped negativity that we see under the RED arrow in lead V1 is highly characteristic of a sinus tachycardia P wave in this lead.
• Confirmation that despite the surprisingly rapid rate, today's rhythm is sinus tachycardia — is forthcoming from clear indication of sinus P waves in other leads (ie, the RED arrow in lead I that occurs simultaneously with those inferior lead subtle BLUE arrow deflections).
• After looking for sinus P waves in leads II and V1 — I often turn next to lead aVR. Note that we also see negative notching indicative of sinus P wave activity in lead aVR of Figure-3.

Final PEARLS regarding Recognition of Sinus Tachycardia:

Most of the time — it is EASY to recognize sinus tachycardia. Today's case is illustrative of one instance in which this diagnosis was not so obvious.

• All bets are off in kids! Although sinus tachycardia faster than ~170/minute is not commonly seen in non-exercising adults — the heart rate of sinus tachycardia in infants and young children can be surprisingly fast (ie, well over 200/minute).
• In addition to hyperthyroidism — a previously healthy young adult who presents acutely ill may be under enough intrinsic catecholamine stimulation to manifest sinus tachycardia rates as fast (or even faster) than that seen in today's case.
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• PEARL: On occasion, we all encounter very fast sinus tachycardia rhythms in which sinus P waves are completely hidden within preceding ST-T waves. While vagal maneuvers (and sometimes AV nodal blocking agents) may facilitate diagnosis in such cases — it helps to remember that: i) Sinus tachycardia is almost always the result of "something else" — such that optimal treatment usually entails finding and "fixing" the precipitating cause of sinus tachycardia (and ideally not giving Adenosine!); and, ii) The heart rate in a patient with sinus tachycardia will usually not remain constant. Instead — the heart rate typically changes, depending on whether the patient's underlying condition is getting better or worse. Attention to this changing heart rate provides an excellent clue that you are dealing with sinus tachycardia (and often, when the heart rate slows just a little bit — you will then be able to make out sinus P waves to confirm the diagnosis).

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NOTE: I've reviewed my approach to assessment of regular SVT rhythms on many occasions in Dr. Smith's ECG Blog. For those interested — Here are some of the more detailed posts with My Comments at the bottom of the page: 

• The October 25, 2022 post —
• The March 6, 2020 post —
• The August 23, 2022 post —
• The October 16, 2019 post —
• The November 12, 2019 post —