Sometimes recognizing sinus tachycardia can give us fits.
What? Sinus tachycardia? One of the most basic rhythms?
The discussion that follows will highlight some of the difficulties sinus tach can present at high rates. The pitfalls of using the generalized term "SVT" will also be discussed. This discussion is not meant to imply that this issue is easy to navigate. It can get very difficult, and very dicey. The consequences of misinterpreting the rhythm and missing sinus tach can have very deleterious effects for our patients.
We are all good at recognizing sinus tachycardia at rates between 100-150, but when rates exceed 150 it seems to become problematic.
Is it difficult to recognize this?
How about this one?
When sinus tachycardia occurs at high rates, our ability to correctly differentiate it from other types of SVT apparently decreases. P waves start to blend into the T waves. Instead of talking about discreet stand alone P waves, we talk about "notches" and "bumps". It is all too easy to look at a rate >150 and simply call it "SVT".
We know what sinus tach is: a sinus rhythm at rates faster than 100 (in adults), which is a normal physiological response to compensate for the increased needs of the body. I won’t spend time listing all of the possible causes, ranging from running around the block to septic shock.
AVNRT, a type of SVT that is responsive to Adenosine, is a re-entrant tachycardia that relies on a circuit through the AV node to sustain it. Block down the AV node, and the dysrhythmia terminates. Quite a bit different from sinus tach. Different mechanisms, different treatments.
Several case studies involving the above strips and ones like it have appeared on our FB page, and the FB pages of other EMS educational sites. What we have seen is that an alarming number of folks incorrectly identify sinus tachycardia as one of the other SVTs and want to treat with Adenosine or cardioversion.
Consider this rhythm strip that appeared on our page and another educational paramedic page:
The patient was a sick adult male, hypotensive. P waves are subtle, but they are there. Due to the rate, however, a majority of providers (hundreds!) identified this as "SVT" and wanted to immediately cardiovert.
Here is the followup ECG taken a couple of hours later. The patient was severely dehydrated and had received a few liters of fluid:
Now that the rate has slowed, sinus tach is clearly visible.
While we are discussing this, we should be clear about our terminology. Sinus tach is one of the Supraventricular Tachycardias. "SVT" is an umbrella term that represents a group of tachydysrythmias that originate above the ventricles. They will generally be narrow tachycardias, unless aberrant conduction is present. Some of the other types of SVT are AVNRT, AVRT, A-Flutter, A-Fib, junctional tachycardias and atrial tachycardia. Not only is sinus tach one of the SVTs, it is by far the most common SVT!
One of the issues that’s come to light is the fact that “SVT” is seemingly often taught as a “dysrhythmia” itself rather than what it really is: a group of dysrhythmias. I really don’t like the term “SVT” because it implies a diagnosis, when in fact it should motivate a provider to form a list of differentials and consider the H’s and T’s.
"Could this be sinus tach? A-Flutter? AVNRT?"
Treating "SVT" as a stand alone dysrhythmia leads folks to believe there is one “treatment” for SVT, when in fact the treatment is determined by which type of SVT the patient has.
What are we even taught about SVT?
Generally speaking these days, when students are taught SVT they are taught that a narrow tachycardia faster than 150 or 160 is "SVT". Simple as that.
How do we differentiate sinus tach from SVT?
That’s easy: rate!
If the rate is over 150 (some use 160), then it is “SVT and not sinus tach” and should be given adenosine or cardioversion! Quickly!
If you were taught that, raise your hand. Wow… that’s a lot of hands!
While we are on the subject, where did the rate limit of 150 or 160 come from?
I have NO IDEA. There does not seem to be any research I can find that even suggests that these numbers can be used to differentiate ST from other SVTs.
In fact, I could not find any research that demonstrates that absolute rate plays any part in differentiating ST from other SVTs.
All I could find is references to the guideline used to determine the theoretical maximum sinus tachycardia in healthy people: “220 – age”.
This “formula” is a guideline at best. It intends to illustrate that very young people can have ST at very high rates, and that as we age, it should be more difficult to achieve higher rates of sinus tach. However, we deal with really sick patients, and theoretical guidelines are not good enough to help us with this issue.
What I know is what you all know. That medics are taught that at rates above 150, you can no longer see P waves, so you have to assume it is “SVT”.
Easy as pie! Whether or not P waves are visible does not seem to factor into the equation.
Perhaps you don’t want to accept that these teachings do not seem to be based on anything concrete, but these are the facts. Sinus tach commonly exceeds rates of 150, and P waves are often discernable. More on this in a bit.
In any event, It is in this region of rates, between 150 and 200, where sinus tach is often mistakenly called “SVT”, and the risk of inappropriate treatment rises. Don’t believe it?
Before you can say “SINUS TACH”, I could show hundreds upon hundreds of comments left by medics stating that a rhythm “could not be sinus tach because the rate is over 150”. And these comments were made by the medics who are motivated enough to visit educational sites and participate.
The result of this is that too many medics are not correctly trained to deal with this issue. Sinus tach is unrecognized. The P waves are ignored, and the rhythm is labeled “SVT”, and the patient is in danger of suffering in more than one way:
For staters, they may receive an inappropriate treatment. A sick patient in sinus tach does not need to go through trials of adenosine, or even worse, cardioversion. In addition to the discomfort, those treatments won’t work. Sinus tach is not a reentrant rhythm that relies on the AV node for its perpetuation, so adenosine or cardioversion won’t resolve the arrhythmia.
One of the most overlooked consequences of mistreating this rhythm is the fact that these patients are not getting the treatment they really need. These patients need lots of fluids. If medics are giving drugs and electricity, they certainly are not administering large boluses of NS.
It is easy to imagine how difficult the choice may seem. The sick patient in sinus tach will look shocky. He may have palpitations or chest pain, and may be altered. In other words, it will be very tempting to attribute the patient presentation to rate problem, even though the rate is compensating for their underlying medical issue.
Without a sound understanding of what sinus tachycardia really is, and what rate ranges are reasonable, it becomes much more difficult to make the right choice.
Probably right about now, some of you will want to blame ACLS for all of this. Consider the 2010 “Adult Tachycardia (with pulse)” algorithm :
Box 1 states: “Heart rate typically greater than or equal to 150 if tachyarrhythmia”.
What does that mean? What it seems to mean to a great many people is that a rate greater than 150 is "SVT".
If the patient appears unstable, we are performing synchronized cardioversion by box 4. There is no mention of sinus tach anywhere on this algorithm.
I’ll admit, I think that algorithm could be better. I think there should be a box that gets you out of that algorithm if sinus tach is recognized, similar to what appears on the ACLS Pediatric Tachycardia algorithm :
Here, if the tachycardia is narrow, you are directed to one of two boxes which require you to assess for the presence of sinus tachycardia. I believe that a box like this in the adult algorithm would help clear up a lot of confusion.
In defense of the AHA, however, the simplified algorithm is based on the assumption that students have read the ACLS Provider Manual, on which the algorithm is based.
The following appears in the “Foundational Facts: Understanding Sinus Tachycardia” box on page 125:
“Sinus tachycardia is caused by external influences on the heart, such as fever, anemia, hypotension, blood loss, or exercise. These are systemic conditions, not cardiac conditions. Sinus tachycardia is a regular rhythm, although the rate may be slowed by vagal maneuvers. Cardioversion is contraindicated.” 
Clearly, on page 125 of the ACLS Provider Manual, sinus tachycardia has been excluded from the adult tachycardia algorithm. It is a shame that fact is not reflected on the algorithm itself, because evidently a very large number of ACLS students do not read the manual and may incorrectly assume that rate is the determining factor.
I know some of you are thinking, “is this much to do about nothing? Is sinus tachycardia at rates above 150 as rare as an isolated posterior STEMI?"
We put this issue to the test. We brought in two well known electrophysiologists, Dr.’s John Mandrola and Mark Perrin, to shed light on this issue and share their perspectives with us. Readers of our blog will recognize them as past contributors and experts in their field.
I asked Dr. Mandrola about the utility of the “220-age” formula, and here is what he had to say:
“The old formula 220- age equals the max heart rate represents only an estimate. It can vary by up to 10-15%. That's a lot. Normally a 30 year-old would have a max of 190. But with the variation, ST could be as high as 200. I see tons of patients for 'tachycardia', that's supposedly abnormal. Often its just ST. The short answer is that human heart rates vary quite a bit–at the high and low end.”
I then asked him what we really want to know: how common is ST at rates above 150:
“The sinus node is highly innervated with both sympathetic and para-sympathetic neurons. Adrenaline can easily push the sinus rate above 150. Stress, anxiety, fever, dehydration, drugs, heat, and many other things can do this.
If a patient has upright p-waves and the diagnosis is ST and is unstable, it's not because of a primary electrical disturbance. ST is a sign not a primary arrhythmia. Patients with ST should be resuscitated, but not with shocks, with fluids, oxygen and rest perhaps and comfort perhaps.”
I asked Dr. Perrin for his thoughts about using a rate of 150 as a cut-off between sinus tach and other types of SVT and he had this to say:
“Thinking that ST has an upper limit of 150-160 is kind of crazy. The septic, those in congestive cardiac failure, people with pulmonary emboli, hemorrhaging patients, etc, etc… all of these could hit heart rates of 190-200 or higher.
It is an easy diagnosis to make as well – because the P will always be present. Perhaps if the rate is > 200 it may disappear into the T wave a little. The only real differential is atrial tachycardia/flutter, and this is pretty unlikely to destabilize a patient.”
We discussed the issue medics are having in the field with inappropriate treatments of sinus tachycardia. I asked if he had any first hand experiences with it:
"In fact, I have found, anecdotally, that paramedics are quick to shock patients. I have misgivings about this, especially for narrow-complex rhythms. We live in a city. ERs are close by. Why shock so quickly? There's some data that shocks harm the heart.”
My sincere thanks to Dr.’s Mandrola and Perrin for their contributions. As always, peer sourcing is great way to gain additional insight and expertise.
Hopefully this discussion has been educational for those who thought that 150 was any kind of limit for sinus tachycardia. The fact of the matter is that sinus tach at rates between 150- 200 not only exists, but is not uncommon. We need to be better at assessing for sinus tachycardia, because it is the most common SVT. We need to make sure we are doing right by our patients, giving them what they need and keeping them our of harm's way.
We also need to be better educators and providers.
Some will say, "we are teaching to the Registry", or "we are teaching to ACLS".
They will say, "in the real world, they will know what to do".
From what I have seen, it doesn't work like that. Providers fall back on what they were taught, which often happens to be incorrect.
It begs the question, why are we teaching something we know is not correct? That can't be good for anyone.
For those who didn't know this information before, you know it now. Let's see if we can change the way we educate and provide care in this area.
It seems to be a deeply rooted problem, ingrained in decades of education. Time for a change. I don’t know if the issue has been raised before, but we are raising it now.
As always, I look forward to your comments!
,– Advanced Cardiovascular Life Support Provider Manual
2011, American Heart Association
 Pediatric Advanced Life Support Provider Manual
2011, American Heart Association