Supraventricular Tachycardias with a Narrow QRS Complex

by Julianna Jung, MD, FACEP

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    00:01 Anytime, you have unstable V-tach, you need to cardiovert your patient.

    00:07 So you're gonna perform synchronized cardio version and get them out of V-tach If they're stable, you might choose to manage them medically.

    00:16 And medical management of V-tach is gonna be antiarrhythmic drugs.

    00:20 The most commonly used one is probably amiodarone at least in the US, although procainamide is a very safe and effective drug, and sotalol can also be used.

    00:29 Now, the reason that we used these antiarrhythmics is that they are non-selective.

    00:34 So they don't just act on the AV node like your beta blockers and your calcium channel blockers do, they act on the entire myocardium and decrease automaticity sort of decrease the willingness of the heart to generate an action potential.

    00:49 So they're gonna work on rhythms that are originating outside of the normal conduction system.

    00:55 Basically, they are gonna work on ventricular rhythms.

    00:59 Now, if you have a patient who has regular, monomorphic ventricular tachycardia, you might think, hey, maybe this is actually a supraventricular rhythm, and you can consider adenosine.

    01:14 It’s the one AV nodal blocking agent that's reasonable to attempt in wide complex rhythms because it is so short acting, its unlikely to cause any major problems like a beta blocker or a calcium channel blocker would.

    01:27 But really, the main stay of treatment for V-tach is gonna be cardioversion for unstable patients and antiarrhythmic medication, specifically amiodarone or procainamide for patients who are stable.

    01:42 All right, so we covered our wide complex rhythms, again, wide complex rhythm, we're gonna treat it like ventricular tachycardia and we're gonna be safe.

    01:55 Now, we're gonna move on to narrow complex rhythms.

    01:57 So narrow complexes suggests a supraventricular origin of the rhythm.

    02:02 All narrow complex rhythms must by definition originate above the AV node because they are using those fast conduction pathways in the His-Purkinje System.

    02:12 There are several different loci from which narrow complex dysrhythmias can originate.

    02:18 So there's of course, the sinoatrial node which is where sinus tachycardia comes from.

    02:23 There's atrial rhythms like atrial fibrillation, atrial flutter, multi focal atrial tachycardia, etc.

    02:30 And then there are ectopic foci of pace making which are gonna be your supraventricular tachycardias.

    02:38 Once you've identified that you have a narrow complex tachydysrhythmia, like we said before, your next question is if it is regular or irregular.

    02:47 So were gonna start off talking about the irregular rhythms.

    02:50 So our two irregular rhythms are atrial fibrillation and atrial flutter.

    02:55 In atrial fibrillation, what's happening is electricity is wheezing around the atria in a completely uncontrolled way, so the conduction in the atria is random, its unpredictable, and impulses are sent down the through AV node from the atria in random intervals.

    03:12 So basically, anytime the node is not refractory, an impulse might be sent to it and would then be conducted to the ventricles.

    03:21 This produces the classic irregularly irregular rhythm of atrial fibrillation.

    03:27 The electrical conduction in the atria is random, the transmission of impulses to the AV node is random, and that produces a rhythm that has no regularity whatsoever in terms of the RR interval.

    03:43 Atrial flutter by contrast is a little bit more organized, when the atria flutter, they typically conduct at a regular rate of 300 atrial beats per minute.

    03:53 This produces what is usually a regular ventricular response rate.

    03:59 Now the ventricles typically cannot conduct at 300 beats per minute.

    04:04 So the most common ventricular rate we see in atrial flutter is gonna be 150.

    04:10 So two to one conduction every other atrial beat gets conducted to the ventricles so the atrial rate is 300, the ventricular rate is 150.

    04:20 However, you can get an irregular rhythm with atrial flutter because you can get sometimes get variable conduction through the AV node.

    04:30 So let's talk about how you diagnose atrial fibrillation, so like we said before the QRS complexes are narrow, so they are less than a 120 milliseconds long.

    04:39 The rate or the RR interval is irregularly irregular.

    04:44 So I've denoted the RR interval for several of the beats on this rhythm strip and you can see that 1 is 7, 1 is 15, 1 is 10, 1 is 8, 1 is 10.

    04:54 There's no predictability to it, they're just randomly fluctuating in terms of how frequently the QRS' are coming along.

    05:02 There's also a randomly fluctuating baseline.

    05:05 So you can see, there's that waviness in the baseline that represents the fibrillatory action of the atria and there are no organized P-waves.

    05:14 So you're not seeing regular, organized atrial activity, you're just seeing this random fluctuation on the baseline.

    05:23 Now by contrast, atrial flutter looks a little bit different.

    05:27 So in atrial flutter, you have this sawtooth atrial waves and I've sort of outlined those for you in green but you can see they go up and down almost like the teeth of a crosscut saw.

    05:38 Like we said before, the most common atrial rate in atrial flutter is gonna be 300 beats per minute and I've marked all of the atrial waves with arrows so that you can see where they are.

    05:49 The ventricles can't conduct at 300 beats per minute so every other atrial beat is conducted to the ventricles producing a QRS rate of 150 and you can see the QRS complexes noted again on this rhythm strip.

    06:05 This produces a two to one atrial ventricular conduction rate.

    06:09 So I've highlighted each set of two atrial waves with the one corresponding ventricular wave and you can see you've got two atrial waves, one ventricular wave, two atrial waves, one ventricular wave, so this is a two to one atrial-ventricular conduction ratio.

    06:27 Now, that's not always what we see, you can see flutter with slower ventricular response rates, so in this particular ECG, we're seeing a four to one conduction ratio.

    06:37 So for every four atrial waves, we have a QRS complex but you can also see three to one, five to one, and variable conduction rates that produce an irregular QRS interval.

    06:53 So how do we manage atrial fibrillation and atrial flutter? First and foremost, if your patient is unstable, you cardiovert them, 'cause that’s what we do for every single unstable tachyarrhythmia.

    07:04 But assuming they’re stable, we’re gonna be using AV nodal blockers to try to decrease the ventricular response rate.

    07:12 So the goal is not to get the patient out of atrial fibrillation or flutter.

    07:17 The goal is to slow down the heart rate by decreasing the ventricular response rate.

    07:23 So you block the AV node, you make it more difficult for impulses from the atria to pass through into the ventricles and you slow down the ventricular rate.

    07:33 Again, calcium channel blockers or beta blockers are the main save of treatment for this.

    07:39 Amiodarone can also be used and is appropriate in some circumstances.

    07:43 It has AV nodal blocking effects as well as global anti dysrhythmic effects.

    07:49 I do wanna mention that A-fib is commonly associated with underlying non-cardiac pathology.

    07:56 So for example, patients with sepsis, patients with inter abdominal catastrophes, patients with pulmonary emboli, they will often present in atrial fibrillation.

    08:06 And if A-fib is a complication of some other underlying disease process, it’s usually safest to focus your treatment on that underlying disease process rather than focusing on rate control or slowing down the atrial fibrillation.

    08:27 There’s actually some studies that show worst outcomes when we treat A-fib aggressively, particularly in patients with sepsis as oppose to when we just leave it alone and focus on the sepsis.

    08:39 So if you think that your A-fib is related to some underlying disease process, you might consider withholding specific rate control agents.

    08:47 But if the patient's coming in with this as their primary complaint then of course you're gonna wanna treat it.

    08:55 All right, so the other thing that we wanna think about with atrial fibrillation is anti-coagulation.

    09:01 Not every patient with A-fib needs to be anti-coagulated, but there are some indications for anti-coagulation that you wanna think about.

    09:09 So any patient with a prosthetic valve is always gonna be anti-coagulated.

    09:13 Honestly, whether they are or aren’t an A-fib.

    09:15 A patient with a prior history of stroke or TIA should definitely be anti-coagulated if they are an A-fib.

    09:23 And then there's a scoring called the CHA2DS2, and I've put it here on the slide, I’m not gonna go through it in any kind of detail.

    09:30 But I want you to be aware that there is this scoring system that helps us assess the risk of stroke related to atrial fibrillation and if your patient has a CHADS2 score of greater than two, you wanna think about anti-coagulating them assuming that there aren’t any counter indications.

    About the Lecture

    The lecture Supraventricular Tachycardias with a Narrow QRS Complex by Julianna Jung, MD, FACEP is from the course Cardiovascular Emergencies and Shock.

    Included Quiz Questions

    1. Cardioversion
    2. Amiodarone
    3. Procainamide
    4. Sotalol
    5. Adenosine
    1. Atrial fibrillation is described as a regularly irregular rhythm
    2. Conduction through the atria is random and unpredictable in atrial fibrillation
    3. Atria conducts at a regular rate in atrial flutter
    4. The rhythm is usually regular in atrial flutter
    5. Impulses are sent to AV node at random intervals in atrial fibrillation
    1. Sawtooth atrial waves
    2. Narrow QRS
    3. Irregularly irregular ventricular rate
    4. Randomly fluctuating baseline
    5. No organized P-waves
    1. If it is associated with a noncardiac pathology, continue rate control agents even when unnecessary
    2. Cardiovert if unstable
    3. Rate control with a calcium channel blocker or beta blocker
    4. Use amiodarone if indicated
    5. Focus on treatment of underlying disease if noncardiac pathology is present
    1. Patients with prosthetic valves will require anticoagulation
    2. Every patient needs anticoagulation
    3. Anticoagulants are contraindicated in patients with prior stroke/TIA
    4. A CHA2DS2-VASc score of > 2 means the patient should not receive anticoagulation
    5. The CHA2DS2 score measures the risk of myocardial infarction associated with atrial fibrillation

    Author of lecture Supraventricular Tachycardias with a Narrow QRS Complex

     Julianna Jung, MD, FACEP

    Julianna Jung, MD, FACEP

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    By ACHRAF A. on 25. December 2017 for Supraventricular Tachycardias with a Narrow QRS Complex

    simplified ,high yield content , Dr Juliana has charisma draws the audience attention