♪ (music) ♪ (Cathy) Hi. Welcome to Harrison's Podclass, where we discuss important concepts in internal medicine. - I'm Cathy Handy. - (Charlie) And I'm Charlie Wiener, and we're coming to you from the Johns Hopkins School of Medicine. (Cathy) Welcome to Episode 16 of A Young Woman Found Down. (Charlie) Here's the question. A young woman is brought to the emergency department after witnesses observed her suddenly lose consciousness, while she was jogging in the nearby park.
She has a fractured nose and broken teeth from her fall. She has no identification. She's awake, but she's confused. Her vitals are notable for a blood pressure of only 60 over palpable, and her heart rate is close to 280 beats/minute. Cathy, what do you think so far, and what more do you want to know? (Cathy) So, this is a case of a young woman with syncope, and we hear that her heart rate is still 280.
I know it's not sinus tachycardia because the max predicted heart rate that we would expect with sinus tachycardia
220 minus age. We don't know her age, but it doesn't matter anyways because 280 is too high for sinus tachycardia. Sounds like she was brought in by EMS, so I assume we have an EKG showing what her heart rhythm is. (Charlie) I'm looking at her rhythm strip, and it shows me that she has a wide complex, irregularly irregular tachycardia, with a rate that is approximately 250-300 beats/minute. How does that help you?
(Cathy) Well, when I'm thinking about tachycardias, and when we have time to think about it, I first look to distinguish whether it's a wide complex tachycardia or a narrow complex tachycardia. Narrow complex tachycardias are generally supraventricular and wide complex tachycardias are generally from the ventricle. (Charlie) But are all wide complex tachycardias from the ventricle? (Cathy) Definitely not all.
So, most of the time they are, and you want to know if it's a ventricular tachycardia right away. But supraventricular tachycardias that do not go through the AV node can give you a wide complex tachycardia. And also, if there's pre-existing conduction system disease, you can also get a wide complex. (Charlie) And when you say pre-existing conduction disease, you mean like a patient with a bundle branch block or something like that? (Cathy) Yeah, absolutely.
And that's common in older people who have a history of ischemic heart disease, or if they have an infiltrative cardiomyopathy. (Charlie) Okay. So, I mentioned that this tachycardia appeared to be irregularly irregular. How does that help you? (Cathy) So, with an irregularly irregular rhythm, it's unlikely that it's ventricular tachycardia, because that usually has a regular rhythm. And it's not ventricular fibrillation, because she's awake.
So, we're thinking of supraventricular rhythms that are irregularly irregular. So, there my sort of differential is, is this atrial fibrillation or is this multifocal atrial tachycardia? And the way to distinguish these are on ECG. If you think about MAT, or multifocal atrial tachycardia, you'll have different P wave morphologies. And in atrial fibrillation, you won't have any recognizable P waves. (Charlie) Okay. So, I'm looking at the ECG, and I see no P waves.
Therefore, you think it's likely atrial fibrillation with antegrade conduction through an accessory tract? (Cathy) Yup. That's what I would think. (Charlie) Okay. Well, the question then asks, What is the most appropriate next step?
a) amiodarone; b) lidocaine; c) metoprolol; d) defibrillation; or e) an emergent CT scan with contrast to evaluate for pulmonary embolism. (Cathy) Well, the patient's unstable with hypotension and poor cerebral perfusion. And that, we suspect, is really because of her wide complex tachycardia. So, defibrillation is really the only therapy that's appropriate and that should be performed as soon as possible.
Frankly, any tachycardia with these symptoms, you would want to defibrillate, and you would save any of the other measures that you mentioned for more non-emergent situations. (Charlie) What do you think of those other options, and where would they be useful? (Cathy) So, if the patient were stable, amiodarone or metoprolol could be used in a patient with atrial fibrillation with a rapid ventricular response.
A CT scan for the etiology could be reasonable if you suspected pulmonary embolism and if the patient had stable vital signs. Also, if PE was really a strong consideration and you couldn't get a CT scan, you could always start empiric anticoagulation. Lidocaine is used for ventricular arrhythmias, so I wouldn't use that in this setting. (Charlie) So, the teaching point in this case, most notably, is that, in any unstable patient with a tachyarrhythmia, DC cardioversion is the first step.
Furthermore, the etiology of the tachycardias may be distinguished by their QRS morphology and their regularity. (Cathy) And for more on this, you can check out Harrison's Disorders of Rhythm in the section on Disorders of the Cardiovascular System. ♪ (music) ♪