Transcript

You are consulted overnight for a 66 year old gentleman found hypothermic and unresponsive in his home.  Check out his EKG here. Anything stand out to you?  Let’s walk through this EKG together like a cardiologist. First, let’s start off looking globally at this EKG. The rhythm looks regular. I see a P wave before every QRS and a QRS after every P, and the P waves are upright in lead 2, so this is sinus rhythm.

Now let’s dissect this EKG a little bit more closely.  First, if we zoom in to lead V2, we see a little bit of artifact pointed out here.  Next, let’s talk about his rate. Based on his RR interval here, he is in sinus bradycardia with a heart rate in the 30s. And speaking of intervals, check out his PR interval over here. His PR interval is prolonged at over 200 milliseconds, so he also has a first degree AV block. Okay, let’s move on to his QRS complex.

His QRS complex also looks prolonged at over 120 milliseconds, so he also has an intra-ventricular conduction delay. And finally, let’s check out that QT interval. When we correct for his heart rate, his QT interval is prolonged at about 570 milliseconds.  Let’s briefly recap these EKG findings. His EKG shows sinus bradycardia with a first degree AV block,  an intra-ventricular conduction delay, and a  prolonged QTC interval.

Okay, now let’s get back to our patient. You know his EKG abnormalities. He’s hypothermic and he’s unresponsive. What other labs would you order?   In our laboratory workup, we should make sure we check a free T4 and a TSH.  So you go ahead and check these labs and you find that his free T4 is undetectable with a TSH of 40.

Now it’s on the top of your differential diagnosis?  If you said myxedema coma, you’re correct. A 66 year old gentleman who’s hypothermic and unresponsive with conduction abnormalities on EKG and an elevated TSH with an undetectable free T4 should raise alarm from myxedema coma.

But what is myxedema coma? Myxedema coma is a life threatening medical emergency caused by severe hypothyroidism. It causes slowing of multiple organ systems, and you may see other hypoabnormalities, like hyponatremia, hypoglycemia, hypoventilation, and hypotension.  Okay, let’s summarize what we’ve learned.

First, what is myxedema coma?  Myxedema coma is a life threatening medical emergency caused by severe hypothyroidism.  Second, what are the effects of myxedema coma on the heart? When we look at impacts of myxedema coma on the heart, I want you to think of it in three big buckets.  Conduction, structure, and contractility.

Starting with conduction, myxedema coma causes slowing of the conduction system. Myxedema causing sinus bradycardia, heart block, intra-ventricular conduction delay, and prolonged QTC.

Structurally, you may see something called myxedema heart. Myxedema heart is an enlargement of the cardiac silhouette on x ray that may be accompanied by  T wave flattening or inversions with or without pericardial effusion.  Although it’s not entirely clear what causes myxedema heart, it may be caused by interstitial edema or dilated chambers and rarely can be complicated by pericardial effusion or pericarditis.

In addition to myxedema heart, another structural change you may see is a decrease in LDL clearance, which  can cause accelerated atherosclerosis. Finally, let’s talk about contractility. Hypothyroidism and myxedema coma decrease cardiac output and contractility, and they also can increase systemic vascular resistance due to endothelial dysfunction.

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Myxedema Coma