Altered mental status, bradycardia

This was written by Hans Helseth.

Paramedics arrived at the house of a 59 year old man after his caretaker called 911 for altered mental status. He was lethargic and slow to respond to questions. He was found to be hypotensive with systolic pressures in the 70s and 80s. An EKG was recorded:

What do you think?

This EKG shows the same 2.5 seconds as recorded by all 12 leads, so it is not ideal for rhythm analysis. However, there are visible upright P waves in front of each QRS complex in inferior leads, which are about 1.28 seconds apart. In other words, there is sinus bradycardia at a rate of about 47 bpm.

In this clinical context, this EKG is also perfectly consistent with a certain pathology which can be easily and quickly confirmed and addressed by any emergency medical staff: Hypothermia.

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Patients with hypothermia typically develop EKG changes like sinus bradycardia or bradyarrhythmias, J waves or Osborn waves, and a prolonged QT interval. The severity of these findings correlate with the patient’s core temperature. Hypothermia is classified as either mild, moderate, or severe:

• Mild: 32°C-35°C (89.6°F-95°F)

• Moderate: 29°C-32°C (84.2°F-89.6°F)

• Severe: <29°C (84.2°F)

Patients with severe hypothermia can develop pathognomonic EKGs with massive Osborn waves, long QT intervals, and bradycardia.

See this post:

What is this ECG finding? Do you understand it before you hear the clinical context?

And this post:

Massive Osborn Waves of Severe Hypothermia (23.6 C), with Cardiac Echo

The EKG in patients with moderate hypothermia may show more subtle changes, but rapid identification of these changes in the right clinical context can accelerate therapy to restore a normal core temperature. 

The EKG in today’s case shows sinus bradycardia with Osborn waves in lateral precordial leads, an ST-T morphology characteristic of hypothermia (an Osborn wave at a similar height to the T wave, with a concave ST segment between them) and QT interval prolongation (See Ken Grauer's comment for more details on QTc calculation).

See this post, with a very similar ST-T morphology to today’s case:

Altered Mental Status, Bradycardia

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Case Continued:

Paramedics noticed that the patient felt cold. They recorded a temperature which

simply read "low" (below 33.9°C or 93°F, the bottom limit of reporting for their thermometer). The patient arrived to the emergency room where a rectal temperature was recorded at 29.2°C (84.5°F). He also had this EKG recorded:

The findings here are similar to those in the prehospital strip. There is also a more pronounced shiver artifact, which is commonly observed in EKGs recorded on patients with hypothermia. 

The patient was externally re-warmed in the ED with a Bair HuggerⓇ. He was admitted to the hospital for sepsis and his temperature returned to normal the next day. There was no EKG recorded after temperature correction. A repeat EKG after temperature correction would likely have shown correction of the ST-T abnormalities, disappearance of the Osborn waves, shortening of the QT interval, and a faster heart rate.

Reference, written by one of the world's experts in Enviromental Hypothermia, from Hennepin (also where Smith is from), Megan Rischall. Doesn't it make sense that the expert would come from one of the coldest winter metro areas in the U.S? Evidence-Based Management Of Accidental Hypothermia In The Emergency Department

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MY Comment, by KEN GRAUER, MD (4/25/2025):

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Most cases of hypothermia are obvious: For example — A patient is "found" outside, exposed to the elements in a cold weather setting. But this is not the only clinical presentation we see for hypothermia.

• My introduction to how subtle the presentation of hypothermia can sometimes be, was during my early days as hospital Attending — when a patient who had been on our hospital Service for several days, was found one morning by nursing staff to be unresponsive. The patient was cool (not cold) to the touch, and was not shivering. It turns out that the patient had developed septicemia from an occult infection.
• Lack of a fever — and stable medical condition in a warm hospital bed initially fooled the in-patient team, with our warm-weather Florida location accounting for limited experience by housestaff with hypothermic patients.

Moral of My Story: Whereas experienced emergency providers are well familiar with hypothermia as a potential manifestation of septicemia — it is easy to overlook a sudden, gradual reduction in body temperature in a poorly responsive, non-shivering patient.

• Hypothermia may occur in warm-weather locations during warm-weather months.
• Older, less responsive patients, especially those with multiple co-morbidities, whose temperature regulatory mechanisms are often compromised — are especially susceptible to hypothermia.
• Hypothermia may be a sign of sepsis. Fever often develops in such patients once the hypothermia is corrected. Check the patient's temperature.
• NOTE: The "telltale" shivering of hypothermia may be absent in poorly nourished, compromised patients, and in those with endocrinopathy (Nice review by Duong & Patel — StatPearls, 2024).

ECG Findings with Hypothermia:

We've periodically reviewed the ECG findings of hypothermia (ie, among other posts, in My Comment in the February 2, 2024 post — in which we illustrate what could be the largest Osborn Waves that you have seen).

• In addition to Osborn waves — other commonly associated ECG features with Hypothermia include: i) Bradycardia (which may be marked); ii) Atrial fibrillation or other arrhythmias (including VFib); iii) Artifact (from baseline undulations resulting from associated shivering); iv) QTc prolongation (which may be marked); v) ST elevation in multiple leads; and, vi) Brugada phenocopy.

Today's Initial ECG: 

For clarity in Figure-1 — I've reproduced today's initial ECG.

• PEARL: It's important to appreciate that there are many different display formats for ECG recordings. As noted by Hans Helseth — the display format in today's initial tracing shows the same 2 beats in each 2.5 second recording for each of the 4 sets of 3 leads. Thus, we only see 2 beats in this entire ECG. 
• The 2 beats that we see in Figure-1 — do appear to be sinus-conducted (since in lead II, we see an upright P wave with fixed PR interval). That said — Because the same single R-R interval is present in each of these 12 leads, we have no idea if the rhythm is a regular sinus bradycardia at ~47/minute — or — if there is irregularity with a significant increase in heart rate elsewhere on the tracing. In a word — We can do no more than guess what the rhythm in this initial tracing is.

Figure-1: Today's initial ECG (showing use of our QTc calculator).

Otherwise in Figure-1:

• There is relatively low voltage (almost a null vector in lead I ). The PR interval for the 2 beats that we see is normal — and the QRS is narrow. But the QTc (ie, the QT interval corrected for the slow heart rate) is prolonged.
• As shown in Figure-2 — We've added a QTc Calculator to the lower line of the Tab Menu that appears at the top of every page of Dr. Smith's ECG Blog. Especially given the challenge of reliably determining the QTc interval with slow rhythms — entering the heart rate (47/minute) and the QT interval that you measure (580 msec.) — instantly yields 5 estimates for the QTc. While there is some variation in these estimated QTc values (depending on the specific method used) — agreement is excellent in Figure-1 for confirming moderate QTc prolongation in today's initial ECG (average QTc ~535 msec.)
• The frontal plane axis is vertical but normal.
• ST-T waves in Figure-1 show nonspecific flattening.
• Osborn Waves are present (RED arrows) — but are subtle, limited to 2 leads, and would be easy to overlook if not attentive to the ECG findings of hypothermia.

Concluding Thoughts:

The etiology of this patient's hypothermia was septicemia. 

• Because of the patients poorly responsive state, and a lack of shivering at the time the paramedics arrived — a high index of suspicion for septicemia was needed to expedite diagnosis. Taking the temperature was confirmatory.
• The patient's initial ECG is consistent with the diagnosis of moderate hypothermia (ie, apparent bradycardia — prolonged QTc — subtle Osborn waves). 
• That said — I thought ECG findings on the initial tracing were more modest than I would normally expect in a patient with an initial rectal temperature of 29.2°C = 84.5°F (? initial core temperature?). I find it instructive that even with this low of an initial temperature — ST-T waves only showed nonspecific flattening — shiver artifact was absent (it became readily apparent on the repeat ECG in the ED) — and Osborn waves were tiny and only seen in 2 leads.
• Apparently — no ECG was repeated after the patient's temperature was corrected. The ECG of a hypothermic patient may mask underlying ECG abnormalities. For this reason — Always repeat the ECG after correcting hypothermia.

Figure-2: Quick link to the QTc Calculator in the Menu on every Blog page.