hypothermia

EKG Challenge #1 - Unresponsive and Bradycardic - Case Conclusion

We'd like to start by thanking everyone who participated in the EKG challenge.  Without further ado, the case conclusion:

You are working in TCC when EMS arrives, bagging an unresponsive elderly-appearing female.   They report that they were called to a nursing home for unresponsiveness, and found the patient on the floor.  On their arrival, she was minimally responsive to noxious stimuli and had a heart rate of 36 on the monitor.  She received atropine 0.5 mg x 3 prehospital with minimal response.   Her blood pressure is 80/60.  To identify if there is heart block, you get an EKG demonstrating marked sinus bradycardia with a 1st degree AV block and possible ST elevation in the inferior and precordial leads (see below):


You intubate the patient, and as you are placing pacer pads on, your attending notes that she feels very cold to touch.  Her temperature by Foley catheter?  28.2 degrees! You take another look at the EKG and think – ah, not ST elevation after all, but J waves. 


After initating the patient on some aggressive rewarming with warmed IV fluids, a bear hugger and warmed ventilator circuit, you take a moment to ask two questions:


[1] Above and beyond the J waves of Osborn, what EKG findings are suggestive of/associated with hypothermia?


Luckily for you, emergency medicine EKG guru Amal Mattu wrote a paper on this very subject.   Entitled simply, “Electrocardiographic Manifestations of Hypothermia” it goes through a series of cases and highlights a few important take homes regarding EKGs in hypothermic patients:
a.  The J-wave is the most common EKG finding in hypothermia, and is found when core body temperatures are < 32 ˚C.  They can be seen in other situations as well, including subarachnoid hemorrhage, acute cardiac ischemia, and normal normothermic patients.
b. Atrial and ventricular arrythmmias become more predominant with the degree of hypothermia.  Marked sinus bradycardia with decreased AV conduction velocity (as seen in this patient) is a common finding.
            c. Intervals (as in all of them) can be prolonged.
d.  A pseudoinfarction, with ST elevation, pattern is sometimes seen.  The pattern should resolve with re-warming.
e. The EKG will not necessarily reflect the peaked T waves of hyperkalemia.  Be wary, this subset of “found down” patients can have hyperkalemia secondary to rhabdo or renal failure, but it won’t be as noticeable in the EKG.


Importantly, the intervention for the above arrythmmias is not anti-arrythmmics , pacing, or even pressors as these have limited utility in a cold myocardium.  The treatment is re-warming (see below), which will resolve most of the above.


[2]  What is the differential diagnosis for hypothermia – i.e., what tests should I send and what interventions should happen for this critically ill patient in the emergency department?
Remember, once you diagnose the patient with hypothermia, your workup and interventions do not stop there – hypothermia has a differential diagnosis: (see ref 2)
A.  Horses – environmental exposure, severe hypothyroidism, diabetic ketoacidosis,                   sepsis, multisystem trauma, and prolonged cardiac arrest
B. Zebras – Hypothalamic lesions, episodic hypothermia with hyperhydrosis


Therefore, there are two main components of the ED intervention:
 1. Diagnose and treat the underlying cause –  Check TSH, Initiate septic workup and broad spectrum antibiotics.
 2. Aggressive rewarming –There are four classifications for types of rewarming
         a Passive external – i.e. blankets – raises temp 0.5 – 4˚C/hr
         b. Active external – i.e BEAR hugger – raises temp 1-2˚C/hr
         c. Active internal – humidified vent, warm IV fluids, body cavity lavage  - raises temp 0.5 –    1.2˚C/hr
         d. Extracorporal – ICY lines and ECMO – raises temp 4-10˚C/hr.

a, b, and c are usually sufficient for mild to moderate hypothermia.
                                                    
In the ER, the patient was intubated, aggressively warmed with a humidified vent, warm IV fluids and a bear hugger -  and had a concordant rise in her heart rate and blood pressure and resolution of her EKG findings: 

 
Clinical takehome – Be suspicious of hypothermia in patients with cardiogenic shock who are found down. Remember, a lot of your “go to” interventions will not work in these patients.  Treat hypothermia and related cardiac complications with aggressive rewarming, and don’t forget that hypothermia has a differential diagnosis.

References:
[1] Mattu, A., Brady, W. J., & Perron, A. D. (2002). Electrocardiographic manifestations of hypothermia. The American journal of emergency medicine, 20(4), 314-326.
[2] Aslam, A. F., Aslam, A. K., Vasavada, B. C., & Khan, I. A. (2006). Hypothermia: evaluation, electrocardiographic manifestations, and management. The American journal of medicine, 119(4), 297-301.


Interested in some more learning about J waves?
and remember to look out for EKG challenge #2 next week.


Contributed by Maia Dorsett, PGY-3