CONTENTS

• Hypothermia
• J-waves
  • [1] Hypothermia
  • [2] Hypercalcemia
  • [3] Brugada type II
  • [4] Acute MI
  • [5] Takotsubo cardiomyopathy
  • [6] Early repolarization
  • [7] Myocarditis

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hypothermia

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rhythm: bradycardias & conduction blocks

• Most common rhythms:
  • Sinus bradycardia.
  • Junctional bradycardia.
  • Atrial fibrillation, often slow AF.  
    • Tremor can mimic atrial fibrillation or flutter.
• Also can see:
  • Atrial flutter.
  • VT & VF.

intervals

• All intervals are prolonged.
• QRS widening occurs below ~29C (85F).

J waves in hypothermia (aka Osborne waves)

• Appearance
  • Positive deflections following the QRS complex.
  • Most often seen in inferior leads and V5-V6.
• Significance
  • Correlate with severity of hypothermia.
    • Don't occur >32C (90F).
    • Seen in 80% of patients below <30C (86F). (15680518)
  • May persist for 12-24 hours after restoration of normal temperature!
  • It probably correlates with the risk of VF.
• The differential diagnosis of J-waves: ⚡️

ST & T changes due to hypothermia

• ⚠️ Caution:  Hypothermia may cause pseudo-infarction patterns with STE or STD.
  • (1) Massive Osborne waves can occasionally mimic STE.
  • (2) Repolarization abnormalities may cause ST changes.
• TWI.
• Brugada morphology can occur.

shivering artifact

• Shivering suggests a core temperature over roughly 90F (mild hypothermia or “HT1” in the Swiss Staging system; see figure below). As such, shivering is a favorable prognostic sign.

⚠️ look for concomitant hyperkalemia

• Excessively peaked T-waves may indicate concomitant hyperkalemia (example below).
• Clinical implications of hyperkalemia include the following:
  • [1] Hyperkalemia often implies cellular damage due to severe hypothermia, with a worse prognosis.
  • [2] Hyperkalemia may worsen with re-warming, so this requires aggressive therapy.

More on hypothermia diagnosis and management here.  

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J-waves

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J-wave basics

• J waves are slow upright deflections between the end of QRS and the early portion of the ST segment.
  • This can look a bit like an RSR pattern, but tends to be more slurred.
• J-waves are most often seen in the inferior leads and V5-V6.
• J-waves seem to be caused by transmural voltage gradients between the endocardium and epicardium during depolarization. This is a risk factor for polymorphic VT and VF.

causes of J-waves (“J-wave syndromes”) 

• Easier to exclude or diagnose:
  • [1] Hypothermia.
  • [2] Severe hypercalcemia.
  • [3] Brugada type 2.
  • [4] Acute MI.
• Then you're left with:
  • [5] Takotsubo cardiomyopathy.
  • [6] Early repolarization.
  • [7] Myocarditis.

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[1/7] hypothermia ⚡️

• J-waves can occur when the core temperature is <32C/90F.
• Hypothermia is the only cause of massive and very wide J-waves.

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[2/7] severe hypercalcemia 

• Hypercalcemia may cause true J waves.
• However, more commonly, the T-wave may occur immediately after the QRS complex, mimicking a J-wave.

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[3/7] Brugada type II

• Look for a saddle pattern in V2.

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[4/7] acute MI

• J-waves aren't common but may occur.
• J-waves seem concordant with the current of injury (so they can indicate the infarcted artery).
• J-waves may occur along with ST elevation, or J-waves may be the most prominent abnormality.
• Ischemic J-waves are dynamic (e.g., they appear with ischemia and may later resolve).
• These are associated with a risk of polymorphic ventricular tachycardia.

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[5/7] Takotsubo cardiomyopathy

• J waves may be seen in ~35% of patients during the hyperacute phase of Takotsubo cardiomyopathy (accompanying STE). (24500071)
• J-waves predict ventricular tachycardia, with a hazard ratio of 3.5 and risk approaching 50%. (Choi et al 2020) 

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[6/7] early repolarization 📖

• 🔑 Usually men (75%), <50-70 years old.
• 🔑 Widespread STE (greatest in V3-V4; often limb leads esp. II).
• 🔑 Notching/slurring at the J-point is followed by concave STE.
• 🔑 T-waves are usually tall and asymmetric, with STE in V6 <25% of the T-wave height (although benign TWI is possible).
• 🔑 R-waves and generally tall.
• 🔑 Often associated with STD in aVR.

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[7/7] myocarditis 

• Some patients may have perimyocarditis (causing a combination of findings seen in pericarditis plus those seen in myocarditis).
• ECG findings in myocarditis are variable (further discussion here: 📖)

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questions & discussion

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