hypothermia defined as a core body temperature < 35 can be a life - threatening emergency , especially in cold winter climates , but can be used therapeutically . therapeutic hypothermia ( th )
has been used to improve neurological outcome in comatose patients after cardiac arrest.1)2 ) the exact mechanism for neuroprotection is unclear ; potential mechanisms include attenuation of deleterious processes occurring after initial hypoxic tissue injury.3)4)5 ) generally , mild hypothermia is defined as a core body temperature between 32 and 34.2 ) this is thought to be appropriate temperature between neuroprotective effects and possible toxicities . the osborn wave ( also known as the j wave )
it is not pathognomonic of hypothermia , but usually occurs in patients with a core temperature < 32 and the magnitude of the j point elevation correlates inversely with the body temperature.6 ) several studies have suggested an arrhythmogenic potential of the osborn wave,7)8)9)10 ) but there is no solid evidence that th - induced osborn wave itself is associated with increased mortality.11)12 ) here we report a case of recurrent ventricular fibrillation ( vf ) after appearance of osborn wave during mild th .
a 56-year - old man with no underlying disease was admitted to the emergency department with sudden cardiac arrest . while having breakfast , he suddenly pounded his chest .
he received cardiopulmonary resuscitation ( cpr ) from his son for about 20 minutes until paramedics arrived with a defibrillator .
1 ) . defibrillation with 200 j was delivered once followed by 5 cycles of cpr . following restoration of cardiac rhythm ,
he was transferred to our hospital for further management . at our hospital , initial ecg ( fig .
2a ) showed sinus tachycardia with a heart rate of 114 beats per minute . on the first day of admission ,
echocardiography was done , which showed no regional wall motion abnormality of the left ventricle .
the initial ph was 7.375 and the levels of electrolytes including sodium , potassium , calcium and magnesium were within the normal ranges .
the target temperature was 33. soon after th was begun , osborn waves appeared in lead ii and v 4 , v 5 , and v 6 ( fig .
two hours after th , vf occurred when the esophageal temperature was 34.9. defibrillation of 150 j was applied ( fig . 2c ) .
not much later atrial fibrillation developed and the osborn waves were prominent in diffuse leads .
three more defibrillations were delivered to terminate vf and the height of osborn waves increased over time ( fig .
two hours after a warmer was applied to the patient , ecg revealed less prominent osborn wave and vf did not recur .
he was diagnosed with idiopathic vf and discharged from our hospital after implantable cardioverter defibrillator insertion ( fig .
it is generally accepted that th has the potential to improve the neurological outcome in comatose patients after cardiac arrest.1)2 ) following initial resuscitation , various mechanisms including ischemia , reperfusion injury , inflammatory response , and free radical production are involved in cerebral damage.1)3)5 ) th lowers the cerebral metabolic rate , blocks the apoptotic pathways , suppresses inflammatory responses , and attenuates production of free radicals.3)4)5 ) however , possible side effects , such as electrolyte imbalance , hemodynamic instability , infection , seizures , and arrhythmias , can rarely occur in patients undergoing th.1)2)5 ) electrocardiogram findings of hypothermia include osborn waves , atrial and ventricular dysrhythmias , and interval ( pr , qrs , qt ) prolongations.11)13)14 ) among these , the osborn wave is a positive deflection occurring at the qrs - st junction and may originate from a transmural voltage gradient during early repolarization due to a transient outward potassium current in the epicardium , but not in the endocardium.15 ) as the osborn wave can be seen in various conditions like acidosis , subarachnoid hemorrhage , and hypercalcemia , it is not pathognomonic of hypothermia .
but , it has been reported that the height of j point elevation is related with the severity of hypothermia.6 ) several mechanisms have been suggested to explain the arrythmogenic potential of the osborn wave .
the prominent action potential notch can lead to loss of the dome of action potential , which can heterogeneously cause a marked dispersion of repolarization .
this eventually can cause extrasystolic activity by a mechanism called phase 2 reentry and vf.15)16 ) another proposed mechanism is triggered automaticity .
intracellular ca overload during hypothermia is a precursor for early or delayed after depolarization , which is associated with triggered activity.17 ) however , other reports have not associated the osborn wave with vf in hypothermic patients.18 ) therefore , the arrythmogenic potential of the osborn wave requires further study .
although various adverse events have been reported during th , th - induced arrhythmia seems not to be related with increased mortality.1)2 ) in one study of ecg changes in th , the osborn wave incidence during th was 30% and no association with unfavorable short - term outcome was evident.11 ) after rewarming , the osborn wave disappears in almost cases .
so , on the basis of many studies , th is well tolerated and relatively safe .
hypothermia is also proarrhythmic and can cause lethal arrhythmias , especially at low temperature and in the presence of low serum ph.19 ) however , in our case , vf developed in normal serum ph , electrolyte levels , and not markedly low body temperature . therefore , vf and osborn wave seem not always to be related to body temperature , and individual variations in response to hypothermia can be more important to determine the vulnerability to arrhythmias . physicians need to monitor patient 's vital signs including core temperature , ecg , and laboratory tests carefully during th .
 therapeutic hypothermia ( th ) has been used to protect neurological functions in cardiac arrest patient . 
 although osborn wave is not pathognomonic of hypothermia , it is a well - known electrocardiogram finding of hypothermic patients 
 . the cellular and ionic mechanisms of the osborn wave have been suggested , and its relationship to tachyarrhythmias , such as ventricular tachycardia and ventricular fibrillation , is being explored . 
 this case highlights the arrhythmogenic potential of osborn wave and individual difference in response of th . 