ST depression after cardiac arrest is frequently not due to ACS

Case 1

A 22 yo male had a cardiac arrest with ventricular fibrillation recorded.  He was resuscitated.  He was comatose.  Here is his initial ECG:

There is widespread ST depression, with ST elevation in aVR.   There are also lateral Q-waves.

 Is this ACS with 3-vessel disease or left main stenosis?  No, and one should not make such an assumption.  The initial ECG after a cardiac arrest frequently shows ischemic ST depression which resolves on subsequent ECGs.  So we waited and recorded a second ECG 27 minutes later:

The ST depression is resolved.  The Q-waves persist.

The patient had myocarditis and no coronary disease.  He underwent therapeutic hypothermia and fully recovered. 



Case 2

A young man presented after resuscitation from asystolic cardiac arrest.  In spite of immediate bystander CPR, he had no brain function on arrival.

There is ST depression in V2-V6.  Is this ACS?

The total absence of brain function in spite of immediate CPR suggested a CNS etiology of arrest.  CT of the brain revealed aneurysmal subarachnoid hemorrhage.  The patient went on to brain death. 

Cardiac arrest was likely due to massive catecholamine surge and stress cardiomyopathy.

Do all cardiac arrest patients need emergent angiography and PCI?

We studied all our cardiac arrests over a 3 year period (Acad Emerg Med 17(S1):S194. Abstract 580) and found that the majority did not have need for immediate PCI.  The incidence of STEMI was only 28%: 38% for those with VF or VT, and only 20% for those with PEA.   We did not assess the incidence of ACS without STEMI as an etiology; however, unless there is instability, these do not need emergent PCI.  In another study in which all arrest patients underwent immediate aniography, just under 60% had any Acute MI (Non-STEMI + STEMI).  In this large study from France, 31% of 435 arrest patients with no obvious extracardiac cause of arrest had STEMI; 170 other patients had at least one significant coronary lesion, as defined by a >50% stenosis.  However, stenoses are not necessarily related to ACS, do not necessarily need PCI, and, if they do, do not necessarily need it emergently.  Studies which associate a very high rate of coronary thrombi with with sudden death are frequently studies of unresuscitated victims.  Similarly, unresuscitated ventricular fibrillation is frequently due to Acute MI.  However, ACS may be more common in patients who are not resuscitated than in those who are.  In  this study, 68% of resuscitated victims were judged to have Acute MI (STEMI + Non-STEMI); given that about 45% of patients with Acute MI in the CK-MB era had STEMI, then perhaps about 30% had STEMI.

Finally, many or most patients with cardiac arrest and positive troponins have "Acute MI" by the new 2007 definition, but do not have type I AMI due to ACS.

Therefore, don't always think "STEMI", or even "cath lab," when you take care of a patient with resuscitated cardiac arrest, and even if they have ST depression; the cath lab need only be emergently activated for definite STEMI-equivalent, persistent ischemia, electrical instability, or hemodynamic instability. 

I know there are differing opinions on this, and no randomized trials.  I would be interested to hear your evidence-based feedback on this.