Atrial fibrillation is the most common arrhythmia we encounter in clinical cardiology .Ironically it is uncommon during ACS and extremely rare in association with UA/NSTEMI. Surprisingly , an entity ” Ischemic AF” is not to be found in cardiology literature.
The incidence of AF in STEMI is less than 5%. Occurs more often due to factors other than primary ischemia of atrial musculature. Of-course , AF in association with Infero posterio MI and RVMI is an important trigger for AF.LCX disease is more often associated with AF as it gives up a consistent branch to left atrium.
Though it is tempting to implicate ischemia as a trigger for AF ,most often it occurs , in elderly ,associated COPD ,hypoxia preexisting atrial disease .Acute elevation of LVEDP and stretch of left atrium could be a more logical mechanism.
Hemodynamic impact
- AF can bring down the blood pressure.
- Worsen ischemia by increasing the MVO2
- Could be very destabilising in RV infarction
- Surprisingly it is well tolerated in many STEMI patients.
AF in STEMI- Is it an emergency ?
It would appear so. But , if hemodyanmicaly stable one need not panic.Many times they are transient .Correcting hypoxia, optimizing beta blocker would help.
Role of DC Shock , Precautions before shocking & Post shock events
- DC shock is done only if there is hemodynamic instability or ongoing ischemia .(Very difficult to rule out the later )
- Mural LV clots can form even within 24 hours and DC shock embolic strokes may ensue .
- Hence it is mandatory to do an echocardiogram prior to shocking.
Drug of choice
- Betablocker
- Class 1c -Flecanide.
- Class 3 -Amiodarone./Ibutilide/
Role of Digoxin
There used to be a concern about usage of Digoxin in the setting of ACS as it pro-arrhythmic , but it remains useful in the management of AF .There is no other anti-arrhymic drug available to control, the heart rate without depression of the LV function
Rate control vs rhythm control
Always aim for rhythm control in the setting of ACS.Rate control is may not be a logical concept in acute settings though Amiodarone does both.
Wide QRS Atrial fibrillation
As we know , AF in STEMI can conduct with aberrancy , and we have a traditional teaching all wide qrs tachycardia are VT in the setting of MI making our patients statistically vulnerable.
After all , both entities lack discernible p waves. At high rates it may be difficult to identify irregularity RR interval. However , one would shock such patients and both AF and VT would respond .All is well that ends well.
Summary
AF during STEMI is a risky arrhythmia and needs urgent intervention , but one need not be alarmed .There is a set of protocol . Only hemodynamically unstable AF require DC shock .Many times it is just transient.There has been instances of physician panicky that has resulted in more adverse events .
Dr.S.Venkatesan MD 