Toprol and MI?

Toprol is not always indicated post-MI. It is useful in reducing cardiac O2 demand. If the ischemia/infarct is demand (tachycardia) related metop can be useful. The heart is unique in that it's tissue oxygen extraction is about 70-75% compared to 25-50% for other organs. Increased blood 02 extraction is not an option so your choicess for treating inadequate myocardial o2 are to increase supply (supplemental O2, coronary vasodilators) or decrease demand (beta 1 specific blockers like metop or esmolol). While morphine has historically been included as an adjunct in MI treatment (MONA) it causes significant histamine release and can cause a reflex tachycardia to compensate for decreased SVR.

Giving a beta blocker to an MI patient is a core measure, unless they have a history of CHF. The reason for this is that multiple studies have shown a significant decrease in cardiogenic shock related to MI, which is thought to be due to decreasing the workload of the heart through beta blockade. The exception to this core measure is a history of CHF, in which case giving a beta-blocker in the treatment of an MI has been shown to significantly increase mortality risk.

Beta blockers blunt the effect of epi on the heart, which as already stated, reduces O2 demand. These patients are under stress and have have a lot of adrenergic activity. It is obviously contraindicated in hypotension and bradycardia.