Beta blockers in myocardial infarction

• the ISIS-1 trial showed that the immediate use of IV atenolol after a myocardial infarction led to an improved survival rate, mainly due to a reduction in the risk of acute cardiac rupture. Contraindications to the use of beta-blockers should be excluded eg bradycardia, hypotension
• oral treatment with a beta-blocker started a few days or weeks after acute myocardial infarction for up to 3 years reduces the risk of death by approximately 20% and the risk of re-infarction by about 25%. Again contra -indications should be excluded
• diabetics should receive beta-blockers after an MI unless after an MI unless there are absolute contra- indications
  
  
• other studies have illustrated the benefits of treatment with beta-blockers after myocardial infarction:
  • the CAPRICORN study showed that adding carvedilol to the short term management of myocardial infarction reduced all-cause an cardiovascular mortality and non-fatal MI in patients with left ventricular dysfunction (1)
  • also the Survival and Ventricular Enlargement (SAVE) trial data revealed that the benefits of beta-blockade were seen in addition to ACE inhibitor treatment (2)

Possible Mechanisms of benefit for use of beta blockers in MI:

• beta-receptor is an adrenergic heterodimeric G-protein-coupled receptor (G protein-coupled receptors are transmembrane proteins that act as key gatekeepers between external signals and cellular responses), located throughout the body
  • beta-receptors are stimulated by the sympathetic nervous system with catecholamines epinephrine (adrenaline) and norepinephrine (noradrenaline) as their primary endogenous agonists
• role of acute treatment or subacute treatment with beta-blockers in patients suspected of or diagnosed with myocardial infarction, rests on their inhibition of the chronotropic and inotropic effects of the beta-receptor
  • may result in a reduction in heart rate, heart contractility, and blood pressure, thereby decreasing the oxygen demand of the heart
  • hence, the inhibition of the beta-receptor is thought to decrease ischaemia and might decrease the risk of life-threatening ventricular arrhythmias and other complications associated with myocardial infarction

Notes:

• a beta blocker is recommended for all people following myocardial infarction unless there are contraindications. The evidence for beta blockade is strongest for those people with a large myocardial infarction, or infarction complicated by heart failure or ventricular arrhythmias (3)
• a systematic review concluded that, with a moderate-quality of evidence, beta-blockers for suspected or diagnosed acute myocardial infarction probably reduce the short-term risk of myocardial infarction during follow up and the long-term risk of all-cause mortality and cardiovascular mortality. Nevertheless, it is most likely that beta-blockers have little or no effect on the short-term risk of all-cause mortality and cardiovascular mortality (5)
  NICE have issued guidance as to the use of beta blockers post myocardial infarction (4):
  
  
  • offer people a beta-blocker as soon as possible after an MI, when the person is haemodynamically stable
    
    
  • communicate plans for titrating beta-blockers up to the maximum tolerated or target dose – for example, in the discharge summary
    
    
  • consider continuing a beta-blocker for 12 months after an MI for people without reduced left ventricular ejection fraction
  • discuss the potential benefits and risks of stopping or continuing beta-blockers beyond 12 months after an MI for people without reduced left ventricular ejection fraction. Include in the discussion:
    • the lack of evidence on the relative benefits and harms of continuing beyond 12 months
    • the person's experience of adverse effects
      
      
  • continue a beta-blocker indefinitely in people with reduced left ventricular ejection fraction
  • offer all people who have had an MI more than 12 months ago, who have reduced left ventricular ejection fraction, a beta-blocker whether or not they have symptoms. For people with heart failure plus reduced left ventricular ejection fraction, manage the condition in line with the NICE guideline on chronic heart failure in adults
    
    
  • do not offer people without reduced left ventricular ejection fraction or heart failure, who have had an MI more than 12 months ago, treatment with a beta-blocker unless there is an additional clinical indication for a beta-blocker

Reference:

1. Coats AJ. CAPRICORN: a story of alpha collection and beta-blockers in left ventricular dysfunction post-MI. Int J Cardiol 2001;78:109-13.
2. Vantrimpont P et al.Additive beneficial effects of beta-blockers to angiotensin-converting enzyme inhibitors in the Survival and Ventricular Enlargement (SAVE) Study. SAVE investigators.J Am Coll Cardiol 1997;29:229-36
3. BS2: Joint British Societies' guidelines on prevention of cardiovascular disease in clinical practice. Heart 2005; 91 (Supp 5).
4. NICE (2020). Acute coronary syndromes
5. Safi S et al. Beta-blockers for suspected or diagnosed acute myocardial infarction. Cochrane Database Syst. Rev. December 2019.