What is the initial treatment approach for patients with Microvascular (MVA) or MINOCA (Myocardial Infarction with Non-Obstructive Coronary Arteries) angina?

Initial Treatment Approach for Microvascular Angina (MVA) and MINOCA

For patients with microvascular angina (MVA) or MINOCA, calcium channel blockers should be used as first-line therapy, particularly for vasospastic forms, while beta-blockers are preferred for MVA with evidence of increased adrenergic activity.

Understanding MVA vs. MINOCA

MVA and MINOCA represent distinct but related conditions characterized by angina symptoms without significant coronary artery obstruction:

• Microvascular Angina (MVA): Characterized by angina due to dysfunction of the coronary microcirculation
• MINOCA (Myocardial Infarction with Non-Obstructive Coronary Arteries): Defined as acute myocardial infarction with angiographically no obstructive coronary artery disease (stenosis ≤50%)

Diagnostic Criteria

MVA Diagnostic Indicators:

• Angina symptoms with normal or near-normal coronary arteries
• Evidence of ischemia during stress testing
• Abnormal coronary microvascular function testing:
  • Increased microvascular resistance (IMR ≥25)
  • Reduced coronary flow reserve (CFR <2.0)
  • Reduced resistive reserve ratio (<2.0)
  • Microvascular spasm during acetylcholine testing 1

MINOCA Diagnostic Approach:

• Confirmation of MI criteria
• Absence of obstructive coronary disease (stenosis ≤50%)
• No other overt cause for the clinical presentation
• Cardiac MRI recommended in all MINOCA patients without an obvious underlying cause 1

Treatment Algorithm

1. First-Line Treatment Options

For Vasospastic Angina/MINOCA with vasospasm:

• Calcium channel blockers (first-line): Prevent spasm in ~90% of patients 1
  • Dihydropyridines (e.g., amlodipine 5-10 mg daily)
  • Non-dihydropyridines (e.g., diltiazem, verapamil) when heart rate control is also needed
• Long-acting nitrates: Add if symptoms persist despite calcium channel blockers 2
  • Isosorbide mononitrate (preferred): 20 mg twice daily or 60-240 mg once daily (slow-release)
  • Maintain a 10-12 hour nitrate-free interval to prevent tolerance

For Microvascular Angina:

• Beta-blockers (preferred in patients with increased adrenergic activity) 1, 2
  • Carvedilol 6.25 mg BID, uptitrated as needed
  • Metoprolol 25-100 mg twice daily 3
• Ranolazine: Particularly beneficial in patients with impaired coronary flow reserve 1, 2
• Trimetazidine: Can be used as part of initial treatment 2

2. Second-Line Treatment Options

• Ivabradine: For heart rate control when beta-blockers are contraindicated 2
  • Superior effects on coronary flow reserve compared to bisoprolol despite similar heart rate reduction
• Higher doses of calcium channel blockers: For refractory vasospastic angina 1, 2
  • Up to 480 mg/day verapamil
  • Up to 260 mg/day diltiazem

3. Additional Treatments

• Baseline therapy for all patients: 1, 2
  • Aspirin (if evidence of atherosclerosis or endothelial dysfunction)
  • Statins (for pleiotropic effects on endothelial function)
  • ACE inhibitors (particularly in patients with hypertension)
  • Sublingual nitroglycerin as needed for acute symptoms
  • Smoking cessation and lifestyle modifications

Important Considerations and Pitfalls

1. Beta-blockers are contraindicated in vasospastic angina as they can precipitate spasm by leaving α-mediated vasoconstriction unopposed 1, 2

2. Avoid nitrates with phosphodiesterase inhibitors (sildenafil, tadalafil, vardenafil) due to risk of profound hypotension 2

3. Monitor treatment response closely, as microvascular angina often has variable responses to different treatments 2

4. Consider tapering and discontinuing treatment after 6-12 months of symptom resolution, as spontaneous remission occurs in about half of patients 2

5. For MINOCA patients, management should be guided by the identified underlying cause 1

Special Situations

• Patients with atrioventricular conduction defects: Avoid beta-blockers and non-dihydropyridine calcium channel blockers 1

• Patients with hyperthyroidism: Consider non-selective beta-blockers (propranolol) or diltiazem/verapamil if beta-blockers are contraindicated 1

• Patients with enhanced pain perception: Consider adenosine antagonists or tricyclic antidepressants (e.g., imipramine) 1

By following this treatment algorithm and considering the specific pathophysiological mechanisms in each patient, clinicians can effectively manage the symptoms and improve outcomes in patients with MVA or MINOCA.