Is coronary artery perfusion determined by diastolic blood pressure?

Coronary Artery Perfusion and Diastolic Blood Pressure

Yes, coronary artery perfusion is primarily determined by diastolic blood pressure. 1, 2 This relationship is fundamental to understanding coronary blood flow physiology and has important clinical implications.

Physiological Basis

• Timing of Coronary Perfusion: Myocardial perfusion occurs almost exclusively during diastole, making diastolic blood pressure the primary determinant of coronary perfusion pressure 1
• Coronary Perfusion Pressure (CPP): Defined as the difference between aortic diastolic pressure and left ventricular end-diastolic pressure (or right atrial diastolic pressure in the case of right coronary artery) 1, 2
• Autoregulation Mechanism: The coronary circulation demonstrates autoregulation, maintaining relatively constant blood flow despite changes in perfusion pressure within certain limits 1

Coronary Autoregulation Details

Coronary autoregulation functions through:

• Coronary vasodilation in response to falling perfusion pressure to maintain blood flow 1
• Limited capacity for vasodilation - once maximal vasodilation occurs, further drops in diastolic pressure will reduce coronary flow 1
• In animal studies, contractile function is maintained at mean coronary filling pressures down to 40 mm Hg (corresponding to DBP of 30 mm Hg) in normal coronary arteries 1

Clinical Implications

Impact of Low Diastolic Pressure

• J-curve Phenomenon: Both very high and very low diastolic pressures are associated with adverse cardiovascular outcomes 3, 4
• Threshold Concerns: In patients with coronary artery disease (CAD), diastolic BP <70 mmHg is associated with increased risk of cardiovascular events 3
• Mortality Risk: A diastolic BP <60 mmHg is associated with significantly increased mortality risk, particularly in patients with evidence of coronary artery calcium 5, 6

Special Considerations in CAD

• Shifted Autoregulation: In patients with coronary artery disease, the lower autoregulatory limit is shifted upward, requiring higher diastolic pressures to maintain adequate coronary flow 1
• Impaired Reserve: Coronary flow reserve is reduced in patients with:
  • Coronary artery stenosis
  • Left ventricular hypertrophy
  • Microvascular disease 1, 2
• Increased Vulnerability: Patients with CAD are more susceptible to myocardial ischemia when diastolic BP falls below their individual threshold 4

Assessment of Coronary Perfusion

• Fractional Flow Reserve (FFR): Measures the ratio of maximal blood flow in a stenotic artery to theoretical normal flow 1, 2

  • FFR ≤0.75: Definitively associated with inducible ischemia
  • FFR ≥0.80: Generally indicates absence of inducible ischemia
  • FFR 0.75-0.80: Clinical "gray zone" requiring judgment

• Coronary Flow Reserve (CFR): Represents the capacity to increase coronary blood flow above baseline during maximal vasodilation 2

  • Normal CFR: 3-5 fold increase above baseline
  • Reduced by coronary stenosis, microvascular disease, and tachycardia

Clinical Pitfalls and Caveats

• Aggressive BP Lowering: Excessive reduction of diastolic BP may compromise coronary perfusion, especially in patients with CAD 3, 4
• Rapid Reduction: Rapid reduction in diastolic BP may be more hazardous than gradual reduction in patients with combined hypertension and CAD 2
• Tachycardia Impact: Increased heart rate reduces diastolic filling time, potentially compromising coronary perfusion 2
• Individual Variability: The "safe" lower limit of diastolic BP varies between individuals based on:
  • Presence and severity of coronary disease
  • Left ventricular hypertrophy
  • Microvascular function 1

In conclusion, while maintaining appropriate blood pressure control is essential for cardiovascular health, clinicians must be mindful of the critical role diastolic blood pressure plays in coronary perfusion, particularly in patients with coronary artery disease or risk factors for it.