What determines coronary artery perfusion in a patient with hypertension, diastolic blood pressure or systolic blood pressure?

Coronary Artery Perfusion in Hypertension Management

Coronary artery perfusion is primarily determined by diastolic blood pressure, which is especially important in patients with coronary artery disease and isolated systolic hypertension. 1

Physiological Basis of Coronary Perfusion

• Myocardial perfusion occurs almost exclusively during diastole, making diastolic blood pressure the primary coronary perfusion pressure 1
• Coronary perfusion pressure equals aortic diastolic pressure minus left ventricular diastolic pressure or central venous pressure 1
• In normal coronary arteries, aortic pressure is transmitted completely without appreciable pressure loss even to distal regions 1
• Coronary flow is normally autoregulated so that within wide limits of changes in perfusion pressure, blood flow to the heart remains constant 2

Coronary Autoregulation and Its Limitations

• When perfusion pressure falls, coronary arterioles dilate to maintain flow; under basal conditions a five-fold increase in coronary flow can occur (coronary flow reserve) 2
• This autoregulatory capacity has limits - at the point of maximal vasodilation, further falls in perfusion pressure will result in decreased coronary flow 1
• Coronary flow reserve is markedly impaired in the presence of:
  • Severe coronary artery stenosis
  • Left ventricular hypertrophy
  • Coronary atherosclerosis and/or microangiopathy 1, 2

Clinical Implications for Elderly Patients with Isolated Systolic Hypertension

• In elderly patients with isolated systolic hypertension (like your 90-year-old patient), the wide pulse pressure is due to increased aortic stiffness 1
• Increased arterial stiffness leads to:
  • Augmentation of central systolic blood pressure (increasing cardiac work)
  • Decreased diastolic blood pressure (potentially compromising coronary perfusion) 1
• This combination creates a challenging clinical scenario where:
  • High systolic pressure increases myocardial oxygen demand
  • Low diastolic pressure may reduce coronary perfusion 3

The J-Curve Phenomenon and Coronary Perfusion

• In patients with coronary artery disease and left ventricular hypertrophy, lowering diastolic blood pressure below the mid-80s may increase risk of myocardial infarction (the J-curve phenomenon) 2
• Recent studies show that systolic blood pressure <120 mmHg and diastolic blood pressure <70 mmHg are each associated with adverse cardiovascular outcomes in patients with coronary artery disease 4
• The worst situation is high systolic blood pressure with low diastolic blood pressure - both hallmarks of increased aortic stiffness 3

Management Considerations for Your Patient

• For your 90-year-old patient with systolic BP >160 mmHg and diastolic BP <50 mmHg:
  • Primary blood pressure goal should be <140/90 mmHg 3
  • Caution is advised with diastolic blood pressure below 60 mmHg due to potential coronary hypoperfusion 3, 4
  • Consider the impact of treatment on both systolic and diastolic components, as further lowering an already low diastolic pressure could compromise coronary perfusion 5

Conclusion

In managing your patient with isolated systolic hypertension, remember that coronary perfusion is primarily determined by diastolic blood pressure. The challenge is to reduce the elevated systolic pressure (to reduce cardiac workload) while avoiding excessive reduction in diastolic pressure that could compromise coronary perfusion, especially given the patient's existing coronary artery disease.