Coronary Physiology: Understanding Blood Flow to the Heart
Coronary physiology refers to the study of how blood flows through the coronary arteries, which supply oxygen and nutrients to the heart muscle (myocardium). It plays a critical role in diagnosing and managing coronary artery disease (CAD) and assessing the functional significance of arterial blockages.
Key Parameters in Coronary Physiology
1. Fractional Flow Reserve (FFR)
FFR measures the pressure differences across a coronary stenosis (narrowed artery) to assess its impact on blood flow. It is performed using a special guidewire equipped with a pressure sensor during cardiac catheterization.
FFR values:
- >0.80: Normal, no need for intervention
- ≤0.80: Indicates a functionally significant blockage, requiring angioplasty or stenting
2. Instantaneous Wave-Free Ratio (iFR)
A non-hyperemic index that evaluates coronary stenosis severity without the need for medication-induced vasodilation (such as adenosine).
iFR values:
- >0.89: No significant blockage
- ≤0.89: Suggests restricted blood flow, requiring further intervention
3. Coronary Flow Reserve (CFR)
CFR evaluates the ability of coronary arteries to increase blood flow in response to increased demand. A CFR of <2.0 indicates impaired coronary circulation, which could be due to microvascular dysfunction or significant stenosis.
4. Index of Microcirculatory Resistance (IMR)
IMR helps assess the health of the microvasculature (smallest blood vessels in the heart), which is crucial for patients with angina but no visible large artery blockages. An elevated IMR suggests microvascular dysfunction, which may require different treatment strategies.
Clinical Importance of Coronary Physiology
Guides decision-making in coronary interventions (angioplasty or stenting). Prevents unnecessary stenting in cases where the blockage does not significantly impair blood flow. Assesses microvascular health, which is often overlooked in traditional angiography. Improves outcomes by tailoring treatment to individual patient needs.
Advanced Techniques in Coronary Physiology
FFR-CT (Fractional Flow Reserve from CT scans) is a non-invasive way to assess blood flow restriction using advanced computational methods. Hybrid iFR & FFR Approach is a combination of both techniques to enhance accuracy in guiding coronary interventions.
By incorporating coronary physiology into routine cardiac assessments, cardiologists can provide more precise, patient-specific treatment, leading to better heart health and outcomes.