From the Guidelines
The coronary arteries are in diastole during the relaxation phase of the cardiac cycle, specifically in mid-diastole, when cardiac motion is minimized and coronary flow is high. This occurs because during systole (heart contraction), the coronary arteries are compressed by the contracting heart muscle, limiting blood flow 1. When the heart relaxes in diastole, the pressure in the aorta exceeds the pressure in the relaxed heart muscle, allowing blood to flow freely through the coronary arteries to supply oxygen and nutrients to the cardiac tissue.
Key Points
- The coronary arteries receive blood flow primarily during diastole 1
- Mid-diastole is the preferred time for image acquisition in coronary MRA, as cardiac motion is minimized while coronary flow is high 1
- The patient-specific diastasis period (of reduced coronary motion) is usually determined by visual inspection of cine images perpendicular to the long axis of the proximal/mid-right coronary artery (RCA) 1
- Understanding the relationship between diastole and coronary blood flow is critical for proper heart function, as the coronary circulation must deliver approximately 250 mL of blood per minute to meet the heart's high metabolic demands.
Clinical Implications
- Patients with shortened diastolic periods (as in tachycardia) or reduced diastolic pressure (as in some forms of hypotension) may experience myocardial ischemia, as coronary perfusion becomes compromised 1
- The lower limit of autoregulation in the human coronary circulation is not well established, but it is known that significant CAD will shift the lower autoregulatory limit upward 1
- The potential for impairment of myocardial oxygen supply may be compounded by an increased myocardial oxygen demand due to exercise, LV hypertrophy (if present), and the increase in the output impedance of the LV because of the increased SBP 1
From the Research
Coronary Arteries in Diastole
The coronary arteries are in diastole when the heart is in its relaxation phase. Here are some key points to consider:
- The heart's relaxation phase, or diastole, is the period when the heart muscle is not contracting and the coronary arteries are filling with blood 2, 3, 4, 5, 6.
- During diastole, the coronary arteries are perfused with blood, supplying oxygen and nutrients to the heart muscle 2, 3, 4, 5, 6.
- The duration of diastole is longer than the duration of systole, allowing for adequate perfusion of the coronary arteries 2, 3, 4, 5, 6.
- Factors such as blood pressure, heart rate, and vascular resistance can affect coronary blood flow during diastole 2, 3, 4, 5, 6.
Key Factors Affecting Coronary Arteries in Diastole
Some key factors that can affect the coronary arteries during diastole include:
- Blood pressure: High blood pressure can increase the workload on the heart and reduce coronary blood flow during diastole 2, 3, 4, 5, 6.
- Heart rate: An increased heart rate can reduce the duration of diastole and decrease coronary blood flow 2, 3, 4, 5, 6.
- Vascular resistance: Increased vascular resistance can reduce coronary blood flow during diastole 2, 3, 4, 5, 6.
- Medications: Certain medications, such as calcium channel blockers and beta-blockers, can affect coronary blood flow during diastole 2, 3, 4, 5, 6.