| Therefore, the only time that blood returns to the heart via the coronary arteries is during diastole. This is one of the reasons for tachydysrhythmias in the heart. Supraventricular tachydysrhythmias are often produced by disorders of impulse formation and/or disorders of impulse conduction. If there is not enough blood returning to the heart the heart will speed up in an attempt to compensate for the lack of adequate blood flow.
This can sometimes be counterproductive. As the heart rate rises, so does the metabolic demand, which can increase, not alleviate, ischemia. In cases (such as coronary artery disease) where blood flow is limited, slowing the heart rate can be beneficial. |
