Effective refractory period

Effective refractory period (ERP) is a term used in cardiology to describe the period of time during which a cardiac cell or tissue is unable to respond to a second stimulus, regardless of its strength. This period is critical in preventing arrhythmia and maintaining the normal rhythm of the heart.

Physiology

The effective refractory period is a part of the cardiac cycle, which is the sequence of events that occur when the heart beats. The ERP begins immediately after the depolarization of the cardiac cell and lasts until the cell is almost completely repolarized.

During the ERP, the cardiac cell is in a state of hyperpolarization, which means that it is more negatively charged than its resting state. This is due to the outflow of potassium ions from the cell. The cell is unable to respond to a second stimulus during this period because the ion channels that allow for depolarization are inactivated.

Clinical significance

The effective refractory period is important in preventing the occurrence of arrhythmias. If a second stimulus occurs before the end of the ERP, it can cause a premature contraction, which can lead to an abnormal heart rhythm.

In certain conditions, such as ischemic heart disease or heart failure, the ERP can be altered. This can increase the risk of developing arrhythmias.

Measurement

The effective refractory period can be measured using electrophysiology techniques. This involves the use of a catheter to deliver a series of electrical stimuli to the heart, and then measuring the response. The ERP is the interval between the first stimulus and the first response that fails to produce a contraction.

See also

• Absolute refractory period
• Relative refractory period
• Cardiac action potential
• Cardiac electrophysiology