AV Interval Optimization in CRT

AV interval optimization in CRT

The aim of AV interval optimization in cardiac resynchronization therapy is to prevent too early or too late atrial contraction. Too late an atrial contraction will cause it to overlap with ventricular systole so that atrial contraction will occur against a closed AV valve. This will lead to a sudden elevation of atrial and pulmonary as well as systemic venous pressure. This discussion is about the manual methods of AV interval optimization. Modern devices have facility for automatic AV interval optimization, which will of course have to be counterchecked by the physician.

Echocardiographic methods to optimize AV delay are Ritter’s method and Ishikawa’s method. In Ritter’s method, long AV delay is calculated when there is partial fusion of E and A waves on mitral Doppler and short AV delay is calculated when A wave truncation occurs due to ventricular contraction before completion of A wave. From these two values, the optimal AV delay is calculated using the Ritter’s formula.

Ishikawa’s method is used when there is significant diastolic mitral regurgitation. Long AV delay is chosen so that it results in diastolic mitral regurgitation or diastasis until isovolumetric contraction, which is the time at which systolic mitral regurgitation starts. It may be noted that there is no true isovolumetric phase when there is systolic mitral regurgitation as mitral valve starts leaking in the potential isovolumetric phase and reduces the ventricular volume. The duration of diastolic mitral regurgitation is subtracted from the long AV delay to get the optimal AV delay.