Patent ID: 7184832

Claim:
A method comprising: estimating a length of a refractory period of a heart; and setting a parameter for delivery of extra-systolic stimulation to the heart based on the estimated length of the refractory period of the heart, wherein estimation the length of the refractory period comprises: detecting a systolic depolarization of the heart; delivering a probe pulse to the heart an interval after detection of the systolic depolarization that is less than an extra-systolic interval; determining whether the probe pulse captured the heart; and estimating the length of the refractory period based on the determination, wherein delivering a probe pulse comprises delivering a probe pulse every N cardiac cycles, N being an integer greater than one, the method further comprising delivering an extra systolic pulse at the expiration of the extra-systolic interval after detection of a systolic depolarization of the heart during cardiac cycles in which a probe pulse is not delivered.