A cardiac rhythm management system includes atrial shock timing
optimization. Because an atrial tachyarrhythmia, such as atrial
fibrillation typically causes significant variability in the ventricular
heart rate, resulting in potentially proarrhythmic conditions. The system
avoids delivering atrial cardioversion/defibrillation therapy during
potentially proarrhythmic conditions because doing so could result in
dangerous ventricular arrhythmias. Using Ventricular Rate Regularization
("VRR") techniques, the system actively stabilizes the ventricular heart
rate to obtain less potentially proarrhythmic conditions for delivering
the atrial tachyarrhythmia therapy. The intrinsic ventricular heart rate
is stabilized at a variable VRR-indicated rate, computed using an
infinite impulse response (IIR) filter, and based on the underlying
intrinsic ventricular heart rate. The system withholds delivery of atrial
cardioversion/defibrillation therapy until the intervals between
ventricular beats ("V--V intervals") meet certain criteria that decrease
the chance that the atrial cardioversion/defibrillation therapy will
induce a ventricular arrhythmia.