Apparatus, systems and methods are provided for prevention and / or remediation of cardiac arrhythmias, e.g. optimizing anti-tachycardia pacing (ATP) algorithms. More particularly, implantable devices are provided that measure and treat cardiac arrhythmias. By monitoring the ATP attempt from additional electrodes, far-field morphology analyses, and / or measuring the return interval from a failed ATP attempt; the devices may estimate when entrainment has occurred, the amount of delay within the reentrant tachycardia, and / or tachycardia termination / acceleration. These variables and occurrences can be used to optimize the first and / or subsequent ATP attempts. Furthermore, other exemplary embodiments describe methods to integrate electrical restitution properties into the design of ATP pacing algorithms to facilitate tachycardia termination.