Beyond PVI, other endpoints, particularly during ablation for persistent AF, are unclear. It has been suggested that regardless of other non-PV targets ablated, the endpoint for ablation of persistent AF should be the termination of AF either to a regular ATA, or to a sinus rhythm. Although termination of AF has been shown by some to be predictive of longer-term outcome, other studies have not confirmed this finding.399,400,401,515,621,641,642 It is unclear whether acute, intraprocedural termination is a true indication of procedural success, or simply might indicate patients with less persistent AF who are destined to do better regardless of the approach used. A substudy of the STAR AF II trial has suggested this latter point.643 Slowing of AF cycle length as measured from the CS or the LA or RA appendage has also been used as a surrogate for acute procedural success. However, AF cycle length prolongation can be difficult to measure reliably in AF, and prolongation is often used as a harbinger of acute termination. Again, longer baseline AF cycle length can be an indication of AF that is more likely to terminate or respond to ablation rather than indicating a procedural endpoint in and of itself.643 Thus, AF termination of cycle length prolongation might not be useful as a sole procedural endpoint.