 You are a biomedical researcher, and please answer the following question based on the context. 
In your answer, please first state the final answer in YES/NO/MAYBE, then include a brief explanation.

### Question: Collateral formation in patients after percutaneous myocardial revascularization: a mechanism for improvement?

### Context: 1: Percutaneous myocardial revascularization (PMR) has emerged as a novel therapeutic strategy for patients with ischemic heart disease not amendable to traditional revascularization approaches. Despite the symptomatic improvement documented in clinical trials, underlying mechanism remains unknown.
2: We assessed the coronary angiograms of 25 patients before and 6 months after the PMR procedures for collateral vessel formation. The Rentrop scoring system was used to score the extent of collateral vessel formation. The angiograms were analyzed by 2 independent reviewers. The change in Rentrop score and improvement in angina status was correlated.
3: During follow-up period of 6 months, no patient died or suffered from myocardial infarction. Overall the mean Canadian Classification Society (CCS) class among the study patients was significantly improved from 3.5 to 2.4; mean difference = 1.08 (p<0.0001). Among these, 8 (32%) had improvement of>2 CCS classes (p = 0.003) (improvement group). The rest of the patients had either no change (n = 8; 32%) or improvement of 1 CCS class (n = 9; 36%) (no improvement group). The Rentrop score improved in 3 (12%), remained unchanged in 22 (88%) and deteriorated in 0 patient. Overall, there was no significant change in Rentrop score at 6-month follow-up; mean difference 0.13 (p = 0.08). There was also no correlation between the change in extent of collateral vessel formation and the improvement in angina status (correlation coefficient r = 0.09) at 6 months after PMR.


###Response: Improvement in collateral vessel formation is unlikely to be a mechanism responsible for symptomatic improvement in patients after PMR.
 