Julius Center for Health Sciences and Primary Care, University Medical Center Utrecht, Utrecht, The Netherlands.
J Hypertens. 2011 Jun;29(6):1145-54. doi: 10.1097/HJH.0b013e328345d85e.
To evaluate the effect of the number and positioning during follow-up of ultrasound examinations on the rate of change in carotid intima-media thickness (CIMT) using METEOR (Measuring Effects on Intima-Media Thickness: an Evaluation of Rosuvastatin) as an example.
METEOR was a randomized, placebo-controlled trial showing that rosuvastatin reduced progression of 2-year change in CIMT among low-risk patients with subclinical atherosclerosis. In the full METEOR protocol, ultrasound examinations were performed twice before randomization, once each at 6, 12, and 18 months after randomization, and then twice at the end of study at 24 months. For the present study, 17 study designs were retrospectively constructed with varying number and position of ultrasound examinations during the study. Differences in the rate of change in maximum CIMT between these study designs were compared.
Variations in frequency of ultrasound visits gave results in the same direction and magnitude for the change in maximum CIMT for both groups (i.e. nonsignificant change for rosuvastatin and significant progression for placebo, and a significant difference between treatments). However, standard errors were larger when the number of exams reduced. This finding was consistent over different lengths of follow-up, sample sizes, and with CIMT measurements made on different locations.
Protocols with different number and timing of ultrasound examinations minimally affect the direction and magnitude of treatment effects on the rate of change in CIMT. However, reductions in exam frequency increase standard errors of rates of change, suggesting larger sample sizes would be required to have the same level of statistical power.
以 METEOR（测量内中膜厚度的影响：评估瑞舒伐他汀的效果）为例，评估超声检查随访时的次数和定位对颈动脉内膜中层厚度（CIMT）变化率的影响。
METEOR 是一项随机、安慰剂对照试验，结果表明瑞舒伐他汀可降低亚临床动脉粥样硬化低危患者 2 年 CIMT 进展。在完整的 METEOR 方案中，在随机分组前进行了两次超声检查，在随机分组后第 6、12 和 18 个月各进行一次，然后在研究结束时在第 24 个月进行两次。本研究回顾性构建了 17 种不同研究设计，在研究期间超声检查的次数和定位各不相同。比较了这些研究设计中最大 CIMT 变化率的差异。
超声检查频率的变化对两组 CIMT 变化的方向和幅度均产生了相同的结果（即瑞舒伐他汀治疗无显著变化，安慰剂治疗显著进展，且两种治疗方法之间存在显著差异）。然而，当检查次数减少时，标准误差会增大。这一发现在不同随访时间、样本量以及在不同位置进行 CIMT 测量时均保持一致。
不同超声检查次数和时间的方案对 CIMT 变化率的治疗效果的方向和幅度影响最小。然而，检查频率的降低会增加变化率的标准误差，这意味着需要更大的样本量才能达到相同的统计效力水平。
