Response to letters regarding article, "Clinical usefulness, angiographic characteristics, and safety evaluation of intracoronary acetylcholine provocation testing among 921 consecutive white patients with unobstructed coronary arteries".

We thank Dr Mohri for his insightful comments. We completely agree with Dr Mohri that standardization of intracoronary provocation testing for coronary spasm with respect to dosage, infusion time, and a route of administration is urgently needed, as mentioned in our article.1 As highlighted in the Methods section of our article, the maximum dosage of 200 μg acetylcholine for the left coronary artery was derived from the Evaluation of Nifedipine on Coronary Endothelial Function (ENCORE) study. In this trial, the dose for the left anterior descending artery and for the left circumflex artery was 100 μg in each vessel injected via a selective catheter in a coronary segment without significant coronary artery disease. In the most constricting segment, this dose of acetylcholine reduced the coronary diameter …