Interesting Cases: Bahman Arrhythmia Clinic : A terrible angiography

Title: A terrible angiography

A 48 year old woman who was severely symptomatic due to recurrent chest pain was admitted in Ahvaz Emam khomeini hospital and coronary angiography was performed by Dr alasti.After catheterization of left main coronary artery ,contrast injection revealed the following angiogram:

As evident severe ostial stenosis at left main artery and a long stenosis at large OM artery are present; What would you do next? do you leave left system angiography with respect to high risk appearance of lesions and request urgent surgery consult or you continue for obtaining another view? The second option was choosed by Dr alasti and the following angiogram was obtained:

interesting!as you see although ostial stenosis of left main artery is evident but the long lesion at OM is disappeared.Why?
To answer this question nitroglycerine injection into left main artery was the only simple work to do.Now you can see an entirely normal left coronary artery.

Although most cardiologists are alert for possible catheter induced spasm as the mechanism for ostial stenosis of left main artery, however such a long stenosis at OM artery may confuse the physician and prinzmetal spasm at such a location may not be in mind.In this case spontaneus disappearance of OM spasm was really a great chance to recognize the mechanism; So if this was not happened what was the next step for Dr Alasti or for you if this was your case?