Prinzmetal's variant angina)(PVA). Circadian variation in response to hyperventilation.

The study reports on the outcome of hyperventilation tests in a 57-year-old male with Prinzmetal's variant angina, formerly often complicated by ventricular fibrillation. It was found that hyperventilation for a period of 6 min after a delay of 4 to 6 min was followed by the development of ST-elevation and pain, but only when the test was performed in the morning, whereas the outcome of tests performed later in the day were negative. Pretreatment with calcium blockers, nifedipine or verapamil proved effective in preventing the anginal response to the test, also when it was performed in the morning. It is concluded that hyperventilation performed in the early morning, but not later in the day, may prove to be an effective and safe procedure for provoking Prinzmetal's variant angina, and that hyperventilation may be useful in the evaluation of the efficacy of drug therapy.