In 10 cases of
Prinzmetal's angina in which episodes of
myocardial ischemia were easily and reproducibly induced by
hyperventilation, this test was performed 111 times, 41 times under control conditions and 70 times during treatment with one or more of the following drugs:
phentolamine,
isosorbide dinitrate,
propranolol,
verapamil,
nifedipine and
amiodarone. Seventeen of 18 negative tests performed under the influence of a long-acting
drug coincided with total remission of the patient's anginal episodes when this
drug was administered on a short- or long-term basis. No patient died or sustained
infarction during a follow-up period of 10.9 months. A negative test was thus a good indication that the clinical response to the corresponding
drug would be favorable. The electrocardiographic changes and
chest pain provoked by
hyperventilation occurred not when
alkalosis was greatest (
hydrogen ion [pH] change from 7.42 to 7.58, p less than 0.001), but when pH was approaching normal or control values. The onset of electrocardiographic changes occurred an average of 175 seconds after the end of
hyperventilation and, in two cases, the time lag was as much as 480 and 705 seconds, respectively. This raises several questions regarding the true mechanism triggering coronary
spasm under such conditions. The
hyperventilation test appears to be a useful and safe procedure for selecting the best possible
drug for long-term treatment of
Prinzmetal's angina as well as for comparing the relative efficacy of different drugs.