Nitroglycerine and Angina
Evolving Clinical Coronary Physiology Beyond Fractional Flow Reserve and Coronary Flow Reserve
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Article, see p 24
Nitroglycerin (NTG) was invented in 1847 and used for angina pectoris or heart failure since 1879 as reviewed by Asrress et al1 in the current issue of Circulation. An extensive literature shows that NTG lowers blood pressure, vasodilates epicardial coronary arteries, and in experimental models increases coronary blood flow to the subendocardium.
What Is New?
What is new about this ancient heart medication documented by an enormous literature that merits publication in Circulation now? The report by Asrress et al1 details physiological mechanisms for angina relief by NTG epitomizing the evolution of clinical coronary physiology in 2 ways. First, it characterizes intracoronary physiological pressure/flow behavior of coronary stenosis during exercise before and after NTG for the first time, thereby explaining physiological consequences directly related to angina relief.
Second, viewed analytically, the data in this article provide the basis for a substantial mechanistic and clinical conceptual leap beyond relief of angina caused by coronary stenosis. This conceptual leap integrates the larger generalized mechanisms of subendocardial ischemia because of any cause, such as severe aortic stenosis, ventricular hypertrophy, or small vessel disease, all without epicardial stenosis, or because of hard exercise with only mild to moderate stenosis. How does subendocardial ischemia relate to fractional flow reserve (FFR), which is now a severity standard for guiding revascularization, or relate to mortality risk, which has not been definitively reduced by revascularization in randomized trials?
Coronary Physiology Background
Understanding this article and its implications requires a brief historical snapshot of NTG-related coronary physiology. Figure summarizes proposed mechanisms for NTG relief of angina over 42 years from initial experimental subendocardial ischemia in 19752,3 to coronary pressure gradient-flow definition of physiological severity in 19784,5 to clinical coronary angiograms in 19896 to clinical coronary pressure flow velocity measurements during exercise …