ASSESSING BAROREFLEX SENSITIVITY IN POSTMYOCARDIAL INFARCTION PATIENTS - COMPARISON OF SPECTRAL AND PHENYLEPHRINE TECHNIQUES

Objectives. This study sought to compare, in post myocardial infarctio n patients, baroreflex sensitivity (BRS) measured by the phenylephrine method (Phe-BRS) with that estimated by the Robbe (Robbe-BRS) and Pag ani (alpha-low frequency [LF] and alpha-high frequency [HF]) spectral techniques. Background. BRS assessed by Phe-BRS has been shown to be o f prognostic value in patients with a previous myocardial infarction, but the need for drug injection limits the use of this technique, Seve ral noninvasive methods based on spectral analysis of systolic arteria l pressure and heart period have been proposed, but their agreement wi th Phe-BRS has never been investigated in post myocardial infarction p atients. Methods. The linear association and the agreement between eac h spectral measurement and Phe-BRS were assessed by correlation analys is and by computing the relative bias and the limits of agreement in 5 1 post-myocardial infarction patients. Results. The correlation with P he-BRS was r = 0.63 for Robbe-BRS, r = 0.62 for alpha-LF and r = 0.59 for alpha-HF, The relative bias was significant for alpha-LF (2.6 ms/m m Hg, p < 0.001) and alpha-HF (2.5 ms/mm Hg, p = 0.01) and not signifi cant (-0.6 ms/mm Hg, p = 0.3) for Robbe-BRS. The normalized limits of agreement ranged from -98% to 95% for Robbe-BRS, from -67% to 126% for alpha LF and from -108% to 143% for alpha-HF. When patients were clas sified according to left ventricular ejection fraction (LVEF, cutoff v alue 40%), the relative bias was higher in patients with a depressed L VEF, although statistical significance was high only for Robbe-BRS and was borderline for alpha-LF. The limits of agreement were similar in both groups of patients (p > 0.3). Conclusions. Despite a substantial linear association, the agreement between spectral measurements and Ph e-BRS in post-myocardial infarction patients is weak because the diffe rence can be as large as the BRS value being estimated. Phe BRS is the measurement most associated with hemodynamic impairment. Because seve ral factors within each method contribute to the overall difference, n either method can be defined as being better than the other in estimat ing baroreflex gain, nor can one be used as an alternative to the othe r. Ad hoc studies are needed to assess which method provides the most useful physiologic or pathophysiologic information or the most accurat e prediction of prognosis. (C) 1998 by the American College of Cardiol ogy.