Timing of Measurement

The baseline measurements ofBNP and NT-proBNP in the aforementioned studies were performed between 9.5 h and 4 d after enrollment. Recent data suggest that even earlier measurements may be of value. A substudy of the Fast Assessment in Thoracic Pain study evaluated NT-proBNP in patients with NSTEMI and unstable angina (50). NT-proBNP levels were drawn on admission in 755 patients, who were subsequently followed for 40 mo. NT-proBNP levels correlated with future risk ofmortality independent ofECG changes and cTnT. In another study, NT-proBNP levels drawn a median of 3 h after the onset of symptoms in patients presenting with STEMI, NSTEMI, or unstable angina were associated with CHF and mortality across the spectrum of ACS independent of other factors, including cTnT (Fig. 6) (51). Compared with the first quartile of NT-proBNP concentration, the second, third, and fourth quartiles had an RR of mortality of 2.9, 5.3, and 11.5, respectively. Mega et al. (52) studied the prognostic value ofBNP drawn within 6 h ofonset

Fig. 6. Association between mortality and NT-proBNP. The first (white bars), second (light gray bars), third (dark gray bars), and fourth (black bars) quartiles according to cTnT levels in patients with STEMI and NSTEACS are shown. (Adapted from ref. 51.)

in patients who presented with STEMI. Patients with a BNP >80 pg/mL had a sevenfold higher risk of mortality than those with a BNP <80 pg/mL independent ofother known clinical prognostic parameters, including cTnl and CRP; a significant difference was noted as early as 48 h after enrollment. Patients with elevated BNP were also more likely to have incomplete reperfusion and incomplete resolution ofST-elevation after thrombolytic therapy. At the other extreme, it appears that BNP measured as late as 3 to 4 wk after MI retains its prognostic capacity (53).

Heeschen et al. (54) found that serial measurements of NT-proBNP at baseline, 48 h, and 72 h after ACS provided additional risk stratification information compared with baseline measurement alone. In this substudy ofthe PRISM trial, clinical stabilization was associated with a 25% reduction in NT-proBNP levels by 48 h and a 50% reduction by 72 h. Patients with persistent elevation in NT-proBNP levels >250 mg/dL at 72 h were at markedly increased risk of death or MI (OR: 33.7; 95% confidence interval [CI]: 8.2-138.8; p < 0.001), as were those who developed new elevation in NT-proBNP >250 mg/dL after hospitalization (OR: 24.0; 95% CI: 8.4-68.5;p < 0.001).

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