B-Type Natriuretic Peptide and Serum Unbound Free Fatty Acid
Levels after Contemporary Percutaneous Coronary Intervention

B-type natriuretic peptide (BNP) and serum unbound free fatty acid (FFAu) are novel cardiac markers. BNP is a polypeptide secreted by the cardiac ventricles in response to volume and pressure overload. Measurement of BNP levels has demonstrated diagnostic value in heart failure and has evolved to be a powerful prognostic marker in acute coronary syndromes, stable coronary heart disease, diabetes and heart failure.^1–3 FFAu is a sensitive marker of myocardial ischemia.⁴ A previous study conducted prior to the era of routine coronary stenting demonstrated a rise in FFAu levels after balloon angioplasty.⁵ Similarly, two small studies demonstrated that BNP rises following balloon angioplasty, but there are no data from the coronary stenting era.^6,7 Contemporary percutaneous coronary intervention (PCI) with routine stenting has reduced balloon inflation times and ischemic complications, which may reduce or eliminate the impact of PCI on FFAu and BNP levels. Our objective was to determine the frequency and timing of BNP and FFAu level elevations after contemporary PCI with short inflation times and routine coronary stenting.

Methods
This was a prospective cohort study to examine the pattern of BNP and FFAu levels after contemporary PCI. Inclusion criteria involved patients undergoing elective PCI without the diagnosis of an acute coronary syndrome (ACS). Patients were enrolled between January 1, 2002 and December 31, 2002. Blood specimens were collected at 4 time points: within 1 hour prior to PCI, immediately after PCI, 6 hours after PCI and 18–24 hours after PCI. The specimen collection tubes included heparin for troponin I analysis and EDTA for FFAu and BNP analysis. Blood specimens were prepared and frozen immediately after collection. Only troponin I and FFAu were measured immediately after PCI. BNP was measured using the Shionogi assay.⁸ FFAu levels were determined using the ADIFAB2 fluorescent probe, as described previously.⁹ Troponin I was measured using standard immunoassay techniques (Access-II, Beckman- Coulter). The upper limits of normal for the BNP, FFAu and troponin I assays are 100 pg/ml, < 2.7 nM, and 0.06 μg/L, respectively.
Continuous variables were summarized as means with standard deviations (SD) and categorical variables as percentages. Pearson’s ¯2 test was used to compare categorical data. Fisher’s exact test was used when 25% or more of the cells had expected counts < 5. The Wilcoxon signed-rank test was used to compare results from the same patient across different time points. Chi square tests were performed for categorical variables. Simple logistic regression was used to examine the relationship between FFAu levels and BNP levels post-PCI. Statistical analysis was performed using SAS software, version 8.02 (SAS Institute, Inc., Cary, North Carolina). The study was approved by the local institutional research ethics board and all patients provided informed consent.

Results
Fifty-five consecutive patients undergoing elective PCI were included in this study. The baseline clinical and procedural characteristics are shown in Table 1. Fifty patients (91%) received stents during their coronary intervention. The mean values for each assay are shown in Table 2. The FFAu levels are shown graphically in Figure 1.

The FFAu levels immediately after PCI were significantly higher than the pre-PCI values (mean increase 4.4 nM; p < 0.0001). The proportion of patients with elevated FFAu levels (> 2.7 nM) rose from 24% pre-PCI to 82% immediately after PCI. At 6 hours after PCI, the FFAu levels had returned to baseline levels. At 18–24 hours after PCI, there was a secondary minor rise in FFAu levels compared with 6-hour values (mean increase 0.3 nM; p = 0.047). There were no significant associations between the peak FFAu level and total balloon inflation duration, electrocardiographic changes, prolonged angina, procedural complications, left ventricular function or number of lesions treated. There were no cases of abrupt closure, however, 10 patients had prolonged angina and 5 patients had complications (2 patients had dissections that resolved with additional stents, 2 patients had sidebranch occlusion and 1 patient developed no-reflow after stent placement). The BNP levels are shown graphically in Figure 2.

The BNP levels did not change significantly at 6 hours after PCI. At 18–24 hours after PCI, there was a trend toward higher BNP levels compared with pre-PCI values (p = 0.056). The proportion of patients with elevated BNP levels > 100 pg/ml was 15%. There was no correlation between peak FFAu and BNP levels. There was no correlation of FFAu or BNP with left ventricular enddiastolic pressure levels.
Post-PCI troponin I values were > 0.06 μg/L in 67% of patients, but utilizing the MI cutoff for troponin I at our center (≥ 1.0 μg/L), only 4 patients (7%) had an elevated troponin I after PCI. The peak FFAu and BNP levels post-PCI for the 4 patients with periprocedural MI were 8.8 ± 9.2 nM and 44.8 ± 31.4 pg/ml, respectively. Troponin I rose significantly at both 6 and 18–24 hours post-PCI, as shown in Table 2. Troponin I levels post-PCI did not correlate with either FFAu or BNP levels post-PCI.

Discussion
In this prospective cohort study of 55 patients undergoing elective PCI, there was a trend towards increased BNP levels 24 hours after PCI and a significant rise in FFAu levels immediately after PCI, which normalized by 6 hours. This is the first study to examine the pattern of change of BNP and FFAu levels after PCI using contemporary techniques, including short inflation times and coronary stenting.
Tateishi et al demonstrated a rise in BNP that peaked at 24 hours post-PCI in a cohort of 30 patients undergoing balloon angioplasty.7 A smaller study of only 13 patients undergoing balloon angioplasty demonstrated a rise in BNP at the end of the procedure, which had normalized by 4 hours.6 The time profile of the changes in BNP in the former study of 30 patients is consistent with that of our study. However, the two previous studies were done prior to the era of coronary stenting and had total mean inflation times ranging from 215–350 seconds, which are much longer than our study, with a total mean inflation time of 123 seconds. The mechanism of BNP rise post-PCI is likely in part related to ischemia during the procedure, with a resulting rise in left ventricular end-diastolic pressure, but also may be related to contrast load and fluid administration, a factor not examined in our study. Our study suggests that BNP levels rise only modestly after contemporary PCI with shorter inflation times, less prolonged myocardial ischemia and the use of coronary stents in over 90% of patients. Furthermore, the differences in BNP levels in this study did not reach statistical significance, and may be due to chance alone. In the JUMBO-TIMI 26 trial, NT-pro-BNP levels were significantly higher than baseline levels at 4–8 hours and 12–24 hours after PCI.¹⁰ The NT-pro-BNP assay has been reported in some studies to have a slightly better sensitivity and specificity for heart failure, which may account in part for the discrepancy between our results and the JUMBO-TIMI 26 trial.^11–13
Kleinfeld demonstrated a significant rise in FFAu after balloon angioplasty at 30 minutes postprocedure independent of significant ST-segment changes on the electrocardiogram.⁵ The current study found a similar rise in FFAu immediately postprocedure, which normalized within 6 hours. Some data suggest that FFAu levels may be falsely elevated if samples are not spun and frozen promptly. In the current study, the samples were spun and frozen in 30 minutes or less. Despite the short inflation times and use of coronary stents, FFAu levels were elevated in over 80% of patients after PCI, demonstrating the high sensitivity of this biomarker for even very transient myocardial ischemia. In vitro studies have demonstrated that acutely elevated FFAu can be deleterious to myocardial cell activity.¹⁴ Furthermore, it has been shown that FFAu levels correlate with mortality in patients with ACS.¹⁵
The pre-PCI FFAu values were elevated in 24% of patients, most likely related to resting ischemia occurring prior to PCI. In a previous study that included patients with unstable angina, the pre-PCI FFAu values were elevated in 59% of patients.⁵
The lack of correlation of troponin I, FFAu and BNP may in part be related to the timing of peak levels and the limited sample size. It is also possible that mechanisms other than ischemia, including volume overload related to contrast and fluid administration, may contribute to BNP elevation post- PCI. In the JUMBO-TIMI 26 trial, the magnitude of NTpro- BNP elevation after PCI correlated with the extent of myocardial injury measured by CK-MB and troponin T levels after PCI.¹⁰ However, as noted above, the NT-pro-BNP may be more sensitive and specific than BNP for measuring periprocedural hemodynamic stress. The limitations of this study include the small sample size and the inclusion of only outpatients undergoing elective PCI. The results may not be generalizable to patients with a higher acuity.

Conclusion
FFAu levels rise significantly after contemporary coronary angioplasty and stenting in stable outpatients. The rise in BNP levels after angioplasty was modest, delayed and of borderline statistical significance. Further studies are required to examine the relationship between these biomarker levels post-PCI and clinical outcomes.

References

1. Valle R, Aspromonte N, Feola M, et al. B-type natriuretic peptide can predict the medium-term risk in patients with acute heart failure and preserved systolic function. J Card Fail 2005;11:498–503.
2. Heeschen C, Hamm CW, Mitrovic V, et al. N-terminal pro-B-type natriuretic peptide levels for dynamic risk stratification of patients with acute coronary syndromes. Circulation 2004;110:3206–3212.
3. Kragelund C, Gronning B, Kober L et al. N-terminal pro-B-type natriuretic peptide and long-term mortality in stable coronary heart disease. N Engl J Med 2005;352:666–675.
4. Apple FS, Kleinfeld AM, Adams J. Unbound free fatty acid concentrations are increased in cardiac ischemia. Clinical Proteomics 2004;1:41–44.
5. Kleinfeld AM, Prothro D, Brown DL, et al. Increases in serum unbound free fatty acid levels following coronary angioplasty. Am J Cardiol 1996;78:1350–1354.
6. Kyriakides ZS, Markianos M, Michalis L, et al. Brain natriuretic peptide increases acutely and much more prominently than atrial natriuretic peptide during coronary angioplasty. Clin Cardiol 2000;23:285–288.
7. Tateishi J, Masutani M, Ohyanagi M, Iwasaki T. Transient increase in plasma brain (B-type) natriuretic peptide after percutaneous transluminal coronary angioplasty. Clin Cardiol 2000;23:776–780.
8. Lapointe N, Nguyen QT, Desjardins JF, et al. Effects of pre-, peri-, and postmyocardial infarction treatment with omapatrilat in rats: Survival, arrhythmias, ventricular function, and remodeling. Am J Physiol Heart Circ Physiol 2003;285:H398–H405.
9. Richieri GV, Ogata RT, Kleinfeld AM. The measurement of free fatty acid concentration with the fluorescent probe ADIFAB: A practical guide for the use of the ADIFAB probe. Mol Cell Biochem 1999;192:87–94.
10. Bonaca MP, Wiviott SD, Sabatine MS, et al. Hemodynamic significance of periprocedural myocardial injury assessed with N-terminal pro-B-type natriuretic peptide after percutaneous coronary intervention in patients with stable and unstable coronary artery disease (from the JUMBO-TIMI 26 trial). Am J Cardiol 2007;99:344–348.
11. Mueller T, Gegenhuber A, Poelz W, Haltmayer M. Head-to-head comparison of the diagnostic utility of BNP and NT-proBNP in symptomatic and asymptomatic structural heart disease. Clin Chim Acta 2004;341:41–48.
12. Lainchbury JG, Campbell E, Frampton CM, et al. Brain natriuretic peptide and N-terminal brain natriuretic peptide in the diagnosis of heart failure in patients with acute shortness of breath. J Am Coll Cardiol 2003;42:728–735.
13. Fonseca C, Sarmento PM, Minez A, et al. Comparative value of BNP and NTproBNP in diagnosis of heart failure. Rev Port Cardiol 2004;23:979–991.
14. de Vries JE, Vork MM, Roemen TH et al. Saturated but not mono-unsaturated fatty acids induce apoptotic cell death in neonatal rat ventricular myocytes. J Lipid Res 1997;38:1384–1394.
15. Kleinfeld A, Kleinfeld K, Adams J. Serum levels of unbound free fatty acids reveal high sensitivity for early detection of acute myocardial infarction in patients samples from the TIMI II trial. J Am Coll Cardiol 2002;39:312A.