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Ischemia modified albumin in relation to pharmacologic stress testing in coronary artery disease
Clinica Chimica Acta 396 (2008) 58–61
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Clinica Chimica Acta j o u r n a l h o m e p a g e : w w w. e l s e v i e r. c o m / l o c a t e / c l i n c h i m
Ischemia modified albumin in relation to pharmacologic stress testing in coronary artery disease Eftihia Sbarouni a, Panagiota Georgiadou a,⁎, Demosthenes Panagiotakos a, Stamatis Kyrzopoulos a, Dimitrios Tsiapras a, Vassilis Voudris a, Dimitrios Th. Kremastinos b a b
2nd Department of Cardiology, Onassis Cardiac Surgery Center, 356 Syngrou Ave., 17674 Athens, Greece Attikon University Hospital, Athens, Greece
A R T I C L E
I N F O
Article history: Received 29 April 2008 Received in revised form 25 June 2008 Accepted 25 June 2008 Available online 30 June 2008 Keywords: Ischemia modified albumin Coronary artery disease Non-invasive diagnosis
A B S T R A C T Background: Ischemia modified albumin (IMA) is considered a biomarker of myocardial ischemia. We sought to investigate whether IMA plasma levels change during pharmacological stress test, in patients with stable coronary artery disease. Methods: We studied 37 patients undergoing non-invasive evaluation with a pharmacological stress test, either with radionuclide myocardial perfusion imaging with adenosine or stress echocardiography with dobutamine. Peripheral venous samples were collected before the stress test (baseline), at the end of adenosine infusion or at the peak dose of dobutamine and 60 min after the completion of the stress test for IMA measurement. Results: IMA plasma levels significantly increased at peak vs. baseline (91.28 ± 9.59 U/ml vs. 97.97 ± 9.69 U/ml, p b 0.0001) and subsequently, decreased significantly at 60 min compared to peak (97.97 ± 9.69 U/ml vs. 94 ± 15.22 U/ml, p = 0.016), returning to values similar to those at baseline (p = 0.134). Similarly, in patients with a negative stress test, IMA significantly increased at peak compared to baseline (91.08 ± 10.03 U/ml vs. 99.58 ± 8.43 U/ml, p = 0.006) and returned to baseline at 60 min (99.58 ± 8.43 U/ml vs. 91.83 ± 7.93 U/ml, p = 0.019), the 60 minute levels being similar to baseline values (p = 0.212). Conversely, in patients with a positive stress test, IMA significantly increased at peak compared to baseline (91.38 ± 10.13 U/ml vs. 97.17 ± 10.34 U/ml, p = 0.006) and although decreased at 1 h, this did not reach statistical significance compared either to the baseline or to the peak values (95.04 ± 17.76 U/ml vs. 91.38 ± 10.13 U/ml, p = 0.315 and 95.04 ± 17.76 U/ml vs. 97.17 ± 10.34 U/ ml, p = 0.235, respectively). Conclusion: IMA plasma levels change significantly during pharmacologic stress testing, in patients with coronary artery disease, but with no difference between the positive and the negative tests. © 2008 Elsevier B.V. All rights reserved.
1. Introduction
association to cardioversion [11], radiofrequency ablation [12,13] and pacemaker insertion [14]. Its role in the non-invasive evaluation of coronary artery disease is under investigation [15–17]. We have previously examined whether IMA plasma levels change during exercise stress testing in patients with coronary artery disease and we found significant changes compared to baseline but there were no differences between positive and negative tests [16]. We now sought to investigate whether IMA changes during pharmacological stress test, either with radionuclide myocardial perfusion imaging with adenosine or stress echocardiography with dobutamine.
Ischemia modified albumin (IMA) is considered a biomarker of myocardial ischemia, in contrast to troponins which reliably discriminate myocardial necrosis. Ischemia, through hypoxia, acidosis, free radical injury and energy dependent membrane disruption, may reduce the binding capacity of the amino terminus of albumin to bind metals such as cobalt, copper and nickel. A biomarker which can distinguish between reversible myocardial ischemia and no myocardial ischemia would be of great interest. IMA increases following percutaneous coronary intervention (PCI) [1–4] and in relation to acute coronary syndromes [5–10] and there are limited reports in
2. Methods
Abbreviations: IMA, ischemia modified albumin; PCI, percutaneous coronary intervention; SPECT, single photon emission computed tomography; NT-pro BNP, aminoterminal part of brain-type natriuretic peptide; NT-pro ANP, aminoterminal part of atrial-type natriuretic peptide. ⁎ Corresponding author. Tel.: +30 210 9493 000; fax: +30 210 9493 373. E-mail address: [email protected] (P. Georgiadou).
We studied stable patients with established angiographically coronary artery disease (CAD); all patients had previously undergone coronary angiography and had significant CAD (N 70% diameter stenosis in one of the epicardial vessels). All patients subsequently underwent non-invasive evaluation with a pharmacological stress test, as part of their risk stratification. All patients were investigated on their medications. We performed pharmacological stress test, either with radionuclide myocardial perfusion imaging with adenosine or stress echocardiography with dobutamine; adenosine, a
0009-8981/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.cca.2008.06.024
E. Sbarouni et al. / Clinica Chimica Acta 396 (2008) 58–61
59
Table 1 Baseline demographic and clinical characteristics of the study population All patients (n = 37) Age, years Female/male, n Cardiac risk factors, n (%) – Hypertension – Hypercholesterolemia – Diabetes mellitus – Current smoking – Family history Ejection fraction, % Disease severity, n (%) – Single vessel disease – Multi-vessel disease Current medications, n (%) – ACE inhibitor or ARBs – b blockers – Calcium blockers – Statins – Antidiabetic drugs – Insulin – Antiplatelet drugs
67.76 ± 9.8 8/29 25 (67) 23 (62) 11 (29) 10 (27) 10 (27) 52 ± 8 18 (49) 19 (51) 25 (67) 24 (65) 9 (24) 18 (49) 5 (13) 2 (5) 29 (78)
Data are presented as mean ± standard deviation or the n (%) of patients. ACE: angiotensin-converting enzyme; ARB: angiotensin receptor blockers. potent vasodilator, produces Tl-201 defects due to intense flow inhomogeneity whereas dobutamine, through its positive chronotropic and inotropic effects, increases myocardial oxygen demand. All patients gave informed consent and the study protocol was approved by the ethics committee of our institution. Patients with symptoms and signs of significant peripheral arterial disease, end-stage renal disease, liver disease, active infection or cancer were excluded. We studied 19 patients who underwent myocardial perfusion single photon emission computed tomography (SPECT) with adenosine stress testing. SPECT was performed according to standard stress and 4-hour redistribution protocol. The scan was considered positive when a reversible defect was found; a reversible defect was present when a perfusion abnormality was observed in the stress images, but was smaller or absent in the corresponding rest images. The scan was considered negative when a normal distribution of the radioisotope was present at stress and at 4 h later or in case of a fixed defect; a fixed defect was present when there was no improvement in the perfusion abnormality from stress to rest images. Evaluation of defect reversibility/ irreversibility was based on semiquantitative interpretation of scans by an experienced nuclear cardiologist; no gated SPECT was performed. Intravenous infusion of adenosine was performed at a rate of 140 μg/kg/min for a total of 6 min. At the end of the third minute of the infusion, thallium-201 (2.5 to 3.5 mCi) was injected intravenously, with dose variation based on patient weight and flushed with 10 mL of normal saline. Imaging commenced 10 min after completion of adenosine administration and was repeated 4 h later. Peripheral venous samples were collected before the stress test (baseline), at the end of adenosine infusion and 60 min after the completion of the infusion, via an indwelling catheter. We also studied 18 patients undergoing dobutamine stress echo. Dobutamine was administered with an infusion pump, starting at a rate of 5 μg·kg− 1·min− 1 increasing the dose every 3 min to 10, 20, 30 and 40 μg·kg− 1·min− 1. Intravenous atropine (0.2 to 0.4 mg every 2 min to a maximum of 2 mg) was infused to achieve peak heart rates of N 120 bpm, if the heart rate was submaximal at the maximal dose of dobutamine. An ischemic response was defined as the development of a new or worsening stressinduced regional wall motion abnormality not present at baseline. A biphasic response was defined as improved wall thickening in ≥ 2 contiguous segments from rest to low dose followed by decreased wall thickening in ≥2 contiguous segments from low to peak dose. Peripheral venous samples were collected before the stress test (baseline), at peak dose and 60 min after the completion of the stress test via an indwelling catheter. Serum IMA was measured with the albumin cobalt binding test on an Integra 800 analyzer (Roche, Rotkreuz, Switzerland), which is an indirect method of IMA measurement. Cobalt not bound to the N-terminus of albumin is detected using dithiothreitol (DTT) as colometric indicator. Blood samples were collected in serum
Fig. 1. Box-plots represent median and quartiles (1st, 3rd) values of IMA at baseline, peak ischemia and at 60 min for all tests and the whiskers show the extreme values within the specific time point, which are defined as cases with values more than 3 inderquartile length (i.e. 3 box lengths). separator tubes, centrifuged at 3000 rounds per minute for 10 min and stored at −70 for 1 month. All samples were tested in one session in triplicates and were thawed only once. According to the manufacturer, expected values determined in a population of 283 healthy individuals range from 52 to 116 U/ml with a 95th percentile at 85 U/ml. The total interassay imprecision (coefficient variation) was 2.7% to 5.7% at 56.3 to 125.9 U/ml for quality control material. Data analysis was based on non-parametric statistical methods. In particular, Wilcoxon test for pair-wise comparisons was applied to evaluate differences between time points. p-values derived from 2-sided hypotheses tests. However, due to the inflation of type-I error because of multiple comparisons, all reported p-values were corrected according to the Bonferroni rule. Data are expressed as mean ± standard deviation. All statistical calculations were performed in SPSS version 14 package (SPSS Inc., Chicago, Il, USA).
3. Results Thirty seven patients were included in the study of whom 8 were women and 29 were men, with a mean age of 67.76 ± 9.8 years (Table 1). Twenty five patients had a positive stress test, either a nuclear scan or a stress echo and 12 a negative one. In further detail, in the scintigraphy group 15 patients had a positive test and 4 a negative and in the stress echocardiography group 10 patients were positive and 8 negative. Baseline, peak and 60 min IMA values are shown in Table 2. IMA serum
Table 2 IMA values at baseline, peak ischemia and at 60 min IMA (U/ml)
Baseline
Peak
60 min
All (n = 37) Negative (n = 12) Positive (n = 25)
91.28 ± 9.59 91.08 ± 10.03 91.38 ± 10.13
97.97 ± 9.69⁎# 99.58 ± 8.43⁎# 97.17 ± 10.34⁎
94 ± 15.22 91.83 ± 7.93 95.04 ± 17.76
Data are expressed as mean ± standard deviation; *p b 0.01 vs. Baseline, #p b 0.02 vs. 60 min.
Fig. 2. Box-plots represent median and quartiles (1st, 3rd) values of IMA at baseline, peak ischemia and at 60 min for negative tests and the whiskers show the extreme values within the specific time point, which are defined as cases with values more than 3 inderquartile length (i.e. 3 box lengths).
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E. Sbarouni et al. / Clinica Chimica Acta 396 (2008) 58–61
levels significantly increased at peak vs. baseline (91.28 ± 9.59 U/ml vs. 97.97 ± 9.69 U/ml, p b 0.0001) and subsequently decreased significantly at 60 min compared to peak (97.97 ± 9.69 U/ml vs. 94 ± 15.22 U/ml, p = 0.016), returning to values similar to those at baseline (91.28±9.59 U/ml vs. 94±15.22 U/ml, p=0.134), (Fig.1). Similarly, in patients with a negative stress test, IMA significantly in creased at peak compared to baseline (91.08 ± 10.03 U/ml vs. 99.58 ± 8.43 U/ml, p = 0.006) and returned to baseline at 60 min (99.58 ± 8.43 U/ml vs. 91.83 ± 7.93 U/ml, p = 0.019), the 60 minute levels being similar to baseline values (91.83 ± 7.93 U/ml vs. 91.08 ± 10.03 U/ml, p = 0.212), (Fig. 2). Conversely, in patients with a positive stress test, IMA significantly increased at peak compared to baseline (91.38±10.13 U/ml vs. 97.17 ±10.34 U/ml, p = 0.006) and although decreased at 1 h, this did not reach statistical significance compared either to the baseline or to the peak values (95.04± 17.76 U/ml vs. 91.38 ± 10.13 U/ml, p =0.315 and 95.04 ± 17.76 U/ml vs. 97.17 ±10.34 U/ml, p = 0.235, respectively), (Fig. 3). The kinetics of IMA for each individual, separated according to whether stress echo or nuclear scan was applied, are presented in Fig. 4; we did not observe meaningful differences in IMA kinetics, according to the agent used, given the small number of patients in each subgroup.
Fig. 4. Dot-plot represents IMA values of individual cases at baseline (1), peak (2) and 60 min post-test (3).
4. Discussion We examined IMA changes in relation to pharmacological stress test, either adenosine thallium scan or dobutamine stress echo. We found that IMA in the overall group significantly increases at stress and subsequently decreases to baseline values at 1 h. Looking at the patients with negative tests, we observed that IMA changes were similar to the overall group, whereas the patients with positive tests had a blunted response; their IMA levels were also significantly raised at peak ischemia but did not return to initial values at 1 h. We have previously examined whether IMA changes during exercise stress testing in patients with known coronary artery disease and we found that IMA significantly decreases at peak exercise compared to baseline and returns to initial values after 60 min; this occurred similarly in both positive and negative exercise tests, possibly due to the hemoconcentration during physical exercise, causing an increase in plasma albumin and subsequently a decrease in the nonbound portion of a fixed amount of cobalt [16]. Similarly, in another study of patients undergoing symptom-limited exercise myocardial perfusion scintigraphy, IMA was significantly lower at maximum exercise and returned to baseline values within 1 h after stress and this did not differ between patients with and without
Fig. 3. Box-plots represent median and quartiles (1st, 3rd) values of IMA at baseline, peak ischemia and at 60 min for positive tests and the whiskers show the extreme values within the specific time point, which are defined as cases with values more than 3 inderquartile length (i.e. 3 box lengths).
inducible ischemia [15]. Furthermore, in a recent report, patients with suspected coronary artery disease were evaluated with a thallium scan either with exercise testing or dipyridamole infusion and IMA levels, after a transient drop at 18 min, significantly increased at 4 h but with no difference in patients with and without reversible defects; in addition, patients on pharmacological stress increased their values at 18 min and 4 h whereas patients on physical stress initially dropped their IMA at 18 min – maybe in relation to the hemoconcentration mechanism – and then raised it at 4 h. In the same study, others markers of ischemia such as NT-pro BNP, NT-pro ANP and placental growth factor did not change significantly after stress testing and these investigators argue that skeletal ischemia is the cause of the IMA variations [17]. Although dobutamine-induced ischemia as well as adenosine-induced ischemia is considered less severe than the maximal exercise-induced ischemia, we observed significant changes in IMA plasma levels during pharmacological stress testing, whereas during physical exercise hemoconcentration seems to predominate over active ischemia [16]. IMA increases within minutes of ischemia and remains high for hours; during PCI, IMA increases immediately post-balloon inflation and 30 min after and returns to baseline in 6– 12 h [1–4]; this may be the reason that IMA levels are not entirely back to baseline in our positive tests at 60 min, whereas in the negative studies IMA increases, possibly due to subclinical ischemia without ECG changes or reversible scintigraphic or echocardiographic defects, but quickly returns to initial values. IMA seems to be sensitive but not specific as it is not only related to cardiac ischemia, but to muscle [18], gastrointestinal [19], brain [20], and pulmonary ischemia [21]. We cannot, however, attribute our findings in this study to peripheral skeletal muscle ischemia, since these patients did not exercise. In another report, patients with peripheral arterial disease who underwent dobutamine stress echo, all of whom were negative, IMA levels were unchanged at baseline, peak stress and 1 h after stress [22]. In the contrary, in our negative tests IMA significantly changed, in a similar way to the overall group. IMA has been shown to be higher in patients with documented peripheral vascular disease than in controls even at rest and this may imply that IMA reflects the total atherosclerotic plaque burden [23]. We conclude that IMA serum levels change significantly during pharmacologic stress testing, in patients with known coronary artery disease but without much difference between the positive and the negative tests; it seems, therefore, that IMA measurement does not increase the diagnostic efficacy of stress imaging.
E. Sbarouni et al. / Clinica Chimica Acta 396 (2008) 58–61
References [1] Bar-Or D, Winkler JV, VanBenthysen K, Harris L, Lau E, Hetzel FW. Reduced albumin-cobalt binding with transient myocardial ischemia after elective percutaneous transluminal coronary angioplasty: a preliminary comparison to creatine kinase-MB, myoglobin, and troponin I. Am Heart J 2001;141:985–91. [2] Sinha MK, Gaze DC, Tippins JR, Collinson PO, Kaski JC. Ischemia modified albumin is a sensitive marker of myocardial ischemia after percutaneous coronary intervention. Circulation 2003;107:2403–5. [3] Quiles J, Roy D, Gaze D, et al. Relation of Ischemia-Modified Albumin (IMA) levels following elective angioplasty for stable angina pectoris to duration of ballooninduced myocardial ischemia. Am J Cardiol 2003;92:322–4. [4] Garrido IP, Roy D, Calvino R, et al. Comparison of ischemia-modified albumin levels in patients undergoing percutaneous coronary intervention for unstable angina pectoris with versus without collaterals. Am J Cardiol 2004;93:88–90. [5] Christenson RH, Duh SH, Sanhai WR, et al. Characteristics of an albumin binding test for assessment of acute coronary syndrome patients: a multicenter study. Clin Chem 2001;47:464–70. [6] Bhagavan NV, Lai EM, Rios PA, et al. Evaluation of human serum albumin cobalt binding assay for the assessment of myocardial ischemia and myocardial infarction. Clin Chem 2003;49:581–5. [7] Sinha M, Roy D, Gaze D, Collinson P, Kaski JC. Role of “ischemia-modified albumin”, a new biochemical marker of myocardial ischaemia, in the early diagnosis of acute coronary syndromes. Emerg Med J 2004;21:29–34. [8] Peacock F, Morris LD, Anwaruddin S, et al. Meta-analysis of ischemia-modified albumin to rule out acute coronary syndromes in the emergency department. Am Heart J 2006;152:253–62. [9] Lee YW, Kim HJ, Cho YH, Shin HB, Choi TY, Lee YK. Application of albumin-adjusted ischemia modified albumin index as an early screening marker for acute coronary syndrome. Clin Chem Acta 2007;384:24–7. [10] Dominguez-Rodriguez A, Abreu-Gonzalez P, Garcia-Gonzalez MJ, Samini-Fard S, Kaski JC. Relation of ischemia-modified albumin levels and left ventricular systolic function in patients with ST-segment elevation myocardial infarction treated with primary percutaneous coronary intervention. Clin Chem Acta 2007;388:196–9. [11] Roy D, Quiles J, Sinha M, ldama G, Gaze D, Kaski JCl. Effect of direct-current cardioversion on ischemia-modified albumin in patients with atrial fibrillation. Am J Cardiol 2004;93:366–8.
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[12] Roy D, Quiles J, Sinha M, et al. Effect of radiofrequency catheter ablation on the biochemical marker ischemia-modified albumin. Am J Cardiol 2004;94:234–6. [13] Sbarouni E, Georgiadou P, Panagiotakos D, Livanis EG, Theodorakis GN, Kremastinos DTh. Ischaemia modified albumin in radiofrequency catheter ablation. Europace 2007;9:127–9. [14] Sbarouni E, Georgiadou P, Panagiotakos D, Livanis EG, Theodorakis GN, Kremastinos DTh. The ischemia modified albumin in relation to pacemaker and defibrillator implantation. PACE 2008;31:83–7. [15] Van der Zee PM, Verberne HJ, Straalen JP, et al. Ischemia-modified albumin measurements in symptom-limited exercise myocardial perfusion scintigraphy reflect serum albumin concentrations but not myocardial ischemia. Clin Chem 2005;51:1744–6. [16] Sbarouni E, Georgiadou P, Theodorakis GN, Kremastinos DT. Ischemia-modified albumin in relation to exercise stress testing. J Am Coll Cardiol 2006;48:2482–4. [17] Kurz K, Voelker R, Zdunek D, et al. Effect of stress-induced reversible ischemia on serum concentrations of ischemia-modified albumin, natriuretic peptides and placental growth factor. Clin Res Cardiol 2007;96:152–7. [18] Falkensammer J, Stojakovic T, Huber K, et al. Serum levels of ischemia-modified albumin in healthy volunteers after exercise-induced calf-muscle ischemia. Clin Chem Lab Med 2007;45:535–40. [19] Apple FS, Quist HE, Otto AP, Mathews WE, Murakami MM. Release characteristics of cardiac biomarkers and ischemia-modified albumin as measured by the albumin cobalt-binding test after marathon race. Clin Chem 2002;48:1097–100. [20] Abboud H, Labreuche J, Meseguer E, et al. Ischemia-modified albumin in acute stroke. Cerebrovasc Dis 2006;23:216–20. [21] Turedi S, Gunduz A, Mentese A, et al. Value of ischemia-modified albumin in the diagnosis of pulmonary embolism. Am J Emerg Med 2007;25:770–3. [22] Roy D, Quiles J, Sharma R, et al. Ischemia-modified albumin concentration sin patients with peripheral vascular disease and exercise- induced skeletal muscle ischemia. Clin Chem 2004;50:1656-1560. [23] Hacker M, Hoyer HX, Fougere C, et al. Effects of peripheral vascular intervention on ischemia-modified albumin. Coron Artery Dis 2007;18:375–9.
Contents lists available at ScienceDirect
Clinica Chimica Acta j o u r n a l h o m e p a g e : w w w. e l s e v i e r. c o m / l o c a t e / c l i n c h i m
Ischemia modified albumin in relation to pharmacologic stress testing in coronary artery disease Eftihia Sbarouni a, Panagiota Georgiadou a,⁎, Demosthenes Panagiotakos a, Stamatis Kyrzopoulos a, Dimitrios Tsiapras a, Vassilis Voudris a, Dimitrios Th. Kremastinos b a b
2nd Department of Cardiology, Onassis Cardiac Surgery Center, 356 Syngrou Ave., 17674 Athens, Greece Attikon University Hospital, Athens, Greece
A R T I C L E
I N F O
Article history: Received 29 April 2008 Received in revised form 25 June 2008 Accepted 25 June 2008 Available online 30 June 2008 Keywords: Ischemia modified albumin Coronary artery disease Non-invasive diagnosis
A B S T R A C T Background: Ischemia modified albumin (IMA) is considered a biomarker of myocardial ischemia. We sought to investigate whether IMA plasma levels change during pharmacological stress test, in patients with stable coronary artery disease. Methods: We studied 37 patients undergoing non-invasive evaluation with a pharmacological stress test, either with radionuclide myocardial perfusion imaging with adenosine or stress echocardiography with dobutamine. Peripheral venous samples were collected before the stress test (baseline), at the end of adenosine infusion or at the peak dose of dobutamine and 60 min after the completion of the stress test for IMA measurement. Results: IMA plasma levels significantly increased at peak vs. baseline (91.28 ± 9.59 U/ml vs. 97.97 ± 9.69 U/ml, p b 0.0001) and subsequently, decreased significantly at 60 min compared to peak (97.97 ± 9.69 U/ml vs. 94 ± 15.22 U/ml, p = 0.016), returning to values similar to those at baseline (p = 0.134). Similarly, in patients with a negative stress test, IMA significantly increased at peak compared to baseline (91.08 ± 10.03 U/ml vs. 99.58 ± 8.43 U/ml, p = 0.006) and returned to baseline at 60 min (99.58 ± 8.43 U/ml vs. 91.83 ± 7.93 U/ml, p = 0.019), the 60 minute levels being similar to baseline values (p = 0.212). Conversely, in patients with a positive stress test, IMA significantly increased at peak compared to baseline (91.38 ± 10.13 U/ml vs. 97.17 ± 10.34 U/ml, p = 0.006) and although decreased at 1 h, this did not reach statistical significance compared either to the baseline or to the peak values (95.04 ± 17.76 U/ml vs. 91.38 ± 10.13 U/ml, p = 0.315 and 95.04 ± 17.76 U/ml vs. 97.17 ± 10.34 U/ ml, p = 0.235, respectively). Conclusion: IMA plasma levels change significantly during pharmacologic stress testing, in patients with coronary artery disease, but with no difference between the positive and the negative tests. © 2008 Elsevier B.V. All rights reserved.
1. Introduction
association to cardioversion [11], radiofrequency ablation [12,13] and pacemaker insertion [14]. Its role in the non-invasive evaluation of coronary artery disease is under investigation [15–17]. We have previously examined whether IMA plasma levels change during exercise stress testing in patients with coronary artery disease and we found significant changes compared to baseline but there were no differences between positive and negative tests [16]. We now sought to investigate whether IMA changes during pharmacological stress test, either with radionuclide myocardial perfusion imaging with adenosine or stress echocardiography with dobutamine.
Ischemia modified albumin (IMA) is considered a biomarker of myocardial ischemia, in contrast to troponins which reliably discriminate myocardial necrosis. Ischemia, through hypoxia, acidosis, free radical injury and energy dependent membrane disruption, may reduce the binding capacity of the amino terminus of albumin to bind metals such as cobalt, copper and nickel. A biomarker which can distinguish between reversible myocardial ischemia and no myocardial ischemia would be of great interest. IMA increases following percutaneous coronary intervention (PCI) [1–4] and in relation to acute coronary syndromes [5–10] and there are limited reports in
2. Methods
Abbreviations: IMA, ischemia modified albumin; PCI, percutaneous coronary intervention; SPECT, single photon emission computed tomography; NT-pro BNP, aminoterminal part of brain-type natriuretic peptide; NT-pro ANP, aminoterminal part of atrial-type natriuretic peptide. ⁎ Corresponding author. Tel.: +30 210 9493 000; fax: +30 210 9493 373. E-mail address: [email protected] (P. Georgiadou).
We studied stable patients with established angiographically coronary artery disease (CAD); all patients had previously undergone coronary angiography and had significant CAD (N 70% diameter stenosis in one of the epicardial vessels). All patients subsequently underwent non-invasive evaluation with a pharmacological stress test, as part of their risk stratification. All patients were investigated on their medications. We performed pharmacological stress test, either with radionuclide myocardial perfusion imaging with adenosine or stress echocardiography with dobutamine; adenosine, a
0009-8981/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.cca.2008.06.024
E. Sbarouni et al. / Clinica Chimica Acta 396 (2008) 58–61
59
Table 1 Baseline demographic and clinical characteristics of the study population All patients (n = 37) Age, years Female/male, n Cardiac risk factors, n (%) – Hypertension – Hypercholesterolemia – Diabetes mellitus – Current smoking – Family history Ejection fraction, % Disease severity, n (%) – Single vessel disease – Multi-vessel disease Current medications, n (%) – ACE inhibitor or ARBs – b blockers – Calcium blockers – Statins – Antidiabetic drugs – Insulin – Antiplatelet drugs
67.76 ± 9.8 8/29 25 (67) 23 (62) 11 (29) 10 (27) 10 (27) 52 ± 8 18 (49) 19 (51) 25 (67) 24 (65) 9 (24) 18 (49) 5 (13) 2 (5) 29 (78)
Data are presented as mean ± standard deviation or the n (%) of patients. ACE: angiotensin-converting enzyme; ARB: angiotensin receptor blockers. potent vasodilator, produces Tl-201 defects due to intense flow inhomogeneity whereas dobutamine, through its positive chronotropic and inotropic effects, increases myocardial oxygen demand. All patients gave informed consent and the study protocol was approved by the ethics committee of our institution. Patients with symptoms and signs of significant peripheral arterial disease, end-stage renal disease, liver disease, active infection or cancer were excluded. We studied 19 patients who underwent myocardial perfusion single photon emission computed tomography (SPECT) with adenosine stress testing. SPECT was performed according to standard stress and 4-hour redistribution protocol. The scan was considered positive when a reversible defect was found; a reversible defect was present when a perfusion abnormality was observed in the stress images, but was smaller or absent in the corresponding rest images. The scan was considered negative when a normal distribution of the radioisotope was present at stress and at 4 h later or in case of a fixed defect; a fixed defect was present when there was no improvement in the perfusion abnormality from stress to rest images. Evaluation of defect reversibility/ irreversibility was based on semiquantitative interpretation of scans by an experienced nuclear cardiologist; no gated SPECT was performed. Intravenous infusion of adenosine was performed at a rate of 140 μg/kg/min for a total of 6 min. At the end of the third minute of the infusion, thallium-201 (2.5 to 3.5 mCi) was injected intravenously, with dose variation based on patient weight and flushed with 10 mL of normal saline. Imaging commenced 10 min after completion of adenosine administration and was repeated 4 h later. Peripheral venous samples were collected before the stress test (baseline), at the end of adenosine infusion and 60 min after the completion of the infusion, via an indwelling catheter. We also studied 18 patients undergoing dobutamine stress echo. Dobutamine was administered with an infusion pump, starting at a rate of 5 μg·kg− 1·min− 1 increasing the dose every 3 min to 10, 20, 30 and 40 μg·kg− 1·min− 1. Intravenous atropine (0.2 to 0.4 mg every 2 min to a maximum of 2 mg) was infused to achieve peak heart rates of N 120 bpm, if the heart rate was submaximal at the maximal dose of dobutamine. An ischemic response was defined as the development of a new or worsening stressinduced regional wall motion abnormality not present at baseline. A biphasic response was defined as improved wall thickening in ≥ 2 contiguous segments from rest to low dose followed by decreased wall thickening in ≥2 contiguous segments from low to peak dose. Peripheral venous samples were collected before the stress test (baseline), at peak dose and 60 min after the completion of the stress test via an indwelling catheter. Serum IMA was measured with the albumin cobalt binding test on an Integra 800 analyzer (Roche, Rotkreuz, Switzerland), which is an indirect method of IMA measurement. Cobalt not bound to the N-terminus of albumin is detected using dithiothreitol (DTT) as colometric indicator. Blood samples were collected in serum
Fig. 1. Box-plots represent median and quartiles (1st, 3rd) values of IMA at baseline, peak ischemia and at 60 min for all tests and the whiskers show the extreme values within the specific time point, which are defined as cases with values more than 3 inderquartile length (i.e. 3 box lengths). separator tubes, centrifuged at 3000 rounds per minute for 10 min and stored at −70 for 1 month. All samples were tested in one session in triplicates and were thawed only once. According to the manufacturer, expected values determined in a population of 283 healthy individuals range from 52 to 116 U/ml with a 95th percentile at 85 U/ml. The total interassay imprecision (coefficient variation) was 2.7% to 5.7% at 56.3 to 125.9 U/ml for quality control material. Data analysis was based on non-parametric statistical methods. In particular, Wilcoxon test for pair-wise comparisons was applied to evaluate differences between time points. p-values derived from 2-sided hypotheses tests. However, due to the inflation of type-I error because of multiple comparisons, all reported p-values were corrected according to the Bonferroni rule. Data are expressed as mean ± standard deviation. All statistical calculations were performed in SPSS version 14 package (SPSS Inc., Chicago, Il, USA).
3. Results Thirty seven patients were included in the study of whom 8 were women and 29 were men, with a mean age of 67.76 ± 9.8 years (Table 1). Twenty five patients had a positive stress test, either a nuclear scan or a stress echo and 12 a negative one. In further detail, in the scintigraphy group 15 patients had a positive test and 4 a negative and in the stress echocardiography group 10 patients were positive and 8 negative. Baseline, peak and 60 min IMA values are shown in Table 2. IMA serum
Table 2 IMA values at baseline, peak ischemia and at 60 min IMA (U/ml)
Baseline
Peak
60 min
All (n = 37) Negative (n = 12) Positive (n = 25)
91.28 ± 9.59 91.08 ± 10.03 91.38 ± 10.13
97.97 ± 9.69⁎# 99.58 ± 8.43⁎# 97.17 ± 10.34⁎
94 ± 15.22 91.83 ± 7.93 95.04 ± 17.76
Data are expressed as mean ± standard deviation; *p b 0.01 vs. Baseline, #p b 0.02 vs. 60 min.
Fig. 2. Box-plots represent median and quartiles (1st, 3rd) values of IMA at baseline, peak ischemia and at 60 min for negative tests and the whiskers show the extreme values within the specific time point, which are defined as cases with values more than 3 inderquartile length (i.e. 3 box lengths).
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levels significantly increased at peak vs. baseline (91.28 ± 9.59 U/ml vs. 97.97 ± 9.69 U/ml, p b 0.0001) and subsequently decreased significantly at 60 min compared to peak (97.97 ± 9.69 U/ml vs. 94 ± 15.22 U/ml, p = 0.016), returning to values similar to those at baseline (91.28±9.59 U/ml vs. 94±15.22 U/ml, p=0.134), (Fig.1). Similarly, in patients with a negative stress test, IMA significantly in creased at peak compared to baseline (91.08 ± 10.03 U/ml vs. 99.58 ± 8.43 U/ml, p = 0.006) and returned to baseline at 60 min (99.58 ± 8.43 U/ml vs. 91.83 ± 7.93 U/ml, p = 0.019), the 60 minute levels being similar to baseline values (91.83 ± 7.93 U/ml vs. 91.08 ± 10.03 U/ml, p = 0.212), (Fig. 2). Conversely, in patients with a positive stress test, IMA significantly increased at peak compared to baseline (91.38±10.13 U/ml vs. 97.17 ±10.34 U/ml, p = 0.006) and although decreased at 1 h, this did not reach statistical significance compared either to the baseline or to the peak values (95.04± 17.76 U/ml vs. 91.38 ± 10.13 U/ml, p =0.315 and 95.04 ± 17.76 U/ml vs. 97.17 ±10.34 U/ml, p = 0.235, respectively), (Fig. 3). The kinetics of IMA for each individual, separated according to whether stress echo or nuclear scan was applied, are presented in Fig. 4; we did not observe meaningful differences in IMA kinetics, according to the agent used, given the small number of patients in each subgroup.
Fig. 4. Dot-plot represents IMA values of individual cases at baseline (1), peak (2) and 60 min post-test (3).
4. Discussion We examined IMA changes in relation to pharmacological stress test, either adenosine thallium scan or dobutamine stress echo. We found that IMA in the overall group significantly increases at stress and subsequently decreases to baseline values at 1 h. Looking at the patients with negative tests, we observed that IMA changes were similar to the overall group, whereas the patients with positive tests had a blunted response; their IMA levels were also significantly raised at peak ischemia but did not return to initial values at 1 h. We have previously examined whether IMA changes during exercise stress testing in patients with known coronary artery disease and we found that IMA significantly decreases at peak exercise compared to baseline and returns to initial values after 60 min; this occurred similarly in both positive and negative exercise tests, possibly due to the hemoconcentration during physical exercise, causing an increase in plasma albumin and subsequently a decrease in the nonbound portion of a fixed amount of cobalt [16]. Similarly, in another study of patients undergoing symptom-limited exercise myocardial perfusion scintigraphy, IMA was significantly lower at maximum exercise and returned to baseline values within 1 h after stress and this did not differ between patients with and without
Fig. 3. Box-plots represent median and quartiles (1st, 3rd) values of IMA at baseline, peak ischemia and at 60 min for positive tests and the whiskers show the extreme values within the specific time point, which are defined as cases with values more than 3 inderquartile length (i.e. 3 box lengths).
inducible ischemia [15]. Furthermore, in a recent report, patients with suspected coronary artery disease were evaluated with a thallium scan either with exercise testing or dipyridamole infusion and IMA levels, after a transient drop at 18 min, significantly increased at 4 h but with no difference in patients with and without reversible defects; in addition, patients on pharmacological stress increased their values at 18 min and 4 h whereas patients on physical stress initially dropped their IMA at 18 min – maybe in relation to the hemoconcentration mechanism – and then raised it at 4 h. In the same study, others markers of ischemia such as NT-pro BNP, NT-pro ANP and placental growth factor did not change significantly after stress testing and these investigators argue that skeletal ischemia is the cause of the IMA variations [17]. Although dobutamine-induced ischemia as well as adenosine-induced ischemia is considered less severe than the maximal exercise-induced ischemia, we observed significant changes in IMA plasma levels during pharmacological stress testing, whereas during physical exercise hemoconcentration seems to predominate over active ischemia [16]. IMA increases within minutes of ischemia and remains high for hours; during PCI, IMA increases immediately post-balloon inflation and 30 min after and returns to baseline in 6– 12 h [1–4]; this may be the reason that IMA levels are not entirely back to baseline in our positive tests at 60 min, whereas in the negative studies IMA increases, possibly due to subclinical ischemia without ECG changes or reversible scintigraphic or echocardiographic defects, but quickly returns to initial values. IMA seems to be sensitive but not specific as it is not only related to cardiac ischemia, but to muscle [18], gastrointestinal [19], brain [20], and pulmonary ischemia [21]. We cannot, however, attribute our findings in this study to peripheral skeletal muscle ischemia, since these patients did not exercise. In another report, patients with peripheral arterial disease who underwent dobutamine stress echo, all of whom were negative, IMA levels were unchanged at baseline, peak stress and 1 h after stress [22]. In the contrary, in our negative tests IMA significantly changed, in a similar way to the overall group. IMA has been shown to be higher in patients with documented peripheral vascular disease than in controls even at rest and this may imply that IMA reflects the total atherosclerotic plaque burden [23]. We conclude that IMA serum levels change significantly during pharmacologic stress testing, in patients with known coronary artery disease but without much difference between the positive and the negative tests; it seems, therefore, that IMA measurement does not increase the diagnostic efficacy of stress imaging.
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