Intravascular Blood Sampling Using the Export Catheter Does Not Induce Artifactual Platelet Activation

From the *Department of Cardiology, Concord Repatriation General Hospital, Sydney, Australia, and the §Vascular Biology Group, ANZAC Research Institute, Sydney, Australia. The authors report no financial relationships or conflicts of interest regarding the content herein. Manuscript submitted November 18, 2008, provisional acceptance given December 22, 2008, final version accepted January 13, 2009. Address for correspondence: Harry C. Lowe, PhD, Department of Cardiology, Level 3 West, Concord Hospital, Hospital Road, Concord, NSW 2139, Australia. E-mail: h.lowe@bigpond.net.au ________________________________ ABSTRACT: We sought to investigate the feasibility of using the Export catheter to sample blood from the coronary arteries for studies of platelet activation. A pilot comparison between the Export catheter and the established Simmons catheter — currently used to sample blood from the coronary sinus — was performed. Triplicate blood samples were obtained from the descending aorta for each catheter in 10 patients, and analyzed for platelet P-selectin expression, PAC-1 expression, and platelet-leukocyte aggregate formation by flow cytometry. We found no significant increase in levels of platelet activation above that of reference values and no significant differences between the two catheters. J INVASIVE CARDIOL 2009;21:159–161 The measurement and characterization of platelet activation in patients with ischemic heart disease are of increasing interest, and flow cytometry-based analyses of platelet surface markers and platelet-leukocyte aggregates have been shown to be sensitive indicators of platelet activation.1,2 Platelets are, however, prone to ex vivo activation, and variations in sampling methods — including the use of different catheters and cannulae — may induce artifactual levels of platelet activation.3,4 Sampling blood from the coronary sinus has been shown to be a sensitive method of detecting platelet activation,5 and previous studies of platelet activation in the coronary sinus have yielded important insights.5,6 In accessing the coronary sinus, prior studies have used the 5 Fr Simmons catheter (Cook, Inc., Bloomington, Indiana), and it has been shown that this coronary sinus catheter does not artifactually increase platelet activation at baseline.5–8 Coronary sinus sampling allows the study of venous blood that has crossed the coronary arteries and myocardium, but does not allow the distinction between the biological effect of passage through coronary arteries with that of passage through the cardiac capillary bed and myocardium. Only sampling of blood from the distal coronary arteries will allow investigation of the local distal coronary environment and differentiate this from the coronary venous environment. The Simmons catheter is unsuitable for sampling in the coronary arteries due to its shape and rigidity. Other catheters that could be used for sampling in the coronary arteries include the over-the-wire Masstransit (Cordis Corp., Miami Lakes, Florida) (internal luminal diameter [ILD] of 0.027 inch) and Tracker catheters (Boston Scientific Corp., Natick, Massachusetts) (inner lumen diameter [ILD]: 0.021 inch), and the now discontinued Multifunction Probing catheter (Boston Scientific) (ILD: 0.018 inch), which features a monorail system. There is, however, a need for an aspiration catheter that can be manipulated into the coronary arteries with a large enough lumen to avoid artifactual platelet activation. The recently published Thrombus Aspiration during Percutaneous coronary intervention in Acute myocardial infarction Study (TAPAS) showed a benefit in using a newer catheter, the Export aspiration catheter (Medtronic, Inc., Minneapolis, Minnesota), for thrombus aspiration during primary percutaneous coronary intervention (PCI),9 which is likely to lead to the increased use of this device. By enabling aspiration from a lumen at the distal tip, this catheter not only allows therapeutic thrombus aspiration, but is a potential vehicle for sampling blood for measurements of platelet activation. The Export catheter permits sampling proximal and distal to coronary lesions, allowing comparison of blood sampled from these sites. The Export catheter has a larger ILD (0.040 inch) than other available intracoronary devices, and, in fact, has a larger lumen than the 5 Fr Simmons catheter (ILD: 0.035 inch). This reflects its purpose-built design to optimize aspiration from the coronary epicardial vessels and should mitigate against platelet activation. However, it is longer than the Simmons catheter (135 cm vs. 100 cm), and its rapid-exchange design requires an adjacent guidewire, which also lies distal to the aspiration lumen. It is therefore not known whether extracting blood through the Export catheter causes artifactual platelet activation. We therefore compared levels of platelet activation for blood sampled via the Export catheter with that of the Simmons catheter, as measured by platelet P-selectin expression, glycoprotein (GP) IIb/IIIa conformational change (PAC-1 expression), platelet-monocyte aggregates and platelet-granulocyte aggregates. Methods Ten consecutive patients who presented to the cardiac catheterization laboratory for elective PCI were randomly recruited. Written, informed consent was obtained from all patients in this study, which was approved by our institutional ethics committee. All patients were on aspirin, clopidogrel and conventional anti-anginal therapy including beta-blockers and nitrates. All patients received 2,500–5,000 U of heparin bolus prior to sampling. A 5 Fr Simmons-1 catheter was introduced through a 6 Fr femoral venous sheath. This was advanced to the descending aorta at the level of the 12th thoracic vertebra. Four mL of blood were aspirated and discarded, and a further 3 aliquots of 8 ml of blood were then aspirated using three separate 10 ml syringes. The Simmons catheter was then removed and replaced with an Export catheter, which was advanced over a 0.014 inch guidewire through a 6 Fr angioplasty guiding catheter (Cordis) to the same site. Blood aspiration was then repeated in the same manner. The rate of aspiration was maintained at 0.5 ml per second for both catheters. The blood samples were then transferred carefully into commercially available tubes containing citrate, theophylline, adenosine and dipyridamole (CTAD, Becton Dickinson, Franklin Lakes, New Jersey) kept at 4ºC. Platelet expression of P-selectin, PAC-1 and levels of platelet-leukocyte aggregates were then measured by flow cytometry, as previously described.10 Comparisons between groups were made using Wilcoxon’s rank-sum test for paired data. A Bland-Altman analysis for the difference minus the average was performed between paired samples to measure agreement. Results The results for comparisons between the Simmons and Export catheters for platelet P-selectin, PAC-1, platelet-monocyte aggregates and platelet-granulocyte aggregates are presented in Figure 1. Platelet P-selectin expression was 1.2 ± 1.5% (Simmons) vs. 1.0 ± 1.1% (Export), platelet PAC-1 expression was 1.1 ± 1.3% (Simmons) vs. 1.4 ± 1.5% (Export), platelet-monocyte aggregate formation was 9.3 ± 4.1% (Simmons) vs. 9.3 ± 3.9% (Export), and platelet-granulocyte aggregate formation was 3.5 ± 1.1% (Simmons) vs. 3.4 ± 0.9% (Export). These levels are consistent with previous observations in patients with coronary disease,2 and there was no significant difference in levels of platelet activation between the two catheters according to any of the markers used. Bland-Altman analysis (plots not shown) revealed that the 95% limits of agreement between the two catheters were -1.22 to 1.68 for percentage of (%) platelet P-selectin, -1.10 to 0.57 for % PAC-1, -2.96 to 2.92 for % platelet-monocyte aggregates, and -1.04 to 1.36 for % platelet-granulocyte aggregates. Discussion Our findings indicate that in patients with coronary disease pretreated with aspirin, clopidogrel and heparin, careful sampling via the Export catheter does not induce significant ex vivo platelet activation and is comparable to the Simmons catheter. The Export catheter therefore provides an easy way to access the distal coronary arteries and potentially other small vessels for studies of platelet activation. Although it is possible that aspirin and clopidogrel pretreatment may attenuate any potential ex vivo activation, our study investigated this question in situations where the Export catheter was used only during PCI, in conjunction with aspirin and clopidogrel administration. A separate study involving a control population not on antiplatelet agents is required for these results to be applicable to a more general population. Given the recognition of ex vivo platelet activation using sampling catheters,4 an increasing awareness of the importance of platelet activation in coronary angioplasty,5 and the likely increasing use of the Export catheter in clinical practice,9 we hope the present observations will guide and encourage future studies of platelet biology within the coronary arteries.

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