© 2001 European Society of Cardiology
Aspirin does not influence the effect of angiotensin-converting enzyme inhibition on left ventricular ejection fraction 3 months after acute myocardial infarction
a Department of Cardiology, Ullevål University Hospital Oslo, Norway
b Medical Department, Central Hospital of Møre and Romsdal Oslo, Norway
c Research Forum, Ullevål University Hospital Oslo, Norway
* Corresponding author. Tel: +47-22-11-80-80; fax: +47-22-11-79-65.
| Abstract |
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The aim of the present study was to evaluate the possible interaction between chronic aspirin therapy and angiotensin-converting enzyme inhibitor (ACE-I) on left ventricular ejection fraction (LVEF) in patients surviving an acute myocardial infarction (AMI). Forty-two patients with reduced LVEF were recruited from the warfarin aspirin reinfarction study (WARIS-II), a randomized, open study comparing enteric coated aspirin (160 mg/d), warfarin (INR 2.8–4.2) and the combination of aspirin (75 mg/d) and warfarin (INR 2.0–2.5) on mortality, reinfarction and stroke after AMI. LVEF and relevant biochemical measurements were performed before discharge and after 3 months. The overall LVEF increased during the study period from median 35 to 39% (P < 0.001). There was no difference between patients on aspirin and warfarin regarding the main end point, LVEF. Furthermore, neither endothelin-1 nor ANP showed significant differences between the treatment groups. A possible interaction between ACE-I and aspirin might theoretically lead to reduced levels of renin activity in patients on aspirin, but we did not find any such inter-group difference. In conclusion, we did not find evidence of interaction between ACE-I and low-dose aspirin.
Key Words: Angiotensin-converting enzyme inhibitor Aspirin Myocardial infarction Interaction Left ventricular ejection fraction
Received April 10, 2000; Revised August 11, 2000; Accepted October 12, 2000
| 1. Introduction |
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Angiotensin-converting enzyme inhibitors (ACE-I) have contributed radically to the treatment of patients with severe heart failure, with respect to survival as well as amelioration of symptoms [1–3]. They are efficacious vasodilators by reduction of angiotensin II and norepinephrine [4]. In addition, ACE-I reduce the degradation of bradykinin, a potent vasodilator, which also augments the synthesis of prostacyclin [5,6], contributing to the vasodilatory effect.
Coronary heart disease is the cause of heart failure in many patients. Aspirin is widely used in secondary prevention after acute myocardial infarction (AMI) and has been shown to reduce mortality and morbidity through inhibition of platelet aggregation [7]. Aspirin blocks the enzyme cyclooxygenase, thereby inhibiting the synthesis of the aggregatory and vasoconstrictory thromboxane, but also the antiaggregatory and vasodilatory prostaglandins. Even the small doses of aspirin used today may, to some degree, affect the synthesis of prostaglandins [8,9].
Theoretically, the effect of ACE-I may be reduced by aspirin and the hemodynamic status of the patients may be adversely affected. This theory was supported by subgroup analyses of the results from studies of left ventricular dysfunction [10], the AIRE study [11] and Consensus II [12], where there was a trend toward less benefit of enalapril in patients using aspirin at baseline. Recent subgroup analyses from the WASH study and the HOPE study [13] also add evidence to the theory.
Short-term studies on hemodynamic parameters and vasoactive substances have been contradictory [14–19]. Most have used a single dose of either drug. The reports on the effect of acetylsalisylic acid vary from little effect to significant attenuations of hemodynamic improvement. As yet, there are no prospective studies on the impact of chronic low-dose aspirin therapy on the effect of ACE-inhibitors on clinical endpoints or left ventricular function in patients with heart failure.
The aim of the present study was to evaluate the possible interaction between chronic aspirin therapy and ACE-I on left ventricular ejection fraction (LVEF) in patients surviving an AMI. In order to elucidate possible mechanisms of drug interaction, biochemical analyses were included in the study protocol.
| 2. Methods |
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The 42 patients were recruited from the warfarin aspirin reinfarction study (WARIS-II), a national multicenter study including 3630 patients with AMI. WARIS-II is a randomized, open study comparing enteric coated aspirin (160 mg/d), warfarin (INR 2.8–4.2) and the combination of aspirin (75 mg/d) and warfarin (INR 2.0–2.5) on mortality, reinfarction and stroke after AMI [20]. The present substudy was performed in two of the study centers, Ullevål University Hospital, Oslo, and Central Hospital of Møre and Romsdal, Ålesund. The inclusion criteria were LVEF<40% or heart failure during hospital stay leading to initiation of ACE-I before discharge. Patients meeting these criteria were enrolled successively into the substudy according to a preformed study protocol. During the study period, captopril was given to 15 patients, nine on aspirin and six on warfarin (mean daily dosage 47 mg and 50 mg, respectively, n.s), 12 patients received enalapril, seven on aspirin and five on warfarin (mean daily dosage 9.6 mg and 8.0 mg, respectively, n.s.) and finally, 15 patients received lisinopril, 11 in the aspirin group and 4 in the warfarin group (mean daily dosage 7.95 mg and 8.75 mg, respectively, n.s.). The choice of ACE-I and titration of dosage was made on an individual basis.
A panel of laboratory measurements was included in 19 of the patients.
LVEF, as well as biochemical measurements, were performed before discharge from hospital (baseline) and after 3 months. The baseline measurements were usually undertaken 6 days after the AMI and 1–2 days after randomization in WARIS-II.
LVEF was determined by gated radionuclide ventriculography according to standard procedure [21].
Plasma for determination of the prostacyclin (PGI2) metabolite 6-keto PGF-1
, endothelin-1 (ET-1), ANP and pro-ANP was prepared from 10 ml ice-chilled vacutainer tubes (Becton Dickinson) containing 0.34 mol/l EDTA-K3, kept on ice and centrifuged at 4°C and 3000 g for 20 min. All samples were kept at –70°C until analysis.
6-keto PGF-1
was analyzed using a commercial enzyme immunoassay system (code RPN 221, Amersham International plc).
Serum for Thromboxane B2 (TXB2) was collected in Vacutainer® tubes without anticoagulants and kept at 25°C for 1 h before centrifugation (2500 g for 15 min). The samples were frozen and stored at –70°C until analysis. The assays were performed using a commercial EIA-kit (code RPN 220, Amersham International plc, Amersham, UK).
Atrial natriuretic peptide (ANP) was measured in EDTA plasma using the radioimmunoassay RIK 8798 from Peninsula Laboratories, San Carlos, CA, USA (alfa-atrial natriuretic polypeptide 1–28 (human, canine). Extraction was performed with C18 columns (Bond–Elut®, 3 cc/200 mg, Varian sample preparation products, Harbor City, CA, USA). The columns were pre-treated with sequential washing in 100% trifluoroacetic acid (TFA, HPLC grade) (1 ml, once) followed by 1% TFA (3 ml, 3 times). Plasma samples (1 ml) were acidified with 1 ml 1% TFA and clarified by centrifugation at 17 400 g for 20 min at 4°C. The clarified plasma samples were loaded onto the pre-treated C18 columns. The columns were slowly washed with 1% TFA (3 mlx2) discarding the wash. The ANP1-28 polypeptide was eluted with 3 ml 60% acetonitrile (HPLC grade in 1% TFA) and the eluants collected in polypropylene tubes. The eluants were evaporated to dryness by nitrogen gas at 37°C and the dried extracts stored at –70°C for maximum 1 week before further analysis. The extracts were reconstructed in 0.5 ml assay buffer, and the radioimmunometric assay was performed according to the manufacturer's instructions. Pro-ANP was performed by radioimmunoassay [22].
Renin activity: 4 ml blood was sampled in tubes containing 0.1 ml 0.4 mol/l BAL (2,3 dimercaptopran-1-ol); and 0.2 ml 0.25 mol/l EDTA in water. The tubes were turned upside down 5 times for adequate mixing and put in ice water for 10 min. After centrifugation renin activity was measured by radioimmunoassay.
Enzyme immunoassays were used for determination of ET-1 (Parameter Human Endothelin-1 Immunoassay, R and D Systems Europe, Abington, Oxon, UK) (reference values 0.3–0.9 pg/ml). Plasma was extracted according to the recommendation of the manufacturer: 1 ml of plasma; and 1.5 ml of a mixture of aceton/1 M HCl/H2O (40:1:5) were mixed in polypropylene tubes and centrifuged for 20 min at 2000 g at 40°C. The supernatant was decanted into polypropylene tubes and dried in a centrifugal evaporator overnight. The pellet was reconstituted in 0.25 ml sample diluent and the immunoassay was performed.
Statistical analyses: For comparison of demographic baseline data Kruskal Wallis test and chi-square tests were performed. Relative changes in LVEF and biochemical measurements were analyzed as delta values and with Mann–Whitney test. A P-value <0.05 was considered statistically significant.
| 3. Results |
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The baseline characteristics are shown in Table 1. The mean age was 59 years (43–74). There were 35 males and 7 females.
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The groups were quite comparable with respect to baseline characteristics, LVEF, initial and follow-up treatment except for the use of ACE-I before randomization, which was given to all patients in the warfarin group.
Because there were no inter-group differences between the two aspirin groups in any measurement, they were combined for further statistical analyses.
The overall LVEF increased during the study period from median 35 to 39% (P<0.001) (Table 2). Simultaneously, there was a borderline significant increase in the metabolite of PGI2, 6-keto PGF-1
, from median 155 to 168 pg/ml (P=0.06) and in TXB2 from median 6.5 to 7.0 ng/ml (P=0.007) (not shown in the table). ANP was slightly, non-significantly reduced, whereas renin activity tended to increase, also non-significantly. Endothelin-1 showed a significant decrease from median 1.28 to 1.09 pg/ml (P=0.03).
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There was a high degree of correlation between ANP and pro-ANP on both first and second measurement (r=0.82 and 0.96, respectively, P<0.001). In the following, only the ANP results are presented.
The comparison of these parameters in patients treated with aspirin vs. warfarin alone is shown in Table 3. It emerges that there was no difference between patients on aspirin and warfarin regarding the main end point, LVEF. Furthermore, the biochemical parameters showed no significant differences between the treatment groups, except for TXB2, which increased during the study period from median 47 to 394 ng/ml on warfarin and remained low (4 ng/ml) on aspirin.
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| 4. Discussion |
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There was an overall increase in LVEF during the first 3 months after the AMI, probably due to initial myocardial stunning. This finding is in accordance with previous studies in post-infarction patients with reduced LVEF treated with ACE-I [23,24]. This increase, however, was equal in patients on aspirin and warfarin. Thus, the improvement in left ventricular function did not seem to be affected by the potential interaction between ACE-I and aspirin. The increase in TXB2 reflects the fact that aspirin was given to most patients initially and discontinued in approximately one third after randomization. This is clearly illustrated in the warfarin group, which had intermediate values at baseline after aspirin therapy in the acute phase.
Small doses of aspirin have been thought to suppress TXB2 and spare prostacyclin [25,26]. In our study, the stable metabolite of PGI2, 6-keto PGF 1
, was suppressed in patients on aspirin as compared to patients on warfarin, indicating that even these small doses of aspirin (75–160 mg) are not completely prostacyclin sparing, as shown also by others [8,9]. At baseline, where samples were usually taken 1–2 days after randomization, it had already increased substantially in the warfarin group, showing that prostacyclin regenerates faster than TXB2, possibly mainly by contribution from the endothelium.
An increase in renin activity during the study period might be expected on treatment with ACE-I, but in the present study the increase was non-significant, probably because the majority of patients had already received ACE-I therapy for some days before baseline sampling. However, there was no inter-group difference. A possible interaction between ACE-I and aspirin might theoretically lead to reduced levels of renin activity in patients on aspirin. This was not demonstrated in our study.
The levels of endothelin-1 decreased during the 3 months period. This may be due to the acute phase reaction at baseline, an effect of ACE-I per sec [27] or as an expression of the improved LVEF [28].
We did not find evidence of interaction between ACE-I and low-dose aspirin on our main outcome LVEF. Naturally, the observation time was only 3 months, but any clinically interesting interaction would probably have influenced the increase in LVEF. Concerning the biochemical variables, the expected influence of aspirin on TXB2 and 6-keto PGF 1
production was the only difference found between the treatment groups with and without aspirin. Of course, the limited number of patients undergoing biochemical analyses may have contributed to the lack of visualization of potential minor differences. Until long-term prospective studies on hard end points have been performed, we do not find reason to avoid the combination of ACE-I with aspirin during the first months after AMI.
| Acknowledgements |
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We wish to thank Torstein Lyberg and Ann Christin Lindgaard for performing the ANP analyses and Christian Hall for the pro-ANP analyses.
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