Abstract

The aim of the present study was to evaluate the possibility that aminophylline could serve as a potential myocardial protectant by measuring cardiac troponin T (TnT) and troponin I (TnI) during coronary artery bypass grafting (CABG). Twenty patients were randomly divided into two groups. Ten patients received aminophylline, 200 mg orally per day for 3 days preoperatively (aminophylline group, AG), and 10 patients received placebo (control group, CG). Blood samples were collected before induction of anesthesia (T0), after 30 min of aortic cross clamping (ACC) (T1), and 1, 24, and 48 h postoperatively (T2, T3, T4). Serum concentrations of TnT, TnI, and creatine kinase-MB (CK-MB) were measured. Perioperative hemodynamic data were recorded and cardiac hemodynamics were evaluated by echocardiography preoperatively and 5–7 days after surgery. There were no adverse events in either group. Preoperative serum levels of TnT and TnI were similar. Their concentrations increased after T1 and, peaked at T2 (0.50±0.30 vs. 0.30±0.40 ng/ml, and 0.50±0.30 vs. 7.90±2.70 ng/ml, respectively, P<0.001), and progressively declined until T4. The CK-MB levels of both groups also supported these results. After completion of cardiopulmonary bypass (CPB), the serum concentrations of all enzymes in both groups were significantly higher than before CPB (P<0.001), and serum TnT and TnI levels were significantly lower at T1, T2, T3, and T4 in AG (P<0.001). There was no significant difference in echocardiographic data, cardiac index, ejection fraction or any other hemodynamic parameter between the groups. Fewer patients needed inotropic support (one vs. three patients) (P=0.6) and experienced atrial fibrillation (AF) (one vs. four patients) (P=0.3) in the AG after surgery, although not statistically significant. Although there was no statistically valid evidence to indicate that aminophylline improved clinical outcome in this study, several biochemical endpoints suggested that it reduced I-R damage at the cellular level, and such subtle improvement could be clinically significant in high-risk patients.

1 Introduction

Despite well-established procedures, inadequate myocardial protection in patients undergoing coronary artery bypass grafting (CABG) operation still contributes to overall hospital morbidity and mortality [1]. Ischemia-reperfusion (I-R) injury impairs myocardial recovery after aortic cross clamping (ACC) during open-heart operations. There is no doubt that the benefit of reperfusion can cause serious arrhythmias, myovascular damage, new necrosis, mechanical stunning, and low cardiac output (CO) syndrome after cardiopulmonary bypass (CPB) [2]. It remains the most uncontrolled phenomenon during cardiac operations. Because of this, various methods and pharmacologic approaches have been examined to discover a drug capable of preserving the myocardium.

Aminophylline, an anti-ischemic drug, is a xanthine derivative, and widely used in the treatment of cardiovascular and respiratory diseases due to its broncodilative and putative anti-inflammatory effects [3]. It is an anti-ischemic and anti-anginal drug that has cardioprotective effects. These effects have been assessed both experimentally [4] and clinically [5–9].

Recently, cardiac markers troponin T (TnT) and troponin I (TnI), which are more specific and sensitive than creatine kinase-MB (CK-MB), have become available [10,11]. Their release into the circulation indicates various degrees of myocardial cell damage. Determination of TnT and TnI provides the highest diagnostic efficiency for detecting myocardial cell necrosis [10,11].

The aim of the present study was to evaluate the potential myocardial protective effects of aminophylline by measuring cardiac TnT and TnI during CABG.

2 Material and methods

2.1 Patients

A cardioplegic, arrested heart during open-heart surgery was the model of myocardial ischemia. We designed a prospective, randomized, placebo-controlled trial to determine the efficacy of aminophylline on I-R injury after CABG operations. Twenty patients, selected from the waiting list, with coronary artery disease (CAD) who had elective, isolated, primary CABG operation (Hacettepe University Hospital, Ankara, Turkey) were randomly assigned by a random number generator to aminophylline (n=10) or placebo (n=10). Patients with rhythm defects by electrocardiography (ECG) and patients receiving dipyridamole, xanthine products, and β-adrenergic blocking agents were excluded from the study. All patients had normal ventriculography and no known associated cardiac or non-cardiac disorders. The institutional review board approved the study and written informed consent was obtained from all patients. Aminophylline, (Aminocardol, Novartis, Istanbul), 200 mg orally per day for 3 days was given to 10 patients (aminophylline group, AG), and placebo was given to the 10 others (control group, CG). Serum concentration of aminophylline was measured daily in all patients and it was 5.12±1.28 μg/ml in the AG just before the operation, but not detectable in the CG. The reported potential side effects of the aminophylline were not observed. In the AG, there were four women and six men with a mean age of 60.7±9.8 years. In the CG, there were two women and eight men with a mean age of 57.2±9.8 years (Table 1 ).

Patients demographic, surgical, and postoperative data
Table 1

Patients demographic, surgical, and postoperative data

2.2 Operative procedures: anesthesia, cardiopulmonary bypass, and surgical technique

Anesthetic management was uniform in all patients. Midazolam was used for premedication, and the anesthetic agent consisted of a combination of fentanyl, midazolam, and pancuronium. After intubation, mechanical ventilation was started with oxygen and nitrogen. Anesthesia was maintained with midazolam, vecuronium, and inhaled sevaflurane.

Patients were operated on by the same surgical team. CABG was done with moderate hypothermia (28°C) and intermittent, cold, anterograde crystalloid cardioplegia (15 ml/kg, Plegisol, Abbott Laboratories, Abbott Park, IL). Topical cooling with cold saline was applied only once at the beginning of cardioplegic arrest. Half dose of cardioplegia was repeated with 20 min intervals as needed. The distal anastomoses were constructed during a single period of total aortic occlusion, and proximal anastomoses were constructed with partial clamping of the aorta. Left internal thoracic artery to left anterior descending artery was used in all cases and additional saphenous vein grafts were used when needed.

If there were no contraindications, the patients were extubated within 4 h after surgery. Postoperative analgesia was maintained with metamisole or meperidine. When there was low cardiac output (CO) state, dopamine was used as the first choice inotropic agent. In the case of new onset of atrial fibrillation (AF), amiodarone was used as the first choice anti-arrhythmic agent.

2.3 Hemodynamic measurements

Standard radial and central venous catheters were inserted preoperatively. Hemodynamic data including heart rate (HR) and blood pressure (BP) were recorded every 2 h about 3 days preoperatively and 5 days postoperatively. Central venous pressure (CVP) was measured every 2 h for the first two postoperative days. A serial 12-lead ECG was obtained every 12 h for 3 days preoperatively and once prior to discharge. Cardiac index (CI) and ejection fraction (EF) were assessed preoperatively just before the operation and 5–7 days after surgery using two-dimensional echocardiography (GE, Vingmed, Harten, Norway). CO, CI, and EF were determined from the method (area length algorithms), described previously [12]. A cardiologist, blinded to the patient's clinical history and biochemical information performed all echocardiographic studies and interpretation of the ECG.

2.4 Metabolic studies

Serial blood samples were collected before induction of anesthesia (peripheral vein) (T0), after 30 min of ACC (T1), and at 1, 24, and 48 h postoperatively (central vein) (T2, T3, T4). The samples were drawn into tubes without an anti-coagulant agent and were kept at room temperature for 20 min to allow clotting. The samples were centrifuged at 3000×g for 10 min and then stored in aliquots at a minimal temperature of (−)20°C until analysis. All measurements were made at all time points and there were no missing data. Serum levels of enzymes were determined for all samples by biochemists unaware of the patient's histories. TnT and CK-MB mass concentrations were assayed by an electrochemiluminescence immunoassay (ECLIA, Roche, Mannheim, Germany) using an Elecsys 1010 System analyzer (Roche, Mannheim, Germany). TnI concentration was assayed by solid phase two side chemiluminescence enzyme immunometric assay (BioDPS, LA, USA) using an Immulite analyzer (BioDPS, LA, USA) in the same samples. Plasma concentrations of theophylline were determined according to a previously described method with a modified fluorescence polarization immunoassay (TDx analyzer, Abbott, IL, USA) [13]. The upper reference limits for the normal ranges were set at TnT 0.1 ng/ml, TnI 1.0 ng/ml, CK-MB mass 5.0 ng/ml, and theophylline 20 μg/ml.

2.5 Statistical analysis

All data were expressed as mean±standard deviations. Statistical significance between the two groups was determined using unpaired Student's t-test and analysis of variance (ANOVA). Enzyme levels were compared at different time points using ANOVA (Bonferroni) to test for interactions. Data were considered significant when the P-value was less than 0.05.

3 Results

There were no hospital mortalities or perioperative MI's in either group. The clinical, operative, and postoperative characteristics of both groups are shown in Table 1. There were no significant differences in these variables between the two groups. Postoperative AF occurred in one patient in the AG and in four patients in the CG (P=0.3). There were no substantial elevations in the enzyme levels of these patients postoperatively. They were treated with amiodarone and converted to sinus rhythm within the first 24 h of onset, and discharged from the hospital in sinus rhythm. Except AF, no significant changes in ECGs (ST changes, new Q-wave) were seen in any of the patients. One patient in the AG and three patients in the CG received dopamine postoperatively (P=0.6). The mean duration of mechanical ventilation and hospital stay was shorter in the AG (P>0.05) (Table 1). There were no significant intergroup differences for echocardiographic values, CI, EF, (Table 1), or any other hemodynamic data such as HR, BP, and CVP during the perioperative period.

The preoperative serum concentrations of TnT, TnI and CK-MB were similar (P>0.05). Serum levels at several sampling times in the groups are presented in Table 2 and enzyme changes are shown in Fig. 1A–C . Serial measurements of these enzymes increased significantly in both groups over time compared with baseline measurements. Myocardial reperfusion after CPB showed significantly elevated release of all cardiac enzymes in both groups. In both groups, baseline TnT, TnI, and CK-MB concentrations increased, in a parallel manner, at 30 min of ACC, and peaked at 1 h after declamping, followed by a progressive decline until postoperative day 2 (Table 2 and Fig. 1A–C). In this study, measured enzyme levels in both groups were significantly higher than preoperative values all through the postoperative study period (P<0.001). These levels were less in the AG group than those of the CG throughout the entire measurement period. However, TnT and TnI levels in the AG were significantly lower at T1, T2, T3, and T4. Additionally, CK-MB levels in the AG were significantly lower at T1 and T2 postoperatively than those of the CG (P<0.001) (Fig. 1A–C).

Mean serum concentrations
Table 2

Mean serum concentrations

A: P<0.05 at 30 min of ACC, 1, 24 and 48 h postoperatively (unpaired Student's t-test and ANOVA); and P<0.001 for Bonferroni. B: P<0.05 at 30 min of ACC, 1, 24 and 48 h postoperatively (unpaired Student's t-test and ANOVA); and P<0.001 for Bonferroni. C: P<0.05 at 30 min of ACC and 1 h postoperatively (unpaired Student's t-test and ANOVA); and P<0.001 for Bonferroni.
Fig. 1

A: P<0.05 at 30 min of ACC, 1, 24 and 48 h postoperatively (unpaired Student's t-test and ANOVA); and P<0.001 for Bonferroni. B: P<0.05 at 30 min of ACC, 1, 24 and 48 h postoperatively (unpaired Student's t-test and ANOVA); and P<0.001 for Bonferroni. C: P<0.05 at 30 min of ACC and 1 h postoperatively (unpaired Student's t-test and ANOVA); and P<0.001 for Bonferroni.

4 Discussion

Aminophylline is a methylxanthine derivative, widely used in the treatment of cardiovascular and respiratory disease. Bioavailability of oral aminophylline is as high as 70–90% [3]. Clinical effects of aminophylline include relaxation of smooth muscles, stimulation of the central nervous system, increase in respiratory drive, decrease in peripheral vascular resistance, and inotropic and chronotropic effects [3,7]. The primary pharmacological effects of aminophylline are that, it increases intracellular cyclic adenosine monophosphate (cAMP) concentration by inhibiting cyclic nucleotide phosphodiesterase activity, influences and decreases the translocation of intracellular calcium by acting on membranes of the sarcoplasmic reticulum, acts as a competitive inhibitor of the adenosine receptor, and increases plasma catecholamine concentrations [3,9].

Despite surgical and pharmacological advances in myocardial preservation during CABG, myocardial I-R damage remains the most uncontrolled aspect of cardiac operations. Aminophylline may be beneficial in many ways. Katircioglu et al. [14] found that aminophylline (3 mg/kg, IV) improved ventricular function and metabolism, and decreased leukocyte activation in CABG patients. Other clinical studies have shown that aminophylline improved exercise capacity in patients with angina pectoris, and reduced the extent of myocardial ischemia [5,7–9], right atrial pressure, LVEDP, left ventricular end-diastolic volume, and myocardial contractility [5]. Studies have also shown aminophylline to increase the time for onset of angina and exercise duration [8,9], work tolerance, ischemic threshold in patients with CAD [7], and to significantly reduce the severity of cardiac ischemic pain as well as myocardial lactate production [9,15].

The chronotropic and pressor response to aminophylline is dose-dependent [6]. However, the positive inotropic response to aminophylline is not dose-dependent [9]. At very low concentrations (5–10 μg/ml), aminophylline did not change the HR and BP, but apparently enhanced cardiac contractility (positive inotropic response) and reduced preload [6,9]. In our study, the mean plasma concentration of aminophylline was 5.12±1.28 μg/ml in the AG. Although it was statistically non-significant, fewer patients needed inotropic support (one vs. three patients) and experienced AF (one vs. four patients) in the AG during the recovery period. However, the echocardiographic data (CI and EF) in this study showed no significant improvement after the treatment with aminophylline. In addition, aminophylline did not have a significant effect on the other hemodynamic variables in this study. Except for AF, no significant changes in ECGs (ST changes, new Q-wave) were seen in any of the patients. Hence, in our study, there was no correlation between the enzyme elevations and electrocardiographic or hemodynamic outcomes of the patients. However, the evaluation of the efficacy of aminophylline in this study was based on a small number of patients, small number of item of measurements, and a limited observation period. Further studies into the efficacy and therapeutic potency of aminophylline, with a greater number of patients, are needed to further evaluate this issue.

The best model of myocardial I-R is the cardioplegic ischemic-arrested heart during open-heart operation. All study patients received preoperative oral aminophylline for myocardial protection. One limitation of our study related to the use of cold crystalloid cardioplegia and cold saline for myoprotection. Since blood cardioplegia is more effective than cold crystalloid cardioplegia, aminophylline could have been more beneficial for patients receiving blood cardioplegia than for those who received cooled crystalloid cardioplegia and topical saline. However, this should not be a major concern as the end point of the study was not the comparison of these two myoprotection methods, but the comparison of the enzyme levels in the patients.

In the past several decades, serum levels of cardiac enzymes and isoenzymes have become the final arbiters by which myocardial damage is diagnosed or excluded. TnT and TnI measurements are highly sensitive in the diagnosis of myocardial injury and accurately detect even small amounts of myocardial necrosis [10,11]. For this reason, in our study, we measured their serum levels to detect the cytoprotective effect of aminophylline during I-R. We noticed a parallel increase and decrease in the enzyme levels of the group. We found significantly lower TnT and TnI levels in the AG postoperatively (P<0.001). The fact that no patient developed MI as indicated by enzymes, proteins, ECG, and echocardiography in this study, may support the following hypothesis: virtually all patients had temporary myocardial ischemia that led to a release of cytosolic molecules leaking from reversibly injured myocytes. Our study showed that the release of cytosolic molecules from reversibly injured myocytes was of a significantly lower extent in the AG. In addition, our data clearly showed that when the cross clamp is applied to the aorta, the unfavorable ischemic effects of CPB are induced, and the enzymatic increment is significantly reduced in patients who received aminophylline therapy before CPB. With this study, we demonstrated the anti-ischemic effect of aminophylline by using highly cardiospecific markers, cardiac TnT and TnI, for I-R injury. However, we cannot explain its anti-ischemic cellular mechanism on the basis of our data.

In conclusion, although there was no statistically valid evidence to indicate that aminophylline improved clinical outcome in this study, several biochemical endpoints suggest that it reduced I-R damage at the cellular level, and such subtle improvement could be clinically significant in high-risk patients.

References

[1]
Kirklin
JW
Barratt-Boyes
BG
,
Cardiac surgery
,
1993
2nd ed.
New York
Churchill Livingstone
 
[pp. 73–116, 143–147, 175–177]
[2]
Braunwald
E
Kloner
RA
,
Myocardial reperfusion: a double-edged sword?
J Clin Invest
,
1985
, vol.
76
(pg.
1713
-
1719
)
[3]
Rall
TW
Gilman
AG
Rall
TW
Nies
AS
Taylor
P
,
Drugs used in the treatment of asthma
Goodman and Gilman's. The pharmacologic basis of therapeutics
,
1990
8th ed.
New York
Pergamon Press
(pg.
618
-
637
)
[4]
Ulus
AT
Gökçe
P
Özgencil
E
Yildiz
Ö
İbrişim
E
Katircioğlu
SF
,
Beneficial effect of aminophylline on ischemia-reperfusion in isolated rabbit heart
Asian Cardiovasc Thorac Ann
,
1999
, vol.
7
(pg.
96
-
100
)
[5]
Crea
F
Gaspardone
A
Araujo
L
Silva
RD
Kaski
JC
Davies
G
Maseri
A
,
Effects of aminophylline on cardiac function and regional myocardial perfusion: implications regarding its anti-ischemic action
Am Heart J
,
1994
, vol.
127
(pg.
817
-
824
)
[6]
Edlund
A
Soderberg
R
Henricksson
P
,
Improved working capacity following theophylline infusion in patients with ischemic heart disease
Clin Physiol
,
1988
, vol.
8
(pg.
453
-
461
)
[7]
Picano
E
Pugliani
M
Lattanzi
F
Distante
A
L'Abbate
A
,
Exercise capacity after acute aminophylline administration in angina pectoris
Am J Cardiol
,
1989
, vol.
63
(pg.
14
-
16
)
[8]
Cannon
RA
,
Aminophylline for angina: the ‘Robin Hood’ effect?
J Am Coll Cardiol
,
1989
, vol.
14
(pg.
1454
-
1455
[Editorial comment]
[9]
Hashino
T
Ikeda
H
Ueno
T
Imaizumi
T
,
Aminophylline reduces cardiac pain during percutaneous transluminal angioplasty
J Am Coll Cardiol
,
1996
, vol.
28
(pg.
1725
-
1731
)
[10]
Baum
H
Braun
S
Gerhardt
W
,
Multicenter evaluation of a second-generation assay for cardiac troponin T
Clin Chem
,
1997
, vol.
43
(pg.
1877
-
1884
)
[11]
Mair
J
Larue
C
Mair
P
Balogh
D
Calzolari
C
Puschendorfer
B
,
Use of cardiac troponin I to diagnose perioperative myocardial infarction in coronary artery bypass grafting
Clin Chem
,
1994
, vol.
40
(pg.
2066
-
2070
)
[12]
Axler
O
Megarbane
B
Lentschener
C
Fernandez
H
,
Comparison of cardiac output measured with echocardiographic volumes and aortic Doppler methods during mechanical ventilation
Intensive Care Med
,
2003
, vol.
29
(pg.
208
-
217
)
[13]
Li
PK
Lee
JT
Conboy
KA
Ellis
EF
,
Fluorescence polarization immunoassay for theophylline modified for use with dried blood spots on filter paper
Clin Chem
,
1986
, vol.
32
(pg.
552
-
555
)
[14]
Katircioglu
SF
Kucukaksu
DS
Bozdayi
M
Dalva
K
Mavitas
B
Zorlutuna
Y
Tasdemir
O
Bayazit
K
,
The beneficial effects of aminophylline administration on heparin reversal with protamine
Jpn J Surg
,
1994
, vol.
24
(pg.
99
-
102
)
[15]
Crea
F
Pupita
G
Galassi
A
El-Tamimi
H
Kaski
JC
Davies
G
Maseri
A
,
Effects of theophylline and atenolol and their combination on myocardial ischemia in patients with stable angina pectoris
Am J Cardiol
,
1990
, vol.
66
(pg.
1157
-
1162
)