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* From the Departments of Internal Medicine (Drs. Nagaya, Sasaki, Sakamaki, Kyotani, and Nakanishi) and Cardiovascular Surgery (Drs. Ando and Ogino), National Cardiovascular Center, Osaka, Japan.
Correspondence to: Noritoshi Nagaya, MD, Department of Internal Medicine, National Cardiovascular Center, 57-1 Fujishirodai, Suita, Osaka 565-8565, Japan; e-mail: nagayann{at}hsp.ncvc.go.jp
| Abstract |
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Methods: Of the 33 patients with CTEPH who were candidates for pulmonary thromboendarterectomy, 12 patients with severe pulmonary hypertension (pulmonary vascular resistance, > 1,200 dyne · s · cm-5) received IV prostacyclin prior to undergoing pulmonary thromboendarterectomy. Right heart catheterization and plasma brain natriuretic peptide (BNP) measurements were repeated at baseline, immediately before surgery, and 1 month after surgery.
Results: During a mean (± SEM) follow-up period of 46 ± 12 days, the IV administration of prostacyclin resulted in a 28% decrease in pulmonary vascular resistance (1,510 ± 53 to 1,088 ± 58 dyne · s · cm-5; p < 0.001) before surgery. Prostacyclin therapy markedly decreased plasma BNP level (547 ± 112 to 188 ± 30 pg/mL; p < 0.01), suggesting improvement in right heart failure. Pulmonary thromboendarterectomy caused a further reduction of pulmonary vascular resistance (302 ± 47 dyne · s · cm-5) and plasma BNP levels (60 ± 11 pg/mL) compared to each preoperative value (p < 0.05). Operative mortality rates were relatively low (8.3%) in patients with the most severe form of CTEPH.
Conclusion: The IV administration of prostacyclin caused beneficial hemodynamic effects in patients with severe CTEPH and may serve as pretreatment for patients undergoing pulmonary thromboendarterectomy.
Key Words: prostacyclin pulmonary hypertension pulmonary thromboendarterectomy pulmonary thromboembolism
| Introduction |
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Prostacyclin produces strong vasodilation and inhibition of platelet aggregation and vascular smooth muscle cell proliferation.7 8 Some studies have shown that the continuous IV infusion of prostacyclin markedly lowers pulmonary vascular resistance and improves survival in patients with precapillary pulmonary hypertension conditions such as primary pulmonary hypertension9 10 and collagen vascular diseases.11 As a result, prostacyclin therapy has become recognized as a therapeutic breakthrough in patients with severe pulmonary hypertension. However, whether IV prostacyclin therapy may attenuate pulmonary hypertension in patients with major-vessel CTEPH remains unknown. The preoperative improvement in pulmonary hemodynamics would result in a beneficial surgical outcome in CTEPH patients after they undergo pulmonary thromboendarterectomy.
Thus, the purpose of this study was to investigate whether the IV administration of prostacyclin ameliorates pulmonary hypertension in patients with the most severe form of CTEPH before they undergo pulmonary thromboendarterectomy.
| Materials and Methods |
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1,200 dyne · s · cm-5 were treated with conventional therapy alone (conventional group). The diagnosis of CTEPH was made on the basis of the previously reported procedure.12
In brief, patients with clinical symptoms suggesting CTEPH underwent ventilation/perfusion lung scanning to detect pulmonary perfusion defects. The diagnosis was confirmed by pulmonary angiography. All patients had occlusion and stenosis from the lobar to segmental arteries.13
Cardiac catheterization was performed to confirm precapillary pulmonary hypertension (mean pulmonary arterial pressure, > 30 mm Hg; pulmonary capillary wedge pressure, < 12 mm Hg). All subjects gave written informed consent.
Prostacyclin Therapy and Other Medication
Prostacyclin therapy was begun at a dose of 2 ng/kg/min and was increased with increments of 1 ng/kg/min over 1 week prior to patients undergoing pulmonary thromboendarterectomy (mean [± SEM] dose, 6 ± 1 ng/kg/min; dose range, 2 to 11 ng/kg/min). The mean duration of prostacyclin therapy immediately before pulmonary thromboendarterectomy was 46 ± 12 days. Pulmonary thromboendarterectomy was performed through two separate arteriotomies on both main intrapericardial pulmonary arteries following the standard technique, which has been described previously.3
14
The infusion of prostacyclin was discontinued while patients were receiving cardiopulmonary bypass. Prostacyclin therapy was restarted at the preoperative dose immediately after the patient was weaned from cardiopulmonary bypass. After surgery, the dose of prostacyclin was gradually reduced, and it was discontinued within 1 week after surgery.
Anticoagulation therapy was continued in all patients before and after surgery. Other medications such as digitalis and diuretics were not significantly changed before and after surgery.
Hemodynamic Studies
Baseline right heart catheterization was performed in all patients (33 patients) during hospitalization. Immediately before and 1 month after patients underwent pulmonary thromboendarterectomy, right heart catheterization was repeated in 31 patients (prostacyclin group, 11 patients; conventional group, 20 patients). Hemodynamic variables, including mean pulmonary artery pressure, mean right atrial pressure, and mean pulmonary wedge pressure, were measured. Cardiac output was determined by the Fick method.15
Pulmonary vascular resistance was calculated using the standard formulas.
Blood Sampling and Assay
Blood samples were taken from the antecubital vein in all patients at baseline, immediately before undergoing surgery, and 1 month after undergoing pulmonary thromboendarterectomy. Blood was immediately transferred into a chilled glass tube containing disodium ethylenediaminetetraacetic acid (1 mg/mL) and aprotinin (500 U/mL), and was centrifuged immediately at 4°C. The plasma was frozen and stored at -80°C until assay. For the noninvasive assessment of right ventricular function, the plasma brain natriuretic peptide (BNP) level was measured directly with a specific immunoradiometric assay kit (Shiono RIA BNP assay kit; Shionogi Co, Ltd; Osaka, Japan).16
17
The investigators collecting the BNP data were blinded to treatment.
Data Analysis
All data were expressed as the mean ± SEM. Comparisons of parameters between two groups were made by Fisher exact test or unpaired Student t test. Changes in clinical and hemodynamic parameters during prostacyclin therapy were compared by paired Student t test. Comparisons of the time course of pulmonary vascular resistance and plasma BNP level between the two groups were made by two-way analysis of variance for repeated measures, followed by a Scheffe multiple comparison test. A p value of < 0.05 was considered to be statistically significant.
| Results |
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Hemodynamic Effects of Prostacyclin Therapy Before Pulmonary Thromboendarterectomy
The IV administration of prostacyclin tended to decrease the mean pulmonary arterial pressure (before administration, 51 ± 2 mm Hg; after administration, 47 ± 2 mm Hg; difference not significant) [Fig 1
] and significantly increased cardiac output (before administration, 2.3 ± 0.1 L/min; after administration, 3.1 ± 0.2 L/min; p < 0.01). Thus, prostacyclin therapy resulted in a 28% decrease in pulmonary vascular resistance (before therapy, 1,510 ± 53 dyne · s · cm-5; after therapy, 1,088 ± 58 dyne · s · cm-5; p < 0.001) before pulmonary thromboendarterectomy. In addition, IV prostacyclin therapy significantly decreased mean right atrial pressure (before therapy, 7 ± 1 mm Hg; after therapy, 4 ± 1 mm Hg; p < 0.05). There was no significant change in heart rate (before therapy, 85 ± 3 beats/min; after therapy, 82 ± 2 beats/min), mean systemic arterial pressure (before therapy, 88 ± 3; after therapy, 87 ± 3 mm Hg), or pulmonary capillary wedge pressure (before therapy, 7 ± 1 mm Hg; after therapy, 6 ± 1 mm Hg). Pulmonary arterial oxygen saturation significantly increased during prostacyclin therapy (before therapy, 51 ± 2%; after therapy, 56 ± 1%; p < 0.01), although systemic arterial oxygen saturation was not significantly altered (before therapy, 88 ± 1%; after therapy, 88 ± 1%). These parameters remained unchanged in the conventional group.
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| Discussion |
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The IV administration of prostacyclin has been established as the most effective treatment for precapillary pulmonary hypertension conditions such as primary pulmonary hypertension9 10 and collagen vascular diseases.11 However, it is not known whether prostacyclin therapy could serve as an effective pretreatment in patients with major-vessel CTEPH before they undergo pulmonary thromboendarterectomy. Thus, in the present study, prostacyclin was administered IV in patients with the most severe form of CTEPH (pulmonary vascular resistance, > 1,200 dyne · s · cm-5). Prostacyclin therapy could be performed in all patients without clinically significant adverse effects such as hypotension and desaturation, although minor complications occurred in several patients. The dosage of prostacyclin used in the present study was relatively low (2 to 11 ng/kg/min) compared with those used in earlier studies9 10 for the treatment of patients with primary pulmonary hypertension. Nevertheless, the continuous administration of prostacyclin markedly increased cardiac output (by 35%) and decreased pulmonary vascular resistance (by 28%) in patients with CTEPH. As a result, preoperative pulmonary vascular resistance did not significantly differ between the prostacyclin group and the conventional group. Considering that prostacyclin produces strong vasodilation, and inhibition of platelet aggregation and vascular smooth muscle proliferation,7 8 it is interesting to speculate that the infusion of prostacyclin may be effective not only by dilating the pulmonary vasculature, but also by inhibiting medial hypertrophy, intimal fibrosis, and thrombotic lesions of the pulmonary arteries. Further studies are necessary to examine the potential mechanisms that are responsible for the beneficial effects of prostacyclin in patients with CTEPH.
BNP is secreted predominantly from the cardiac ventricles via a constitutive pathway in association with the degree of myocardial stretch and damage.18 19 Thus, the increased plasma BNP levels in patients with pulmonary hypertension is considered to reflect the degree of right ventricular dysfunction.16 17 In the present study, the baseline plasma BNP level was markedly higher in the prostacyclin group than in the conventional group, suggesting the presence of right heart failure in the prostacyclin group. However, prostacyclin therapy markedly decreased plasma BNP levels immediately before surgery. Consequently, preoperative plasma BNP levels did not significantly differ between the two groups. These results suggest that the decrease in pulmonary vascular resistance by prostacyclin therapy may ameliorate increased wall stress in the right ventricle and may improve right ventricular dysfunction in patients with CTEPH.
Earlier studies5 6 have shown that high pulmonary vascular resistance before surgery is associated with perioperative mortality. In the present study, patients in the prostacyclin group had markedly high pulmonary vascular resistance (1,631 ± 136 dyne · s · cm-5) compared with patients in the conventional group (893 ± 49 dyne · s · cm-5) and those patients included in earlier studies (937 to 988 dyne · s · cm-5).3 6 20 21 Nevertheless, the surgical mortality rate of patients who had received prostacyclin was relatively low (8.3%) and was comparable to those reported in earlier studies (6.4 to 10.1%).3 6 20 21 As a result, the mortality rate for all patients in the present study was 3.0% (33 patients). These results may be attributable to the preoperative improvement in pulmonary hemodynamics that was accomplished by prostacyclin therapy. The consecutive pulmonary thromboendarterectomy caused further improvement in pulmonary hemodynamics and plasma BNP levels in such patients. Thus, combined therapy with preoperative prostacyclin administration and pulmonary thromboendarterectomy may have beneficial effects in patients with the most severe form of CTEPH.
Study Limitations
The present study was neither randomized nor placebo-controlled. Prostacyclin therapy was performed in 12 consecutive patients who had a pulmonary vascular resistance > 1,200 dyne · s · cm-5 at diagnostic catheterization. Thus, the severity of disease differed between patients in the prostacyclin group and the conventional group, which may bias the comparison. A prospective, randomized, multicenter trial should be planned based on the results of this study.
| Conclusion |
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| Footnotes |
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This work was supported by Grant From Japan Cardiovascular Research Foundation and the Uehara Memorial Foundation.
Received for publication November 19, 2001. Accepted for publication May 16, 2002.
| References |
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