Asian Cardiovasc Thorac Ann 1999;7:263-266
© 1999 Asia Publishing EXchange Pte Ltd
Influence of Lactation on Internal Mammary Artery Size and Flow
Erkan Kuralay, MD,
Ufuk Demirkiliç, MD,
Ertu
rul Özal, MD,
Bilgehan Öz, MD,
Faruk Cingöz, MD,
Harun Tatar, MD
Department of Cardiovascular Surgery
Gülhane Military Medical Academy
Ankara, Turkey
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For reprint information contact: Erkan Kuralay, MD Tel: 90 312 326 3855 Fax: 90 312 426 2732 email: ekural{at}gata.edu.tr Gülhane Lojmanlari Pamir Apt. No. 15, Etlik, Ankara 06010, Turkey.
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Abstract
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This prospective study compared internal mammary artery blood flow and diameter and hospital mortality after coronary artery bypass grafting in 3 groups of patients: group 1, 32 women who had breast fed; group 2, 21 women who had not breast fed; and group 3, 30 average-sized males. Mean internal mammary artery flow was significantly lower in group 2 (94 mL•min–1 in group 1, 65 mL•min–1 in group 2, 105 mL•min–1 in group 3). Mean distal internal mammary artery diameter was also less in group 2 (1.35 mm in group 1, 1 mm in group 2, 1.5 mm in group 3). Postoperative myocardial infarction occurred in 1 patient in group 1, 4 in group 2, and 1 in group 3. Anterior myocardial infarction in the 4 patients in group 2 was caused by internal mammary artery spasm. Hospital mortality was 3.13% in group 1, 9.52% in group 2, and 3.33% in group 3. The angina-free period in group 1 was significantly longer than in group 2 (4.5 versus 1.7 years). It was concluded that in women who had not breast fed, the internal mammary artery diameter was inadequate to supply myocardial demand and the graft was prone to lifethreatening spasm.
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Introduction
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Operative mortality and morbidity for women undergoing coronary artery bypass grafting (CABG) are higher than those in men.1–9 The increased incidence of small-vessel disease and the suboptimal patency rates of vein grafts indicate that internal mammary artery (IMA) should be the ideal conduit for myocardial revascularization in women.9–12 However, in spite of the superior patency rate and low mortality associated with IMA grafts, they are not used as commonly in women as in men. IMAs in women are thought to be smaller and more susceptible to spasm than those in men. The IMA provides the largest source of blood to the breast, supplying more than 50% of the blood to this organ. Mammary blood flow and milk yield correlate closely during normal lactation and blood flow to the breasts increases proportionally with the duration of lactation.13,14 The close correlation between mammary blood flow and milk yield may be regulated by local mechanisms that adjust blood flow according to changes in activity of the milk synthesizing cells. Although there have been many studies on the flow characteristics of the mammary arteries, few have examined the flow differences between male and female arteries. This study tested the hypothesis that internal mammary arteries in women with a history of lactation have better flow characteristics and are larger in size than those in women who have not breast fed.
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Patients and Methods
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Fifty-three women underwent CABG between April 1991 and September 1992 in Gülhane Military Medical Academy. These patients were divided into two groups. Group 1 consisted of 32 women who had breast fed following birth of an average of 2.3 babies with a mean duration of lactation of 16.1 months. The other 21 women who either did not breast feed or had not given birth were assigned to group 2. A third group of 30 male patients was included to serve as a control. Patients undergoing reoperation were excluded from the study. The patient characteristics are shown in Table 1
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All patients underwent standard general anesthesia with fentanyl and pancuronium. A Swan-Ganz catheter was inserted through the right internal jugular vein. The internal mammary artery was dissected on a pedicle including the pleura, extrapleural fat, and surrounding veins, from the subclavian vein to just beyond the bifurcation into the superior epigastric and musculophrenic arteries. Dissection was performed with electrocautery and occlusion of side branches with metal clips. Five to 10 minutes after systemic heparinization, the artery was divided distally and occluded at its tip with a bulldog clamp. Papaverine (50 mg diluted in 15 mL saline) was sprayed onto the mammary artery pedicle that was then wrapped with a gauze swab. Flow was determined by measuring the volume of blood expelled from the end of the freely bleeding artery in a 60-second period just before going on cardiopulmonary bypass. Stable measurements were obtained in all patients. The time of measurement, heart rate, mean arterial pressure, and central venous pressure were measured and recorded simultaneously with IMA flow. In all patients, an intra-arterial probe was used to assess the IMA and vein grafts after anastomosis, to eliminate any technical errors.
All results are expressed as the mean ± standard error of the mean. Results were compared by analysis of variance with subsequent paired comparisons according to Duncan's multiple range test. A p value of less than 0.05 was considered to be statistically significant. Statistical analyses were made using the NWAstatpak (Northwest Analytical, Inc., Portland, OR, USA) statistical software package.
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Results
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There were no significant differences (p > 0.05) between the three groups in terms of body surface area as shown in Table 1
. Mean IMA flow in group 2 was significantly lower than in groups 1 and 3 (Table 2). The mean diameters of the internal mammary arteries were significantly different between groups 1 and 2. Although the mean IMA diameter was slightly larger in group 3 than in group 1, this did not reach statistical significance. Heart rates, mean arterial pressure, and central venous pressure at the time of flow measurement were not significantly different between the groups. Postoperative myocardial infarction occurred in 1 patient in group 1, 4 patients in group 2, and 1 patient in group 3 (p < 0.05). All myocardial infarctions in group-2 patients were located in the anterior segment of the left ventricle and caused by IMA spasm. Two of these patients required intraaortic balloon pump support and both died. One patient in group 1 required intraaortic balloon pump support because of IMA spasm; the hemodynamic situation rapidly resolved after balloon insertion but the patient died on the 16th postoperative day from intracranial hemorrhage due to atriovenous malformation. Postoperative myocardial infarction occurred in 1 patient in group 3 who needed an intraaortic balloon pump but his hemodynamic situation gradually deteriorated and he died. Hospital mortality rates were 3.13% in group 1, 9.52% in group 2, and 3.33% in group 3.
All patients were followed up at 6-month intervals. ST-segment changes, T waves, and new Q wave formations on the electrocardiogram were recorded. The mean follow-up period was 4.5 ± 0.7 years. Two patients in group 3 died from noncardiac disease, 3 patients died in group 2 (1 from noncardiac disease), and 1 patient in group 1 died during the follow-up period. The late postoperative mean angina-free period in group-3 men was comparable with that of the group-1 women (Table 2). Patients in group 2 had a significantly shorter angina-free period (p < 0.05 for group 2 compared to the other groups). Group 3 had a longer follow-up period because most of the patients were operated on in the first 5 months of 1991.
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Discussion
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Several studies have demonstrated that hospital mortality among women undergoing CABG is more than twice that of men.5,6,11,12 The increased mortality has been variously attributed to urgent or emergency CABG, greater technical difficulty (due to small coronary arteries), more severe coronary artery disease, and less use of IMA grafts in women (64.8% versus 78.4% in men).10,11 Sex-related differences in diagnosis and treatment of coronary artery disease have also been reported.15,16 Smaller body size and consequently smaller coronary arteries are known to be risk factors in CABG.17,18 Khan and colleagues9 did not find a significant association between hospital mortality and body surface area and they attributed the sex-related difference in mortality to differences in age and New York Heart Association functional class, although they also noted a lower frequency of IMA grafting in women. The reason for the lower frequency of IMA grafting in women is obscure. However, a study by Suma and colleagues19 indicated that IMA grafting can be successfully undertaken in patients of small body size in whom the IMA graft patency rate is high (95%). Although smaller body surface area and lack of IMA grafting are both associated with increased risk of death from heart failure, the reason for avoiding IMA grafting is usually a small IMA diameter with inadequate flow. The mean free IMA flow was 65.6 mL•min–1 in the study on IMA grafts in small patients.19 Rankin and colleagues20 stated that a free flow rate of more than 100 mL•min–1 is necessary in the left anterior descending artery or sequential grafts and that a narrow IMA with a flow rate of 50 mL•min–1 is acceptable only for smaller coronary arteries.
We used IMA grafts in all patients in this study and found that IMA flow and diameter in women who had breast fed were higher than in other women, and comparable to men of similar body size. During lactation, IMA flow increases and we suggest that IMA regression is incomplete so that IMA diameters and blood flow rates are higher than in women who have not experienced lactation.13,14 The mass of the pectoral muscles may also influence IMA flow rates but we did not address that issue in this study. It was also noted that the wall of the IMA in group-1 women was more suitable for suturing than that of group-2 patients. In the postoperative period, myocardial infarction in the anterior left ventricular area due to IMA spasm occurred in 4 group-2 patients (19%), which was fatal in 2 of them. In contrast, there was only one incidence of cardiac death in each of the other groups (p < 0.05). The angina-free period was longer in the women who had breast fed than in those with no history of lactation, and comparable to that of men.
It was concluded from this study that hospital mortality and the long-term benefit from IMA grafts for CABG in female patients is affected by whether they have breast fed. Those who had breast fed had IMAs with sufficient blood flow for use as sequential grafts, whereas IMA flow in female patients who have not experienced lactation may be inadequate to meet myocardial demands and such grafts are prone to lifethreatening spasm.
Presented at the 7th World Congress of the World Society of Cardio-Thoracic Surgeons, Dusseldorf, Germany, September 2–5, 1997.
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References
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Abstract
Introduction
