Eur J Cardiothorac Surg 2006;29:492-495
© 2006 Elsevier Science NL
Coronary artery size and disease in UK South Asian and Caucasian men
Dlear Zindrou
a
,
b
,
Kenneth M. Taylor
a
,
b
,
Jens Peder Bagger
a
,
b
,
*
a Imperial College London, Hammersmith Hospital, Du Cane Road, London W12 0NN, United Kingdom
b Cardiothoracic Directorate, Hammersmith Hospital, Du Cane Road, London W12 0NN, United Kingdom
Received 17 October 2005;
received in revised form 23 December 2005;
accepted 9 January 2006.
* Corresponding author. Address: Cardiothoracic Directorate, Hammersmith Hospital, Du Cane Road, London W12 0NN, United Kingdom. Tel.: +44 208 383 3171; fax: +44 208 740 8373. (Email: p.bagger{at}imperial.ac.uk).
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Abstract
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Objective: South Asian patients in the UK have a higher mortality rate after coronary artery bypass grafting (CABG) than Caucasian patients. As coronary artery size has been shown to correlate to outcome from bypass grafting, it has been suggested that smaller coronary arteries in South Asians as compared to Caucasians could contribute to a poorer outcome in the Asian population. We aimed to measure coronary artery size and disease in matched South Asian and Caucasian men undergoing first time coronary artery bypass grafting. Methods: Coronary arteriograms from 53 matched first generation South Asian and Caucasian men were examined. The patients had no history of myocardial infarction, coronary revascularisation, familial dyslipidaemia, diabetes or renal disease. They were individually matched for age, height, weight, body mass index and body surface area. Thereafter, coronary artery diameters and significant (
50%) diameter stenoses were measured in a blinded fashion using quantitative coronary angiography (QCA). Results: In South Asian men, diameters of the left main stem (LMS) and the proximal left anterior descending, the circumflex and the right coronary arteries were 4.6 ± 0.9 mm, 3.5 ± 0.8 mm, 3.4 ± 0.8 mm and 3.5 ± 0.8 mm, respectively. The corresponding arterial diameters among Caucasian men (4.5 ± 0.9 mm, 3.5 ± 0.7 mm, 3.5 ± 0.8 mm and 3.8±0.8 mm) did not differ from those in South Asians. There was no difference in the number of significant coronary artery stenoses between the two groups and no difference in bypass and cross-clamp times or in adverse outcome (one from each group died after coronary artery bypass grafting). Conclusion: Proximal coronary artery size and number of significant coronary stenoses did not differ between matched pairs of South Asian and Caucasian men using strict inclusion/exclusion criteria.
Key Words: Coronary artery disease • Coronary artery diameter • South Asian • Caucasian
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1. Introduction
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South Asian patients in the United Kingdom (UK) have a higher mortality rate from coronary heart disease (CAD) than Caucasian patients [1–3]. We have, furthermore, reported a significantly higher coronary artery bypass grafting (CABG) mortality rate in South Asians as compared to Caucasians in the UK [4]. Our findings could not be fully explained by traditional risk factors. In this respect, it has been suggested that South Asian patients have smaller coronary arteries than Caucasian patients which could contribute to a poorer outcome in the South Asian population [5]. Thus, it has been reported that coronary artery size correlates to outcome from coronary revascularisations [6–8].
The objective of the present study was to compare coronary artery size and disease of matched South Asian and Caucasian male patients.
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2. Materials and methods
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2.1 Patients
From an existing database of 447 first generation UK South Asian patients who underwent CABG between January 1, 1993 and December 31, 1997, we excluded women (n
= 86), patients with a history of myocardial infarction (n
= 258), diabetes mellitus (n
= 190), impaired renal function (n
= 30), re-operation (n
= 11) or previous coronary angioplasty (n
= 47); some of the patients had more than one of these variables. None of the patients had familial dyslipidaemia. The remaining patients constituted a group of 85 South Asian men. We attempted to match these patients individually with white men (with identical exclusion criteria), from the same database, who underwent a diagnostic coronary angiography in the same week as the respective Asian match. We did the best match between patients from the two groups with respect to age, height, weight, body mass index and body surface area. Only, thereafter, the diagnostic angiograms were analysed with the examiner being blinded to the identity and sequence of patients.
2.2 Quantitative coronary angiography (QCA)
Cine-film angiograms were inspected and subsequent optimal frames were digitised on an optimally calibrated cine-video converter (Cap 35E-II, Nishimoto, Japan) for QCA. Calibrations were made in relation to the contrast filled angiography catheter diameter at the centre of the cine frame. Artery size and lesions were quantified by fully automated edge detection technique based on the least-cost minimization of the sum of the first and second derivatives of the vessel edge (Medis Medical Imaging Systems, Leiden, The Netherlands). Precision for same frame repeated measurements was less than 0.1 mm. Six French size Cordis diagnostic catheters were used in all procedures. The standard 15 coronary segments were studied [9]. Measurements of artery size were done on the most proximal disease-free part of each segment. In this respect, diffusely diseased or occluded segments were excluded in the analysis, as were similar segments in the matched patient. Readings were made in three views at end-diastolic cine-frames. The mean of the readings of each segment was used for comparison. Total coronary artery diameter was calculated as the sum of the diameters of the left main stem (LMS) and the proximal right coronary artery (RCA) or the sum of the proximal diameters of the left anterior descending artery (LAD), the circumflex artery (CX) and the RCA.
The number and severity of stenoses were measured and recorded. For the purpose of simplicity, we used two groups of stenosis severity (<50% and 50% diameter stenosis). According to the notes, no patient took nitrates before the coronary angiography and nitrates were not administrated to the patients during the procedure.
2.3 Statistics
Two-tailed Student's t-test, Mann–Whitney test and chi-square tests were used for comparison of variables. A P value <0.05 was regarded as significant.
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3. Results
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3.1 Clinical characteristics
Following our exclusion/inclusion criteria it was possible to match 53 pairs of male patients. Demographic and clinical data are shown in Table 1
.
The two ethnic groups differed only with respect to smoking and lipid-lowering treatment.
3.2 Quantitative coronary angiography
The two patient groups had similar pattern of coronary artery dominance. The mean diameters of the LMS, the LAD, the CX and the proximal RCA did not differ between the two groups (Table 2
). Furthermore, the combined coronary artery size, by adding the diameter of the LMS to the proximal diameter of RCA, or by adding the proximal diameters of the LAD, the CX and the RCA did not differ between the two groups. The mid- and distal segments of the RCA were significantly smaller in South Asians than in Caucasians. There were no interethnic differences in the number of significant stenoses in all coronary artery segments (Table 3
). Although the number of insignificant stenoses in the distal LAD and in segment-3 of the RCA differed in opposite directions in the two ethnic groups, there were no overall differences with respect to insignificant stenoses between the groups.
3.3 Operative characteristics
There was no difference in Parsonnet risk score (7.8 ± 3.8 vs 6.9 + 3.0, P
= 0.2) between South Asians and Caucasians, and three patients in each group had emergent operative priority. South Asian and Caucasian patients had similar bypass times (79 ± 27 min vs 78 ± 24 min, P
= 0.9), and cross-clamp times (44 ± 16 min vs 41 ± 15 min, P
= 0.5). Fifty-two patients in each group received an internal mammary artery conduit (P
= 1.0). There was no difference in the postoperative need for vasodilators, ionotropic drugs or intra aortic balloon pump treatment between the two groups (P
= 0.08). One patient in each ethnic group suffered a perioperative myocardial infarction, and one patient from each group died while hospitalised.
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4. Discussion
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We found no significant differences in the size of the proximal coronary arteries or in the number of significant stenoses between South Asian and Caucasian men with comparable clinical characteristics and demography. This was reflected in the fact that there was no significant difference in bypass time and cross-clamp time between South Asian and Caucasian men during CABG, and no difference in adverse outcome between the two groups.
We excluded patients with familial dyslipidaemia, diabetes and renal impairment, diseases that are known to influence the extent of CAD [10,11]. Patients with previous myocardial infarction were excluded as coronary arteries may unpredictably differ in size dependent on whether they supply viable or non-viable myocardium. Women were excluded due to the relatively small number of Asian women having had an angiogram during the study period and because women have been reported to have smaller coronary artery diameters than men even after correcting for body surface area [12,13]. Hypertension is not likely to influence coronary artery size and was not adjusted for [14]. Furthermore, we did not attempt to match the groups according to patients being active smokers, ex-smokers or if they had been exposed to passive smoking.
Although many investigators have attempted to measure coronary artery size [12,15–17], few have compared coronary anatomy between ethnic groups. In a postmortem study, Sahni and Jit [5] examined the hearts from 500 Northwest Indians. They found the mean diameter of the ostium of the RCA of about 3.6 mm and the LMS ostium of 4.0 mm in males of the same age as in our study. They also recorded a correlation between heart size and the size of the coronary artery diameters, which again related to body weight and height, and therefore assumed that Northwest Indians are likely to have smaller coronary arteries than Caucasians as they are shorter and weigh less. They also highlighted a steady increase of coronary artery size with age until the age of 65. These results were obtained in postmortem cadaver samples using special cones and plastic tubes to measure coronary artery size. This method is a reliable way of measuring artery size, but the results do not necessarily correlate to in vivo findings [15–17]. Dhawan and Bray [18] compared coronary angiograms from a consecutive series of Asian males with those from randomly selected Caucasian males and found a smaller mean total coronary artery diameter in the Asian group than in the Caucasian cohort. They also demonstrated a correlation between body surface area and coronary artery size. When they adjusted total coronary artery diameter for body surface area the interethnic difference in coronary artery size between South Asian and Caucasian patients was neutralised. Budoff et al. [19] compared diagnostic angiograms from different ethnic groups of whom 69% were men in the USA and concluded that whites (n
= 453) and Asian–Americans (n
= 44) had a significantly higher prevalence of coronary artery obstructions than blacks and Hispanics. There was no significant difference in the prevalence of significant CAD between whites and Asians. In these studies, coronary artery anatomy from random groups of Asian and Caucasian patients were compared and findings were adjusted for by post hoc analysis.
In the present study, we measured both coronary artery size and extent of CAD in matched pairs of South Asian and Caucasian males living in the UK and excluded diseases and conditions known to influence the degree of CAD. We used QCA and took great care to minimise possible sources of error. Although we compared all 15 coronary segments, we made our measurements as close to the centre of the cine frame as possible to avoid pincushion distortion at the periphery of the frame [20]. For this reason, we put most weight on measurements of the size of the proximal segments of the three main coronary arteries. A LMS diameter of 4.5 mm and proximal/distal LAD diameters of 3.7 and 1.9 mm, respectively, as reported by Dodge et al. [12] in 83 patients (88% men) are similar to our measurements in both ethnic groups. Depending on anatomic dominance, Dodge et al. [12] found RCA diameters ranging from 2.8 to 3.9 mm and Cx diameters from 3.4 to 4.2 mm.
Coronary artery size has impact on treatment options and outcome such as attachment of grafts during CABG (smaller arteries causing anastomotic technical difficulties and poor run-off) as well as difficulties during balloon angioplasty and stenting. Smaller body surface area (and thereby smaller coronary artery size) was associated with increased risk of in-hospital death from heart failure after CABG [6]. Furthermore, small target vessel size is associated with an increased risk of restenosis and repeat revascularisation [7,8].
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5. Limitations
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Although matching took place before the blinded viewing of the angiograms, this was essentially a retrospective study. We did not record the angiographic catheter tip before each contrast injection and the catheter tips were not available for correction of measurements in the individual case but we at least used the same type of diagnostic catheter. Using different types of diagnostic catheters is an important source of error [21]. Although we did not inject intracoronary nitrate before angiography, the number of patients on long-acting nitrates did not differ between groups (Table 1) and none of the patients received short-acting nitrates immediately before or during the diagnostic angiography.
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6. Conclusion
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South Asian and Caucasian men with comparable demographic and clinical characteristics have angiographically similar proximal coronary artery size and severity of CAD. This finding refutes any suggestion that South Asian patients have smaller coronary arteries per se. For more accurate measurements of coronary artery size (three-dimensional) and pattern and severity of CAD (plaque volume and characteristics), the use of other modalities such as intracoronary ultrasound [13], cine computed tomography or nuclear magnetic resonance imaging is essential.
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Abstract
1. Introduction
