Carotid Bifurcation Atherosclerosis in the Over-65s: a Prevalence Study

Written By: Sam Savage

Published Date: June 25, 2008 Last Edited: June 25, 2008

By Vallina-Victorero, M Vaquero, F; Alvarez, A; Ramos, M J; Vicente, M; Alvarez, J

Aim. The aim of this study was to determine the prevalence of carotid stenosis (CS) in the over-65 population segment residing in a catchment area (Gijon) served by the Asturias Health Service (Spain) as a necessary step in planning medical care for treating cerebrovascular disease in the elderly. Methods. In this descriptive transversal study, 232 subjects (114 men and 118 women) randomly chosen from health card data underwent colour-flow duplex scanning of the supra-aortic trunks.

Results. The prevalence of CS in this sample was 21.5%. When stratified by sex and age (65-74 and >75 years of age), the CS rate was 5 points higher in the older than in the younger group, and 4 points higher among males (23.6%) than among females (19.2%).

Conclusion. Approximately one in every 5 subjects over 65 years of age presents with CS; CS prevalence was higher in the over-75s and among males, although the differences were not statistically significant.

KEY WORDS: Atherosclerosis – Carotid arteries – Prevalence – Risk factors – Ultrasonography.

On Stroke Day, held in Spain in November 2006, Dr. Sabin, the coordinator of the Cerebrovascular Disorders Study Group of the Spanish Neurology Society, disclosed recent stroke statistics for the Spanish population: one stroke-related death occurs every 14 minutes; 26% of stroke victims die within 6 months of the first episode; 120 000 cases are reported every year, 20% of which die after the first stroke and 34.7% after the second attack (around 80 000 deaths in all); 39% of those who suffer a second stroke risk loss of functional dependence; one in every 10 deaths in Spain is caused by a stroke, ranking it the second cause of death in the country and the first among women; as the population ages, the number of people who will suffer their first stroke is estimated to increase by 30% over the coming 15 years.

Equally alarming is the general epidemiological trend: 700 000 strokes per year,1 with 165 000 deaths in the United States alone2 where it is now the third cause of death1 and the second worldwide.2 It is estimated that approximately 20% of strokes are due to carotid disease.

According to the Transatlantic Inter-Society Consensus (TASC) study, around half of patients with peripheral arteriopathy have a heart complaint that can be detected by means of simple tests.3 While the proportion of demonstrable cerebrovascular disease is much lower,4-7 Dormandy et al.8 report that over 60% of persons with claudication present some evidence of cerebrovascular disease. Between 12.5 and 60.5% of patients with intermittent claudication were found to have carotid disease at duplex ultrasonography, 9-18 Studies on the general population have reported an even wider prevalence of carotid disease (7.9-82.5%), 1926 depending on the age groups evaluated.

The aim of this study was to determine the prevalence of carotid stenosis (CS) in persons over 65 years of age residing in Gijon (Spain), as an essential step to planning medical care for treating cerebrovascular diseases in the elderly.

Materials and methods

A descriptive transversal study was carried out in a health services catchment area with a population of around 300 000 inhabitants, of which 64 133 are aged over 65 years. The sample size was calculated (EPIDAT 3.1 software package) for finite populations to define an expected prevalence of 7.5% with a precision of +-3% at the 95% confidence level. The result obtained was 295 individuals.

Three hundred men and women over 65 years of age were then randomly chosen from individual health card data. Written informed consent was obtained from all subjects.

Data were collected from January through March 2006 by means of interviews investigating the subjects’ medical history in relation to age, cardiovascular risk factors (smoker, ex-smoker, high blood pressure, diabetes, cholesterol), episodes of prior illness and treatments received. Obesity was classified according to the Body Mass Index (BMI) or the Quetelet Index.

Blood chemistry laboratory determinations included renal and hepatic function, glucose, total cholesterol and fractions, triglycerides, sodium and potassium ions, c-reactive protein (CRP) and homocysteine tests.

Elevated arterial blood pressure was defined as >140 mm Hg systolic pressure and >90 mm Hg diastolic pressure.

Colour-flow duplex scanning of the supra-aortic trunks was carried out (Toshiba Aplio Model SSA70OA Colour Doppler ECHO System) to determine the possible presence of carotid stenosis (CS). Stenosis severity was classified as: grade I (0-20% reduction in diameter – normal calibre or slight stenosis); grade II (21-50% reduction – moderate stenosis); grade III (SI70% reduction – significant stenosis); grade FV (71-99% reduction – severe-critical stenosis; grade V (occlusion).

Spectral parameters for stenosis grade evaluation were standardized according to diagnostic criteria validated for the vascular laboratory of Cabuenes Hospital Vascular Surgery Service. Grade I was defined as a maximum systolic velocity (MSV) 120 cm/s with a final diastolic velocity (FDV) 200 cm/s, with the stenosis considered critical when FDV was >130 cm/s); grade V was the absence of the wave. Stenosis grades II, III, IV and V were analyzed for the purposes of this study.

Statistical analysis

The data were entered on an Excel spreadsheet and processed using the SPSS-10 statistical software package. Univariate and bivariate descriptive analysis of the variables was carried out to calculate frequencies and means. Confidence intervals were calculated for a confidence level of 95%. The chi^sup 2^ test with correction for continuity and Fisher’s exact test were applied. Student’s t-test and analysis of variance were used to compare the means. Stratified analysis and control for possible confounding factors between the different risk factors and CS were performed using logistic regression analysis for descriptive purposes, constructing a model that included the different risk factors and the disease under study. Given the purely descriptive nature of this study, no procedure was employed in the selection of variables.

Results

The study population was 232 subjects (114 males and 118 females; average age 74.1 years, range 65-96) and constituted 78.6% of the initially calculated sample. The prevalence of CS was 21.5% (confidence interval [CI] 16.04-27.05). The sample was subdivided into two age groups: 135 (58.2%) subjects aged 65-74 years and 97 (41.8%) aged over 75 years.

The prevalence of CS was higher in the older group, although this difference was not statistically significant (P=0.3). The CS rate in the 65-74 age group was 19.2% (CI 12.2-26.2) versus 24.7% (CI 15.6- 33.8) in the older group and was higher among the men than the women, but here, too, this difference was not statistically significant (23.6% [CI 15.4-31.91 versus 19.4% [CI 11.9-27]; P=0.4). Table I lists CS prevalence by grade of severity.

The prevalence of CS in symptomatic and asymptomatic patients was 6% (CI 1.2-16.5) and 94% (CI 83.4-98.7), respectively; carotid disease was unilateral in 38% (CI 23.5-52.4) and bilateral in 62% (CI 47.576.4).

Table II summarises the risk factors and concomitant conditions in the subject sample. The average number of vascular risk factors presented by a patient with CS was 1.2 per subject versus an average of 1 in those without the disease. The difference was not statistically significant (P=0.09).

TABLE I.-Prevalence of carotid stenosis by different grades of severity (95% CI).

TABLE II.-Prevalence of cardiovascular risk factors and other conditions (95%CI).

TABLE III.-Blood chemistry values vs case history data.

TABLE IV.-Percent of subjects who referred taking a prescription drug.

In our sample, 25% of the smokers were found to have CS, 27.6% also had hypertension, 40% had insulindependent diabetes mellitus (IDDM), 25.8% had noninsulin dependent diabetes (NIDDM) and 20.7% had elevated cholesterol levels. Logical regression analysis of the relationship between CS and the risk factors for atherosclerosis showed a statistically significant association only with arterial hypertension (P=0.03). The estimated risk of suffering from CS was 2.1 times higher in patients with hypertension, 1.9 times in those with IDDM, and 2.4 times in those with diagnosed chronic lower limb ischemia. In contrast, this risk was not found to increase in patients with high cholesterol levels (odds ratio [OR] = 0.9). Table III lists the blood pressure values and blood chemistry parameters.

The prevalence of other disorders was also noted: obesity (55.7%), chronic renal insufficiency (CRI) (3.4%), chronic obstructive pulmonary disease (COPD) (10.3%), ischemic cardiopathy (IC) (16.8%), auricular fibrillation (CaxAF) (6.9%), cerebrovascular insufficiency (CVI) (7.8%) and deep vein thrombosis (DVT) (2.2%).

Approximately 76% of subjects referred using prescription drugs: 22.4% regularly took an antiaggregant and 22.8% a lipid-lowering agent (statins 21.1%)(Table IV).

Discussion and conclusions

The over-65 age segment accounts for nearly 21.4% of the general population and makes up a large proportion of patients with vascular diseases. In this sample, the prevalence of carotid stenosis (CS) was high, affecting approximately one in every 5 subjects. However, as O’Leary et al.23 underline, the frequency of severe disease is low. Compared with other studies on the general population, our data (7.8% prevalence of CS ?50% in both men and women) are in line with those reported in other studies: O’Leary et al.,23 CS >50% in 7% of men and in 6% of women; Ramsey et al.19 7% of CS >50%; Toshifumi et al,26CS >50% in 7.9% of men aged 50-79 years. Our rates are slightly higher than those given by Josse et al.,21 (CS >50% in 6.1% of men aged 75-89 years) and higher still than those reported by Colgan et al.,20 5% prevalence of CS >50%, probably because of the extremely wide age range (24-91 years) since it included younger subjects who contributed to lowering the overall CS prevalence. This might be the same reason why Prati et al.22 found a CS prevalence of 2.7% in men and 1.5% in women (age range 18-79 years). Bonithon-Kopp et al.,25 however, pointed out that there are very few longitudinal studies on early atherosclerotic lesions in the general population.

The high percentage of subjects with asymptomatic CS is noteworthy. Early detection of CS through programmes targeting people presenting with certain risk factors or associated illnesses could be one way to develop prophylactic strategies, including medical treatments. Detection of severe CS would permit prompt conventional or endovascular surgical treatment as recommended by scientific societies guidelines.

Studies on patients with peripheral arterial disease or cardiac ischemia obtained higher prevalence figures due to the multifocality of this disease. Published data report a CS prevalence ?30% (range 210 -60.57%.12, 15, 27 In studies on CS ?50% the rates range between 14% and 33%,13, 14, 16, 17 and between 12.5% and 14.9% in CS ?700 – 75%.11, 18All these studies included patients with peripheral arterial disease, except for Rajamani et al.,27 who refered to Afro- American patients with cardiac ischemic disease. Klopp et al.,11 Marek et al.13 and Kurvers et al.18 reported that the high prevalence of CS in peripheral arterial disease suggests the need for ultrasound screening of these patients to detect high grade stenosis. However, Cina et al.17 state that, while justifiable, such imaging studies are not mandatory. It should be remembered that in our sample the risk of suffering from CS was 2.4 times higher for patients diagnosed with peripheral arterial disease, although this association was not statistically significant.

As regards risk factors, in our sample there was a low prevalence of smokers, a high prevalence of exsmokers, as well as patients with high blood pressure and elevated hypercholesterolemia. The prevalence of MDDM was also high, though less so. The figures for smokers and ex-smokers could be explained by the presence of a concomitant illness that had forced them to stop smoking. Related studies conducted in Spain report similarly low prevalence rates for smokers.28,29

Analysis of the number of subjects with altered blood chemistry values shows that diabetes, hypertriglyceridemia and, above all, chronic renal insufficiency may be underdiagnosed (a bias could have been introduced by subjects not having correctly followed instructions not to eat before blood sample drawing, etc.), while hypercholesterolemia was correctly identified. The prevalence of increased homocysteine is not considered representative because this test was performed in only 22 patients owing to laboratory problems (Table III).

Approximately three in every four patients (75.9%) receive some kind of medical treatment. Besides hypercholesterolemia, the prevalence of ischemic cardiopathy and cerebrovascular insufficiency is noteworthy-all pathologies for which statins are given prophylactically-suggesting that this group of drugs is used less than advisable. These figures cannot be correlated with those published in the REACH study (31), in which the sample was composed of patients already diagnosed with an arterial disease (coronary, cerebrovascular or peripheral), which increases the percent of subjects taking these drugs.

Recruiting patients was the most laborious phase of the study because of their elevated age, which imposes physical limitations, and because of a lack of health education. A percentage loss

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M. VALLINA-VICTORERO, F. VAQUERO, A. ALVAREZ, M. J. RAMOS, M. VICENTE, J. ALVAREZ

Section ofAngiology

Vascular and Endovascular Surgery

Hospital de Cabuenes, Gijon, Spain

Fundings -The authors are grateful to the Asturian Society of Angiology, Vascular and Endovascular Surgery for funding this study.

Received on October 9, 2007.

Accepted for publication on February 8, 2008.

Address reprint requests to: M. Javier Vallina-Victorero Vazquez, Servicio de A. y Cirugia Vascular, Hospital de Cabuenes, Cabuenes s/ n 33394, Gijon, Asturias, Spain. E-mail: [email protected]

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