Cardiovascular screening or comic opera?
Janet T Powell
Imperial College London
Screening programmes fail their participants when the quality control systems are not robust and population screening programmes, particularly for breast and cervical cancer have failed their participants because of lapses in quality control [1]. Screening programmes for cancer are more widespread than screening programmes for vascular disease. Sweden and the United Kingdom are the only countries to have national screening programmes for abdominal aortic aneurysm, although screening for hypertension by family practitioners is mandatory in many countries. The purpose of screening is to detect a disease early so that the course of the disease can be mitigated; therefore there must be an effective treatment for example prophylactic abdominal aortic aneurysm repair to prevent the disastrous event of rupture. So what are the prospects for screening programmes for other vascular disorders including carotid stenosis and peripheral arterial disease?
In this issue of the journal Kvist et al report their experience of a multifaceted research screening programme for subclinical vascular disease, centred around a CT scan to assess arterial calcification [2]. Their aim is to develop a screening programme which, in due course, will conform to WHO and other established screening criteria [3]. These criteria include recognition that preclinical vascular disease (the condition) is an important health problem, an effective intervention exists and there is evidence that treatment of the pre-symptomatic phase leads to improved outcomes compared with the treatment of the symptomatic phase. In addition, the screening tests should be simple, safe, precise, validated and acceptable to the population. Moreover, the distribution in the sample population should be known, with well-defined and agreed thresholds.
In the pilot study from DANCAVAS [2], several of the screening tests used do not meet these standards. Screening was in 4 parts at 10 minute intervals: consent and interview, CT scan, ankle and brachial pressure measurements and phlebotomy. The health questionnaire was created for this project, without any evidence of its reliability and validation. The aortic measurements taken from the CT scan are not reported to the expected standards [4] and the distribution of coronary artery calcification in the relevant Danish population is not provided. Blood pressures are measured after the CT scan without an adequate rest period and the thresholds used to define the presence of hypertension in this situation (systolic >160 and diastolic >100 Hg) have not been validated or agreed in any consensus guidelines. Only the measurement of serum cholesterol and glycosylated haemoglobin appear to be subject to satisfactory quality control but the threshold used to define hypercholesterolaemia appears to be very high at 8 mmol/l, higher than the 7 mmol/l used elsewhere in Denmark [5]: if there is no national agreement for treatment thresholds how can there be international agreement? Of the 12 cases of unknown atrial fibrillation picked up with the CT scan, only 10 were confirmed: screening is expected to have a much lower rate of false positive detection, since false-positive diagnoses may cause harm.
There is little evidence of an effective treatment for pre-symptomatic peripheral arterial disease (other than perhaps smoking cessation and treatment of hyperlipidaemia). In contrast, there is good evidence that the treatment of high grade asymptomatic carotid artery stenosis is associated with improved outcomes [6]. However, the DANCAVAS screening programme appears to ignore carotid artery disease.
Despite these criticisms, the authors should be congratulated for showing the feasibility of screening in an ambitious research programme. The DANVACAS screening programme is an important research tool but if this vascular surgical research is not to be regarded as a comic opera [7], the programme of research now needs to develop a crucial quality control framework, and develop a consensus with other cardiovascular disciplines for agreed thresholds for their screening tests.
References
1Miller AB. Failures of cervical cancer screening. Am J Pub Health 1995;85:761-2
2Kvist TV, Lindholt JS, Rasmussen LM, Sogaard R, Lambrechtsten J, Steffensen FH et al. The DanCavas pilot study of multifaceted screening for subclinical cardiovascular disease in men and women aged 65-74 years. Eur J VascEndovascSurg 2016 (in press)
3Public Health England. Criteria for appraising the viability, effectiveness & appropriateness of a screening programme, updated 23rd October 2015. (accessed 28th October 2016)
4Long A, Rouet L, Lindholt JS, Allaire E. Measuring the maximum diameter of native abdominal aortic aneurysms: review and critical analysis. Eur J VascEndovasc Surg. 2012;43:515-24.
5Kanstrup H, Refsgaard J, Engberg M, Lassen JF, Larsen ML, Lauritzen T.Cholesterol reduction following health screening in general practice. Scand J Prim Health Care 2002;20:219-23
6Halliday A, Harrison M, Hayter E, Kong X, Mansfield A, Marro J et al. 10-year stroke prevention after successful carotid endarterectomy for asymptomatic stenosis (ACST-1): a multicentre randomised trial. Lancet 2010;376:1074-84
7Horton R. Surgical research or comic opera: questions but few answers. Lancet 1996;347:984-5