- Email: [email protected]
Multicentre Aneurysm Screening Study (MASS)
CORRESPONDENCE
Dink A Legemate Academic Medical Center, University of Amsterdam, PO Box 22700, 1100 DE Amsterdam, Netherlands (e-mail: [email protected]) 1
Scott RAP and The Multicentre Aneurysm Screening Study Group. Multicentre Aneurysm Screening Study (MASS) into the effect of abdominal aortic aneurysm screening on mortality in men: a randomised controlled trial. Lancet 2002; 360: 1531–39. Blankensteijn JD, Lindenburg FP, van der Graaf Y, Eikelboom BC. Influence of study design on reported mortality and morbidity rates after abdominal aortic aneurysm repair. Br J Surg 1998; 85: 1624–30. Lederle FA, Wilson SE, Johnson GR, et al. Immediate repair compared with surveillance of small abdominal aortic aneurysms. N Engl J Med 2002; 346: 1437–44.
2
3
Sir—The UK National Screening Committee emphasises the need to ensure that screening decisions are informed.1 The MASS study provides evidence to inform a decision about ultrasound screening for abdominal aortic aneurysm.2 Patients (or physicians acting on their behalf) must weigh up several different outcomes: some will be told they have an aneurysm but offered no treatment; some will undergo elective surgery. Information on these outcomes is best presented in the form of visual decision aids.3 Absolute rather than relative risks should be presented, since the use of relative risks increases the tendency of lay people to accept screening4 and of physicians to recommend treatment.5 The 53% reduction in aneurysm-related mortality seen in MASS translates into a 0·2% reduction in 4-year risk of death. The figure shows a visual representation of the 4-year outcome of Death from any cause Aortic surgery Aneurysm detected, no action Alive, no further investigation
1000 Number of men affected
900
113
111 4
13
33
800 700 600 500 883
843
400 300 200 100 0 Unscreened
Screened
Visual presentation of 4-year outcomes of screening
screening for abdominal aortic aneurysm. The effectiveness of screening has been adjusted to reflect the experience of those who attended screening, rather than the invited population. Screening 1000 men will prevent two deaths; nine additional men will undergo aortic surgery; 33 will be told that they have an aneurysm but will not be offered surgery; and 111 will die from other causes whether or not they are screened. With information such as this, patients can make an informed decision about participating in screening. Without it we are in danger of manipulating their decisions. Tom Marshall Department of Public Health and Epidemiology, University of Birmingham, Birmingham B15 2TT, UK (e-mail: [email protected]) 1
2
3
4
5
Second Report of the UK National Screening Committee. http://www.doh.gov.uk/ nsc/library/lib_ind.htm (accessed June 21, 2002). Scott RAP and The Multicentre Aneurysm Screening Study Group. Multicentre Aneurysm Screening Study (MASS) into the effect of abdominal aortic aneurysm screening on mortality in men: a randomised controlled trial. Lancet 2002; 360: 1531–39. O’Connor AM, Stacey D, Rovner D, et al. Decision aids for people facing health treatment or screening decisions (Cochrane Review). In: The Cochrane Library, Issue 2. Oxford: Update Software, 2002. Sarfati D, Howden-Chapman P, Woodward A, Salmond C. Does the frame affect the picture? A study into how attitudes to screening for cancer care are affected by the way benefits are expressed. J Med Screening 1998; 5: 137–40. Cranney M, Walley T. Same information, different decisions: the influence of evidence on the management of hypertension in the elderly. Br J Gen Pract 1996; 46: 661–63.
Sir—The MASS Study Group1 report on a group of 33 839 patients invited for ultrasound screening; 1333 abdominal aortic aneurysms (AAAs) were detected, and 321 patients underwent elective surgical repair. We have concerns about some of the data presented for this “invited” group, and feel that more information and clarification of the following points are important. There seem to be 13 potentially avoidable deaths from aneurysm rupture. These occurred before intervention in patients known to have surgical aneurysms—ie, screen-detected AAAs that met the study intervention criteria for elective surgical repair. This occurrence is rare in our experience, but these 13 patients represent 1% of all those with AAA detected in the “invited” group, and 4·3% of all those with AAA that met intervention criteria (291 underwent elective surgery). Were these large or symptomatic aneurysms?
THE LANCET • Vol 361 • March 22, 2003 • www.thelancet.com
The study methods were flawed because detection of AAAs did not trigger automatic surgical assessment, but only notification of the family doctor and “in such instances referral to a vascular surgeon was suggested”. Did any patients die of an inordinately lengthy referral process? What were the time intervals between detecting a surgical aneurysm, surgical review, and scheduled surgery? How did that compare with those who underwent elective surgery? We are aware of instances in our locality where AAA surgery has been postponed on the day of scheduled surgery (and for up to 3 weeks) due to lack of beds in the intensive therapy unit. Was this a factor delaying surgery for any of these cases? A further seven deaths from aneurysm rupture occurred in patients who had “false negative” scans (normal aorta in five, aorta not visualised in two); the aorta was not visualised in 329 (1·2%) of 27 147 patients scanned. Although we accept that lack of visualisation is an occasional problem, AAA rupture within 4 years of a normal ultrasound scan of the aorta is very unusual. What information do the authors have to justify AAA rupture as the terminal event in the five patients who had normal scans at screening? Elective AAA surgery was done in 322 patients; 31 (9·6%) of these had not met the defined study criteria for intervention. We accept that numbers are small, but the mortality rate for that group was 13% versus 4% for the group that met intervention criteria. Why did these patients undergo surgery outside the study criteria? Were they known to be higher risk cases? Their operative mortality undermines the good overall results of the screening programme and criteria-based elective surgery. The above points highlight factors that potentially cause the MASS results to underestimate the benefit of screening with respect to reducing AAA-related mortality. If a national screening programme is to be proposed, we urge that inherent in it should be a fast-track protocol such that, on detection of a surgical aneurysm meeting intervention criteria, the patient is admitted promptly for urgent assessment and surgery, and that adequate bed availability in intensive care is ensured. Mark Tomlinson, Ilyas Arshad, *David Gerrard, Peter Leopold Frimley Park Hospital, Frimley, Camberley GU16 7UJ, UK (e-mail: [email protected]) 1
Scott RAP and the Multicentre Aneurysm Screening Study Group. Multicentre Aneurysm Screening Study (MASS) into the effect of abdominal aortic aneurysm screening on mortality in men: a randomised controlled trial. Lancet 2002; 360: 1531–39.
1057
For personal use. Only reproduce with permission from The Lancet Publishing Group.
Dink A Legemate Academic Medical Center, University of Amsterdam, PO Box 22700, 1100 DE Amsterdam, Netherlands (e-mail: [email protected]) 1
Scott RAP and The Multicentre Aneurysm Screening Study Group. Multicentre Aneurysm Screening Study (MASS) into the effect of abdominal aortic aneurysm screening on mortality in men: a randomised controlled trial. Lancet 2002; 360: 1531–39. Blankensteijn JD, Lindenburg FP, van der Graaf Y, Eikelboom BC. Influence of study design on reported mortality and morbidity rates after abdominal aortic aneurysm repair. Br J Surg 1998; 85: 1624–30. Lederle FA, Wilson SE, Johnson GR, et al. Immediate repair compared with surveillance of small abdominal aortic aneurysms. N Engl J Med 2002; 346: 1437–44.
2
3
Sir—The UK National Screening Committee emphasises the need to ensure that screening decisions are informed.1 The MASS study provides evidence to inform a decision about ultrasound screening for abdominal aortic aneurysm.2 Patients (or physicians acting on their behalf) must weigh up several different outcomes: some will be told they have an aneurysm but offered no treatment; some will undergo elective surgery. Information on these outcomes is best presented in the form of visual decision aids.3 Absolute rather than relative risks should be presented, since the use of relative risks increases the tendency of lay people to accept screening4 and of physicians to recommend treatment.5 The 53% reduction in aneurysm-related mortality seen in MASS translates into a 0·2% reduction in 4-year risk of death. The figure shows a visual representation of the 4-year outcome of Death from any cause Aortic surgery Aneurysm detected, no action Alive, no further investigation
1000 Number of men affected
900
113
111 4
13
33
800 700 600 500 883
843
400 300 200 100 0 Unscreened
Screened
Visual presentation of 4-year outcomes of screening
screening for abdominal aortic aneurysm. The effectiveness of screening has been adjusted to reflect the experience of those who attended screening, rather than the invited population. Screening 1000 men will prevent two deaths; nine additional men will undergo aortic surgery; 33 will be told that they have an aneurysm but will not be offered surgery; and 111 will die from other causes whether or not they are screened. With information such as this, patients can make an informed decision about participating in screening. Without it we are in danger of manipulating their decisions. Tom Marshall Department of Public Health and Epidemiology, University of Birmingham, Birmingham B15 2TT, UK (e-mail: [email protected]) 1
2
3
4
5
Second Report of the UK National Screening Committee. http://www.doh.gov.uk/ nsc/library/lib_ind.htm (accessed June 21, 2002). Scott RAP and The Multicentre Aneurysm Screening Study Group. Multicentre Aneurysm Screening Study (MASS) into the effect of abdominal aortic aneurysm screening on mortality in men: a randomised controlled trial. Lancet 2002; 360: 1531–39. O’Connor AM, Stacey D, Rovner D, et al. Decision aids for people facing health treatment or screening decisions (Cochrane Review). In: The Cochrane Library, Issue 2. Oxford: Update Software, 2002. Sarfati D, Howden-Chapman P, Woodward A, Salmond C. Does the frame affect the picture? A study into how attitudes to screening for cancer care are affected by the way benefits are expressed. J Med Screening 1998; 5: 137–40. Cranney M, Walley T. Same information, different decisions: the influence of evidence on the management of hypertension in the elderly. Br J Gen Pract 1996; 46: 661–63.
Sir—The MASS Study Group1 report on a group of 33 839 patients invited for ultrasound screening; 1333 abdominal aortic aneurysms (AAAs) were detected, and 321 patients underwent elective surgical repair. We have concerns about some of the data presented for this “invited” group, and feel that more information and clarification of the following points are important. There seem to be 13 potentially avoidable deaths from aneurysm rupture. These occurred before intervention in patients known to have surgical aneurysms—ie, screen-detected AAAs that met the study intervention criteria for elective surgical repair. This occurrence is rare in our experience, but these 13 patients represent 1% of all those with AAA detected in the “invited” group, and 4·3% of all those with AAA that met intervention criteria (291 underwent elective surgery). Were these large or symptomatic aneurysms?
THE LANCET • Vol 361 • March 22, 2003 • www.thelancet.com
The study methods were flawed because detection of AAAs did not trigger automatic surgical assessment, but only notification of the family doctor and “in such instances referral to a vascular surgeon was suggested”. Did any patients die of an inordinately lengthy referral process? What were the time intervals between detecting a surgical aneurysm, surgical review, and scheduled surgery? How did that compare with those who underwent elective surgery? We are aware of instances in our locality where AAA surgery has been postponed on the day of scheduled surgery (and for up to 3 weeks) due to lack of beds in the intensive therapy unit. Was this a factor delaying surgery for any of these cases? A further seven deaths from aneurysm rupture occurred in patients who had “false negative” scans (normal aorta in five, aorta not visualised in two); the aorta was not visualised in 329 (1·2%) of 27 147 patients scanned. Although we accept that lack of visualisation is an occasional problem, AAA rupture within 4 years of a normal ultrasound scan of the aorta is very unusual. What information do the authors have to justify AAA rupture as the terminal event in the five patients who had normal scans at screening? Elective AAA surgery was done in 322 patients; 31 (9·6%) of these had not met the defined study criteria for intervention. We accept that numbers are small, but the mortality rate for that group was 13% versus 4% for the group that met intervention criteria. Why did these patients undergo surgery outside the study criteria? Were they known to be higher risk cases? Their operative mortality undermines the good overall results of the screening programme and criteria-based elective surgery. The above points highlight factors that potentially cause the MASS results to underestimate the benefit of screening with respect to reducing AAA-related mortality. If a national screening programme is to be proposed, we urge that inherent in it should be a fast-track protocol such that, on detection of a surgical aneurysm meeting intervention criteria, the patient is admitted promptly for urgent assessment and surgery, and that adequate bed availability in intensive care is ensured. Mark Tomlinson, Ilyas Arshad, *David Gerrard, Peter Leopold Frimley Park Hospital, Frimley, Camberley GU16 7UJ, UK (e-mail: [email protected]) 1
Scott RAP and the Multicentre Aneurysm Screening Study Group. Multicentre Aneurysm Screening Study (MASS) into the effect of abdominal aortic aneurysm screening on mortality in men: a randomised controlled trial. Lancet 2002; 360: 1531–39.
1057
For personal use. Only reproduce with permission from The Lancet Publishing Group.