Jump to: Page Content, Site Navigation, Site Search,
You are seeing this message because your web browser does not support basic web standards. Find out more about why this message is appearing and what you can do to make your experience on this site better.
Raj Padwal a Division of
General Internal Medicine, University of Alberta, Edmonton, AL, Canada
T6G 2R7, b Division of General Internal Medicine, Mount Sinai Hospital,
Toronto, ON, Canada M5G 1XS
Correspondence to: F A McAlister
Finlay.McAlister{at}ualberta.ca
Blood pressure, like any physiological variable, is
normally distributed in the population. Not surprisingly, expert bodies disagree substantially on the definition of hypertension
Relative risk
of the 27 national hypertension societies represented at the 17th world conference of the Hypertension League Council held in Montreal in 1997, 14 use 140/90 mm Hg to diagnose hypertension and 13 use 160/95 mm
Hg.1
Summary points
There is a continuous, strong, and graded relation between blood
pressure and cardiovascular disease, but no clear threshold value
separates hypertensive patients who will experience future
cardiovascular events from those who will not
Risk of cardiovascular disease depends on blood pressure, coexistent
risk factors, and whether there is hypertensive damage to target organs
Numerous factors definitely increase cardiovascular risk, including
age, male sex, family history, raised cholesterol, smoking, diabetes
mellitus, obesity, sedentary lifestyle, and left ventricular
hypertrophy
Models can be used to predict an individual's risk of cardiovascular
disease to define the expected benefits and harms of treatment
![]()
Hypertension and cardiovascular risk
Top
Hypertension and cardiovascular...
Other risk factors affecting...
Conclusion
References
Most population based studies confirm that hypertension increases
an individual's risk of various cardiovascular consequences
approximately two to three times (figure). Large population based
cohort studies consistently show continuous, strong, and graded
relations between blood pressure (particularly systolic pressure) and
the subsequent occurrence of various atherosclerotic events.
2 3
The sizes of the relative risks reported in
each study depend on the duration of follow up and the definition of hypertension in use.4 These relative risks are consistent
across all settings5 and for all patient subgroups,
including those with and without known atherosclerotic
disease.6

View larger version (20K):
[in a new window]
Risk of atherosclerotic disease in people with
hypertension
Absolute risk
As hypertension is only one of the many risk factors for
cardiovascular disease, a patient's prognosis depends more on the sum
of their risk factors than on their blood pressure.
2 5
Numerous methods to calculate a patient's absolute cardiovascular risk
have been described (table 1).
|
The Framingham risk equations
were developed to predict coronary disease, heart failure, or
stroke,9-11 and they estimate the 10 year risk of each
event and the average risk in controls matched for age and sex.
Although the Framingham investigators have urged caution in
extrapolating from their cohort of predominantly middle class white
people, the risk equations have been shown to be reasonably
accurate when applied to other populations in northern Europe and the
United States (although they may overestimate risk
elsewhere).12 The equations have been criticised for not
including several atherosclerosis risk factors (such as family history,
sedentary lifestyle, and obesity).
Cardiovascular disease life expectancy model
The
cardiovascular disease life expectancy model is a Markov model
developed using data from the Lipid Research Clinics Follow-up Cohort,
the Canadian Heart Health survey, and Canadian life
tables.13 It has two key advantages over the Framingham
risk equations. Firstly, it provides a single estimate for the risk of
non-fatal or fatal coronary events and strokes in any one person (the
Framingham equations for coronary events and for strokes are different,
and there is no way of combining them). Secondly, this model was
derived from a cohort of patients with and without overt coronary heart disease and thus can be used to predict the potential benefits (and
cost effectiveness) of modifying risk factors both before and after the
development of overt atherosclerotic disease (the Framingham equations
were derived only from people without coronary disease). The major
disadvantage of this model is that it requires access to the original
formulas and is not yet available in a simple form.
Dundee coronary risk disk
The Dundee coronary risk disk
provides an estimate of a patient's relative risk for coronary
mortality matched for age and sex.14 It was derived solely
in men and has not been independently validated in women; there is no
information on its generalisability to other populations; and its
predictions correlate only moderately well with the Framingham
estimates.12
PROCAM risk function
Estimates derived from the
PROCAM risk function15 correlate reasonably well
with those derived from the Framingham equation, but it cannot be used
to predict coronary risk in women and, again, its generalisability to
other populations is unknown.12
British regional heart study risk function
The British
regional heart study function16 has never been validated
in an independent test set, cannot be used to predict coronary risk in
women, and has been found to systematically underestimate risk when
compared with all other risk functions.17
| |
Other risk factors affecting cardiovascular prognosis |
|---|
|
|
|---|
Unmodifiable risk factors for cardiovascular disease include age, male sex, and family history. The effect of race is unclear, although most high quality evidence that adjusts for differences in baseline risk factors suggests that cardiovascular mortality, and the relative risks from modifiable risk factors, are similar across ethnic groups.17 A number of potentially modifiable risk factors have been reported, and those for which strong evidence supports an independent causal effect are described in table 2. Wherever possible, we have summarised relative risks for cardiovascular morbidity and mortality (the potential effects of therapy on these factors are described in the next paper in this series).
|
Cholesterol
A strong, graded relation between raised serum cholesterol and
coronary artery disease is seen with total cholesterol values above
4.65 mmol/l.18 The protective effect of high density lipoprotein cholesterol seems to be at least as strong as the atherogenic effect of the low density fraction, particularly in women.18
Smoking
The risk of cardiovascular disease in smokers is proportional to
the number of cigarettes smoked and how deeply the smoker inhales, and
it is apparently greater for women than men.
18 19
The
risks of pipe and cigar smokers seem to fall between those of
non-smokers and cigarette smokers (relative risk 1.3 (95% confidence
interval 1.1 to 1.5)) for ischaemic heart disease, with a dose-response
relation.20
Diabetes mellitus
Diabetes is one of the strongest modifiable risk factors for
cardiovascular disease, and its effect in women is relatively greater
than in men for all cardiovascular events except congestive heart
failure.9 Diabetes often coexists with obesity,
dyslipidaemia, hypertension, and hyperuricaemia ("syndrome X");
these patients are particularly predisposed to atherosclerotic disease.
Sedentary lifestyle
A high quality cohort study in middle aged men followed for 16 years showed that physical fitness is a graded and independent
predictor of cardiovascular mortality: after adjustment for baseline
risk factors, the relative risks were 0.41 (0.20 to 0.84) in the
fittest fourth, 0.45 (0.22 to 0.92) in the second fittest group, and
0.59 (0.28 to 1.22) in next fourth, compared with the group with the
lowest fitness ratings.21
Body weight and obesity
Body weight and incidence of cardiovascular disease are positively
associated in both sexes after adjustment for other risk factors, but
obesity is a more potent risk factor in women than men and in younger
than older people.22
Alcohol
Observational studies consistently show inverse (or U shaped)
relations between alcohol intake and death from coronary heart
disease.24 While mild to moderate consumption seems to be
protective, taking more than two drinks a day is associated with
increased mortality, primarily from cancer, trauma, and cirrhosis.
Left ventricular hypertrophy
Left ventricular hypertrophy is a common effect of hypertension
and a strong independent predictor of future cardiovascular events.
25 26
Left ventricular hypertrophy with
repolarisation changes on the electrocardiogram carries a higher
risk than hypertrophy diagnosed solely on voltage
criteria.26
Risk factors of uncertain significance
The evidence supporting independent causal effects for other
potentially modifiable cardiovascular risk factors is conflicting
and weak (because the epidemiological studies have been done in highly
selected populations, often with many confounding factors, or no
randomised trials to evaluate the effects of modifying these factors
have been carried out). Furthermore, there is no evidence that
measuring these newer risk factors improves our prognostic ability
beyond that provided by the established risk factors discussed above.
These factors are briefly reviewed here, but a more complete discussion
is contained in Evidence-Based Hypertension.27
Analysis of data from three large prospective
studies (almost 16 000 subjects) found that measuring serum
triglycerides for estimation of cardiovascular risk had no advantage
over using measurements of cholesterol alone.28 In view of
the skewed distribution of fasting triglyceride concentrations in the
population, their high intraindividual variability, their high degree
of correlation with cholesterol subfractions (particularly HDL-C), and
the lack of trial evidence that lowering triglyceride levels reduces
coronary events, their value in screening for high risk patients is
debatable.29
Lipoprotein(a)
Evidence of an association of lipoprotein(a)
with cardiovascular disease is conflicting: two of the four largest cohort studies reported no independent association.30 No
trials have investigated the effects of treatment for excess lipoprotein(a).
Microalbuminuria
Other risk factors (such as
hyperlipidaemia, obesity, and smoking) may increase urinary albumin
excretion, and microalbuminuria is commoner in patients with severe
hypertension, advanced target organ damage, high renin or insulin
concentrations, or a non-dipping profile on ambulatory
monitoring.31 It is unclear whether microalbuminuria is an
independent cardiovascular risk factor or even if it predicts renal
failure in hypertensive patients, and additional data are needed from
larger numbers of patient numbers followed for a longer period.
Uric acid
Hyperuricaemia is commonly associated with other
coronary risk factors and may complicate treatment with
blockers or
diuretics, so it is still not clear whether it will remain an
independent cardiovascular risk factor after adjustment for other
risk factors.32 33
Plasma renin
A cohort study of 2902 treated hypertensive
patients reported that raised plasma renin increased the relative risks
for myocardial infarction (3.8 (1.7 to 8.4)), total cardiovascular disease (2.4 (1.3 to 4.5)), and mortality from all causes (2.8 (1.2 to
6.8)) in those patients with elevated renin
concentrations.34 These results need to be confirmed in
larger studies, however, and trials to establish whether treatment of
high renin levels reduces cardiovascular risk are needed before high
renin can be accepted as an independent risk factor.
Fibrinogen
Although increased fibrinogen often
coexists with other cardiovascular risk factors, there is substantial
interindividual variability and no standardised assay, and a
meta-analysis of six studies reported an odds ratio of 2.3 (1.9 to
2.8) for coronary disease for the highest compared with the lowest
third of fibrinogen levels.35 Subsequent subgroup analyses
(without adjustment for treatment allocation or differences in lipid
profiles) suggest that treatment of raised fibrinogen levels (in
association with abnormal lipid findings) may help secondary prevention
of cardiovascular disease, but further studies are needed to
confirm these results.36
Homocysteine
While a meta-analysis of 27 observational
studies reported that 5 µmol/l increases in serum homocysteine were associated with 1.6 to 1.8-fold increases in coronary
disease,37 a more recent systematic review of the five
highest quality studies found substantial variations between
them, and after adjustment for differences in other risk
factors a less convincing association (odds ratio 1.3 (1.1 to 1.5)) for
each 5 µmol/l increase in homocysteine concentrations.38
Until trials currently under way show that reducing raised homocysteine
levels reduces cardiovascular disease, the role of this risk factor
remains uncertain.
Chlamydia pneumoniae
A meta-analysis of all 15 prospective
studies evaluating serological evidence of Chlamydia
pneumoniae infection excluded any strong association between
titres of C pneumoniae IgG and incidence of coronary heart
disease.39
Inflammatory markers
A meta-analysis of 14 prospective
studies found that people in the highest third of levels of C-reactive protein had more coronary heart disease than those in the lowest third
(relative risk 1.9 (1.5 to 2.3)).40 However, it is still unclear whether C-reactive protein is an independent risk factor for
atherosclerotic disease, since there is no direct evidence that it
contributes to vascular damage, and adjustment for baseline confounders
markedly reduces the size of the putative effect.40
| |
Conclusion |
|---|
|
|
|---|
Raised blood pressure is only one of many risk factors for
atherosclerosis. The decision to treat it should rest on careful consideration of the absolute cardiovascular risk. A number of equations to predict risk are available to clinicians; those most frequently used are the Framingham equations. A number of potential risk factors additional to the established atherosclerotic risk factors
have recently been described, but further research is needed to
determine their exact role.
| |
Acknowledgments |
|---|
We thank Karen Stamm and Jennifer Arterburn for administrative assistance, Molly Harris for assistance with the literature searches, and Drs Cindy Mulrow and Steven Grover for feedback on parts of this manuscript.
| |
Footnotes |
|---|
Funding: FAM is a Population Health investigator of the Alberta Heritage Foundation of Medical Research. SES is supported by a Career Scientist Award from the Ontario Ministry of Health and Long-term Care.
Competing interests: None declared.
| |
References |
|---|
|
|
|---|
| 1. | Mulrow PJ. Hypertension: a worldwide epidemic. In: Izzo JL, Black HR, Goodfriend TL, eds. Hypertension primer: the essentials of high blood pressure. 2nd ed. Baltimore: Williams and Wilkins, 1999:271-273. |
| 2. | Kannel WB. Blood pressure as a cardiovascular risk factor. JAMA 1996; 275: 1571-1576[Abstract]. |
| 3. |
Klag MJ, Whelton PK, Randall BL, Neaton JD, Brancati FL, Ford CE, et al.
Blood pressure and end-stage renal disease in men.
N Engl J Med
1996;
334:
13-18 |
| 4. |
Marang-van de Mheen PJ, Gunning-Schepers LJ.
Variation between studies in reported relative risks associated with hypertension: time trends and other explanatory variables.
Am J Public Health
1998;
88:
618-622 |
| 5. |
Van Den Hoogen PCW, Feskens EJM, Nagelkerke NJD, Menotti A, Nissinen A, Kromhout D, for the Seven Countries Study Research Group.
The relation between blood pressure and mortality due to coronary heart disease among men in different parts of the world.
N Engl J Med
2000;
342:
1-8 |
| 6. | MacMahon S, Peto R, Cutler J, Collins R, Sorlie P, Neaton J, et al. Blood pressure, stroke, and coronary heart disease. Part 1. Prolonged differences in blood pressure: prospective observational studies corrected for the regression dilution bias. Lancet 1990; 335: 765-774[CrossRef][Medline]. |
| 7. |
Gueyffier F, Boutitie F, Boissel JP, Pocock S, Coope J, Cutler J, et al.
Effect of antihypertensive drug treatment on cardiovascular outcomes in women and men. A meta-analysis of individual patient data from randomized, controlled trials. The INDANA Investigators.
Ann Intern Med
1997;
126:
761-767 |
| 8. | Levy D, Larson MG, Vasan RS, Kannel WB, Ho KKL. The progression from hypertension to congestive heart failure. JAMA 1996; 275: 1557-1562[Abstract]. |
| 9. |
Wilson PW, D'Agostino R, Levy D, Belanger AM, Silbershatz H, Kannel WB, et al.
Prediction of coronary heart disease using risk factor categories.
Circulation
1998;
97:
1837-1847 |
| 10. |
Wolf PA, D'Agostino RB, Belanger AJ, Kannel WB, Silbershatz H, Kannel WB.
Probability of stroke: a risk profile from the Framingham study.
Stroke
1991;
22:
312-318 |
| 11. |
Kannel WB, D'Agostino RB, Silbershatz H, Belanger AJ, Wilson PWF, Levy D.
Profile for estimating risk of heart failure.
Arch Intern Med
1999;
159:
1197-1204 |
| 12. |
Haq IU, Ramsay LE, Yeo WW, Jackson PR, Wallis EJ.
Is the Framingham risk function valid for northern European populations? A comparison of methods for estimating absolute coronary risk in high risk men.
Heart
1999;
81:
40-46 |
| 13. |
Grover SA, Paquet S, Levinton C, Coupal L, Zowall H.
Estimating the benefits of modifying cardiovascular risk factors: a comparison of primary versus secondary prevention.
Arch Intern Med
1998;
158:
655-662 |
| 14. | Tunstall-Pedoe H. The Dundee coronary risk-disk for management of change in risk factors. BMJ 1991; 303: 744-747. |
| 15. | Assmann G. Lipid metabolism disorders and coronary heart disease: primary prevention, diagnosis, and therapy: guidelines for general practice. 2nd ed. München: MMV-Medizin-Verl, 1993. |
| 16. | Shaper AG, Pocock SJ, Phillips AN, Walker M. Identifying men at high risk of heart attacks: strategy for use in general practice. BMJ 1986; 293: 474-479. |
| 17. | Stamler J, Stamler R, Neaton JD. Blood pressure, systolic and diastolic, and cardiovascular risks: US population data. Arch Intern Med 1993; 153: 598-615[Abstract]. |
| 18. | Neaton J, Wentworth D. Serum cholesterol, blood pressure, cigarette smoking, and death from coronary heart disease. The Multiple Risk Factor Intervention Trial Research Group. Arch Intern Med 1992; 152: 56-64[Abstract]. |
| 19. |
Prescott E, Hippe M, Schnohr P, Hein HO, Vestbo J.
Smoking and risk of myocardial infarction in women and men: longitudinal population study.
BMJ
1998;
316:
1043-1047 |
| 20. |
Irbarren C, Tekawa IS, Sidney D, Friedman GD.
Effect of cigar smoking on the risk of cardiovascular disease, chronic obstructive pulmonary disease, and cancer in men.
N Engl J Med
1999;
340:
1773-1780 |
| 21. |
Sandvik L, Erikssen J, Thaulow E, Mundal R, Rodahl K.
Physical fitness as a predictor of mortality among healthy, middle-aged Norwegian men.
N Engl J Med
1993;
328:
533-537 |
| 22. |
Hubert HB, Feinleib M, McNamara PM, et al.
Obesity is an independent risk factor for cardiovascular disease: a 26-year follow-up of participants in the Framingham Heart study.
Circulation
1983;
67:
968-977 |
| 23. |
Folsom AR, Prineas RJ, Kaye SA, Munger RG.
Incidence of hypertension and stroke in relation to body fat distribution and other risk factors in older women.
Stroke
1990;
21:
701-706 |
| 24. |
Thun MJ, Peto R, Lopez AD, Monaco JH, Henley SJ, Heath CW, et al.
Alcohol consumption and mortality among middle-aged and elderly US adults.
N Engl J Med
1997;
337:
1705-1714 |
| 25. | Dunn FG, McLenachan J, Isles CG, Brown I, Davgie HJ, Lever AF, et al. Left ventricular hypertrophy and mortality in hypertension: an analysis of data from the Glasgow Blood Pressure Clinic. J Hypertens 1990; 8: 775-782[CrossRef][Medline]. |
| 26. |
Levy D, Salomon M, D'Agostino RB, Belanger AJ, Kannel WB.
Prognostic implications of baseline electrocardiographic features and their serial changes in subjects with left ventricular hypertrophy.
Circulation
1994;
90:
1786-1793 |
| 27. | Padwal R, Straus SE, McAlister FA. Mulrow C, ed. Evidence-based hypertension. London: BMJ Publishing Group, 2001:33-38. |
| 28. |
Avins AL, Neuhaus JM.
Do triglycerides provide meaningful information about heart disease risk?
Arch Intern Med
2000;
160:
1937-1944 |
| 29. |
Bloomfield Rubins H.
The trouble with triglycerides.
Arch Intern Med
2000;
160:
1903-1904 |
| 30. |
Harjai KJ.
Potential new cardiovascular risk factors: left ventricular hypertrophy, homocysteine, lipoprotein(a), triglycerides, oxidative stress, and fibrinogen.
Ann Intern Med
1999;
131:
376-386 |
| 31. | Luft FC, Agrawal B. Microalbuminuria as a predictive factor for cardiovascular events. J Cardiovasc Pharmacol 1999; 33(suppl 1): S11-S15. |
| 32. | Ward H. Uric acid as an independent risk factor in the treatment of hypertension. Lancet 1998; 352: 670-671[CrossRef][Medline]. |
| 33. |
Culleton BF, Larson MG, Kannel WB, Levy D.
Serum uric acid and risk for cardiovascular disease and death: the Framingham Heart Study.
Ann Intern Med
1999;
131:
7-13 |
| 34. | Alderman MH, Ooi WL, Cohen H, Madhavan S, Sealey JE, Laragh JH. Plasma renin activity: a risk factor for myocardial infarction in hypertensive patients. Am J Hypertens 1997; 10: 1-8[CrossRef][Medline]. |
| 35. |
Ernst E, Resch KL.
Fibrinogen as a cardiovascular risk factor: a meta-analysis and review of the literature.
Ann Intern Med
1993;
118:
956-963 |
| 36. | Behar S. Lowering fibrinogen levels: clinical update. Bezafibrate Infarction Prevention Study Group. Blood Coagul Fibrinolysis 1999; 10(suppl 1): S41-S43. |
| 37. | Boushey CJ, Beresford SA, Omenn CS, Motulsky AG. A quantitative assessment of plasma homocysteine as a risk factor for vascular disease. Probable benefits for increasing folic acid intakes. JAMA 1995; 274: 1049-1057[Abstract]. |
| 38. | Danesh J, Lewington S. Plasma homocysteine and coronary heart disease: systematic review of published epidemiological studies. J Cardiovasc Risk 1998; 5: 229-232[Medline]. |
| 39. |
Danesh J, Whincup P, Walker M, Lennon L, Thomson A, Appleby P, et al.
Chlamydia pneumoniae IgG titres and coronary heart disease: prospective study and meta-analysis.
BMJ
2000;
321:
208-213 |
| 40. | Danesh J, Whincup P, Walker M, Lennon L, Thomson A, Appleby P, et al. Low grade inflammation and coronary heart disease: prospective study and updated meta-analysis.(www.bmjbookshop.com) |
Read all Rapid Responses