Cardiovascular Risk factors

Cardiovascular Risk factors*

·        Ref: 1996 National Heart Foundation Clinical Guidelines for the Assessment and Management of Dyslipidaemia, NZMJ, 1996; 109:224-32

·        Framework:

o   Collect information on risk factors

o   Estimate prognosis

o   Decide on Treatment based on assessment of benefits and risks:

Assessment of risk

·        Absolute risk of cardiovascular disease depends on the combination of all risk factors. Treatment decisions should be based on assessment of total risk – not one factor in isolation (eg raised blood pressure or cholesterol)

·        Absolute risk is usually stated as the risk of a cardiovascular event in the next 5 years (Based on the Framingham Study):

o   Very high risk: > 20% risk in next 5 years.  Includes by definition people with:

§  Proven cardiovascular disease (past MI, positive treadmill, stroke, claudication, etc)

§  Familiar hypercholesterolaemia and familial combined hyperlipidaemia

§  Established diabetic nephropathy (albumin excretion > 300 mg/day)

o   High risk: 15 – 20% risk in next 5 years

o   Moderate risk: 10 – 15% risk in next 5 years

o   Mild risk: < 10% in next 5 years

o   Over age 70, risk for all individuals is very high, and age effect dominates

·        Risk factors in the Framingham tables are age, gender, blood pressure, dyslipidaemia, smoking and diabetes/IGT

·        Risk factors not included in the tables are: Family history of coronary disease, physical inactivity, obesity (especially BMI > 27), left ventricular hypertrophy, fibrinogen, lipoprotein (a). The presence of these should bias treatment decisions towards treatment at any level of risk.

Dyslipidaemia

·        High levels of LDL („bad‟ cholesterol), low levels of HDL (“good” cholesterol) : normal ratio < 4.5

·        LDL reflects heredity, diet (both high cholesterol & high saturated fat) and exercise

·        ­TAG and ¯ HDL may be related to insulin resistance, without total Cholesterol being appreciably raised

·        Raised triglyceride levels are closely related to low HDL levels Þ hard to separate their independent effects on risk

·        Secondary causes: diabetes mellitus, obesity, alcohol abuse, hypothyroidism, renal disease, corticosteroids, exogenous sex hormones, pregnancy

·        Levels should be measured in early adulthood, especially if other risk factors or significant family history of heart disease

·        Fasting lipids best measure of TAGs (from which LDL can be inferred – more accurate than total cholesterol)

·        Within 24 hours of an MI, and up to 3 months later, total cholesterol ¯ and HDL ­, so measurements over this period are not reliable

·        Treatment:

·        A 10% relative reduction in total cholesterol reduces relative risk by 15 – 20% over 5 years

·        Treatment goal: total cholesterol < 5 , HDL > 1, TAG < 2. TC: HDL < 4.5. Realistic goal is 25% reduction in total cholesterol through diet and drugs

·        Thresholds for drug treatment following dietary treatment:

o   For very high risk: treat if TC or TC:HDL > 5.5

o   For high risk: treat if TC or TC:HDL > 6.5

o   For moderate risk: treat if TC or TC:HDL > 7.5

o   For mild risk: treat if TC or TC:HDL > 8.0

·        Dietary advice: reduce saturated and trans unsaturated fats + exercise

·        For drugs, see Lipid Lowering Drugs

Other Specific Risks

·        Hypertension: Blood pressure > 160/95 has 5 times risk. Vibrational stress damages intima. Pressure wave tears the intima and this heals by scarring. Large pulse pressure also significant. Atheroma occurs most commonly at vascular bifurcations. See Hypertension.

·        Cigarette smoking: 2 times risk. Intimal microulceration (a complication to a plaque) predisposes to thrombosis. Tobacco oxidises LDL ® poorly digested form that accumulates in the intima

·        Diabetes: 2 times risk factor ®advanced glycosylation end-products (non-enzymatically glycosylated proteins) bind to endothelium ® permeable, causes cells to produce fibrous tissue