PREDICT CVD-DIABETES

Transcription

1 PREDICT CVD-DIABETES ECDS CVD RISK ASSESSMENT : CALCULATION, ADJUSTMENT AND CLASSIFICATION VERSION 1.6 Dr Sue Wells, University of Auckland Chris Wiltshire, Enigma Aug 05, 2005

2 Preface CVD risk assessment (including adjustment and classification) is the pivotal factor determining clinical CVD risk management. This report was prepared for the Electronic Clinical Decision Support (ECDS) Steering Group in August It documents the New Zealand Guideline Group CVD guideline committee approved interpretation to decision support for each step of risk assessment, adjustment and classification. The document contains both proposed technical standards, interpretations and, for the purposes of illustration only, screen shots from the Predict application. It includes the risk calculation using Framingham absolute CVD risk prediction equation, events prevented, number needed to treat (NNT), rounding and guideline group agreed recommendations when risk assessment occurs in those under 35yrs or over 75yrs. The ECDS Steering Group acknowledged receipt of the document on the 12 th August 2005 and endorsed the proposed technical standards and interpretations as valuable contributions to public domain knowledge to develop consistency of use of the CVD risk equations across all forms of decision support. The ECDS Steering Group recommended to NZGG that it consider the proposed technical standards and interpretations as a reference with the source CVD guidelines 2

3 Table of Contents Preface...2 Purpose...4 Exclusion criteria...4 Conditions where people are determined clinically as being at very high risk (>20% over 5 years)...5 Framingham risk assessment...5 CVD outcomes predicted...5 Fields:...6 Rounding...8 Extremes of CVD absolute 5yr risk: less than 1% and greater than 30%...9 CVD risk assessment when patient is younger than 35 years or when patient is older than 75 years...10 CVD risk adjustment...10 Ethnicity coding and PREDICT CVD-Diabetes...11 Classification where risk factor levels are extreme...14 Risk calculation using the Framingham equation and displayed risk using the colour chart

4 Purpose To document for clinicians and people working in the clinical-it interface, the implementation into clinical decision support of the CVD risk assessment component of the Guideline for the Assessment and Management of Cardiovascular risk (NZGG 2003). This document is intended for use in conjunction with the guideline. Exclusion criteria The guideline covers the assessment and management of people with known cardiovascular disease, including people with type 1 and type 2 diabetes. The guideline excludes children (defined as less than 18 years of age), specific management of genetic lipid disorders, heart failure, acute coronary syndromes, sleep apnoea. Risk assessment and management is also not appropriate for pregnant women. CVD-Diabetes decision support module If a patient is pregnant or has gestational diabetes or aged less than 18yrs, clinicians are advised with the following messages and no risk assessment may proceed. This module is not applicable to a pregnant patient. This module is not applicable to patients under the age of 18 4

5 Conditions where people are determined clinically as being at very high risk (>20% over 5 years) Patients having one or more of the following conditions are defined as clinically being at high risk and the Framingham equation is not applicable: Previous cardiovascular event (angina, myocardial infarction, angioplasty, coronary artery bypass grafts, transient ischaemic attack, ischaemic stroke or peripheral vascular disease) Diagnosed genetic lipid disorder (familial hypercholesterolaemia, familial defective ApoB and familial combined dyslipidaemia) Diabetes and overt nephropathy (albumin:creatinine ratio greater than 30 mg/mmol) Diabetes and other renal disease Example of message to clinician Framingham risk assessment If the patient s profile does not meet exclusion criteria or is not clinically determined as being at very high risk, then the Framingham risk calculation is performed using the CVD equation from Anderson et al. CVD risk profiles. Am Heart J 1991;121: CVD outcomes predicted This equation predicts the risk of the following fatal and non-fatal CVD events: myocardial infarction, angina, coronary insufficiency, sudden and non sudden coronary death, stroke, transient ischaemic attack, peripheral vascular disease (claudication), left ventricular failure (symptomatic). The fields (as below) are A through Z and AA through AE and include the necessary instructions. Once completed eg, using an xcel spreadsheet, the users can feed in any patient's risk factors and determine their probability of a CVD event over 5 years. The equation is applicable to patients aged years and may be used for estimating outcome probabilities over a range from 4-12 years. 5

6 Fields: Risk Factors: A Gender (female =1, male=0) B Age (years) C SBP (mmhg) the average of two systolic blood pressures is used Smoking (no=0, yes =1): considered as smoker= 0 if non-smoker or quit smoking more than D 12 months previously, otherwise smoking= 1 E/F Total cholesterol /HDL ratio (ideally fasting but not mandatory) G Diabetes (type 1, 2 or type unknown =1, no=0) H ECG LVH (yes=1, no=0) note this is not used in New Zealand risk prediction tables For SBP prediction equation co-efficients I ß0= J ß1= *(A) K ß2= *LN(B) L ß3= Blank M ß4= *LN(B)*(A) N ß5= Blank O ß6= *LN(C) P ß7= *(D) Q ß8= *LN((E)/(F)) R ß9= *(G) S ß10= *(G)*(A) T ß11= *(H) U ß12= Blank V q1= W q2= X m= SUM((I):(T)) Y g= EXP((V)+((W)*(X))) Z Time (years) (Set at 5 years) AA U= (LN(Z)-(X))/(Y) AB Probability of CVD = 1-EXP(-EXP(AA)) Relative risk reduction (Set at 25% for one intervention, 45% for 2 interventions and 55% for 3 AC interventions) AD Absolute risk reduction = (AB)*(AC) AE NNT (numbers needed to treat for 5 years to prevent an event) = 1/(AD) Notes: * LN is natural log * EXP = exponential * Some of the coefficients are blank because other versions of the same basic equation can be used for other endpoints and use additional coefficients 6

7 To check that equation is correct: To check if the equation is written correctly use the following example: woman, aged 70 years, SBP 174 mmhg, smoker, TC = 6 mmol/l, HDL= 1.4 mmol/l, no diabetes, 5 year probability of CVD =22.641% (equation reads ), Treatment benefits according to the guidelines: These may be used to estimate the risk reduction that would occur for an individual on no CVD treatments at the time of the risk assessment. Treatment benefit from one intervention (applying a 25% relative risk reduction) absolute risk reduction = 5.7% (equation reads ), NNT= 18 (equation reads ) Treatment benefit from two interventions (applying a 45% relative risk reduction) absolute risk reduction = 10.2% (equation reads ), NNT= 10 (equation reads ) Treatment benefit from three interventions (applying a 55% relative risk reduction) absolute risk reduction = 12.4% (equation reads ), NNT= 8 (equation reads ) 7

8 Rounding There is a statistical confidence interval around each estimated risk. Given this imprecision, it is appropriate only to round up or down to the nearest whole number. For example, if the CVD risk =22.641%, the rounded CVD risk is 23%. The absolute risk reduction and NNT are based on this rounded CVD risk. 8

9 Extremes of CVD absolute 5yr risk: less than 1% and greater than 30% No person is at 0% risk of a CVD event. Therefore where a patient s risk is less than 1% then the actual risk displayed is rounded up to 1%. If patient CVD risk is over 30% then actual risk is not displayed but given >30% as per the CVD guideline colour chart. 9

10 CVD risk assessment when patient is younger than 35 years or when patient is older than 75 years The Framingham equation is not directly applicable for those below 35yrs or for those above 75yrs. The CVD risk guideline committee recommended the following wording to be displayed when patients in these age groups were risk assessed; For those below 35 years The Framingham equation is not directly applicable for those below 35yrs. and this risk has been calculated as if they were 35yrs as an approximation. The result is given to guide clinical decision making only. Consideration should be given to factors which might require more intensive intervention or specialist referral: suspected genetic lipid disorder type 1 diabetes diabetes with microalbuminuria type 2 diabetes of long duration HDL either very low or very high (<0.7mmol/l or >2 mmol/l) For those above 75 years The Framingham equation is not directly applicable for those above 75yrs and this risk has been calculated as if they were 75yrs as an approximation. The result is given to guide clinical decision making only. CVD risk adjustment If the patient does not meet exclusion criteria or is not clinically determined as being at very high risk, then the Framingham risk calculation is performed. After this calculation, the following groups should be moved up one risk category (5%), as their cardiovascular risk may be underestimated in the Framingham equation: People with a family history of premature coronary heart disease or ischaemic stroke in a first degree male relative before the age of 55 years or a first degree female relative before the age of 65yrs Maori Pacific peoples or people from Indian subcontinent People with both diabetes and microalbuminuria People who have had type 2 diabetes for more than 10 years or who have an HbA1c consistently greater than 8% People with metabolic syndrome These adjustments should only be made once for people who have more than one criteria (i.e. the maximum adjustment is 5%). 10

11 Ethnicity coding and PREDICT CVD-Diabetes The following code list is the Statistics New Zealand Standard Classification of Ethnicity, Level 2 (except '99', which has been added by NZHIS). 10 European Not Further Defined 11 New Zealand European/Pakeha 12 Other European 21 New Zealand Maori 30 Pacific Island not further defined 31 Samoan 32 Cook Island Maori 33 Tongan 34 Niuean 35 Tokelauan 36 Fijian 37 Other Pacific Islands (not listed) 40 Asian not further defined 41 Southeast Asian 42 Chinese 43 Indian 44 Other Asian 51 Middle Eastern 52 Latin American / Hispanic 53 African 54 Other 99 Not Stated As indicated by the grey shading, the self-identified ethnicity codes that were used to apply the 5% upward adjustment were. Ethnicity code 21 (New Zealand Maori) Ethnicity codes 31 through to 37 (all Pacific islands) Ethnicity codes 43 (all Indian including Fijian Indian), and the 44 codes (Other Asian). However we were advised by the CVD-Diabetes guideline project manager that "Indian sub-continent" included ethnicity codes 43 (Indian) and all 44 codes except Japanese and Korean (in grey below). Level 2, and higher coding levels for Other Asian Ethnicity codes 44 Other Asian 441 Sri Lankan Sri Lankan nfd Sinhalese Sri Lankan Tamil Sri Lankan nec 444 Other Asian Afghani Bangladeshi Nepalese Pakistani Tibetan Other Asian nec 442 Japanese Japanese 443 Korean Korean 11

12 Currently PMS systems are only able to pass Level 2 codes (which will include Japanese/Korean).Therefore until PMS systems are able to pass Level 3 ethnicity coding there will be some Japanese and Korean patients whose risk may be overestimated by 5%. New Zealand risk thresholds for treatment are quite conservative compared with other countries. Therefore in consultation with Prof Rod Jackson (Epidemiologist, University of Auckland) it was considered that overestimating CVD risk in a small group of people would be less of an issue than not adjusting and therefore underestimating risk for people of any of 44 codes(other Asian). The Predict CVD Diabetes module contains a mix of Level 2 and relevant Level 3 and 4 codes. Note: Even if PMS systems change over to Level 3 coding, it is still likely that some GPs will retain their Level 2 'legacy' ethnicity data rather than recode. 12

13 Example of PREDICT CVD-DIABETES assessment and risk adjustment 13

14 Classification where risk factor levels are extreme The NZGG CVD guidelines state; If blood pressure is consistently greater than 170/100 or total cholesterol greater than 8mmol/L or TC:HDL ratio greater than 8, the person is classified at least at high risk (>15%) and should receive specific lifestyle advice and medication to lower their risk, irrespective of their calculated risk. The average of two sitting blood pressures are recommended by the guideline when measuring and recording risk factors. Therefore CVD-Diabetes input template includes today s sitting BP and the most recent previous blood pressure (can be 2 sitting blood pressures taken at least 10 minutes apart). An average of the two systolic blood pressures is calculated to contribute to the CVD risk prediction equation. If a person s calculated and adjusted risk was less than 15% but the profile contained extreme values of blood pressure or cholesterol then classification of CVD risk 15% was undertaken when; TC/HDL OR Total cholesterol greater than or equal to 8 mmol/l { (systolic BP1 was greater than or equal to 170mmHg or diastolic BP1 was greater than or equal to 100mmHg) AND (systolic BP2 was greater than or equal to 170mmHg or diastolic BP2 was greater than or equal to 100mmHg) } Example of output given below 14

15 Risk calculation using the Framingham equation and displayed risk using the colour chart There are occasions where the calculated risk and the risk indicated in the colour charts may vary. This is due to a combination of factors mostly related to the limitations imposed by the use of categorical variables (colour chart) compared to use of continuous variables (risk prediction equation). The colour charts are the best fit rather than a mathematical equation. Factors contributing to variation: Patient age on the cusp of next colour chart block eg; 45yrs, 55yrs, 65yrs Risk equation uses systolic not diastolic blood pressure Risk equation uses actual systolic number not within a 20mmHg range as the colour charts Risk equation uses actual lipid number not just whole number ie, 6, or 7 as the colour charts When this variance occurs an explanatory note appears in the CVD-Diabetes module (see below). 15

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