High calcium scores in patients with a low Framingham risk of cardiovascular (CVS) disease: implications for more accurate CVS risk assessment in New Zealand.

Aims: New Zealand (NZ) patients are recommended to undergo an 'adjusted' Framingham score to assess their cardiovascular (CVS) risk. The current (2009) NZ CVS Risk Guideline does not recommend the use of a 'calcium score' as an additional risk tool, although it has been shown to be powerfully predictive of CVS events above the predictive power of traditional Framingham risk factors. Calcium scores of >400 are very strongly predictive of a future CVS event and give direct evidence of atheromatous disease in the coronary circulation. Identification of people with advanced, premature coronary atheroma would allow early treatment of those who may benefit from more vigorous preventative strategies, including statin therapy.
Methods: Using a prospectively acquired, comprehensive database we audited the first 1000 patients (7 August 2006 to 28 November 2008) to undergo a 64-slice computed tomographic (CT) cardiac angiogram (GE Light Speed), which included a scan for a 'calcium score', at the Mercy Hospital, Auckland. We excluded 58 patients who had experienced one or more of a previous myocardial infarction (MI) (n=21), coronary artery bypass graft (CABG) surgery (n=15), percutaneous coronary intervention (PCI) (n=13) or stroke (n=21) and who therefore already had definite evidence of vascular disease and would be automatically placed in a high risk strata. We calculated each patient's Framingham risk from the original 'Anderson' equation, used by the 1996 NZ CVS risk Guideline, and the 'adjusted' Framingham 5-year CVS risk using the NZ Guidelines Group 2003/2009 recommendations, and then compared this with the observed calcium scores.
Results: The mean patient age was 56 (SD 9) years; 364 (39%) patients were female, 82% patients were Caucasian. 41% were current (4.6%) or previous (36%) cigarette smokers, 35% had a history of hypertension, 44% hyperlipidaemia and 5.6% had diabetes mellitus. The percentage of patients at 'low' 5-Year CVS risk (0-10% 5-year risk), using the 1996 and 2003/2009 guideline methods, was 78% and 58% respectively. Of patients in these Framingham 'low-risk' groups, 10% and 8.8% had a calcium score of >400 Agatston units, indicating that they were actually at very high CVS risk, and 203 (28%) and 147 (27%) respectively had a calcium score of >100 Agatston units, indicating that they were actually at 'high risk' and not 'low risk'.
Conclusion: Approximately 10% to 27% of patients with a low CVS risk as assessed by the established Framingham equation have a markedly increased calcium score and hence a significantly increased risk of a CVS event. Currently promoted methods of risk assessment may be inadvertently, falsely re-assuring these patients. Clinicians managing patients may consider a calcium score as an additional tool to the standard risk assessment strategies.