Introduction Cardiac computed tomography (CT), consisting of coronary artery calcium (CAC) scoring and CT angiography (CTa), is recommended by NICE for the exclusion of coronary artery disease (CAD) in intermediate-risk symptomatic patients. Coronary calcification is pathognomonic of underlying CAD, but a zero CAC score cannot exclude CAD with certainty due to non-calcified coronary plaques. We evaluated the prevalence of CAD and the rate of major adverse cardiac events (MACE) in patients with a zero CAC score in comparison to patients with a non-zero CAC score.
Methods From November 2009 to April 2013, 458 patients with chest pain underwent CT to exclude CAD. All subjects had CAC scoring. The majority of studies included contrast-enhanced, 128-slice, dual-source CTa. Scans were dual-reported by a cardiac radiologist and a cardiologist. MACE and all-cause mortality were determined through searches of regional databases.
Results 458 symptomatic patients underwent CAC scoring. 247 patients (53.9%) had a CAC score of zero and 211 (46.1%) had non-zero CAC score, with a median score of 74 (interquartile range [IQR]: 13–223). Patients with a zero CAC score were younger (52 vs. 62 years, p < 0.0001) and more likely to be female (59.9 vs. 39.8%, p < 0.0001), but less likely to be hypertensive (26.3% vs. 44.1%, p < 0.0001), diabetic (6.9 vs. 14.7%, p = 0.0065), or have a smoking history (29.6 vs. 40.8%, p = 0.0121). Current smoking status and obesity did not differ between groups. There was a trend towards a family history being more common in those with zero CAC scores (37.2 vs. 29.9%, p = 0.09). 424 studies (92.6%) included CTa. Table 1 illustrates the breakdown of CTa findings according to CAC score.
Over a median follow-up of 536 days (IQR: 316–925), 2 MACE events (0.8%) were recorded in the cohort with zero CAC (n = 247), compared to a MACE rate of 1.9% (4 events) in those with non-zero CAC scores (n = 211). Both MACE events in the zero CAC group (1 acute MI and 1 emergent revascularisation) occurred in patients with CTa results suggesting normal coronaries.A CAC of zero was associated with a 99.2% negative predictive value for MACE over the course of follow-up. When MACE and all-cause mortality were combined, a CAC score of zero was associated with significant protective effect (Hazard Ratio 0.24, 95% CI: 0.07–0.86, p = 0.028, Figure 1).
Conclusion Cardiac CT is an increasingly important tool for risk stratification. Reassuringly, a zero CAC score is associated with low rates of both obstructive CAD and MACE, emphasising its utility as a means to rule out CAD. Despite the presence of non-calcified CAD in some patients with a CAC of zero, these patients had a good prognosis.
- Calcium Scoring
- Cardiac CT
- Coronary artery disease
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