[Importance of ECG-triggering with the multi-slice CT for ruling out coronary calcification in individuals without...

To avoid unnecessary cardiac catheterization, ruling out coronary calcification has become increasingly important. On the other hand, the detection of coronary calcification is proof of coronary atherosclerosis and therefore requires a reduction of the LDL-cholesterol < 100 mg/ml according to the NCEP guidelines. The "gold standard" for calcium scanning is traditionally ECG-triggered electron beam tomography (EBT). In addition, mechanical multi-slice CTs (MSCT) have been used without ECG-triggering for more than 6 years for calcium scanning.

The importance of ECG-triggering was assessed by examining apparently healthy subjects referred by their physicians (n = 1,206, 57 +/- 10 years, 75% male) using an Mx-8000 four-slice CT (Marconi, USA). Data were obtained from the MUNICH-Registry (MUltislice Normal Incidence of Coronary Health). Image acquisition without ECG-triggering was performed in spiral mode at 120 kV and 249 mAs using a collimation of 2.5 mm, resulting in an effective slice width of 3.2 mm. Prospective ECG-triggering was achieved in sequential ("axial") mode at 120 kV and 165 mAs using an effective collimation of 2.5 mm. The trigger was set at 333 ms prior to 90% of the expected RR-interval.

With both groups well comparable regarding age, sex and risk factors, calcium was ruled out in 51.5% of the individuals without and in 34% of the persons with ECG-triggering (p < 0.001). An Agatston score > 100 was detected in 14.2% without and in 33.1% with ECG-trigger. The loge-transformed calcium scores were 1.7 +/- 2.2 for persons without and 2.9 +/- 2.6 with ECG-trigger (p < 0.001). Multivariate linear regression analysis showed that the application of ECG-triggering was an independent and the strongest predictor for the proof of calcium. With ECG-triggering, calcium was detected in 1.51 +/- 1.42 major coronary arteries (median 1.0), whereas without ECG-triggering, calcium was detected in 1.03 +/- 1.33 major coronary arteries (median 0.0, p < 0.001).

Since without ECG-triggering every fifth patient with coronary atherosclerosis is erroneously classified as "healthy" and only the sensitive exclusion of coronary calcium is helpful in avoiding unnecessary cardiac catheterizations, the use of ECG-triggering for calcium scanning with MSCT is mandatory.