208 consecutive and unselected patients were eligible.
8 were not included because of refusal (n =3),
coronary bypass surgery (n = 3),
and calcium channel blockade administration (n = 2).
The remaining 200 patients (mean age 60±12,
range 20-86 years; 92 females) were enrolled in this prospective study (Flowchart,
figure 1); their clinical characteristics and cardiovascular risk factors are given in table 1,
and in figures 2 and 3.
47 patients were receiving an oral beta-blocker as part of baseline medication,
and 56 patients were prepared by receiving 5mg of Bisoprolol both the evening before and the morning of the examination (Emconcor mitis,
Merck,
Overijse,
Belgium) and/or intravenous bolus administration of 5 to15mg of metoprolol (Seloken,
AstraZeneca,
Brussels,
Belgium) at the time of imaging.
Therefore,
a total number of 103 patients had beta-blockade administration and 97 patients had no beta-blockade prior to CCTA.
Comparaison between the group with beta-blockade administration and the group without beta-blockade
No significant difference (p>0,05) was observed between the two groups of patients regarding the BMI,
the age of the patient,
the radiation dose (mSv),
the scan length,
coronary stenting,
Agatston coronary calcification score and the SNR,
although the mean HR tended to be higher in the group without beta-blocker administration (63.1 versus 59.77 bpm) (p =0.05) (Table 2).
This result may be regarded as a selection bias in our study population with only beta-blockade preparation in patients with high baseline HR.
Conversely,
it may be regarded as a failure of beta-blockade to control HR,
as reported in other studies (7,8).
The scanning conditions and parameters in the two groups were also quite similar (Table 3).
Radiation dose
The median DLP of all CCTA examinations was 105.3 ± 96.1 (range: 10.6–627.1) mGy.cm.
Using a (k = 0,014) CT organ-specific effective dose index,
the median radiation dose was 1.47± 1.35 (range: 0.15–8.78 mSv).
Overall,
the radiation dose was ≤ 1 mSv in 98 (49 %) patients,
and more than 4 mSv in 11 (5.5%) patients,
including 6 with arrhythmia (Figure 4),
one with (BMI>35) (Figure 5) and 4 with both overweight (BMI>25) and 2-heartbeat scan.
Image quality
695 of the 3200 coronary segments were absent or < 1.5 mm diameter,
the image quality of the remaining 2505 (78.3%) was graded 1 or 2 in 2500 (99.8%) segments.
The agreement between the two readers was good (κ=0.61).
5 segments were scored “3” by both readers (Figure 6).
The image quality score was not significantly impacted by beta-blockade administration (p = 0.27).
Identifying the predictors for the radiation dose (mSv) of CCTA
The distribution of the effective radiation dose (mSv) is skewed (Figure 7).
The adjusted coefficient of determination R²adjusted is 0.6448.
There was a significant impact of the number of heart beats,
patient age,
BMI,
arrhythmia,
scan length and the Agatston calcification score on the effective radiation dose (p < 0.001),
while the use of beta-blockers,
HR and the SNR had no significant impact (Table 4).
Identifying the risk factors that are associated with image quality (mean quality of the two readers)
A greater caliber and a higher SNR have a positive effect on the image quality,
while the age of the patient,
a higher Agatston calcification score,
and a higher HR have a negative effect (Table 5).
Cut-off values for heart rate
To determine a HR cut-off value for good to excellent image quality (mean image quality grade 1 or 1.5 of the two readers),
a population-averaged cumulative probability with p=0.90 and p=0.95 is calculated.
For patients with median values of the variables Age (61 years),
Caliber (2.8 mm),
Calcification Agatston score (75) and SNR (21.91),
HR cut-off values with 90% and 95% probability for good to excellent image quality were 73 and 60 bpm respectively (Figure 7).
This curve has a quadratic fit and the probability for good image quality seems to decrease rapidly above a HR of 80 bpm.
HR cut-off values for good to excellent image quality are also measured for different scenarios using the minimal and maximum values of age,
coronary artery caliber,
Calcification Agatston score and SNR (Table 6).
This confirms the impact of these parameters on the HR cut-offs for mean image quality grade 1 or 1.5.