Although there have been many improvements over the past decades in optimizing coronary angiography, ionizing radiation remains an important issue. Chronic exposure to low-dose radiation as experienced by interventional cardiologists confers an increased risk for skin damage, eye lens opacities or cataracts, and various malignant diseases [1–4].

In any coronary angiography, the amount of radiation exposure to the operator is determined among other factors by the body mass index (BMI) of the patient, by the duration of the fluoroscopic procedure, and by the respective experience of the operator.

The RADPAD (Worldwide Innovations & Technologies, Inc., Kansas City, Kan.) is a sterile surgical drape containing bismuth and antimony. When positioned correctly on the patient between the image intensifier and the operator, the RADPAD has been shown to reduce the effect of scatter radiation on the operator. Utilization of the RADPAD has already been shown to reduce radiation exposure in routine percutaneous coronary intervention (PCI) procedures, complex PCI procedures [5], peripheral endovascular procedures [6], cardiac resynchronization therapy device implantation [7, 8], and fluoroscopically guided electrophysiological procedures [9].

We sought to assess the efficacy of RADPAD shields in reducing the radiation dose experienced by operators during routine diagnostic coronary angiography via transfemoral access.

Patients and methods

In total, 60 consecutive patients due to undergo elective coronary angiography were identified and randomized in a 1:1 pattern to have their procedures performed with and without the RADPAD drape. Patients with a history of coronary bypass surgery (CABG) were excluded.

During the angiography, standard shielding equipment was used, including a lead coat, thyroid shield, and protective lenses, in addition to a lead shield suspended from the ceiling between the image intensifier and the operator. All operators had undergone radiation awareness courses and were trained in the optimal placement of the RADPAD drape.

All coronary angiographies were performed from the right femoral artery. The RADPAD was positioned superior to the sheath insertion point, immediately below the lead shield suspended from the ceiling between the image intensifier and the operator (Fig. 1). All coronary angiographies were performed using the same angulations, the same number of frames, and the same settings in the same biplane cardiology intervention suite (Artis zee, Siemens, Germany).

Fig. 1
figure 1

Positioning of RADPAD. This figure shows the correct positioning of the RADPAD. The shield is placed on the patient’s leg around the area of sheath insertion (red lines)

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The dosimeter was placed on the upper, outer aspect of the left arm of the operator, at the level of the mid humerus of the operator. Dosimetric measurements were obtained using an Unfors EDD meter (Unfors Instruments AB, Billdal, Sweden). The dosimeter was commenced at the start of the procedure, and the dose was recorded immediately after the end of the procedure. Screening times (ST) and dose–area ratios (DAR) for each individual procedure were collected prospectively. The study was approved by the local ethics committee of the Charité – Universitätsmedizin Berlin, and every patient gave informed consent to this study.

For continuous data with normal distribution, an independent-samples t test was used. Otherwise, the nonparametric Mann–Whitney U test was used. Continuous data with normal distribution are reported as mean ± SD, or otherwise as median and quartiles. A p value of <0.05 was accepted as statistically significant.

Results

During the study period, 60 patients were successfully randomized to undergo diagnostic angiography with RADPAD or no shield (no RADPAD). The mean age of the study group was 62.5 ± 12.8 years and 37% were female. The baseline characteristics of the study population according to the randomization groupings were similar (Table 1).

Table 1 Baseline characteristics
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There was no significant difference in the two main determents of radiation exposure in both groups: the screening times (102 ± 86 s for the RADPAD group vs. 105 ± 36 s for the control group, p = 0.89) and BMI (27.7 ± 4.24 kg/m2 for the RADPAD group vs. 27.9 ± 5.53 kg/m2 for the control group, p = 0.85).

Furthermore, there was no difference in the DAR (1336.9 ± 581.6 cGy/cm2 for the RADPAD group vs. 1541.0 ± 803.7 cGy/cm2 for the control group, p = 0.26) between the two patient groups (Table 2).

Table 2 Radiation dose
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The primary operator radiation dose was significantly lower in the RADPAD group at 8.0 µSv (Q1: 3.2, Q3: 20.1) compared with 19.6 µSv (Q1: 7.1, Q3: 37.7) for the control group (p = 0.02).

The dose rate, however, was not significantly lower in the RADPAD group at 5.8 μSv/min (Q1: 2.0, Q3: 15.8) compared with 11.0 μSv/min (Q1: 4.3, Q3: 19.3) for the control group, (p = 0.08; Table 2).

Next we analyzed operator radiation dose according to the BMI. We therefore divided the patients into two different BMI groups. The analysis revealed a significant dose reduction in the BMI group of >25 kg/m2 (RADPAD group 12.9 µSv [Q1: 4.5, Q3: 21.0] vs. 32.7 [Q1: 17.1, Q3: 39.0] for the control group, p = 0.006), whereas in the BMI group of <25 kg/m2 (RADPAD group 2.2 µSv [Q1: 2.1, Q3: 9.0] vs. 6.4 µSv [Q1: 3.7, Q3: 16.9] for the control group, p = 0.15) there was no statistically significant reduction (Table 3).

Table 3 Radiation dose according to BMI
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We then analyzed the effects of the RADPAD in reducing radiation exposure to the operator. Total radiation exposure to primary operators was reduced using the RADPAD by 59% overall. In the BMI group of >25 kg/m2 there was a 61% reduction in radiation exposure, whereas in the BMI group of <25 kg/m2 there was a 66% reduction (Table 3; Fig. 2).

Fig. 2
figure 2

Dose reduction. Primary operator dose reduction in all patients with a BMI of <25 kg/m2 and in patients with a BMI of >25 kg/m2. Data are expressed as mean ± SD. Red labels percent dose reduction

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Discussion

The number of cardiologic interventional procedures has dramatically increased in the past decade [10] exposing the interventional cardiologist to more cumulative radiation exposure. Minimizing radiation exposure to patients and staff members is, therefore, important to interventional cardiologists. Even with standard protection equipment – including a lead coat, thyroid shield, and protective lenses, in addition to a lead shield suspended from the ceiling between the image intensifier and the operator – and techniques to minimize scatter radiation, including performing fluoroscopic imaging at the lowest available pulse rate, minimizing the number and duration of cine runs, minimizing the cine frame rate, and minimizing image amplification and collimation to areas of interest during PCI [4], radiation dose for the interventional cardiologists and the catheterization laboratory members remains a task of paramount importance.

Usage of the RADPAD has already been shown to reduce radiation exposure in complex PCI procedures with prolonged screening times [5]. The present randomized trial shows, however, for the first time that a sterile lead-free drape significantly reduces the radiation exposure to the interventional cardiologist already during routine diagnostic coronary angiography performed via the right femoral artery access with short screening times. Moreover, the study confirms that the use of the RADPAD is feasible and does not prolong the procedure as demonstrated by the short time employed for fluoroscopy.

This study had certain limitations. Radiation levels were measured only on the operator’s chest. It is conceivable that differences in radiation doses between the two groups may have been different from those observed if radiation levels had been measured at various sites including the left eye, the thyroid regions, and the left wrist.

Conclusion

This study showed that by using the RADPAD protection, total radiation exposure to primary operators could be reduced by half (59%) the amount without prolonging the procedure, despite the short screening time of a diagnostic coronary angiography. We therefore recommend, despite the additional costs involved (currently € 45, not reimbursed by the German health-care system), the integration of the RADPAD in diagnostic coronary angiography in patients with a BMI of >25 kg/m2. This probably also applies to non-coronary artery interventions, such as endomyocardial biopsy in patients with cardiomyopathies of heart failure with preserved ejection fraction either via a transradial or a transfemoral approach [11–13], and to electrophysiological ablation procedures [14].