Radiation Dose During Percutaneous Treatment of Structural Heart Disease

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ORIGINAL ARTICLE

Heart, Lung and Circulation (2014) xx, 1–9 1443-9506/04/$36.00 http://dx.doi.org/10.1016/j.hlc.2014.04.258

Radiation Dose During Percutaneous Treatment of Structural Heart Disease

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Cardiac Catheterisation Laboratories, St Vincent’s Public and Private Hospitals, Sydney, Australia Received 29 September 2013; received in revised form 26 February 2014; accepted 13 April 2014; online published-ahead-of-print xxx

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[TD$FIRSNAME]John E.[TD$FIRSNAME.] [TD$SURNAME]Boland[,TD$SURNAME.] MSc, [TD$FIRSNAME]Louis W.[TD$FIRSNAME.] [TD$SURNAME]Wang[TD$SURNAME.], MBBS, MM, [TD$FIRSNAME]Bernard J.[TD$FIRSNAME.] [TD$SURNAME]Love[TD$SURNAME.], MHSc, [TD$FIRSNAME] Dylan G.[TD$FIRSNAME.] [TD$SURNAME]Wynne[TD$SURNAME.], MBBS, PhD, FRACP, [TD$FIRSNAME]David W.M.[TD$FIRSNAME.] [TD$SURNAME]Muller[TD$SURNAME.], MBBS, MD, FRACP, FACC *

Background

With the increased application of structural heart intervention techniques, there is concern over increasing radiation dose, especially during lengthy procedures.

Methods

We compared data from 91 consecutive single-vessel percutaneous coronary interventions, 69 patent foramen ovale closures, 25 atrial septal defect closures, 49 transvenous mitral valvuloplasties, 57 balloon aortic valvuloplasties, 53 trans-catheter aortic valve implantations (TAVI), 21 left atrial appendage occlusions and 7 MitraClip1 procedures.

Results

The following fluoroscopy times and dose-area product (median, interquartile range) were recorded: patent foramen ovale closure (7.8, 5.3-10.9 minutes; 16.9, 7.5-30.6 Gycm2), atrial septal defect closure (10.1, 7.3-13 minutes; 15.5, 11.6-30.5 Gycm2), percutaneous transvenous mitral valvuloplasty (14.3, 11.4-24.2 minutes; 37.4, 19.8-87.0 Gycm2), balloon aortic valvuloplasty (8.4, 5.2-13.2 minutes; 19.8, 10.2-30.0 Gycm2), Edwards Lifescience1 TAVI (24.0, 19.3-34.4 minutes; 86.4, 64.0-111.4 Gycm2), CoreValve1 TAVI (19.4, 15.0-26.0 minutes; 101.9, 52.6-143.2 Gycm2), left atrial appendage occlusion (18.5, 15.7-29.1 minutes; 84.1, 36.4-140.0 Gycm2), Mitraclip1 procedures (37.2, 14.2-59.9 minutes; 89.1, 26.2-118.7 Gycm2), coronary angiography and single vessel percutaneous coronary intervention (6.6, 5.1-11.0 minutes; 62.5, 37.0-95.8 Gycm2).

Conclusion

For structural heart interventions, dose area product was not significantly greater than coronary angiography with single-vessel percutaneous coronary artery intervention. This should be reassuring to patients and staff attending prolonged structural heart interventions.

Keywords

Structural heart intervention  Radiation  Percutaneous coronary intervention

Introduction Interventional cardiology has progressed to include the percutaneous correction of structural heart disease along with treatment of coronary artery disease. In recent years, an increasing number of centres have commenced structural heart intervention (SHI) programs worldwide. With the introduction of these newer SHI modalities, there is concern over increasing radiation exposure to both patients and staff, especially during lengthy procedures. Extended

fluoroscopy and acquisition times for patients in prolonged interventional procedures can be associated with undesirable radiation-induced effects such as burns, depilation, dermal necrosis and future risk of malignancy [1]. This perceived increase in radiation risk is of particular concern to those who are young and in their fertile years [2]. We therefore compared differences in procedure time, fluoroscopy time and dose-area product (DAP) between single-vessel percutaneous coronary intervention (standard PCI) and various SHIs.

*Corresponding author at: Director of Cardiac Catheterisation Laboratories, St Vincent’s Public and Private Hospitals, 390 Victoria Street, Darlinghurst NSW 2010, Emails: [email protected], [email protected] © 2014 Published by Elsevier Inc on behalf of Australian and New Zealand Society of Cardiac and Thoracic Surgeons (ANZSCTS) and the Cardiac Society of Australia and New Zealand (CSANZ).

Please cite this article in press as: Boland JE, et al. Radiation Dose During Percutaneous Treatment of Structural Heart Disease. Heart, Lung and Circulation (2014), http://dx.doi.org/10.1016/j.hlc.2014.04.258

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Methods

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The interventional suite at St Vincent’s Hospital, Sydney, consists of one public and two private cardiac catheterisation laboratories. Each laboratory houses a Philips singleplane Allura FD201 (Koninklijke Philips Electronics, The Netherlands) angiography unit that records DAP and exposure times. Procedure times were monitored with either a Philips Exper Xims1 (Koninklijke Philips Electronics, The Netherlands) or a Siemens Cathcor system1 (Siemens-Elema AB Electromedical Systems Division, Solna, Sweden).

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Inclusion and Exclusion Criteria

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All patients who had SHI or PCI between July 1, 2008 and June 30, 2012 were included in the initial search. This four-year time span was selected to coincide with the introduction of percutaneous trans-catheter aortic valve implantations (TAVI) at the study site in 2008. Up to this time, SHI consisted only of percutaneous trans-venous mitral valvuloplasty (PTMV), balloon aortic valvuloplasty (BAV), atrial septal defect (ASD) closure and patent foramen ovale (PFO) closure. Informed, written consent was obtained from each patient. All SHI in both public and private laboratories were performed by four senior consultant interventional cardiologists and these procedures were compared only with PCI performed by the same senior cardiologists in one of the suite’s three cardiac catheterisation laboratories. Additional PCI undertaken by three other experienced consultant interventional cardiologists in the same unit during the same study period were used to establish and compare baseline values. PCI involving radial artery access and additional diagnostic evaluation such as intravascular ultrasound (IVUS), pressure wire analysis of fractional flow reserve (FFR), and complex additional interventions such as rotational arterectomy were excluded from comparison with SHI procedures. These ancillary diagnostic modalities were excluded because they were relatively infrequent in our practice at the time and to avoid potential bias in selecting the index PCI procedure used for comparison with SHI.

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PCI

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Given that the ratio of total PCI to SHI during the entire study period was in the order of 10:1, we selected a representative number of consecutive successful PCI performed mid-way through the study period, rather than analysing every PCI conducted during the entire four year period. This was done in order to facilitate statistical comparison between thousands of PCI with the limited number of SHI over the specified timeframe and because including thousands more PCI was unlikely to affect the results obtained or to contribute any additional information. In keeping with laboratory practice at our institution at the time, all PCI procedures were performed via femoral arterial puncture. Low-osmolar, non-ionic contrast medium (Ultravist-370, Schering Australia, Sydney) was used. Haemostasis of the femoral artery was usually achieved by means of a closure device such as a collagen plug (Angioseal,

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St. Jude Medical, Minnesota, USA) or internal suture device (Perclose, Abbott Laboratories, California, USA).

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SHI

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The SHI procedures performed at St Vincent’s Hospital during the study included PTMV, BAV, trans-septal closure of PFO and ASD, TAVI, occlusion of the left atrial appendage (LAA), and MitraClip1 correction of severe mitral regurgitation. The same contrast medium was used for all procedures. Femoral arterial closure was also achieved by the same suture device, as indicated, while manual compression was applied for venous closure.

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The Index PCI Procedure

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In order to compare radiation dose between different procedures performed by various operators in different angiography suites, it was considered necessary to first determine a standard basis for comparison. On the basis that diagnostic coronary angiography in combination with single-vessel PCI (‘‘standard’’ PCI) was the most common procedure performed in the cardiac catheterisation laboratories at our institution, and because this represented a ‘‘reasonable’’ level of radiation risk that was accepted by laboratory staff at a single sitting, this became the index procedure for comparison with SHI. The alternative, classifying each PCI according to various levels of complexity using current guidelines [3], was considered unnecessarily complex for our purposes, and potentially subjective. Data from 385 consecutive successful coronary angiography and single-vessel PCI performed by the seven skilled consultant interventional cardiologists were categorised by operator and stent number, and analysed to establish baseline values. 220/385 cases were single-vessel PCI. Of these, 91 were performed by the four specialists performing both PCI and SHI. Data from these 91 single-vessel PCI were selected for comparison with all consecutive, successful SHI (49 mitral valvuloplasties, 57 aortic valvuloplasties, 53 trans-catheter aortic valve implantations, 69 patent foramen ovale closures, 25 atrial septal defect closures, 7 MitraClip1 procedures and 21 left atrial appendage closures. Pooled PCI and SHI data were also used to evaluate patient demographics for both cohorts.

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Instrumentation

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All procedures were performed in the cardiac catheterisation laboratories and not in a hybrid surgical suite. TAVI patients all received the received either a Medtronic CoreValve1 (Medtronic Inc, Minnesota, USA) or Edwards Lifesciences Sapiens1 (Edwards Lifesciences, Irvine, California, USA) prosthetic aortic valve. The transfemoral approach was used for all TAVI patients included in this study. For PFO closure, an Amplatzer PFO OccluderTM (St Jude Medical, Minnesota, USA) device was used. LAA closure was achieved using a Watchman1 device (Atritech Inc, Plymouth, Minnesota, USA). An Abbott MitraClip1 system (Abbott Vascular, Illinois, USA) was used for patients undergoing percutaneous intervention of severe mitral regurgitation. PTMV, used in

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Please cite this article in press as: Boland JE, et al. Radiation Dose During Percutaneous Treatment of Structural Heart Disease. Heart, Lung and Circulation (2014), http://dx.doi.org/10.1016/j.hlc.2014.04.258

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the treatment of severe mitral valve stenosis, was performed using an Inoue Mitral valvuloplasty balloon (Toray Medical Co. Ltd, Chiba, Japan). BAV was performed using a NuCleus1 aortic valvuloplasty balloon (NuMED Inc., New York, USA). For TAVI, MitraClip1 and LAA occlusion procedures, patients required general anaesthesia, which was either initiated on the catheterisation table or performed in the operating theatre prior to transfer to the cardiac catheterisation laboratory. All other SHI procedures were performed using conscious sedation with intravenous midazolam and fentanyl. Transoesophageal echocardiographic (TOE) guidance was performed for all Edwards Lifesciences1 TAVI, MitraClip1, LAA occlusion procedures, PTMV and ASD closures, and to assist with PFO closure. To determine whether there were potential differences in X-ray efficiency among the three angiography units, a quality assurance test was conducted for each suite by the manufacturers (Philips Healthcare, Sydney, Australia). The average input dose rate for each of the three units was 120 mGy/min for 11 < 14 cm field size, 80 mGy/min for 14 < 23 cm field size, and 60 mGy/min for > 23 cm field size. To eliminate potential bias in room selection, all SHI cases were performed in all three angiography suites, and were randomly allocated, excepting TAVI cases (n = 51/281), which were required to be performed in the one public, TAVI-accredited suite.

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Data and Definitions

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For this analytical cross-sectional study, data for all parameters were entered prospectively into an interventional cardiology database. Patient demographics were routinely recorded along with all operational parameters as required. Fluoroscopy and cineangiography were performed on each patient as required and at the discretion of each cardiologist. Standard ALARA (as low as reasonably allowable) principles were followed [4]. Ventriculography and aortography required 25 frames per second (fps), selective coronary angiography and other routine cineangiography 12.5 fps. In all cases, it was standard practice to reduce screening to a minimum. Fluoroscopy time is the total x-ray screening time during an angiographic procedure. Dose-area product (DAP, in Gycm2) is defined as the absorbed dose times the area irradiated. It is a measure of the total amount of energy delivered to a patient by the x-ray beam during a procedure. It is widely applied in assessing clinical radiation dosages [5–7], and is the radiation dose index used for this study. As the main objective was to compare differences in radiation risk between individual interventional procedures, and as DAP is currently the most common and convenient means of assessing risk from angiographic exposure, FT in conjunction with DAP provided the most practical and meaningful analysis for comparison. No attempt was made to relate dosage or risk to individual staff or patients. Procedure time (or case time) was defined as the period between injection of local anaesthetic (often called ‘‘needle-toskin’’ time) and sheath withdrawal (‘‘case end’’ time); the same

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definition applied for both PCI and SHI procedures. All PCI cases were initially grouped together for analysis, irrespective of operator, relative urgency (elective or emergency PCI), number of vessels treated (single or multiple), and severity of vessel disease (complete occlusion or partial stenosis). A sub-group analysis was performed to determine the effects of vessel number and operator variability. PCI success was determined as successful stent deployment and otherwise subsequent uneventful discharge without immediate complications. SHI success was defined as successful deployment of device without any evidence of immediate complications relating to deployment, and otherwise subsequent uneventful discharge. Need for permanent pacing after TAVI was not considered a complication or procedural failure as this was an expected consequence related to the procedure, and did not, per se, compromise operational success [8].

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Statistical Analysis

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Data was tabulated in Microsoft Excel 20101 (Microsoft Corporation, Redmond, USA) and imported into the SAS9.21 (www.sas.com) statistical software package. We compared proportions using the x2 test, and means using a two sample t-test for normally distributed data. Normality of the variables was tested using a normal probability plot and by comparing a histogram of the sample data with a normal probability curve. For data that did not conform to a normal distribution, medians were compared using the Wilcoxon Rank Sum test for non-normally distributed data.

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Results

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The impact of stent number on PCI case time, fluoroscopy time and DAP is shown in Figure 1. All 385 consecutive, successful PCI procedures performed by seven interventional cardiologists during the six months between July 1, 2010 to Jan 1, 2011, which was mid-way during the study period and was considered representative of the unit’s practice, were used to evaluate individual operator differences. As shown, all parameter values (case time, fluoroscopy time, DAP) increased with increasing PCI complexity (P < 0.001), despite wide variations in spread. Of the 385 PCI cases, 220 involved deployment of one stent, 103 two stents, 37 three stents and 19 four stents in any one vessel. A breakdown of each parameter for the 91 single-vessel PCI performed by the four dedicated SHI specialists is presented in Figure 2. There were no significant differences in median case time, fluoroscopy time or DAP among different operators. Figure 3 presents a comparison of median case time, fluoroscopy time and DAP between PCI and individual SHI procedures. Patient demographic parameters are also presented in Table 1, which is a summary of data for all procedures and all patients, grouped by procedure type. A total of 281 SHI procedures were performed, including 49 PTMV, 57 BAV, 53 TAVI (23 CoreValve1, 30 Edwards Lifesciences1 TAVI), 69 PFO closures, 25 ASD closures, 7 MitraClip1 procedures and 21 LAA occlusion procedures. Parameters from the 91 singlevessel PCI performed by the four SHI interventionalists were

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Figure 2 Graphs of case time, fluoroscopy time and DAP for single vessel PCI (n = 91), presented for each of the four SHI operators (Dr 1, n = 28; Dr 2, n = 19; Dr 3, n = 21; Dr 4, n = 23). There was no significant difference between any parameters for any operator (P = NS). Results are reported as median  interquartile range. Figure 1 Graphs of case time, fluoroscopy time and total DAP for all PCI procedures, performed by seven experienced interventional cardiologists, grouped by stent number deployed. As expected, increasing PCI complexity results in increasing values for all parameters in each group (P < 0.0001). Results are reported as median  interquartile range. 247 248 249 250 251 252 253

used for direct comparison with those from each SHI. Table 1 includes median and interquartile ranges for case time, fluoroscopy time and DAP for each PCI and SHI intervention. Also shown are P values for differences between individual SHI and PCI procedures. As shown in Table 1, there were significant differences in patient demographics between the pooled SHI cohort (n = 281) and the pooled PCI cohort (n = 220); (gender: SHI 44% male

versus PCI 74% male, P < 0.0001; age (mean  SD): SHI 64.2  21.0 years versus PCI 69.7  11.1 years, P < 0.0001; weight (mean  SD) SHI 73.4  17.4 kg versus PCI 82.0  16.5 kg, P < 0.0001). Within the SHI group there were also significant differences in gender (P < 0.0001), age (P < 0.0001) and weight (P < 0.0001) between different SHI procedures. Procedures such as TAVI, BAV and MitraClip1 were generally performed on older patients compared with PTMV, PFO and ASD closures, which were generally performed on younger patients. The distributions of case time, fluoroscopy time and DAP were skewed to the right, and assumed a normal distribution following logarithmic transformation. Case times (median, interquartile range), in minutes, when compared with PCI (65.0, 55.0-75.0), were significantly lower for PFO closures (45.6, 30.6-52.7, P < 0.0001), were comparable

Please cite this article in press as: Boland JE, et al. Radiation Dose During Percutaneous Treatment of Structural Heart Disease. Heart, Lung and Circulation (2014), http://dx.doi.org/10.1016/j.hlc.2014.04.258

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Figure 3 Comparison of case time, fluoroscopy time and DAP for individual SHI versus index PCI. Results reported as median  interquartile range.

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for ASD closures (53.0, 48.0-80.0) and BAV (67.2, 55.4-80.0, P = NS for both), and were longer for PTMV (80.0, 70.0-95.0), Edwards Lifesciences1 TAVI (89.5, 83.0-125.0), CoreValve1 TAVI (108.0, 93.0-135.0), LAA closures (105.0, 90.0-120.0) and MitraClip1 (215.0, 118.0-339.0, P < 0.0001 for all, except MitraClip1, where P = 0.02). The SHI procedures thus fall into three separate groups: Those with case times significantly higher (PTMV, TAVI, LAA, MitraClip1), lower (PFO), or similar (ASD, BAV) to index PCI values. Fluoroscopy times (median, interquartile range), in minutes, when compared with PCI (6.6, 5.1-11.0), were not significantly different for PFO closures (7.8, 5.3-10.9), BAV (8.4, 5.2-13.2) or

ASD closures (10.1, 7.3-13.0; P = NS for all), and were significantly greater for PTMV (14.3, 11.4-24.2), CoreValve1 TAVI (19.4, 15.0-26.0), Edwards Lifesciences1 TAVI (19.4, 15.0-26.0), LAA closures (18.5, 15.7-29.1) and MitraClip1 (37.2, 14.2-59.9; P < 0.0008 for all, except LAA closures, where P = 0.02). The SHI procedures fall into two separate groups: Those with fluoroscopy times significantly higher (PTMV, TAVI, LAA, MitraClip1), or similar (PFO, BAV, ASD) to index PCI values. DAP (median, interquartile range), in Gycm2, when compared with PCI (62.5, 37.0-95.8), were significantly lower for PFO closures (16.9, 7.5-30.6), BAV (19.8, 10.2-30.0), ASD closures (15.5, 11.6-30.5) and PTMV (37.4, 19.8-87.0; P < 0.0001 for

Please cite this article in press as: Boland JE, et al. Radiation Dose During Percutaneous Treatment of Structural Heart Disease. Heart, Lung and Circulation (2014), http://dx.doi.org/10.1016/j.hlc.2014.04.258

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Table 1 Differences in patient demographics, case and fluoroscopy times, and DAP by procedure. Procedure

Number

% Male

Mean age

Mean

Median case

Median

Median DAP

in years

weight

time in

fluoroscopy

in Gy.cm2

(SD)

in kg

minutes

time in

(Interquartile

(SD)

(Interquartile range)

minutes (Interquartile

range)

range) SHI (all)

281

44

64.2 (21.0)

73.4 (17.4)

75.0 (51.3-95.0)

12.8 (7.4-21.4)

30.0 (14.7-79.4)

49

16

44.2 (15.5)

75.8 (18.1)

80.0 (70.0-95.0)

14.3 (11.4-24.2)

37.4 (19.8-87.0)

<0.0001

<0.0001

<0.0001

<0.0001

84.3 (6.6) <0.0001

66.8 (15.4) <0.0001

67.2 (55.4-80.0) 0.92

84.0 (7.6)

71.9 (11.5)

108.0 (93.0-135.0)

PTMV Comparison with PCI* BAV Comparison with PCI*

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53 0.009

CoreValve1 TAVI

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39

Comparison with PCI*

0.002

Edwards Lifesciences1

<0.0001 85.3 (4.7)

0.32

0.004 69.4 (15.8)

0.03

8.4 (5.2-13.2) 0.11

19.8 (10.2-30.0) <0.0001

19.4 (15.0-26.0)

101.9 (52.6-143.2)

<0.0001

<0.0001

89.5 (83.0-125.0)

24.0 (19.3-34.4)

<0.0001

<0.0001

0.06

30

60

86.4 (64.0-111.4)

PFO

69

52

49.9 (12.0)

77.4 (14.9)

45.6 (30.6-52.7)

7.8 (5.3-10.9)

16.9 (7.5-30.6)

Comparison with PCI* ASD

25

0.005 20

<0.0001 45.3 (16.2)

0.56 70.4 (17.7)

<0.0001 53.0 (48.0-80.0)

0.85 10.1 (7.3-13.0)

<0.0001 15.5 (11.6-30.5)

<0.0001

<0.0001

TAVI Comparison with PCI*

0.16

Comparison with PCI* MitraClip1

7

Comparison with PCI*

100 0.12

LAA

21

Comparison with PCI*

57

<0.0001

76.4 (6.3) 0.11 70.4 (10.3)

0.01

0.04

0.19

73.3 (8.0) 0.13

215.0 (118.0-339.0) 0.02

82.1 (27.0)

105.0 (90.0-120.0)

0.12 37.2 (14.2-59.9) 0.008 18.5 (15.7-29.1)

0.12

<0.0001 89.1 (26.2-118.7) 0.85 84.1 (36.4-140.0)

0.14

0.61

0.61

<0.0001

0.02

0.40

<0.0001

<0.0001

<0.0001

<0.0001

<0.0001

<0.0001

91

74

71.7 (11.1)

78.9 (16.8)

65.0 (55.0-75.0)

6.6 (5.1-11.0)

62.5 (37.0-95.8)

220

74

69.7 (11.1)

82.0 (16.5)

70.0 (60.0-80.0)

8.1 (6.1-11.4)

79.4 (49.3-129.5)

P value for differences

-

among different SHI procedures Coronary angiogram + Single vessel PCI (SHI operators) Coronary angiogram + Single vessel PCI (all) PTMV: Percutaneous trans-venous mitral valvuloplasty; BAV: Balloon aortic valvuloplasty; TAVI: Trans-catheter aortic valve implantation; PFO: patent foramen ovale closure; ASD: atrial septal defect closure; LAA: Left atrial appendage occlusion; SHI: Structural heart intervention; PCI: percutaneous coronary intervention. *

P value calculated using a t-test assessing mean differences for log case time, log fluoroscopy time and log total radiation dose between SHI procedure and PCI performed only by SHI operators.

290 291 292 293 294 295 296 297 298 299

all, except PTMV, where P = 0.03) and were not significantly different for Mitraclip1 (89.1, 26.2-118.7), LAA closures (84.1, 36.4-140.0), Edwards Lifesciences1 TAVI (86.4, 64.0-111.4), or CoreValve1 TAVI (101.9, 52.6-143.2; P = NS for all). The SHI procedures fall into two separate groups: Those with DAP significantly lower (PFO, BAV, ASD, PTMV), or similar (Mitraclip1, LAA, TAVI) to index PCI values. The DAP values from the latter group, although not significantly different from the PCI group, all recorded higher median DAP than standard PCI. The highest DAP was recorded for Corevalve1 TAVI.

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Discussion

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As expected, median case times, fluoroscopy times and DAP increased with increasing PCI complexity (Figure 1, P < 0.001).

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Also, operator performance was unlikely to cause undue influence on PCI case time, fluoroscopy time or DAP in this study as the four SHI operators did not differ from each other with regards to any of the three parameters recorded for the index PCI (Figure 2, P < 0.001). It was also unlikely that these individual operators would differ from each other in the application of their interventional techniques and ALARA principles for either PCI or SHI. There was significant variability and spread in case time, fluoroscopy time and DAP for both SHI and PCI (Figure 3), suggesting that even within each group, cases were often very different and were likely to be affected by factors such as individual case complexity. It should be noted that PCI cases included the diagnostic component at the one sitting, whereas SHI procedures did not include radiation dosage

Please cite this article in press as: Boland JE, et al. Radiation Dose During Percutaneous Treatment of Structural Heart Disease. Heart, Lung and Circulation (2014), http://dx.doi.org/10.1016/j.hlc.2014.04.258

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from previous diagnostic procedures such as computed tomography. Differences in median case time between certain SHI (PTMV, TAVIs, PFO closure, LAA occlusion) and PCI groups were highly statistically significant from each other and from standard PCI, confirming that real differences do exist in performance times. In general, SHI is performed less frequently and often requires additional time during the procedure for on-table device preparation, modification of access site, corroboration with other imaging modalities and induction of general anaesthesia. The shortest procedures were PFO (45.6 min) and ASD closure (53.0 min). The longest were Edwards Lifesciences1 TAVI (89.5 min), LAA occlusion procedures (105 min), CoreValve1 TAVI (108.0 min) and MitraClip1 (215 min). The fact that the MitraClip1 procedure had the highest median value and widest range for case time is not surprising given that the procedure is still in its infancy (n = 7) in our institution. The more complex SHI procedures (PTMV 14.3 min, CoreValve1 TAVI 19.4 min, Edwards Lifesciences1 TAVI 24.0 min, MitraClip1 37.2 min, LAA occlusion 18.5 min) had significantly longer median fluoroscopy times than the index PCI (6.6 min), yet their median DAP were no higher than for PCI, while fluoroscopy times for PFO closure, BAV and ASD closure were no different than for PCI (P = NS for all). Median DAP was highly significantly lower than the index PCI (62.5 Gycm2) for PFO closure (16.9 Gycm2, P < 0.0001), BAV (19.8 Gycm2, P < 0.0001) and ASD closure (15.5 Gycm2, P < 0.0001), while being not significantly higher for MitraClip1 procedures, LAA occlusion or TAVI (P = NS for all). Although CoreValve1 TAVI had the highest DAP, it is reassuring to find that even the more complex SHI procedures did not result in significantly higher DAP values than standard PCI. SHI procedures such as PFO, PTMV and ASD closure are often performed in younger, female patients. The fact that these three procedures have the lowest DAP is also reassuring, especially given concerns regarding long term risk of radiation-induced malignancy and effects on breast and reproductive organs. These results include the learning curve associated with the initial experience of TAVI, MitraClip1 and left atrial appendage occlusion at St Vincent’s hospital. New procedures often are associated with increased case time and radiation doses, which diminish with familiarisation and increasing experience. Increased procedural time and screening time associated with the initial learning curve were not associated with any increase in DAP, when compared with standard PCI. In order to compare fairly performance times between PCI and SHI, only PCI and SHI procedures performed by the four SHI operators were analysed, and median case time, fluoroscopy time and DAP for standard PCI (i.e. angiography with single-vessel PCI via the femoral approach and without FFR, IVUS or atherectomy) were used as the benchmark against which SHI data were compared. Although it may have been preferable to analyse all procedures performed by a single

dedicated team in a single suite, in order to standardise skill level and establish benchmark parameters regardless of procedural complexity, the intention of this study was to derive a benchmark for comparison with other units and to quantify the range of radiation dosage with different interventional procedures. In this sense, our results represent the real world setting, where operators of varying levels of expertise perform cases of different complexity using different angiography equipment and with different operational protocols. Reference levels for radiation doses delivered to patients during diagnostic angiography and coronary interventions exist [9,10] but there are no guidelines for radiation doses during structural heart interventions. Until formal organisations make their own recommendations, our figures may serve as a standard for comparison. Patient DAP during cardiac catheterisation depends on multiple factors including patient weight, equipment used, entrance dose, X-ray tube angulation, case complexity, operator training, beam collimation, magnification used and application of ALARA principles [11,12]. Another important factor is the number and length of cine acquisitions, which involve a much higher radiation dose than simple fluoroscopy [13]. Variations in these factors undoubtedly contributed to the higher DAP recorded for the more complex SHI such as TAVI, MitraClip1 and LAA occlusion procedures. Factors such as magnification and field of view used may also affect DAP, but all procedures were routinely performed with 17-inch (43 cm) magnification, although PCI may occasionally use a higher magnification for specific imaging. SHI often uses TOE to assist with device positioning and deployment, which reduces the amount of fluoroscopy time required, particularly for PFO and ASD. Biplane scanners are unlikely to have an effect on fluoroscopy time and DAP for SHI but may reduce DAP for PCI. Our catheterisation laboratories use single plane scanners. Since staff radiation dose is directly proportional to the patient dose [14], which in turn depends on the X-ray dose generated, quantifying patient DAP provides a standardised basis from which to determine potential staff risk per procedure. Furthermore, by measuring and comparing DAP, we are better able to identify high-risk procedures and perhaps implement safe practice mechanisms to mitigate risk to staff most likely to suffer a high radiation burden. Wide variations in radiation dose are known to occur, up to 1000-fold per procedure [15]. Our study did not directly aim to analyse radiation exposure to staff or patients through the use of dosimeters, and thus was not a true study of occupational radiation risk, rather an exploration of potential sources of high-level procedural risk encountered in a busy cardiac catheterisation unit. As such, there is reassurance in finding that complex and involved SHI procedures may only generate marginally higher DAP compared with our index PCI. Previous studies concerning occupational radiation dose of TAVI versus PCI have reported slightly higher radiation doses and longer fluoroscopy times compared with PCI, which is consistent with our results [16–19]. Our results for Edwards Lifescience1 TAVI implantation (fluoroscopy

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time: 24.0, 19.3-34.4 minutes; DAP 86.4, 64.0-111.4 Gycm2) are similar to those published in American centres. A study of 79 transfemoral Edwards Lifescience1 TAVI from Columbia University Medical Center, New York Presbyterian Hospital, New York, had a DAP of 236, 164-338 Gycm2 and fluoroscopy time of 30, 24-34 minutes)[18]. A cohort of the first 44 transfemoral Edwards Lifescience1 TAVI at the Mayo Clinic in Rochester, Minnesota fluoroscopy time of 17.9, 14.7-25.7 minutes [20]. Radiation dose could not be directly compared due to different units of measurement. Our results compare favourably with a study of 76 TAVI from San Raffaele Scientific Institute, Milan, Italy, where the mean fluoroscopy time was 29.2 minutes, and DAP 218.5, 147-312.8 Gycm2 [19]. This centre also found that TAVI radiation dose was double that of simple PCI (mean fluoroscopy time 16.1 minutes, mean DAP 111, 71-176 Gycm2). A study from Amsterdam found that median DAP for PCI via the femoral artery was 75, 44-135 Gycm2 and 72, 42-134Gycm2 for radial artery [21]. In comparison, our results for PCI via the femoral route were fluoroscopy time 6.6, 5.1-11.0 minutes, and DAP 62.5, 37.0-95.8 Gycm2. Our results for PFO closure (fluoroscopy time 7.8, 5.3-10.9 minutes; DAP 16.9, 7.5-30.6 Gycm2), ASD closure (fluoroscopy time 10.1, 7.3-13 minutes; DAP 15.5, 11.6-30.5 Gycm2) are comparable with those in Europe (mean fluoroscopy time 6.3 minutes and mean DAP of 32.6 Gycm2 in a study of 50 consecutive patients undergoing ASD or PFO closure in Zurich, Switzerland [22]; mean fluoroscopy time 5.1 minutes, mean DAP 22.0 Gycm2 in a study of ASD or PFO closure in Rovigo, Italy [23]; median fluoroscopy time 16.5 minutes, median DAP 8.7 Gycm2 for ASD closure in Athens, Greece [24]). To date, there is no other published study on radiation exposure in MitraClip1 or percutaneous left atrial appendage occlusion. SHI is expected to feature strongly in the future of interventional cardiology. Although many SHI procedures include new modalities and can be associated with long case and fluoroscopy times, the radiation dose for the patient in certain SHI can be less than with the index PCI. Similarly, apart from the highly complex and time-consuming procedures such as TAVI, occupational radiation risk from SHI is likely to be less than for PCI, and this should provide some reassurance to both patients and staff. Fluoroscopy times and DAP are likely to continue to improve with increasing operator experience and advances in instrumentation and technology. Individual operators can thus decide to what extent they implement the various options available to reduce radiation doses [25,26].

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Despite wide variations in case time, fluoroscopy time and DAP for all procedures, SHI could all be grouped into three categories: Those with significantly higher, lower, or similar values to standard PCI (i.e. coronary angiography with singlevessel PCI via the femoral approach and without FFR, IVUS or atherectomy). Overall, median DAP was less than standard PCI for percutaneous transvenous mitral valvuloplasty,

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balloon aortic valvuloplasty, patent foramen ovale closure and atrial septal defect closure, but not significantly higher for TAVI, MitraClip1 procedures and LAA occlusion.

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No external financial support.

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Acknowledgements

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The authors wish to thank Drs Paul Roy, David Baron, Brendan Gunalingam, Stephanie Wilson, Krishna Kathir, Laurence Schneider, Cameron Jeffries, Gary Gazibarich and the St Vincent’s Hospital cardiac catheterisation laboratory nursing and allied health teams for their commitment to the St Vincent’s structural heart intervention program and percutaneous coronary intervention service.

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