Study population
This is a retrospective observational study. The study design was approved by the Institutional Review Board of the Yonsei University Health System (Approval Number: 4–2019-0661) and was conducted in accordance with the guidelines stipulated by the Declaration of Helsinki. The institutional review board waived both the need for the acquisition of informed consent from the patients to be included in the analysis and the need for review by a critical event committee because of the study’s retrospective nature and the absence of data that could be used to identify patients in this study.
Patients who underwent cardiac CT after CIED implantation in a tertiary hospital were retrospectively included in this study. The inclusion criteria were as follows: (1) patients > 18 years; (2) patients with CIED (pacemaker, implantable cardioverter-defibrillator (ICD), and cardiac resynchronization therapy (CRT)), who underwent cardiac CT for cardiovascular anatomy or coronary artery disease assessment after CIED implantation; and 3) patients with CIED interrogation data (pacing threshold, P or R wave amplitude, and impedance). The exclusion criteria were as follows: 1) epicardial CIED leads; 2) poor quality of CT images (e.g., presence of severe metallic artifacts); 3) absence of short-axis CT image; and 4) patients with symptoms and signs that were suggestive of cardiac perforation (such as, pleuritic chest pain, dyspnea, pericardia effusion, pleural effusion, and pneumothorax). Cardiac CT images of 463 CIED leads in 271 consecutive patients from February 2006 to May 2019, were reviewed by one radiologist and two cardiologists (Additional file 1: Figure S1).
CIED implantation technique
For all right ventricular (RV) “septal” implant cases, the standard practice is to target the middle RV septum using a hand-fashioned stylet with a proximal large primary curve and a smaller distal secondary posterior curve as described by Rosso et al. [17] RV apical leads are then implanted with a slightly curved or straight stylet. In all participants in this study, right atrial (RA) leads were implanted in the standard manner with a curved J-shaped stylet. After conventional implantation of RV and RA leads with passive or active fixation, left ventricle (LV) pacing lead implantation is usually performed via a transvenous approach, which cannulates one of the tributaries of the coronary sinus.
Cardiac CT
For each patient, cardiac CT was performed using multidetector CT systems (Aquilion ONE; Toshiba Medical Systems, Tokyo, Japan) or Light Speed Volume CT scanners (Philips, Brilliance 63, Amsterdam, The Netherlands). Cardiac phase reconstruction images were taken, usually at the mid diastole which corresponds to approximately 70%-80% of the RR interval. A slice thickness of 0.75 mm was used, with incremental interval of 0.5 mm in axial source data of cardiac CT. Using an image reconstructed in mid-diastole, orthogonal oblique multiplanar reformats were created with slice thickness of 1 mm, incremental interval of 1 mm. The images of CT were analyzed mainly in a mediastinal setting using a center around 50 Hounsfield unit (HU) and a narrower width of approximately 400 HU.
Definition of terms
MR-conditional leads were defined as CIED leads that were initially designed for MR scanning (e.g., CapSureFix MRI 5086 lead, Medtronic; Tendril MRI lead, Abbott; and Ingevity MRI lead, Boston Scientific). MR-unsafe leads were defined as CIED leads that were not initially designed for MR scanning. Subclinical perforation was defined as traversal of the lead tip past the outer myocardial layer from at least two different views in cardiac CT, without symptoms and signs related to cardiac perforation [16].
Anatomical distributions of RV lead in patients with CIED
RV lead positions were categorized according to the short-axis views of cardiac CT. We hypothesized that positioning the lead in the thicker, non-apex site instead of the traditional RV apex may alleviate the risks of cardiac perforation. In the short-axis views of the RV, we established 6 anatomical categories of leads [16]. The actual ventricular lead locations observed were in the infero-septal junction, inferior, lateral, anterior, antero-septal junction, and septal locations (Fig. 1). In the long-axis views of cardiac CT of the RV, the lead positions were divided into 3 anatomical categories: namely, RV outflow tract, middle RV, and RV apex. In the chest posteroanterior (PA) view, the region from the pulmonary artery bulge to the inferior border of the cardiac silhouette was divided into three equal parts by horizontal lines, similar to what was done in a previous study [18]. The inferior third on cardiac CT scans and PA view on chest X-ray films was defined as the RV apex.
Statistical analysis
Continuous variables are reported as medians (interquartile range) and were analyzed using the Wilcoxon rank sum test and Mann–Whitney U test. Categorical variables were reported as counts and proportions and analyzed using Pearson chi-square test or Fisher’s exact test as appropriate. A logistic regression analysis was conducted to determine odds ratios (OR) for subclinical cardiac perforation. A P value < 0.05 was considered to be statistically significant. Statistical analyses were performed using SPSS version 23.0 (IBM Corp., Armonk, NY, USA).