Author + information
- Robert Donnino, MD∗ (, )
- Monvadi B. Srichai, MD, MS,
- Vinay D. Madan, MD,
- Scott A. Bernstein, MD and
- Jill E. Jacobs, MD
- ↵∗Department of Veterans Affairs Medical Center, New York University School of Medicine, Departments of Medicine (Cardiology Division) and Radiology, 423 East 23rd Street, 12 West, New York, New York 10010
We read with interest the article by Hussein et al. (1). The publication focused on non-cardiovascular (and therefore non-ECG-gated) studies. Although we agree with the authors’ conclusions supporting the clinical safety of computed tomography (CT) scans in patients with these devices, we have observed several cases of CT-induced arrhythmia during gated cardiac examinations in patients with rhythm management devices. The resultant arrhythmias rendered the examinations non-diagnostic, thus exposing patients to unnecessary radiation.
Our observed cases involved apparent ventricular oversensing, which led to pacemaker suppression, causing brief periods of ventricular asystole (Figure 1). These occurred while the CT beam was directly in line with the pacemaker generator. As suggested by Hussein et al. (and others) (2,3) the effects were transient, lasting <4 s. Consistent with the authors’ findings, none of our cases led to clinically significant adverse events. CT interference was detected because these studies were electrocardiography (ECG)-gated, and demonstrated temporary pacemaker suppression on recorded ECG strips. More importantly, evaluation of ventricular function, the primary reason for the examinations, was precluded by the resultant temporary cessation of the cardiac cycle, which was imaged as a nonmoving heart.
These cases are important for several reasons. First, they confirm the prior reports cited by the authors that CT beams do indeed transiently interfere with pacemaker function, leading to ventricular oversensing during routine clinical scans. This interference, however, is transient and unlikely to lead to serious adverse clinical events. Second, they highlight a novel concern from the imaging standpoint—that gated studies may be rendered nondiagnostic due to pacemaker interference. Finally, these cases further emphasize a point touched on by the authors in their discussion. That is, while routine CT studies are unlikely to cause serious clinical events, this cannot be extrapolated to other applications that may involve longer exposure of a rhythm management device to CT irradiation.
Fortunately, these cases are uncommon for several reasons. First, transient suppression of pacemaker function only occurred when the beam was in line with the generator. Thus, when the generator is positioned higher in the chest, it is less likely to suffer from interference while scanning cardiac structures. Second, because the effect was ventricular oversensing, only patients who are pacemaker dependent are affected. Finally, the cases that will be affected are those for which multiple phases of the cardiac cycle are necessary for dynamic evaluation (e.g. ventricular function), and coronary imaging may still be possible using a single cardiac phase. While ventricular function is not a common indication for cardiac CT, it is often indicated for patients who have poor acoustic windows on echocardiography and cannot undergo magnetic resonance imaging (i.e., with indwelling pacemaker). Knowledge of this fact is useful, as patients who are pacemaker dependent and are undergoing cardiac CT for evaluation of ventricular function can have their pacemaker settings changed to an asynchronous pacing mode prior to the examination to avoid potential oversensing.
- American College of Cardiology Foundation