Inhibition of the Oversensing of Cardiac Pacemakers in Chest CT ()
1. Introduction
In 2005, the first case of the pacemaker-related defect was reported in Japan claiming that a pacemaker induced a partial electric oversensing in X-ray CT [1-8,11,12]. Ministry of Health, Labor and Welfare issued the reminder to medical institutions titling “Precautions for the use of X-ray CT and implantable cardiac pacemakers with regard to their interactions” [11,12].
In 2009, the precautions were revised [13], and recommended to monitor pulses at the fixed pacing mode or to stop X-ray irradiation in the patient with a pacemaker because X-ray irradiation temporarily suppresses the pacing, and may induce bradyarrhythmia with dizziness or fainting.
As of 2011, the reports of oversensing and reset of the cardiac pacemaker still have been observed [7]. Therefore, in this article we investigated the way to inhibit the oversensing in X-ray CT.
2. Materials and Methods
CT unit (Aquilion PRIME, 80-detector row, Toshiba), four models of pacemakers (St. Jude Medical, and Medtronic) and two pacemaker programmers were used. Pacing rate and refractory period were set at 60 ppm and 300 msec, respectively. A pacemaker was attached on the subclavicular fossa of the chest phantom (Kyoto Kagaku) and was scanned by helical CT at 15.6 helical pitch (0.195 beam pitch), rotation time of 0.35 msec, and tube voltage of 120 kVp in Automatic Exposure Control mode 12 (AEC 12) used in Toshiba CT units (Figure 1).
2.1. Detection of the Oversensing of a Pacemaker
Four models of pacemakers were investigated to detect the oversensing induced by non-ECG-gated CT helical scans. The same scan parameters were used with the ones above-mentioned. The time of X-ray exposure to pacemakers was set at 2.0 sec.
2.2. Inhibition of the Oversensing of a Pacemaker
The intermittent switching X-ray was exposed to the pacemaker detected oversensing. ECG-gated CT helical scan was performed in the Prospective CTA Model in Toshiba CT units (Aquilion PRIME, Toshiba Medical Systems, Tokyo, Japan) [14]. IVY Model (Ivy Biomedical Systems, Inc.) was used for ECG synchronizationing the ECG.
In the sensible period (non-refractory period, defined as alert period), intermittent switching X-ray was exposed at 300 msec per second were to the pacemaker attached on the chest phantom. Similarly, the intermittent switching X-ray was exposed in the non-sensible period (refractory period) (Figure 2).
3. Results
3.1. Detection of the Oversensing of a Pacemaker
X-ray was irradiated to the pacemakers in CT (Figure 3). Three (models II - IV) of 4 pacemakers (II - IV) did not observe oversensing (Table 1). Both atrial pacing (AP) and ventricular pacing (VP) were normal in all three pacemakers without oversensing. In the pacemaker (model I) which showed oversensing, AP and VP were changed to atrial oversensing (AS) and ventricular oversensing (VS), respectively (Figure 4). These results show that oversensing suppressed the changes of AP and VP (AP→AS and VP→VS). The time when the pacing was blocked by oversensing was 3.8 sec. Figure 5 shows that oversensing occurred in the atrium and ventricle and that pacing rate was changed by oversensing in the range between 50 and 180 ppm.
Figure 2. The image of the timing of intermittent switching exposures to the pacemaker at the interval of 60 ppm. In the sensible period defined as alert period and the non-sensible period defined as refractory period, intermittent switching X-ray was exposed at 300 ms per second in chest phantom CT.
Figure 3. ECG of the pacemakers which did not show oversensing. In ECG, 3 (models II - IV) of 4 pacemakers did not show oversensing after exposure for 2.0 sec. Both atrial pacing (AP) and ventricular pacing (VP) were normal in these 3 pacemakers.
Table 1. The results of 4 pacemaker models after CT irradiation and the results of the over-sensing-positive model I in the alert and refractory periods. Three (models II-IV) of 4 pacemakers did not show oversensing. In the model I which showed oversensing, the intermittent switching exposure induced oversensing in the alert period, but not in the refractory period.
Figure 4. ECG of the pacemaker which observed oversensing. In ECG, one pacemaker (model I) showed oversensing after exposure for 2.0 sec. In this model I, atrial pacing (AP) and ventricular pacing (VP) were changed to the atrial oversensing (AS) and ventricular oversensing (VS), respectively. It is evident that oversensing suppressed the changes of AP and VP (AP→AS and VP→VS). Not-pacing time caused by oversensing was 3.8 sec.
Figure 5. Atrial and ventricular long-term histograms (% of beats) of the pacemaker which observed oversensing (model I). The graphs show that oversensing occurs in the atrium and ventricle, and pacing is changed in the range between 50 and 180 ppm by oversensing.
3.2. Inhibition of the Oversensing of a Pacemaker
Figure 6 shows the results in the sensible alert period. Intermittent switching X-ray was exposed at 300 msec per second and followed chest phantom CT. ECG showed the changes from AP to AS and from VP to VS. These results show that oversensing suppressed the changes of AP and VP (AP→AS and VP→VS, arrows in Figure 6). The time when the pacing was blocked by was oversensing was 4.8 sec (Table 1, Figure 6).
Figure 7 shows the results of the non-sensable refracttory period. The intermittent switching X-ray was exposed at 300 ms per second and followed chest phantom CT. In ECG, both AP and VP were normal and no oversensing was observed (Table 1). Oversensing of the pacemaker was not induced by X-irradiation in the refractory period.