Researchers find 'magic angle' for CT pacemaker imaging

A lead-tip angle of 70 degrees has been established as CT pacemaker imaging’s “magic angle,” according to research published in Academic Radiology this month.

More than one million metallic cardiac devices are implanted in patients each year, wrote Sebastian D. Reinartz, MD, and colleagues at University Hospital in Aachen, Germany, and pacemakers (PMs) and implantable cardioverter-defibrillators (ICDs) are commonalities when it comes to CT imaging.

PMs and ICDs are typically implanted in an infraclavicular subcutaneous or submuscular pocket, the authors explained, with an transvenous lead. The majority of ventricular leads are placed in the apex of a patient’s right ventricle, while most atrial leads are implanted in the right atrial appendage. But, within a year of receiving these devices, a fraction of cardiac patients still experience function and dislodgement issues.

“There is a 4.4 percent incidence of lead dislodgement or malfunctioning—around 44,000 patients—one year after implantation, from which approximately 10,000 patients are suffering from possible lead perforation,” Reinartz and co-authors wrote.

This isn’t a rarity in clinical settings—according to the study, lead protrusion or perforation is a recurring problem in patients with implantable devices due to the stiffness of the lead and thin nature of the heart’s right ventricle. And if a lead perforates the ventricular wall, there’s often a loss of ventricular pacing capture.

Diagnosing incomplete perforations is challenging, the authors wrote, because PM performs within “normal” boundaries. It then becomes impossible for clinicians to diagnose patients through echocardiography, x-rays or MRI.

“Therefore, pertinent guidelines stipulate an electrocardiography-synchronized CT of the heart,” they said. “However, metal artifacts often hamper the proper visualization of of the lead tip in the right ventricular myocardium, which is crucial to safely avoid thoracotomy.”

Reinartz et al.’s study focused on comparing two CT techniques—dual-energy CT (DECT) and dual-source CT (DSCT)—as well as studying the impact of incremental alterations of current-time product and PM lead-tip angle with respect to the gantry plane in an effort to determine how various parameters could possibly reduce imaging artifacts.

The authors studied the two CT methods in an ex-vivo phantom study of four pacemaker leads and one ICD lead. Images were assessed using a 5-point Likert scale, in which numbers 1-3 represented diagnostic image quality.

Of 400 total images captured, 344 were of diagnostic quality, the researchers reported. While, statistically, DECT images showed significantly improved image quality, both DECT and DSCT techniques scored 86 percent on diagnostic image quality. When it came to lead-tip positioning, the authors found an angle of 70 degrees or less yielded 100 percent diagnostic image quality.

“Surprisingly, the lead-tip angle of 70 degrees has been established as the key angle under which diagnostic image quality is always ensured, regardless of the imaging technique,” Reinartz and colleagues wrote. “Thus, we call 70 degrees the ‘Magic angle’ in CT pacemaker imaging.”