NEW YORK (Reuters Health) – Beta blockade before computed tomographic coronary angiography (CTA) can improve image quality, but a substantial number of patients who require CTA have contraindications to beta blockers, new research shows.
In the study from The Netherlands, patients who couldn’t take beta-blockers were significantly less likely to have adequate heart rate control during CTA, and significantly less likely to have good-quality images – pointing to a need for other strategies to reduce heart rates during these procedures, the researchers say.
In patients undergoing CTA, beta blockade is routinely used to extend the diastolic interval and reduce heart rate variability, senior author Dr. Jeroen J. Bax of Leiden University Medical Center in The Netherlands and colleagues point out. But little is known about how many patients have contraindications to beta blocker use before CTA, as well as the efficacy of beta blockade in improving image quality.
To investigate, Dr. Bax and his team looked at 537 consecutive patients referred for CTA. Out of 283 patients (53%) with heart rates above 65 beats per minute, 237 received one dose of metoprolol an hour before CTA. In the remaining 46 patients, beta blockade was contraindicated.
In their online report February 8 in the American Journal of Cardiology, the authors note that contraindications included systolic blood pressure below 100 mm Hg, severe chronic obstructive pulmonary disease (COPD), aortic valve stenosis with valve area less than one square millimeter, ejection fraction below 35%, second- or third-degree atrioventricular block, and metoprolol allergy.
Patients with heart rates between 65 and 75 beats per minute received 50 mg metoprolol, while those with faster rates received 100 mg. Patients already taking up to 100 mg metoprolol daily, as well as those with less severe COPD, were considered to have relative contraindications to beta blockade and were given lower doses. Patients already taking more than 100 mg of metoprolol or another beta blocker were not given the medication before CTA.
Among the 237 patients given metoprolol, 26 received a lower dose than prescribed by the protocol due to contraindications. Of the 211 patients who did receive optimal beta blockade, 27% failed to achieve a target heart rate below 65, compared to 60% of the patients who didn’t receive beta blockers.
The researchers also found that patients who didn’t achieve optimal beta blockade were more likely to have exams with poor image quality (20% versus 6% for those who had optimal heart rate control), and less likely to have good image quality exams (40% versus 74%).
“Contraindications to beta blockade are present in a substantial proportion of patients,” Dr. Bax and his colleagues write. “This results in suboptimal HR control and image quality, indicating the need for alternative approaches for HR reduction.”
The researchers point out that even patients with normally slow heart rates sometimes need beta blockade during CTA, due to anxiety.
Am J Cardiol 2010.