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Commentary |
1 Department of Imaging Science, University of Southern California, 1744 Zonal Ave., Los Angeles, CA 90033.
Received October 4, 2007; accepted after revision October 4, 2007.
Address correspondence to P. M. Colletti
(colletti{at}usc.edu).
Keywords: ß-blockers • cardiac imaging • CT angiography • heart disease
The goal in cardiac imaging is to optimize the timing of the physical image
acquisition with the physiologic motion of the heart. Ideally, one would match
the fastest available imaging with the slowest available heart motion.
Advances in MDCT technology allow faster image acquisition (
82.5
milliseconds with dual-source CT)
[1–4]
or greater coverage (15 cm with 256-detector-array CT) so that an entire
coronary data set can be acquired in one heartbeat.
Heart motion can be reduced in two manners: First, select a phase in the cardiac cycle known for relatively reduced motion [5–7]; and, second, apply pharmacologic heart rate reduction with ß-blockers or calcium channel blockers [8–10].
It is logical that given rapid enough image acquisition, heart rate control becomes less important for the acquisition of high-quality coronary CT. Optimal coronary imaging occurs during periods of relative minimal physiologic vessel motion. Individual coronary arteries have their motion minimized at different phases of the cardiac cycle. Seifarth et al. [1] showed, using dual-source 64-MDCT, that the beginning of optimal systolic reconstruction window (median) was at 30% of the R-R interval for heart rates of 50–60 beats per minute (bpm) to 40% for rates of above 80 bpm. The beginning of the optimal diastolic reconstruction median window was at 70% for heart rates of 50–60 bpm to 85% for rates of > 80 bpm. Image quality deteriorated somewhat with heart rates of > 80 bpm [1].
The mean heart rate of the population studied by Seifarth et al. [1] was 68.7 bpm (SD, 15.3 bpm; range, 43–119 bpm). All 90 examinations were performed satisfactorily without ß-blocker preparation. Matt et al. [11] reported similar dual-source coronary CT angiography (CTA) results in 80 participants, with a mean heart rate of 65.3 ± 13.9 bpm.
Beta-blockers have been added to the treatment of a number of acute and chronic coronary conditions including stable angina and recent myocardial infarction [12]. Presumably, a significant portion of patients with cardiac signs and symptoms will be on ß-blockers during cardiac imaging [12, 13], with 51% of patients > 65 years old with stable angina having ß-blockers prescribed in one study [13]. Although Seifarth et al. [1] did not record the number of participants on daily oral ß-blockers in their study, Brodoefel et al. [14] report that nine (45%) of 20 of their coronary CTA participants were on daily oral ß-blockers at the time of examination, with a mean heart rate of 63.0 ± 8.2 bpm. Matt et al. [15] reported that 44 (55%) of 80 participants were on daily oral ß-blockers, with heart rates of 62.2 ± 12.9 bpm compared with 69.0 ± 14.4 for those not on ß-blockers. Brodoefel and colleagues acquired coronary dual-source CTA images with dual-segment reconstruction applied to all data regardless of patient heart rate. Temporal resolution varied as a function of the patient's heart rate between 83 and 42 milliseconds, for a mean temporal resolution of 60 milliseconds [14]. This allowed full cardiac cycle volumetry for systolic and diastolic function evaluation and yielded results comparable to cardiac MR without the use of additional ß-blockers.
Interest in showing the efficacy of dual-source CTA is apparent. Reports of the Matt et al. publication were presented in the Radiological Society of North America's The Daily Scan [16] and in AuntMinnie.com [17]. Those of us with early mixed experience with 16-MDCT coronary CTA without heart rate control particularly appreciate this situation. For now, radiologists should develop comfort with the safe and efficacious use of ß-blockade for heart rate control for coronary CTA [9]. In the near future, perhaps advancing technology and cardiologist's prescribing practices will help relieve us of this task.
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