Sudden death and physical exercise: timely diagnosis of congenital anomalies of the coronary arteries with the new 320-slide multi-detector computed tomography
- First Online:
- Cite this article as:
- Gaudio, C., Pelliccia, F., Evangelista, A. et al. Intern Emerg Med (2013) 8: 35. doi:10.1007/s11739-013-0923-0
Congenital abnormalities of the coronary arteries here described are an uncommon form of structural heart disease. Nevertheless, they deserve attention because may cause chest pain and, in some cases, sudden cardiac death even during exercise. Traditional angiography has limitations due to its projectional and invasive nature. The recent development of the 320-slide multi-detector computer tomography with low radiation exposure has the potential to modify the current diagnostic work-up, as it allows even in young people a timely identification of clinical significant coronary anomalies minimizing the risks related to radiation exposure.
KeywordsCongenital coronary anomaliesCoronary angiographyMulti-detector computed tomography
Congenital coronary anomalies have been found in 0.3–0.5 % of cases in autopsy series and in 0.3–1.3 % of patients undergoing cardiac catheterization . A 1956 autopsy study showed a 70–80 % incidence of sudden cardiac death among patients with isolated coronary artery anomalies .
Classification of congenital anomalies of coronary arteries according to Greenberg et al
Anomalies of origin
Single coronary artery
Anomalous origin of coronary artery from pulmonary arterya
Origin of coronary artery or branch from opposite or non-coronary sinus and an anomalous [retroaortic, interarterial,aprepulmonic, septal (subpulmonic)] course
Anomalies of course
Duplication of arteries
Anomalies of termination
Coronary artery fistulaa
Most congenital coronary anomalies have little clinical significance and therefore are often discovered incidentally during invasive coronary angiography performed to rule out coronary artery disease. A minority of cases, however, is clinically significant primarily due to an interarterial course (between the aorta and pulmonary artery) and may present with symptoms of myocardial ischemia, malignant ventricular arrhythmias, and sudden cardiac death. Indeed, an anomalous coronary artery originating from the opposite sinus of Valsalva that courses between the aorta and pulmonary artery is associated with substantial morbidity and mortality . Also, myocardial bridging has been found to be the cause of effort-induced angina and sudden death, and tunneled coronary arteries have been reported in approximately 5 % of athletics field deaths in the absence of any other structural anomaly . For this reason, a timely identification of congenital coronary arteries when clinical suspicion arises has been claimed.
Current diagnostic work-up
Echocardiography can address the correct diagnosis, because it provides good anatomic definition of the ostium and proximal epicardial course of coronary arteries. When echocardiography fails to demonstrate that coronary arteries actually originate from their usual location in people with impaired consciousness or angina further anatomic investigation is needed. Pelliccia et al.  in a series of 1,360 young athletes prospectively evaluated by ECG, visualized the ostium and proximal course of the left coronary artery in 97 % and right coronary artery in 80 % of subjects. False negatives, however, may occur when using transthoracic echocardiography, as demonstrated by Davis et al.  due to either misinterpretations or the inability to fully identify coronary arteries origin because of poor acoustic windows. To date, the main diagnostic method has been selective coronary angiography. However, coronary angiography is clearly invasive and associated with procedural morbidity (1.5 %) and mortality (0.15 %) risks . The exact three-dimensional course of the abnormal artery can be difficult to ascertain from the fluoroscopic two-dimensional summation projections obtained during conventional invasive coronary angiography. These limitations can be overcome by using a noninvasive diagnostic modality that acquires full three-dimensional data from both the heart cavities and the coronary arteries.
Technical advances of MDCT
With recent advances in technology, multi-detector computer tomography (MDCT) has become a highly accurate noninvasive approach for delineation of coronary arteries. Unfortunately, while the number of MDCT examinations continues to increase, concerns in the widespread use of MDCT have arisen, given to the fact that MDCT is a high-radiation imaging modality. Conventional coronary angiography is effective at a radiation dose from 3 to 9 mSv, while MDCT angiography delivers a radiation dose as high as 20 mSv according to early studies . The radiation risks arising from cardiac MDCT have raised serious concerns in the medical field as the technique is associated with a non-negligible life attributable risk of cancer. Using methods previously described for estimating the risk of thyroid malignancy from cervical spine computed tomography, Einstein et al.  estimated a significant number of potential radiation-induced neoplasms from coronary MDCT. Therefore, the benefit of the use of MDCT in the diagnostic work-up and patient management has long been counterbalanced by the potential risks related to radiation exposure.
Expansion of MDCT systems from 64-slice to the latest models of 256-slice and 320-slice systems has allowed whole heart coverage in one gantry rotation with a slice thickness of 0.5 mm . With 320-slice MDCT, 16 cm of craniocaudal coverage can be obtained in a single heartbeat, with excellent image quality and demonstration of the entire coronary arteries, and therefore, the entire cardiac volume data can be acquired in 0.35 s without of the need for patient movement during the scan. The increase in the number of detector rows in the 320-slide MDCT scanner does not increase radiation dose to patients, as shorter scanning time and other technical solutions translate to lower than expected radiation dose despite the higher number of detector rows in these wide-coverage MDCT scanners. As a matter of fact, effective reduction in radiation dose can be achieved by changing or selecting appropriate parameters without compromising diagnostic image quality .
Adjustment of tube voltage (kVp). Lowering the tube voltage is widely undertaken in clinical practice to reduce radiation dose, since radiation dose varies with the square of the kVp. MDCT acquisition with 100 kVp is possible and allows dramatic dose reductions. A recent study with 320-slice MDCT has shown that decreasing the X-ray tube voltage from 120 to 100 kVp resulted in up to a 70 % reduction in radiation exposure, with increased image noise and unchanged contrast/to noise ratio .
Adjustment of tube current (mAs). Another effective approach to reduce radiation dose for MDCT relies on the automatic adjusting of the tube current in the X, Y plane (angular modulation) or along the scanning direction (Z-axis modulation) or both (combined modulation) according to the anatomic geometry of the body region to be scanned to obtain diagnostic image quality while lowering radiation dose .
Increasing pitch value. It is well known that radiation dose is inversely proportional to the pitch value. Increasing pitch to a higher value is made possible with 320-slide MDCT which enables high detector coverage. Accordingly, high pitch and large detector coverage have been combined in order to reduce the acquisition time of coronary MDCT angiography from the previous 5–10 s to a quarter of a second, allowing depiction of the entire heart within a single heartbeat .
Prospective ECG-gating. One of the most effective approaches for dose reduction is adjustment of the tube current according to ECG signal, which is defined as ECG-controlled tube current modulation. Traditionally, cardiac MSCT angiography is performed using a retrospective ECG-gating technique, which indicates that the volume data are acquired during the entire cardiac cycle within a single breath-hold helical scan. A significant reduction in radiation dose can be achieved from prospective ECG-triggering, which is used to acquire data by selectively turning the X-ray tube on only in the selected cardiac phase, triggered by the ECG signal, and turning off during the rest of the R–R cycle (Fig. 1). The main advantage of this scanning protocol is the lower radiation dose as X-ray exposure only occurs during the selected cardiac phase rather than throughout the entire cardiac cycle. The disadvantage of using a prospective gating strategy is that cardiac function cannot be assessed .
The 320-slice MDCT for the evaluation of anomalies in coronary origin
The 320-slice MDCT for the evaluation of anomalies in coronary course
A myocardial bridge is a congenital condition in which a segment of a coronary artery goes intramurally through the myocardium beneath a muscle bridge . It has been associated with angina, arrhythmia, depressed left ventricular function, myocardial stunning, early death after cardiac transplantation, and sudden death. The coronary artery segment covered by the myocardial bridge is called “tunneled” artery. The myocardial bridge is most commonly seen with the left anterior descending coronary artery . With each systole, the coronary artery is compressed. Generally, the incidence of myocardial bridge is between 0.5 and 2.5 % angiographically and between 15 and 85 % pathologically , but different findings have been recently reported with MDCT. Investigations with both 16-slice and 64-slice MDCT have shown that the incidence of myocardial bridges (ranging from 6 to 30 %) is higher than reported with invasive angiography .
Therefore, the new 320-slice MDCT has the potential to become the technique of choice for the noninvasive definition of myocardial bridges.
MDCT is emerging as an essential imaging tool for evaluating the coronary arteries. Although congenital coronary artery anomalies are uncommon, many of them are easily assessed with this modality, which, compared with conventional invasive angiography, offers superior definition of the ostial origin and proximal path of the anomalous coronary artery. The new 320-slice MDCT is a further step for changing the current diagnostic work-up. Notably, the dramatic reduction in overall radiation exposure associated with 320-slide MDCT has the potential to broaden the use of noninvasive angiography to subgroups, such as young people and athletes, in whom exclusion of congenital anomalies of the coronary arteries has long been limited because of an unfavorable risk/benefit ratio.