Key points
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Myocardial ischemia can be due to diseases other than coronary atherosclerosis. Examples include endothelial dysfunction, bridging of coronary arteries, coronary artery spasm, LV hypertrophy, and certain types of anomalous origins of the coronary arteries. The ischemia in these patients can be detected by stress MPI.
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Anomalous origin of the left main coronary artery from the pulmonary artery in children may produce severe LV dysfunction; this represents a nice example of hibernating myocardium (if treated early, before necrosis).
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First-pass RNA can be used to detect and quantify intracardiac shunts, a seldom used indication because of the wide availability of alternative methods.
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Dextrocardia can affect image interpretation if unrecognized. Attention to the position of the RV is a good clue to the diagnosis.
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Cardiac transplantation continues to pose a challenge because the vasculopathy can be diffuse or focal. A combination of rest and exercise RNA and MPI might be of special interest in these patients.
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Attention to RV size and uptake on MPI can be good clues to the presence of an alternative etiology for chest pain in patients with a normal LV perfusion pattern (such as unsuspected pulmonary thromboembolism).
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Incidental findings on MPI are not uncommon and are discussed in Chapter 16 .
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As more children with congenital heart disease are surviving into adulthood, increasing numbers of them also are requiring evaluations for chest pain, heart failure, and arrhythmias. Kawasaki disease, anomalous origin of the coronary arteries, and LV/RV hypertrophy are some of the causes of chest pain in this age group. Knowledge of the anatomy is important for precise interpretation of the images, whether by RNA or MPI.
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Although other imaging methods are used in adults with valvular heart diseases, MPI and RNA are still used to assess LV/RV function, ischemia, and LV dysfunction etiology in those with concomitant CAD.
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Some forms of reversible cardiomyopathy, such as cardiotoxicity, peripartum, and tako-tsubo cardiomyopathy, are discussed in Chapter 12 .
Background
In this chapter, we discuss less common applications of MPI and RNA in unique or special forms of heart disease. Alternative imaging methods, such as echocardiography, MRI, and CT, are more widely and appropriately used in some of these patients, but nuclear imaging remains an important imaging modality for some of them. The list of these diseases is long and some of the principles were outlined in the introductory bullets to this chapter and, thus, only a few examples will be used.
Case 13-1
Dextrocardia ( Figure 13-1 )
A 71-year-old man with ESRD, peripheral vascular disease, severe three-vessel CAD by coronary angiography ( Figure 13-1, A ), and moderate aortic stenosis presented with heart failure symptoms. Right heart catheterization demonstrated severe elevation of pulmonary capillary wedge pressure, severe pulmonary hypertension, and depressed cardiac index. The LV function was poor. He underwent rest and 4-hour delayed thallium-201 imaging to assess the extent of viability. The raw images show dextrocardia and situs inversus ( Figure 13-1, B , and Video 13-1). The MPI showed a large perfusion abnormality in the territories of the LAD and RCA, with partial redistribution. There was severe LV dilatation and LV dysfunction ( Figure 13-1, C , for uncorrected images and D for corrected images). If the dextrocardia is unrecognized, the abnormality could have been attributed to the LCX and RCA disease. He was offered CABG plus aortic valve replacement, but he declined. He died shortly afterward from sudden cardiac death.
Comments
Dextrocardia is a rare congenital heart disease, which can be either isolated or associated with other severe congenital abnormalities. Dextrocardia can be part of situs inversus (mirror-image dextrocardia), where the abdominal organs are also displaced in a mirror image. If unrecognized, an incorrect diagnosis could be made as the shortened septum is now in the usual position of the lateral wall. The images can be corrected after acquisition or the 180-degree acquisition arc can be changed from the standard RAO→LPO to LAO→RPO.
Case 13-2
Anomalous Origin of Coronary Arteries ( Figure 13-2 )
A 68-year-old woman underwent CT for suspected pulmonary embolism. The CT angiogram was negative, but the RCA was reported to have an anomalous origin. Subsequent coronary angiography confirmed that the RCA had an anomalous origin at the left coronary sinus of Valsalva ( Figure 13-2, A ). She underwent treadmill exercise testing and exercised for 7 minutes, achieving her target heart rate without angina or ST changes. The myocardial perfusion images were normal ( Figure 13-2, B ). She was managed conservatively.
