Teaching cases in nuclear oncology: Investigating the heart in cancer patients

Cardiovascular disease is a frequent comorbidity in cancer patients. Ischemia occurring during therapy, especially perioperative ischemia, is a serious event, associated with increased morbidity and mortality (see Chapter 53, "Imaging the Heart in the Cancer Patient"). Detecting ischemia in patients at intermediate risk of a cardiovascular event is a major indication for myocardial perfusion imaging in cancer patients. Many patients referred for myocardial perfusion imaging are frail and cannot exercise. These patients usually undergo stress testing with pharmacologic agents. Although pharmacologic stress can be performed with agents that increase myocardial oxygen consumption, such as dobutamine, these agents have largely been replaced by vasodilator agents, such as adenosine (adenosine triphosphate in Japan) or the synthetic adenosine A_2A agonist, regadenoson, because of their relative safety. Adenosine infusion or regadenoson administration causes a generalized vasodilatation, often associated with a slight decrease in blood pressure, and may also be accompanied by a pounding sensation in the head and a feeling of abdominal fullness. The coronary vasodilatation during infusion of adenosine (0.14 mg/kg/min) increases coronary blood flow velocity by more than 3.5-fold over baseline [1]. Regadenoson, on the other hand, raises coronary flow about 2.5-fold within approximately 2 min of IV administration, and it remains over twofold increased for about 10 min [2]. Both adenosine and regadenoson also cause vasodilatation of splanchnic blood vessels, increasing splanchnic flow, which in turn increases subdiaphragmatic activity that may interfere with the evaluation of inferior wall perfusion on stress-injected images. To minimize activity in the splanchnic bed, it is helpful to combine pharmacologic vasodilator stress with low-level exercise (if technically and clinically feasible). Walking, even at 1-2 mph with 0% grade, is sufficient to reduce splanchnic perfusion. The following cases illustrate some of the clinical and technical issues that arise in the performance and interpretation of these studies.