Transthoracic two-dimensional echocardiography appears to be inadequate for identifying cardiomyopathy in adults who survive childhood cancer, according to a cross-sectional study published online July 16 in the Journal of Clinical Oncology.
Compared with cardiac magnetic resonance imaging (CMRI), which is considered the reference standard to which other cardiac imaging techniques are compared, 2-D echocardiography had a sensitivity of only 25% and a false-negative rate of 75% in identifying cardiomyopathy in a study of 134 adult survivors of childhood cancer, said Dr. Gregory T. Armstrong of the department of epidemiology and cancer control at St. Jude Children’s Research Hospital, Memphis, and his associates.
In these relatively young and apparently healthy study subjects who had never been diagnosed as having any cardiac abnormality, nearly half (48%) were found to have the reduced cardiac mass indicative of cancer therapy–related injury. And fully 11% of subjects who were judged to have a normal ejection fraction (EF) on 2-D echocardiography were actually proved to have an EF of less than 50% on CMRI, the researchers noted.
That number easily could have been higher, but there happened to be a low absolute number of patients (16) with this degree of EF impairment in the small cohort, they pointed out.
Adults who survive childhood cancer are at risk for cardiomyopathy because of their exposure to chemotherapy and radiotherapy. Current guidelines recommend screening such adults by transthoracic 2-D echocardiography because it is noninvasive, widely available, and less expensive than other techniques.
However, the quality of the acoustic windows obtained on 2-D echo varies widely, and the method depends on geometric assumptions that may not be valid in patients who have dilated or remodeled ventricles. Three-dimensional echocardiography yields somewhat more accurate results but is not as widely available. CMRI is the most accurate noninvasive imaging technique, but is more expensive and is even less widely available, Dr. Armstrong and his colleagues explained.
They assessed the accuracy of 2-D and 3-D echocardiography against CMRI as a screen for cardiomyopathy in a longitudinal cohort of 134 adults who had been treated at St. Jude’s for childhood cancer 18-38 years earlier. All had received chest-directed radiotherapy and/or anthracycline chemotherapy, both of which are known to impair cardiac function during treatment and to raise the risk of reduced left ventricular function later in life.
The most common pediatric malignancies were acute lymphoblastic leukemia (44 subjects) and Hodgkin’s lymphoma (37 subjects).
The median age at echocardiographic screening in adulthood was 39 years (range, 22-53 years).
Of the study subjects, 20 were unable to complete CMRI for a variety of reasons. Future studies that compare imaging techniques should take into consideration this relatively high noncompletion rate (15%) for CMRI, especially in cost-benefit analyses, Dr. Armstrong and his colleagues said (J. Clin. Oncol. 2012 July 16 [doi:10.1200/JCO.2011.40.3584]).
In the remaining 114 subjects, 2-D echocardiography consistently overestimated left ventricular ejection fraction (LVEF) and underestimated both end-systolic and end-diastolic ventricular volumes.
In all, 16 subjects were identified as having markedly decreased LVEF (50% or more) by CMRI, but only 4 of them were so identified by 2-D echocardiography and only 11 of them by 3-D echocardiography.
Compared with CMRI, the sensitivity of 2-D echocardiography was only 25%; that of 3-D echo was better but still inadequate, at only 53%. And false-negative rates were high with both 2-D echocardiography (75%) and 3-D echocardiography (47%).
Of particular concern was the finding that on CMRI, 32% of the study subjects had an LVEF that was well below normal. The rate in the subgroup of patients who had received both chest irradiation and anthracycline during childhood cancer treatment was even higher, at 42%.
A total of 48% of the study subjects had a cardiac mass that was at least 2 standard deviations below normal for their age and sex, a clear sign of cardiotoxicity from their childhood cancer treatment. "Notably, even patients who received less than 150 mg/m2 of anthracyclines had a high prevalence of reduced EF (27%), stroke volume (29%), or cardiac mass (56%)," the investigators said.
Estimates derived from Medicare data suggest that at roughly $449 each, CMRI examinations cost about $217 more than does echocardiography ($232 each). Given the high rate of cardiomyopathy discovered in this cohort, and the poor sensitivity of echocardiography as a screening tool, this cost difference may be small enough to warrant a switch in the current screening recommendations from echocardiography to CMRI.
The additional cost of a CMRI-only screening strategy per case of cardiotoxicity correctly identified would be only $1,973, they noted.
The study findings suggest that in this high-risk patient population that was exposed to cardiotoxic therapy during childhood, "consideration should be given to referring survivors with an EF of 50%-59% on [2-D echocardiography] for comprehensive cardiology assessment that includes cardiac history, symptom index, and examination; biomarker assessment; consideration of [CMRI]; functional assessment by treadmill testing; and possibly medical therapy to prevent progression of disease," Dr. Armstrong and his associates said.