Craniospinal irradiation is a common therapeutic option for patients with CNS malignancies. Traditionally, CSI has been associated with improved survival rate in these patients, however it is believed that long-term effects include remodeling of the extracellular matrix yielding fibrosis of the surrounding cardiac tissue.14, 15 Recent data from the Childhood Cancer Survivor Study showed a significant reduction in coronary artery disease and a non-significant reduction in cardiomyopathy for survivors of pediatric cancer, largely attributed to historical reductions in cardiac exposure to radiation.16 In addition efforts have been made to decrease cumulative doses of cardiotoxic chemotherapy agents such as anthracyclines. Despite attempts to reduce therapy while maintaining disease control, survivors of pediatric cancer may show evidence for ventricular dysfunction or subclinical cardiotoxicity.17
The present study sought to examine the degree of left ventricular systolic dysfunction in patients undergoing CSI by two-dimensional conventional and speckle tracking echocardiography. When compared to an age-matched control group, patients at both early (< 12 months after therapy completion, mean 0.22 years) and late ≥12 months after therapy completion, mean 13.1 years) time points demonstrated depressed GLS in the presence of normal left ventricular EF and SF, evidence of subclinical myocardial dysfunction, while GCS was no different, and GRS only showed a decrease at the later time point. This finding is in line with previous studies showing GLS as a marker of dysfunction in patients receiving chemotherapy with otherwise normal EF.
The diagnosis and management of cardiovascular injury in pediatric patients undergoing CSI may be delayed due to the misconception that this particular cancer-directed therapy results in only long-term cardiovascular side effects due to the absence of studies documenting the clinical and advanced imaging manifestations from craniospinal irradiation. Indeed, current guidelines in pediatrics for the surveillance of cardiovascular disease in patients undergoing CSI call for screening many years after completion of therapy. On the other hand, strain analysis during the past decade has facilitated significant advances in noninvasive myocardial mechanics and cardiac function assessment.18 Myocardial strain can assess myocardial deformation longitudinally, circumferentially, radially, as well as in the form of twist or torsion, thereby generating data that ought to be taken advantage while assessing early subclinical dysfunction in cancer patients receiving treatment, including radiotherapy.18–20 Whether this will lead to improved outcomes, particularly in patients undergoing CSI, needs to be determined and is worthy of further investigation.
The current study has several limitations. First, the patients included were treated over a 2-decade period. Therapeutic approach in that time has evolved, and an overall decreased scatter in radiation doses has limited the incidence of cardiotoxicity, and this could decrease the signal for cardiotoxicity in patients treated in the recent era.16 However, no significant difference was detected between our limited subset of patients who received proton therapy vs. photon at both timepoints. Second, while myocardial strain analysis has been available for better than a decade, it has yet to be regularly employed in pediatric surveillance, and for studies from the first part of the study period there may have been incomplete imaging planes captured to allow for retroactive strain analysis. This contributed to having fewer patients available for strain analysis than for standard echocardiographic assessment. Additionally, in some cases of historic echocardiograms imaging windows limited measurement of some standard parameters. Finally, because echocardiography has not been a regular part of management of this patient group, there were limited cases in which an echocardiogram was performed in the early period after treatment, and even fewer in which a baseline echocardiogram was performed. Simply put, we could not determine if there was a baseline level of cardiac disease in this patient population prior to therapy, nor did we have an appropriate number of patients with studies both early and late after therapy to determine if there was worsening or improvement with time. It is tempting to assume there is no significant disease in this population prior to therapy, however in patients with leukemia there is a baseline increase in troponin and natriuretic peptide that is improved shortly after cancer therapy is initiated, suggesting an underlying state of cardiac stress related to the illness.21 Additionally, measures of diastolic function were not included until the most recent few years, and this is known to be an important component to ventricular dysfunction caused by radiation therapy.