Cardiac consequences of spinal cord injury: a meta-analysis
Williams A, Gee C, Voss C, West C
University of British Columbia, Vancouver, BC, Canada
Objective. High-level spinal cord injury (SCI) causes autonomic dysfunction and subsequent dysregulation of the heart and peripheral vasculature. To date, much of the cardiovascular research in SCI has focused on alterations to vascular control and blood pressure, meaning little is understood concerning the cardiac consequences of SCI. Of those studies that have examined cardiac structure and function significant variability with regards to their participant criteria, specific methodologies, and main outcomes have precluded any clear conclusions surrounding the impacts of SCI on the heart. Therefore, this meta-analysis aimed to assess the alterations to left ventricular (LV) structure and function (assessed via echocardiography) in individuals with SCI. It was hypothesized that SCI causes reductions to LV stroke volume (SV), end-diastolic volume (EDV) and mass in comparison to uninjured individuals.
Design. The current meta-analysis was conduced in accordance to PRISMA guidelines and registered in the PROSPERO international prospective register of systematic reviews. All searches and data extraction were completed independently by two authors and thereafter compared for agreement. Primary data sources included Medline (Ovid) and Embase (Ovid), and expanded searches were conducted using Web of Science, Google Scholar, PubMed, and Proquest. Prospective studies with echocardiographic measurements of LV structure and/or function in individuals with traumatic SCI were eligible for inclusion. Sub-analyses were performed for level of injury and position.
Results. Twenty-seven studies met all inclusion criteria, and all data are reported as pooled effect estimates (95% confidence interval). In 22 studies comparing SCI with uninjured individuals, those with SCI had reductions to LVSV of 11.8 ml (-17.8 to -5.9, p<0.001), EDV of 19.6 ml (-27.2 to -11.9, p<0.001) and LV mass index of -7.7 g/m^2 (-11.6 to -3.8, p<0.001). LV ejection fraction was not different from uninjured individuals (-1.0 % (-2.6 to 0.6, p=0.236)). Furthermore, the early-to-late diastolic filling ratio (E/A) was reduced (p=0.039) and the early diastolic filling-to-myocardial velocity ratio (E/E') was augmented (p=0.021) in SCI. Effect sizes for LV mass index and internal diameter were higher when considering just individuals with cervical SCI.
Conclusions. In agreement with our hypotheses, the current meta-analysis has identified that SCI leads to reductions to LV volumes and mass, as well as altered indices of systolic and diastolic function. While the echocardiographic measures assessed in this meta-analysis describe alterations to resting cardiac function, future studies should aim to assess the cardiac responses to physiological challenges (i.e. orthostatic stress, physical activity) to determine how the heart's functional capacity or 'reserve' is impacted following SCI.
Support. C.R.W is supported by Scholar awards from the Michael Smith Foundation for Health Research (MSFHR), the Rick Hansen Institute, and the Heart and Stroke Foundation of Canada. A.M.W. is supported by a postdoctoral fellowship award from MSFHR.
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