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Ann Thorac Surg 2007;83:1922-1923
© 2007 The Society of Thoracic Surgeons
Department of Radiology, University of California, 410 Dickinson St, San Diego, CA 92103
(Email: rmattrey{at}ucsd.edu).
As an investigator interested in the applications of perfluorocarbon (PFC) compounds in medicine, I note the article published by Hill and colleagues [1]. I suggest an alternate explanation for their reported increase in "cerebral emboli" that they observed in patients undergoing cardiopulmonary bypass (CBP) who received PFC emulsion instead of the control solution. They used an automated transcranial Doppler ultrasound device to detect emboli that is directly affected by the presence of PFC emulsion in blood, and they failed to control for this interference in their experimental design.
They were so convinced that these "cerebral emboli" are real that they labeled them as adverse events, recommended that this agent not be used in patients undergoing aortic manipulation, and inferred that the occurrence of these "emboli" must have been the cause for the sponsor to suspend the phase III trial in which there was an imbalance of stroke rate in the experimental arm. These conclusions were accepted into the final article despite the fact that their patients suffered no ill effect while experiencing a 3-fold to 8-fold increase in "emboli" compared with the controls (Table 3), and they blamed that on the small sample size (25 treated vs. 11 control subjects). They also dismissed that PFC emulsion can interfere with their device because the 0.18 µm particles are too small, but they accepted that an 8-fold increase in emboli of the size that is detectable by their device may not cause overt clinical effects.
There are many published reports from 1982 [2] through 2006 [3] describing PFC emulsions as effective ultrasound contrast agents. Among those published by my group, I highlight two relevant reports demonstrating that PFC emulsion enhances Doppler signal [4] and that 2.7 g/kg is sufficient for ultrasound grayscale imaging of veins to detect thrombi [5]. They noted that "... the time periods in which AF0144 would most likely be circulating in highest concentration (from aortic cannulation to aortic cross clamp and from aortic cross clamp to aortic reperfusion) showed the largest increases." This is in keeping with the fact that what they observed was a direct effect of ultrasound signal enhancement and not necessarily the generation of emboli. Further, they did not offer an explanation of why the presence of PFC emulsion in blood would result in a continuous release of debris from aortic atheromas when aortic manipulation occurs during a small portion of the time. If what they speculate is true, they should have surely observed a greater bolus of emboli during manipulations.
Their conclusion that "AF0144 may not be suited for use in cardiac surgery" is certainly not supported by their data; their conclusion that its use should be limited to "a patient population not exposed to emboli generating manipulations" is not based on fact but rather on speculation. Their observation is most likely an artifact of using a device to assess emboli that is directly affected by the experimental substance.
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  S. E. Hill and H. P. Grocott Reply Ann. Thorac. Surg., May 1, 2007; 83(5): 1923 - 1923. [Full Text] [PDF]
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