PCI时代的假阳性：约1/10的患者并不真正需要介入治疗

False-positives in the PCI era: Roughly one in 10 patients sent to cath lab unnecessarily

　　根据目前的指南，在被怀疑发生ST段抬高心梗后，患者应该尽快被送入导管室，减少发病－治疗时间，以获得最佳治疗时机。但这一策略最近受到了一些置疑，一份关于假阳性率的研究指出，这样做出错的几率大约为9-14%。

　　来自Ridgeview医学中心的David M Larson在12月19日的Journal of American medical Association杂志上撰文指出，医院为了做到更短的发病－治疗时间所付出的努力和开销应该重新被评估，因为这很可能导致误操作率的增加。

　　在接受采访时，Larson称在溶栓时代，接受溶栓但最终发现并非心梗发作的几率约为10%。PCI时代的假阳性率尚未有明确报道，无论是节约发病－治疗时间还是不刻意去做。Larson指出，在努力的缩短这一时间和评判患者是否真的需要介入治疗之间应该做出一个平衡。

　　他说：“有很多病例实际处于灰色地带，如果发病时更加深入的评判，就能够降低假阳性率，但势必要浪费时间。而现在的做法则会增加假阳性率但节省了时间，这是一个平衡。”

　　Larson对Minneapolis心脏病中心的所有STEMI可疑患者及从30家乡村医院转移而来的共1345名患者的病例进行了回顾。在所有病例中，急诊人员都在患者到达之前启动了导管介入设备。但实际上有14%的患者并非冠脉问题，其中9.5%并非急性心梗发作。在无冠脉疾病的人群中，38%的心脏标志物阳性，心肌炎为31%，耐力试验阳性为31%。总体来说，有9.2%的患者的心脏标志物指标和冠脉情况均为阴性，这也就是作者所指的假阳性。

　　有些时候需要放慢脚步

　　在随文评论中，来自Denver医学中心的Frederick A Masoudi等指出近年来刻意缩短发病－治疗时间的做法可能的确会增加假阳性率的可能。在一期PCI中，应该根据患者的具体情况来选择治疗。为降低这种类型的假阳性率，学者们应该淡化将发病－治疗时间来衡量医院诊疗水平的指标。

　　Larson同意上述看法：“现在对发病－治疗时间看得太重了，我们应该意识到有些治疗应该仔细斟酌后再进行，比如再做一次心电图或超声检查，我们应该关注介入的质量。这不是用时间来评判的领域，这是严肃的医学。如果一个医院的假阳性率超过25%，而这个区域的平均水平仅为10%，那么无论他的时间多快，也不能说它做得很好。”

　　但Larson指出有些做法能够降低这类假阳性率。他们发现心电图和超声被误读的几率很低，仅为2%左右，如果这方面的培训做的好，那么可以有效的规避假阳性病例。Larson还指出医生不应该把每一个患者假定为ST抬高心梗的患者来看待，这样的做法可能会暗示他们自己做出错误的选择，而是应该依赖于确凿的证据。如果可能，应尽可能置疑自己的判断，获得更多的数据，请其他心脏病科医生会诊或重读心电图。但我也不赞成对所有的病例都如此精细，因为毕竟有90%的病例是明确的，我们也不必因为这10%的患者而耽误大多数的心梗患者。

　　了解自己的速度

　　来自Abbott西北医院的Timothy Henry医生指出：“每个人都在谈假阳性率，但没人确切的知道自己的速度或什么速度是最合适的。如果你的假阳性率是2%到5%，那么你一定错过了一些患者。但如果你的假阳性率是25%，那么你应该反省一下自己的判断。最中药的是每一个人都确切的知道自己的速度，我们以往太重视发病－治疗时间这一指标，而忘记了其他方面。”

　　（北京协和医院　鲁勖　编译）

　　（来源：www.theheart.org）

False-positives in the PCI era: Roughly one in 10 patients sent to cath lab unnecessarily
 
December 18, 2007  
Shelley Wood

Minneapolis, MN - Having emergency-room physicians diagnose ST-segment-elevation MI (STEMI) and "activate" cardiac cath labs directly—cutting out the delay associated with seeing a cardiologist—is a key recommendation for efforts to trim door-to-balloon times for patients with STEMI. But a new analysis suggests that this strategy may lead to false-positive activation of cath labs anywhere from 9% to 14% of the time.

Writing in the December 19, 2007 issue of the Journal of the American Medical Association, Dr David M Larson (Ridgeview Medical Center, Waconia, MN) and colleagues point out that hospitals planning and budgeting for strategies to cut door-to-balloon times will need to take into account this relatively common and unavoidable consequence of direct cath-lab activation.

To heartwire, Larson, an ER physician, commented that he thinks a false-positive rate somewhere in the region of what they found is appropriate. In the thrombolytic era, he notes, the false-positive rate of patients who received lytics and later were found not to have an MI (by cardiac biomarkers) was about 10%; false-positive rates in the PCI era have not previously been reported, with or without door-to-balloon time-saving strategies. Larson also thinks that while hospitals should always strive to reduce the rates of patients being sent to the cath lab unnecessarily, there needs to be a balance.

"There are a lot of cases that are in the gray zone," he said. "If you’re more specific, and you decrease the rate of false positives, you’re probably going to increase your rate of false negatives. It’s a trade-off."

Larson et al reviewed all cases of suspected STEMI patients presenting to the Minneapolis Heart Institute or transferred from one of 30 community hospitals—a total of 1345 patients between March 2003 and November 2006. In all cases, emergency-department staff, on the basis of electrocardiogram results, activated the cath lab at the tertiary hospital before transferring patients for angiography. In the authors’ subsequent review, however, 14% of patients were found to have no culprit coronary artery and 9.5% had no significant coronary artery disease. Of those with no CAD, 38% had positive cardiac biomarkers, pointing to myocarditis (31%), stress cardiomyopathy (31%), or STEMI confirmed by cardiac MRI—in some of these patients, angiography did not pave the way for PCI but was at least an appropriate diagnostic test. In all, just 9.2% of patients had both negative cardiac biomarkers and no culprit artery, which the authors believe is likely the "true measure" of unnecessary cath-lab activation in this study.

Sometimes you do need to slow down

In an accompanying editorial, Dr Frederick A Masoudi (Denver Health Medical Center, CO) points out that the push in recent years to reduce door-to-balloon times may have the unintended consequence of increasing false-positive rates [2]. "In the case of primary PCI, the view of quality should extend beyond the time to treatment to include patient selection and ultimately to outcomes," he writes. To reduce the number of false positives that arise from overly zealous efforts to shorten door-to-balloon times, false-positive rates could, like door-to-balloon times, be a measure in the overall assessment of hospital performance.

Larson agrees: "There’s so much emphasis on door-to-balloon time and time to reperfusion; I think sometimes we have to realize that there are cases where we need to slow down and maybe get another ECG or an echocardiogram and not penalize people for slower door-to-balloon times in those cases. When you’re looking at quality, it’s not just the process measures like time to treatment, it’s patient selection as well. If one hospital has a false-positive rate of 25% and the standard in the community is 10%, you have to take a closer look at that."

But Larson also believes there is "always room for improvement." In his study, roughly 2% of electrocardiograms were "overread," resulting in patients heading to the cath lab unnecessarily. Better education would help reduce this problem, and centers with higher rates of false positives could perhaps be targeted for this kind of education, Larson suggests. He also notes that many patients who undergo an urgent diagnostic catheterization and are not found to have occlusive disease are patients who would likely have ended up undergoing angiography at a later date anyhow and, in some cases, may at least be less at risk from an invasive catheterization than if they underwent unnecessary fibrinolytic therapy: for example, patients having a dissection or who have pericarditis.

Larson also emphasized that the results should not be interpreted to mean that a cardiologist should see each and every patient with presumed STEMI in the emergency room—bypassing the cardiologist has proved key to improving door-to-balloon times. "There should always be the opportunity, on questionable cases, to get more data, get help from a cardiologist if necessary, have someone else look at the ECG, without penalizing somebody for having a slower door-to-balloon time. But I don’t think we should change the whole system: most of the cases—90%—are clear-cut. You don’t want to hurt the whole system because of the remaining 10% of patients."

Know your rates

Also commenting on the study for heartwire, senior author and cardiologist Dr Timothy Henry (Abbott Northwestern Hospital, Minneapolis, MN) noted that this study "sets a benchmark."

"Everyone talks about false positives, but no one knows what their rates are or what the rates should be," he said. "If your false-positive rate is 2% or 5%, you’re doing something wrong and you’re missing patients. But if your false-positive rate is 25%, you need to be talking to people about what you could do differently. . . . The most important thing is that everyone should know what their own rate is. We’ve been so focused on reducing door-to-balloon times that we’ve forgotten about some of these other things."