Читать книгу Practical Cardiovascular Medicine - Elias B. Hanna - Страница 29

According to multiple large registries and meta-analyses, a single undetectable or very low hs-troponin (eg, <0.005 ng/ml) is associated with <0.3% risk of acute MI and nearly 0% risk of cardiac death at 30 days^{28–30,45,47–55} Even 1-year events were very low at 0.6% in several registries, with a cardiac death ≤0.1%.^28,47,51 This risk is further reduced in patients whose ECG is not suggestive of ischemia. Therefore, discharge is safe in those patients, at least as safe as in patients with negative stress tests, with no need for serial troponin measurement.

For patients acutely presenting with chest pain and no other critical illness, ESC and multiple European investigators suggest checking hs-troponin at presentation and at 1 or 2 hours after presentation (0/1 or 0/2 strategy) (Figure 1.3).^{4,28–30,45,47–55} An undetectable hs-troponin, or a detectable hs-troponin with insignificant change at 1 or 2 hours rules out MI with >99.5% confidence. However, the issue is that a substantial proportion of patients who rule in for MI have non-MI troponin elevation or type 2 MI, rather than type 1 MI. ACS/type 1 MI is the diagnosis in 70-75% of the rule-in cases with no other critical illness, but is much lower in all comers (type 1 MI is the diagnosis in only 50% of patients with troponin up to 3-fold the upper reference limit).⁴

Note that the MI cutoff of hs-troponin is close to that of conventional troponin (eg, ~0.04 ng/ml), but is slightly lower and more precise than conventional troponin, with precision at the 3^rd decimal, and the cutoff is lower in women than men with many assays.⁴⁵ Thus, hs-troponin slightly increases the diagnosis of MI in comparison to conventional troponin (by 20%). More importantly, it allows delineation of a very low level and a very low risk population that cannot be delineated with conventional troponin and allows early and safe discharge of these very low risk patients. Based on this strategy, over 60% of patients may be discharged at presentation or 1 to 2 hours later. In fact, up to 50% of patients presenting with chest pain have undetectable or very low hs-troponin I (<0.005 ng/ml).^51,52

If hs-troponin is not available or not used, conventional troponin is rechecked 3-6 hours after symptom onset (<3-6 hours from presentation) (ACC guidelines). Late troponin abnormality beyond 3 hours is rare, ~1%;⁴ rarely, troponin may need to be checked beyond 6 hours, in patients with worrisome ECG or recurrent severe symptoms (ACC).³⁶ A negative conventional troponin is less reassuring than a low/undetectable hs-troponin, and thus, the patient frequently requires non-invasive testing for CAD; stress testing or coronary CT angiography may be performed after the second troponin, at 3-6 hours after symptom onset, or may be deferred up to 72 hours after discharge in patients with atypical symptoms and no prior CAD. The patient with persistent atypical chest pain and negative troponin has a low likelihood of CAD and may undergo stress testing while having the atypical pain.

Figure 1.3 0/1-hour or 0/2-hour ESC algorithm using hs-troponin in patients presenting to the emergency department with suspected ACS. This example uses the cutoff values specific for Roche Elecsys hs-troponin T assay. Of note, with this assay, the 99 ^th percentile threshold is 22 ng/L in men, and 14 ng/L in women, yet 52 ng/L is chosen as the MI rule-in value. As per ESC, this is done to improve the positive predictive value for MI, particularly that the 99^th percentile threshold varies with the population studied and is not highly specific.

This algorithm may be applied to other hs-troponin assays using different cutoffs (Abbott hs-troponin I, rule-in value=64). Hs-troponin is expressed in ng/L, which may be divided by 1000 to obtain conventional values in ng/ml.

Clinical scores (eg, HEART) do not improve the safety of this algorithm and unnecessarily reduce the proportion of patients ruled out.⁴⁷

Most patients who rule out with the hs-troponin strategy have non-cardiac pain. Hence, further testing is not definitely required in patients who rule out with the hs-troponin strategy, particularly when hs-troponin is undetectable. Yet some of the rule-out patients have true angina, especially those with exertional chest pain. CTA or stress imaging (>stress ECG, as per ESC) remains necessary in exertional chest pain and in patients with intermediate hs-troponin findings: a normal or low-risk stress imaging suggests no CAD, microvascular disease, or low-risk CAD for which medical therapy is appropriate. Medical therapy is tailored to how much the physician believes the chest pain is anginal, based on the exertional component, and is somewhat comparable to the management of chronic CAD. As such, coronary angiography is performed in patients whose chest pain is: (i) predominantly exertional, and (ii) occurring during low levels of activity.

Rule-in patients frequently require coronary angiogram, in the absence of a concomitant type 2 MI setting.