Читать книгу Practical Cardiovascular Medicine - Elias B. Hanna - Страница 30

In patients with elevated troponin, the most important step is to distinguish type 1 MI from secondary myocardial injury (which does not dictate acute antithrombotic therapy or coronary angiography). In a patient presenting with chest pain and no other obvious cardiac or systemic insult (HF, critical illness), any troponin elevation, even if mild (eg, 0.04 ng/ml), is a high-risk feature suggestive of type 1 MI and treated as such, with an initial invasive strategy. More severe troponin elevation or ischemic ST depression increases the likelihood of underlying CAD and, in this setting, type 1 MI (rather than MI secondary to an overlooked type 2 MI setting, hypertension, or microvascular disease). Per ESC guidelines, elevations up to 3-fold the upper reference limit (~0.15 ng/ml) have limited positive predictive value for type 1 MI (~50%). Conversely, “elevations beyond 5-fold the upper reference limit have high (>90%) positive predictive value for type 1 MI” (this corresponds to a troponin >0.25 ng/ml).⁴ Severe hypertension, elevated LVEDP from acute diastolic dysfunction, and vasospasm (micro- or macrovascular) are common causes of mild troponin elevation in patients with non-obstructed coronary arteries.

All patients with elevated troponin are categorized as “high risk”, but additional features imply a further increase in risk and probability of type 1 MI, such as ischemic ST changes (more extensive disease), severe troponin rise >0.5-1 ng/ml,⁵⁶ elevated BNP, or high-risk scores (TIMI risk score ≥ 3 or GRACE risk score >140^*).

The TIMI, HEART and GRACE risk scores are used in ACS once the diagnosis of ACS is established. These scores should not be used for the diagnosis of ACS; they have a prognostic rather than a diagnostic utility. Also, scores are one risk stratifier out of many. An elevated troponin may be associated with a TIMI risk score of only 1, yet still implies NSTEMI. In the right setting, even a mild troponin rise (e.g., 0.05 ng/ml) is a high-risk feature.

Unstable angina- Some patients qualify for an initial invasive strategy even if troponin is below MI cutoff, and may be placed under the category of “unstable angina”, although “severe stable angina” is a better nomenclature (intermediate-risk ACS per ACC, low-risk ACS per ESC):

 Typical angina at mild exertion, with a typical timing and duration of angina (angina occurs with exertion, is relieved with rest, and lasts few minutes)

 Typical exertional angina in a patient with diabetes, PAD, or CKD stage 3

 Typical exertional angina with prior PCI <6-12 months (time frame of restenosis) or prior CABG

 Low EF<40% or segmental wall motion abnormality

Hs-troponin is usually detectable in those patients, albeit below MI cut-off. This resembles the hs-troponin behaviour after a stable angina episode or a positive exercise stress testing: hs-troponin rises to detectable levels but remains well below MI cutoff, even if stress-induced ischemia is severe. Ischemia must be sustained to induce a troponin rise above MI cutoff.⁵⁷

Diabetes is associated with a higher risk of adverse outcomes in NSTEMI and in typical exertional angina, and thus, an invasive strategy may be considered even with the latter case. Women with negative troponin do not generally qualify for an initial invasive strategy, as there is evidence of harm with this strategy in low-risk women.

Rest pain with negative troponin is not usually ACS and does not qualify for initial coronary angiography. Conversely, exertional pain with negative troponin may reflect CAD, a stable CAD with no plaque rupture which may, nonetheless, be severe or extensive; when angina occurs on mild exertion, initial coronary angiography is justified.