Читать книгу Practical Cardiovascular Medicine - Elias B. Hanna - Страница 228

In patients undergoing coronary angiography for typical angina who are found to have unobstructed coronary arteries, the following invasive strategy may be performed to diagnose “coronary vasomotion disorders:”

 Intracoronary acetylcholine assessment for macrovascular spasm and macrovascular endothelial dysfunction. Normally, when the endothelium is normal, acetylcholine vasodilates the coronary arteries at the macro- and microvascular levels. Macrovascular spasm is defined as >75-90% epicardial narrowing. Macrovascular endothelial dysfunction is defined as a paradoxical, mild diffuse narrowing of the epicardial coronary arteries >20% with acetylcholine (not as severe as vasospasm).

 Intracoronary acetylcholine assessment of the microcirculation if no macrovascular spasm occurs, via ST-segment response (Ong et al studies and CorMicA) or via coronary blood flow measurement.6,120–122 In microvascular endothelial dysfunction, coronary blood flow declines with acetylcholine, or remains unchanged (<50% increase).

  Intravenous adenosine assessment of the microcirculation via coronary flow reserve OR index of microvascular resistance*Coronary blood flow may be calculated using a Doppler wire (flow=velocity x vessel area), but also a more widely available FFR pressure wire that has a temperature sensor. The wire is advanced midway in the coronary artery. Depending on the transit time of a 3-ml saline injection through the coronary guiding catheter, the thermodilution sensor estimates coronary flow at rest and during IV adenosine-induced hyperemia (flow=1/transit time)*Coronary flow reserve (CFR) is the ratio of flow or velocity with adenosine vs rest. CFR < 2.3 (2-2.5) is abnormal.*Index of microvascular resistance is calculated with the FFR wire at hyperemia (=distal coronary pressure/flow). An index ≥25 is indicative of microvascular dysfunction.

Acetylcholine causes vasodilatation if the endothelium is intact and able to generate NO, whereas adenosine vasodilates by directly acting on smooth muscle cells; thus, acetylcholine tests “NO- or endothelium-dependent” vascular function, whereas adenosine tests “endothelium-independent” function. Acetylcholine is administered in slow, incremental intracoronary boluses, over 3 min for each, and adenosine is administered as IV infusion.

Albeit safe, the acetylcholine testing is skipped at some institutions. By adopting this protocol in patients with angina and unobstructed coronary arteries, macrovascular endothelial dysfunction is found in ~40%, microvascular dysfunction in 30-50%, and epicardial vasospasm in 20-30% of patients.^{120–122,130,138,139} Overall, abnormal vasomotion is found in ~70% of patients. Preferably, microvascular dysfunction is assessed in each coronary artery, as microvascular dysfunction is frequently a localized process and patients most commonly have microvascular dysfunction in one vessel (nearly equal distribution among LAD and RCA, less likely in LCx).¹³⁸ For safety, most studies have only assessed one vessel, the LAD ^122,130,139

Also, consider performing FFR if diffuse luminal irregularities are present (the mild diffuse epicardial disease may be significant in ~5% of the cases). If bridging is present, consider calculating diastolic FFR using dobutamine.

CorMicA trial showed that anti-anginal therapy tailored to the results of the above functional testing significantly improves angina severity and quality of life, compared to presumptive therapy.¹²² As such, patients with microvascular angina received: (1 ^st line) ß-blocker; ( 2 ^nd line) CCB; (3 ^rd line) ranolazine. Patients with epicardial vasospasm received CCB +/-nitrates.

Non-invasive strategy- Microvascular dysfunction may also be diagnosed non-invasively, after a negative coronary angiogram, via adenosine stress PET or adenosine MRI perfusion imaging.

Unlike SPECT imaging which qualitatively compares signal intensity of myocardial territories, PET perfusion imaging can accurately quantify myocardial blood flow, using the linear relationship between myocardial blood flow and the speed of radioisotope signal uptake during dynamic imaging. Cardiac MRI can assess myocardial perfusion based on the myocardial signal intensity of gadolinium upon first pass imaging (not late gadolinium imaging); perfusion reserve is reflected by the change of this signal intensity with adenosine. Both modalities can calculate CFR non-invasively.