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Coronary microcirculatory vasoconstriction during ischemia in patients with unstable angina
M Marzilli1, G Sambuceti, S Fedele
1CNR Institute of Clinical Physiology, Pisa, Italy.
Insights
In unstable angina (UA), spontaneous ischemia causes vasoconstriction in both the main coronary artery narrowing and the smaller microcirculation vessels. This finding highlights the dual role of vasoconstriction in UA pathophysiology.
Area of Science:
- Cardiology
- Vascular Physiology
- Ischemic Heart Disease
Background:
- Unstable angina (UA) traditionally implicates vasoconstriction at the site of coronary artery stenosis.
- Emerging evidence suggests a potential role for microcirculatory vasoconstriction in UA.
- This study investigates microvascular behavior during spontaneous ischemia in UA patients.
Purpose of the Study:
- To assess coronary microvascular tone during episodes of spontaneous ischemia in patients diagnosed with unstable angina (UA).
- To determine if microvascular vasoconstriction contributes to ischemia in UA.
- To compare microvascular resistance during ischemia with responses to pharmacological vasodilation.
Main Methods:
- Inclusion of 10 patients with unstable angina (UA) and single-vessel coronary artery disease (CAD).
- Monitoring of coronary blood flow velocity, transstenotic pressure gradients, and distal coronary pressure.
- Calculation of stenosis and microvascular resistance at baseline, after intracoronary adenosine, and during transient ischemia induced by balloon occlusion.
Main Results:
- Adenosine reduced microvascular resistance but did not alter stenosis resistance.
- Spontaneous ischemia, associated with angina and ST-segment changes, increased both stenosis resistance (1233%) and microvascular resistance (671%).
- Distal coronary pressure during ischemia was similar to adenosine-induced vasodilation, but significantly lower during balloon occlusion, indicating limited collateral flow.
Conclusions:
- Transient myocardial ischemia in UA patients is accompanied by vasoconstriction in both the stenotic coronary segment and the downstream microcirculation.
- These findings suggest that microvascular dysfunction plays a significant role in the pathophysiology of unstable angina.
- The study underscores the importance of considering both epicardial and microvascular components in UA management.
Objective:
To verify the behavior of coronary microvascular tone during spontaneous ischemia in patients with unstable angina (UA).
Background:
In UA, the pathogenetic role of vasoconstriction is classically confined at the stenotic coronary segment. However, microcirculatory vasoconstriction has been also suggested by previous experimental and clinical studies.
Methods:
The study included 10 patients with UA (recent worsening of anginal threshold and appearance of angina at rest) and single-vessel CAD. Blood flow velocity was monitored by a Doppler catheter in the diseased artery. Transstenotic pressure gradient was monitored by aortic and distal coronary pressure monitoring. Stenosis resistance was calculated as the ratio between pressure gradient and blood flow, microvascular resistance as the ratio between distal pressure and blood flow. Measurements were obtained at baseline, following intracoronary adenosine (2 mg) and during transient ischemia. Aortic and distal coronary pressures were also measured during balloon coronary occlusion.
Results:
Adenosine did not affect stenosis resistance, while it decreased (p < 0.05) microvascular resistance to 52 +/- 22% of baseline. Angina and ischemic ST segment shift were associated with transient angiographic coronary occlusion in 7 of 10 patients; however, in no case was ischemia associated with interruption of flow. Despite markedly different flow values, distal coronary pressure was similar during adenosine and during spontaneous ischemia (48 +/- 15 vs. 46 +/- 20 mm Hg, respectively, NS). During ischemia, a marked increase in the resistance of both coronary stenosis and coronary microcirculation was observed (to 1,233% +/- 1,298% and 671% +/- 652% of baseline, respectively, p < 0.05). Distal coronary pressure was markedly reduced during balloon coronary occlusion (14 +/- 7 mm Hg, p < 0.05 vs. both adenosine and ischemia), suggesting the absence of significant collateral circulation.
Conclusions:
In patients with UA, transient myocardial ischemia is associated with vasoconstriction of both stenotic arterial segment and downstream microcirculation.