Multicenter Prospective Assessment of Coronary Microvascular Dysfunction: Primary Results of the FlowLab Study.

BACKGROUND

Coronary microvascular dysfunction (CMD) and vasospastic angina (VSA) are common, yet underdiagnosed. Existing studies of invasive CMD/VSA assessment have specified patient selection and procedural technique, with little known about testing use in real-world practice.

OBJECTIVES

The purpose of the study was to observe procedural and therapeutic decision-making for patients undergoing invasive CMD/VSA assessment.

METHODS

FlowLab was a multicenter, prospective study of patients with possible CMD in whom the treating physician used the CoroFlow bolus thermodilution system to measure coronary flow reserve and index of microcirculatory resistance (IMR). As the purpose was to observe how testing is performed in current practice, procedural technique, including whether to perform vasospasm testing, was at operator discretion. Procedural data were collected in real-time.

RESULTS

A total of 253 procedures were performed at 14 U.S. sites. The most common presenting symptoms were chest pain (222/253; 88%) and dyspnea (93/253; 37%). The median CoroFlow duration was 10 (IQR: 7-14) minutes and provocative vasospasm testing was performed in 50% (124/246). Forty-three percent (110/253) of patients had abnormal coronary flow reserve (<2.5) and 28% (72/253) had abnormal IMR (≥25). CMD/VSA was identified in 53% (135/253) of patients, with a final diagnosis of CMD in 59% (19/32) of these and VSA in 28% (9/32). Anginal therapy addition was more common in those with elevated IMR (61% [44/72] vs 29% [53/181]; P < 0.0001).

CONCLUSIONS

In a prospective assessment of invasive testing for CMD/VSA, we observed varied procedural and technical approaches. Testing was rapid, and a final diagnosis of CMD or VSA was common with immediate implications for patient management. Further integration of CMD/VSA evaluation may help address current gaps in diagnosis and treatment.