Coronary slow flow and myocardial contractile reserve: a speckle‑tracking echocardiography study.

BACKGROUND

The Coronary Slow Flow Phenomenon (CSF) is increasingly recognized as a distinct phenotype of Ischemia with Non-Obstructive Coronary Arteries (INOCA). However, debate persists regarding whether CSF represents fixed structural microvascular remodeling or functional dysregulation. Conventional Left Ventricular Ejection Fraction (LVEF) is often insensitive to the subtle subendocardial mechanics associated with this condition.

OBJECTIVES

This study aimed to interrogate the functional reserve of the left ventricle in patients with angiographically defined CSF using Two-Dimensional Speckle-Tracking Echocardiography (2D-STE) during physiological exercise stress.

METHODS

We conducted a prospective case-control study enrolling 63 patients evaluated for angina pectoris. The cohort comprised 33 patients with angiographically defined CSF (Corrected TIMI Frame Count > 27) and 30 age- and sex-matched controls with normal coronary flow. All participants underwent symptom-limited treadmill exercise testing (Bruce protocol). Left ventricular Global Longitudinal Strain (GLS) was quantified at rest and at peak stress.

RESULTS

At rest, despite comparable LVEF between groups (CSF: 65.6 ± 3.5% vs. Control: 66.3 ± 3.6%; P = 0.423), the CSF group exhibited significantly impaired GLS compared with controls (-18.37 ± 0.85% vs. -20.07 ± 1.33%; P < 0.001), indicating subclinical systolic dysfunction. Upon peak exercise, both groups demonstrated significant augmentation in GLS (P < 0.001). Although peak stress GLS remained numerically lower in the CSF group (-22.10 ± 2.08% vs. -23.27 ± 1.74%; P = 0.020), the magnitude of functional recruitment (ΔGLS) was fully preserved in CSF patients (3.73 ± 1.54% vs. 3.19 ± 1.41%; P = 0.154).

CONCLUSIONS

Patients with CSF exhibit distinct subclinical longitudinal dysfunction at rest, likely attributable to elevated resting microvascular resistance. However, the preservation of contractile reserve during physiological stress suggests that the underlying microvascular dysfunction is predominantly functional and reversible. 2D-STE provides incremental diagnostic value over conventional angiography in stratifying the pathophysiology of INOCA.