Higher hemoglobin levels are associated with impaired left ventricular global strains in metabolic syndrome: a 3.0 T CMR feature tracking study

Metabolic syndrome (MetS) is a known contributor to increased cardiovascular risk and all-cause mortality. Recent literatures suggested that higher hemoglobin (Hb) levels were associated with Mets, left ventricular (LV) dysfunction and adverse events in general population. This study aimed to assess the associations between Hb levels and LV global strains in patients with MetS.

A retrospective analysis included 254 patients with MetS and 78 sex-, age-, and Hb-matched controls. The MetS patients were stratified into five groups based on Hb levels: anemia, low-normal Hb, moderate-normal Hb, high-normal Hb, and high Hb. LV global radial, circumferential, and longitudinal strains (LVGRS, LVGCS, and LVGLS, respectively) were measured using the cardiac magnetic resonance feature tracking technique. Associations between Hb levels and LV global strains were evaluated using multiple linear regression, restricted cubic spline (RCS), and subgroup analyses.

After full adjustment, the LV global strains from three directions in the high Hb groups (LVGRS: β = −  4.943, 95% CI −  7.673 to − 2.213; LVGCS: β = −  2.341, 95% CI − 3.608 to − 1.074; LVGLS: β = −2.797, 95% CI − 4.049 to − 1.546, all p < 0.05) were significantly reduced than those in their respective moderate-normal Hb groups. Full adjusted RCS plots revealed inverted L-shaped associations between Hb levels and LV global strains, with significant reductions observed above 143 g/L (all p for nonlinearity < 0.05). Subgroup analyses indicated that the associations were more pronounced in MetS patients with obesity (LVGRS: β = −  0.005 [95% CI − 0.087 to 0.097] versus −0.087 [95% CI − 0.145 to − 0.030]; LVGCS: β = −0.006 [95% CI − 0.045 to 0.034] versus −0.048 [95% CI − 0.075 to − 0.021]; LVGLS: β = −0.011 [95% CI −  0.053 to 0.032] versus −0.063 [95% CI − 0.089 to − 0.036] for non-obese and obese patients; all p for interaction < 0.05).

Higher Hb levels are significantly associated with more severe LV dysfunction in MetS patients, particularly in those with obesity. Targeted monitoring and management of higher Hb levels in MetS patients may help mitigate further deterioration of cardiac function.