Muscle ultrasound in heart failure: pathophysiological profiling and clinical stratification

Heart failure (HF) management increasingly requires multimodal assessment beyond cardiac function. Although echocardiography remains central, skeletal muscle and diaphragmatic dysfunction-key drivers of exercise intolerance-are underdiagnosed. This review synthesizes two critical aspects: (1) the pathophysiological heterogeneity of muscle involvement across HF subtypes [HF with reduced ejection fraction (HFrEF), HF with mildly reduced ejection fraction (HFmrEF), and HF with preserved ejection fraction (HFpEF)] and (2) the clinical utility of muscle ultrasound as a dynamic, bedside-compatible tool for risk stratification and personalized interventions. Emerging evidence reveals distinct mechanisms: HFrEF predominantly associates with diaphragmatic atrophy and mitochondrial dysfunction, whereas HFpEF is characterized by reduced diaphragmatic motion and skeletal muscle fat infiltration. Ultrasound-derived parameters, such as echo intensity for quadriceps fat quantification and diaphragm thickness ratio for inspiratory weakness, strongly correlate with functional outcomes (e.g., 6-min walk distance and peak VO₂). Notably, a quadriceps echo intensity > 28 dB in HFrEF or a diaphragmatic excursion < 2.5 cm in HFpEF independently predicts adverse prognosis, guiding targeted interventions such as inspiratory muscle training or anti-inflammatory therapies. However, critical gaps persist, including the lack of standardized cutoff values for HF subtypes and insufficient data on ultrasound-guided therapeutic monitoring. Future research should prioritize subtype-specific protocols and validate cost-effective ultrasound algorithms against standard modalities. By bridging pathophysiology and clinical application, this review underscores muscle ultrasound's transformative potential in refining HF phenotyping, ultimately enhancing exercise capacity and reducing hospitalizations.