diabetic cardiomyopathy

DEFINITION: Ventricular dysfunction in a patient with diabetes mellitus (type 1 or 2) that cannot be attributed to CAD, hypertension, valvular, or congenital heart disease. It is a diagnosis of exclusion (first described by Rubler, 1972).

PATHOPHYSIOLOGY: - Metabolic: insulin resistance and hyperglycemia shift myocardial metabolism from glucose to free fatty acid oxidation. This causes lipotoxicity (ceramide and lipid accumulation), increased oxygen consumption, reduced cardiac efficiency, and mitochondrial dysfunction with excess reactive oxygen species. - Advanced glycation end products (AGEs): cross-link collagen, increasing myocardial stiffness and impairing relaxation. - Fibrosis and hypertrophy: activation of RAAS and TGF-beta causes interstitial and perivascular fibrosis and cardiomyocyte hypertrophy. - Impaired calcium handling (reduced SERCA2a activity) contributes to slowed relaxation. - Microvascular disease and endothelial dysfunction cause small-vessel ischemia. Cardiac autonomic neuropathy also contributes. - Inflammation and oxidative stress promote cardiomyocyte apoptosis and necrosis.

CLINICAL COURSE: - Early stage: asymptomatic diastolic dysfunction with normal EF and impaired relaxation. Left atrial enlargement and LV hypertrophy may be present. - Later stage: symptomatic heart failure with preserved EF (dyspnea, exercise intolerance, edema), which can progress to reduced EF with LV dilation and systolic dysfunction. - Increased risk of arrhythmias (including atrial fibrillation) and sudden cardiac death. Silent ischemia is common because of autonomic neuropathy.

DIAGNOSIS: - Echocardiography: diastolic dysfunction (E/e' elevated, reduced e'), LV hypertrophy, and later reduced EF. Strain imaging (global longitudinal strain) detects early dysfunction. - Elevated BNP/NT-proBNP. - Cardiac MRI shows fibrosis (late gadolinium enhancement, T1 mapping). - Must exclude ischemic cardiomyopathy (coronary angiography or stress testing), hypertensive heart disease, and other causes.

MANAGEMENT: - Glycemic control and risk-factor modification (BP, lipids). - SGLT2 inhibitors (empagliflozin, dapagliflozin) reduce HF hospitalization in both HFrEF and HFpEF and are high-yield for boards. - Standard HF therapy: ACE inhibitors/ARBs/ARNI, beta-blockers, MRAs, and diuretics for congestion. - AVOID thiazolidinediones (pioglitazone, rosiglitazone) because they cause fluid retention and can worsen HF. Also use caution with saxagliptin and alogliptin (increased HF hospitalization signal). Metformin is safe in stable HF. - GLP-1 agonists show cardiovascular benefit in ASCVD, with mixed HF data.

HIGH-YIELD PEARLS: - Diabetes confers a 2–5x increased risk of HF independent of CAD and HTN. - Most common early finding is diastolic dysfunction. - Histology: interstitial and perivascular fibrosis, myocyte hypertrophy, and PAS-positive material deposition (glycoprotein) in the myocardium. - Distinguish from diabetic ischemic heart disease, which results from accelerated atherosclerosis in epicardial coronaries.