SGLT-2 Inhibitors in Heart Failure and Diabetes

Primary Mechanism: Renal Glucose Reabsorption Inhibition

• SGLT-2 cotransporters in the proximal convoluted tubule reabsorb 90% of filtered glucose (normally 1-5 g/day)
• SGLT-2 inhibitors block this transporter, causing osmotic diuresis with glucosuria of 40-100 g/day
• Results in caloric loss (~240 kcal/day), natriuresis, and mild volume depletion
• Reduces hyperglycemia independent of insulin secretion or action

Cardiac Metabolic Benefits

• Shifts cardiac energy substrate from fatty acid oxidation to ketone body and lactate utilization, improving myocardial efficiency
• Increases myocardial ATP production and reduces oxidative stress through improved mitochondrial function
• Reduces intracellular sodium and calcium overload via decreased Na+/H+ exchanger activity (primary mechanism of diastolic dysfunction)
• Decreases cardiac fibrosis through reduced TGF-β signaling and prevention of myocardial hypertrophy
• Improves diastolic function and left ventricular compliance before systolic improvements manifest

Renal and Systemic Hemodynamic Effects

• Creates osmotic diuresis without activation of renin-angiotensin-aldosterone system (RAAS), avoiding reflex tachycardia
• Produces mild volume contraction (2-3% body weight reduction) that normalizes preload without excessive afterload reduction
• Reduces intraglomerular pressure through preferential afferent arteriole vasoconstriction, protecting against hyperfiltration injury
• Modulates sympathetic nervous system activity, reducing norepinephrine levels and heart rate
• Enhances parasympathetic tone and improves heart rate variability

Inflammatory and Oxidative Stress Reduction

• Decreases inflammatory cytokines (IL-6, TNF-α) and C-reactive protein
• Reduces reactive oxygen species production and improves endothelial function
• Decreases uric acid reabsorption (uricosuric effect), potentially anti-inflammatory
• Activates AMP-kinase and promotes mitochondrial biogenesis through AMPK-dependent pathways

Adipose Tissue and Metabolic Effects

• Reduces visceral adiposity and improves insulin sensitivity
• Enhances adiponectin secretion
• Improves lipid profile with modest triglyceride reduction and potential HDL elevation
• Weight loss of 2-4 kg independent of caloric restriction

Indications for SGLT-2 Inhibitor Use

Type 2 Diabetes Mellitus with Cardiovascular Disease

• Established coronary artery disease, prior MI, or coronary revascularization
• Cerebrovascular disease or peripheral arterial disease
• Chronic kidney disease (CKD stages 1-4)
• High-risk features: age >55 years (men) or >65 years (women) with ≥1 cardiovascular risk factor

Heart Failure with Reduced Ejection Fraction (HFrEF)

• LVEF ≤40% (primary indication)
• Class II-IV symptoms or asymptomatic with prior decompensation
• Both diabetic and non-diabetic cardiomyopathy
• All racial/ethnic groups benefit equally

Heart Failure with Preserved Ejection Fraction (HFpEF)

• LVEF ≥40% with HF symptoms and elevated natriuretic peptides
• Dapagliflozin FDA-approved for symptomatic HFpEF (DELIVER trial)
• Benefit extends to entire EF spectrum

Chronic Kidney Disease

• CKD stage 2-4 (eGFR 20-90 mL/min/1.73m²)
• Albuminuria present or absent
• Non-diabetic CKD (CREDENCE, DAPA-CKD trials)
• Progressive decline in GFR

Risk Factors for SGLT-2 Inhibitor Benefit

• Age (benefit consistent across ages but greatest in elderly >75 years)
• Elevated baseline N-terminal pro-B-type natriuretic peptide (NT-proBNP)
• Prior HF hospitalization
• Reduced baseline eGFR (stronger CKD benefit)
• Female sex (improved HFpEF outcomes in women)

In Diabetes (Pre-Heart Failure)

• Polyuria, polydipsia (glucosuria)
• Progressive dyspnea on exertion or fatigue (subclinical HF progression)
• Weight loss (2-4 kg, gradual)
• Minimal symptoms; often asymptomatic
• Genital mycotic infections (candidal balanitis/vulvovaginitis) in 10-15% of patients

In Acute Decompensated Heart Failure

• Dyspnea at rest or with minimal exertion (orthopnea, paroxysmal nocturnal dyspnea)
• Fatigue and reduced exercise tolerance
• Peripheral edema, ascites, hepatomegaly
• Sudden weight gain (>2-3 lbs/day)
• Reduced urine output despite diuretics

Physical Examination Findings in Heart Failure

• Elevated jugular venous pressure (JVP) with prominent hepatojugular reflux
• S3 gallop (ventricular diastolic dysfunction)
• Diminished S1, paradoxically split S2
• Bilateral crackles/rales at lung bases
• Peripheral edema (lower extremities, sacral in bedridden patients)
• Hepatomegaly with hepatic tenderness (passive congestion)
• Tachycardia and hypotension (decompensated state)
• Cool extremities, poor perfusion (cardiogenic shock)
• Laterally displaced, hyperdynamic point of maximal impulse (PMI)

Asymptomatic Presentation

• Incidental finding on echocardiography (reduced EF without symptoms)
• Elevated natriuretic peptides on screening
• Many SGLT-2 inhibitor benefits occur subclinically

Laboratory Studies

Glycemic Control Assessment

• Hemoglobin A1C (baseline): diagnostic for diabetes; monitors glycemic control (goal varies by patient)
• Fasting glucose: baseline assessment
• Home glucose monitoring/continuous glucose monitor (CGM): real-time assessment; SGLT-2i typically reduce A1C by 0.5-1.5%
• C-peptide or fasting insulin: to assess residual beta-cell function (optional)

Natriuretic Peptides (Critical for HF Diagnosis)

• B-type natriuretic peptide (BNP) or N-terminal pro-BNP (NT-proBNP)
• BNP >100 pg/mL or NT-proBNP >125 pg/mL: supportive of HF diagnosis
• BNP >400 pg/mL or NT-proBNP >900 pg/mL: marked elevation in decompensation
• Higher levels correlate with worse prognosis; SGLT-2i reduce natriuretic peptide levels
• Serial measurements track therapeutic response

Renal Function and Electrolytes

• Serum creatinine and calculated eGFR (Modification of Diet in Renal Disease [MDRD] or CKD-EPI)
• Baseline assessment; critical for dosing
• Empagliflozin/dapagliflozin approved down to eGFR 20 mL/min/1.73m²
• SGLT-2i slow decline in eGFR by 30-40%
• Blood urea nitrogen (BUN): elevated in decompensated HF or renal dysfunction
• Sodium, potassium, chloride
• Hyponatremia (Na <135 mEq/L): marker of severe HF
• Hyperkalemia is NOT typical with SGLT-2i (mild potassium-lowering effect); safe with ACE-inhibitors/ARBs/aldosterone antagonists
• Monitor closely during initiation (1-2 weeks) and after dose changes

Metabolic Panel

• Liver function tests: exclude hepatic dysfunction (baseline)
• Uric acid: baseline; SGLT-2i are uricosuric and reduce uric acid 10-15%
• Lipid panel: baseline; SGLT-2i provide modest TG reduction (-5-10%), variable LDL effect

Complete Blood Count

• Baseline hemoglobin/hematocrit
• Monitor for hematocrit elevation (mild increase common with diuretic effect)

Cardiac Biomarkers and Risk Stratification

• Troponin (high-sensitivity): assess for acute coronary syndrome
• Lipoprotein(a): if available; risk stratification in diabetes

Urinalysis and Urine Studies

• Urinalysis: baseline; glucosuria expected with SGLT-2i
• Urine albumin-to-creatinine ratio (UACR)
• Baseline assessment of proteinuria
• SGLT-2i reduce UACR by 30-50% (albuminuria reduction independent of blood pressure)
• Guides intensity of renal protection strategy

Imaging Studies

Echocardiography (Essential for HF Diagnosis)

• Two-dimensional and Doppler echocardiography: gold standard for HF classification
• Left ventricular ejection fraction (LVEF): <40% = HFrEF; 40-49% = HFmrEF; ≥50% = HFpEF
• SGLT-2i benefit across all EF ranges; strongest data for LVEF ≤40%
• Left atrial volume index: elevated in HF; predicts progression
• E/e' ratio (diastolic dysfunction marker): SGLT-2i improve diastolic function
• Right ventricular function and TAPSE: assess RV involvement
• Pulmonary artery systolic pressure: elevated in decompensated HF
• Baseline assessment critical; repeat every 6-12 months or with clinical change

Electrocardiography (ECG)

• Sinus rhythm vs. atrial fibrillation: AF common in HF
• QRS duration: ≥120 ms suggests need for CRT evaluation
• LVH pattern: common in HF, especially HFpEF
• Q waves: evidence of prior MI
• Baseline before initiation; monitor for arrhythmias

Chest X-ray

• Pulmonary congestion: Kerley B lines, interstitial edema, alveolar edema
• Cardiomegaly: cardiothoracic ratio >0.5
• Pleural effusions: usually bilateral in HF
• Assess response to therapy; less reliable than echocardiography

Cardiac MRI (Advanced Assessment)

• Assess myocardial fibrosis and scar burden
• Infiltrative cardiomyopathy evaluation
• Not routine but useful in unclear etiology

Stress Testing/Coronary Angiography

• Indicated in HF if ischemic etiology suspected or persistent angina
• Rule out CAD before attributing cardiomyopathy to other causes
• Not universally required; guided by clinical presentation

Diagnostic Criteria

Heart Failure Diagnosis (2022 AHA/ACC/HFSA Guidelines)

HFrEF (LVEF ≤40%)

• Symptoms or signs of HF (dyspnea, fatigue, edema, orthopnea, PND)
• Objective evidence of cardiac dysfunction: LVEF ≤40% on echocardiography
• Response to HF-directed therapy supports diagnosis

HFmrEF (LVEF 41-49%)

• HF symptoms/signs
• LVEF 41-49%
• Objective structural/functional cardiac abnormality (LVH, elevated filling pressures)
• SGLT-2i have emerging benefits; dapagliflozin studied in this range

HFpEF (LVEF ≥50%)

• HF symptoms/signs
• LVEF ≥50%
• Evidence of diastolic dysfunction: elevated E/e' ratio, elevated NT-proBNP/BNP, LA enlargement
• Dapagliflozin approved for symptomatic HFpEF (DELIVER trial)

Type 2 Diabetes Diagnostic Criteria (ADA)

• Fasting glucose ≥126 mg/dL (×2 occasions), OR
• 2-hour glucose ≥200 mg/dL during 75-g oral glucose tolerance test, OR
• A1C ≥6.5%, OR
• Random glucose ≥200 mg/dL with symptoms

CKD Staging (KDIGO)

• Stage 1: eGFR ≥90 mL/min/1.73m² (with albuminuria)
• Stage 2: eGFR 60-89
• Stage 3a: eGFR 45-59
• Stage 3b: eGFR 30-44
• Stage 4: eGFR 15-29
• Stage 5: eGFR <15

SGLT-2 Inhibitor Selection and Dosing

Agents with Heart Failure Indications

First-Line Treatment: SGLT-2 Inhibitors for HFrEF

Mechanism of Benefit

• Empagliflozin (10 mg daily): EMPEROR-Reduced trial showed 25% relative risk reduction (RRR) in HF hospitalization/death in HFrEF; LVEF ≤40%, irrespective of diabetes status
• Dapagliflozin (10 mg daily): DAPA-HF trial demonstrated 26% RRR in HF hospitalization/cardiovascular death; benefits in LVEF ≤40%
• Both agents improve symptoms, reduce hospitalizations, and slow HF progression
• Independent of ejection fraction: benefit extends to HFmrEF and HFpEF

Initiation and Titration

• Check baseline eGFR ≥20 mL/

Metabolic

• Euglycemic diabetic ketoacidosis (eDKA): the class-defining toxicity. Glucosuria lowers plasma glucose and thus insulin secretion; the fall in the insulin:glucagon ratio unleashes lipolysis and hepatic ketogenesis, while SGLT-2 blockade also promotes renal ketone reabsorption. The result is an anion-gap acidosis with glucose often <250 mg/dL, which delays recognition. Precipitants include surgery, fasting, acute illness, very-low-carbohydrate diets, alcohol, and insulin dose reduction. There is no reversal agent: treat with IV fluids, insulin infusion given together with dextrose, and drug discontinuation. The ADA Standards of Care and FDA labeling advise holding the drug several days before scheduled surgery and during acute illness or prolonged fasting (sick-day rules).
• Hypoglycemia: minimal as monotherapy because the mechanism is insulin-independent; risk rises when combined with insulin or sulfonylureas, which may need dose reduction.

Genitourinary

• Genital mycotic infections: glucosuria feeds perineal Candida, causing vulvovaginitis or balanitis, more common in women and uncircumcised men. Usually treated topically without stopping the drug.
• Fournier gangrene: rare necrotizing fasciitis of the perineum; FDA-warned. Perineal pain, swelling, fever, or crepitus mandates immediate surgical debridement and broad-spectrum antibiotics.
• Urinary tract infection/urosepsis: less consistent than mycotic infection but reported.

Hemodynamic and renal

• Volume depletion, orthostatic hypotension, AKI: osmotic diuresis plus natriuresis, amplified by loop diuretics, RAAS blockade, or advanced age. Loop diuretic dose reduction is often needed at initiation.
• Expected early eGFR dip: afferent arteriolar constriction lowers intraglomerular pressure, producing a small acute creatinine rise that then plateaus — this is the mechanism of long-term renoprotection and is not a reason to stop.

Other and contraindications

• Canagliflozin-specific signals: amputation and fracture risk seen in trial data; use caution with peripheral arterial disease.
• Avoid in: type 1 diabetes (high eDKA risk), active DKA, dialysis-dependent ESKD, prior serious hypersensitivity, and pregnancy/lactation.
• Monitoring: renal function and volume status after initiation, foot care, and beta-hydroxybutyrate rather than glucose when ketoacidosis is suspected. Urine glucose strips will always be positive and are useless for monitoring.

• Euglycemic DKA is the tested toxicity: a diabetic on empagliflozin who is post-op, fasting, or acutely ill presents with nausea, dyspnea, and an anion-gap metabolic acidosis but glucose only mildly elevated. Best next step is to check serum beta-hydroxybutyrate and a basic metabolic panel/ABG, not to be reassured by a normal glucose. Treatment is insulin plus dextrose with fluids.
• Four pillars of HFrEF: per the 2022 AHA/ACC/HFSA guideline, guideline-directed therapy is ARNI (or ACEI/ARB), beta blocker, MRA, and SGLT-2 inhibitor. A stem listing only three and asking "what is missing?" is a classic setup.
• Benefit is independent of diabetes: empagliflozin and dapagliflozin reduce HF hospitalization and cardiovascular death in nondiabetic HFrEF. "Patient does not have diabetes" is not a reason to withhold the drug.
• The early creatinine bump is expected: afferent arteriolar constriction lowers hyperfiltration. The correct answer is continue the drug and recheck, not discontinue — the same trap tested with ACE inhibitors.
• Perineal pain plus fever on an SGLT-2 inhibitor = Fournier gangrene until proven otherwise; the answer is emergent surgical debridement, not outpatient antifungals.
• The one association examiners love: glucosuria → candidal vulvovaginitis/balanitis, the most common adverse effect; manage topically and continue therapy.
• Hold before surgery and during acute illness (ADA Standards of Care) to prevent eDKA — a favorite perioperative medication-management question.
• Common distractors: SGLT-2 inhibitors do not cause hyperkalemia (that is the MRA), do not cause hypoglycemia as monotherapy (that is sulfonylureas/insulin), and are not the agent behind pancreatitis or medullary thyroid carcinoma concerns (those belong to the incretin drugs). They also lose glycemic potency as eGFR falls while retaining cardiorenal benefit.