How do you differentiate between cardiac and pulmonary related breathlessness?

Differentiating Cardiac from Pulmonary Breathlessness

The most useful diagnostic tools to distinguish cardiac from pulmonary dyspnea are B-natriuretic peptide (BNP) measurement, echocardiography, and if needed, cardiopulmonary exercise testing. 1

Clinical History and Symptom Patterns

Key Historical Features

• Orthopnea (breathlessness when lying flat) strongly suggests cardiac origin, as it results from increased venous return and pulmonary venous pressure from left-sided heart disease 2
• "Air hunger" and "inability to get a deep breath" characterize heart failure due to increased respiratory drive and limited tidal volume 2
• Wheezing with orthopnea may indicate "cardiac asthma" from reflex bronchoconstriction due to pulmonary venous hypertension 1, 2
• Associated symptoms like chest pain improving with beta-blockers suggest cardiac etiology 1

Physical Examination Findings

• Cardiac dyspnea indicators: jugular venous distension, peripheral edema, S3 gallop, displaced apical impulse 1
• Pulmonary dyspnea indicators: wheezing, prolonged expiration, use of accessory muscles, barrel chest 1
• Clinical examination combined with chest radiography and ECG has 96% specificity but only 59% sensitivity for cardiac causes, necessitating additional testing 1

Laboratory and Diagnostic Testing

First-Line Diagnostic Studies

• BNP or NT-proBNP measurement: Values >500 pg/dL (BNP) or >1,000 pg/dL (NT-proBNP) confirm heart failure as the cause 3
• Echocardiography should be performed in all patients with suspected cardiac dyspnea to assess cardiac structure, function, and valvular disease 1
• Chest radiography: Evaluates for cardiomegaly, pulmonary congestion, and pleural effusions in cardiac causes versus hyperinflation and infiltrates in pulmonary disease 1, 3

Pulmonary Function Assessment

• Peak expiratory flow (PEF) and arterial blood gases provide rapid differentiation in emergency settings 4
• Dyspnea Discrimination Index (DDI = PEF × PaO₂/1000): Values >1.6 suggest cardiac pathology with 76.7% sensitivity and 67.2% specificity 4
• PaCO₂ elevation (sensitivity 50%, specificity 93%) favors pulmonary causes 4
• Spirometry showing obstructive pattern (reduced FEV₁/FVC) indicates pulmonary disease, while normal spirometry with dyspnea suggests cardiac etiology 1

Advanced Testing When Diagnosis Remains Unclear

• Cardiopulmonary exercise testing is the definitive noninvasive tool for distinguishing cardiac from pulmonary dyspnea when initial evaluation is inconclusive 1
• Lung ultrasonography has 98% sensitivity and 95.5% specificity for differentiating causes, with B-lines indicating pulmonary edema (cardiac) versus A-lines suggesting pulmonary disease 5
• CT chest is most appropriate for excluding pulmonary causes when suspected 1

Cardiac-Specific Causes to Consider

Structural and Functional Cardiac Disease

• Cardiomyopathies (ischemic and non-ischemic), valvular heart disease (aortic stenosis/insufficiency, mitral valve disease), arrhythmias (atrial fibrillation, bradycardia), and constrictive pericarditis all cause dyspnea 1
• Congestive heart failure presents with dyspnea on exertion, with hyperpnea occurring even without lung function impairment 1

Uncommon Cardiac Mimics

• Idiopathic pulmonary arterial hypertension can masquerade as asthma with wheezing and cough, caused by dilated pulmonary arteries compressing bronchi 1
• Hypertrophic cardiomyopathy causes dyspnea and chest pain that improve with beta-blockers 1
• Cardiac dysrhythmias including supraventricular tachycardia can cause exercise-induced breathlessness 1

Common Pitfalls and Caveats

Diagnostic Challenges

• COPD is frequently over-diagnosed in patients with systolic heart failure and dyspnea 6
• Concomitant conditions are common—do not stop at the first diagnosis if comorbidities may contribute 6
• "Cardiac asthma" presents with wheezing that can be mistaken for primary pulmonary disease 1, 2
• Clinical tools alone have low sensitivity (59%) despite high specificity, requiring objective testing 1

Special Populations

• Young patients with unexplained dyspnea require evaluation for congenital heart disease, vascular rings, or pulmonary arteriovenous malformations 1
• Psychological factors including hyperventilation and anxiety disorders can obfuscate diagnosis and should be considered when organic causes are excluded 1

Practical Algorithmic Approach

1. Obtain detailed history focusing on orthopnea, paroxysmal nocturnal dyspnea, edema, and cardiac risk factors versus cough, wheezing, and smoking history
2. Perform focused physical examination for jugular venous distension, edema, cardiac murmurs versus wheezing and prolonged expiration
3. Order BNP/NT-proBNP, chest radiography, and ECG as initial screening 1, 3
4. If BNP elevated or cardiac findings present: Proceed with echocardiography 1
5. If pulmonary findings predominate: Obtain spirometry and consider chest CT 1
6. If diagnosis remains unclear: Perform cardiopulmonary exercise testing as the definitive discriminator 1
7. Consider lung ultrasonography in emergency settings for rapid, highly accurate differentiation 5