What differentiates cardiac symptoms from pulmonary symptoms in patients with chest pain, shortness of breath, or palpitations, particularly those with a history of cardiovascular disease, hypertension, chronic obstructive pulmonary disease (COPD), or asthma?

Differentiating Cardiac from Pulmonary Symptoms

The most reliable approach to distinguish cardiac from pulmonary symptoms involves B-natriuretic peptide (BNP) measurement, echocardiography, and cardiopulmonary exercise testing when initial evaluation is inconclusive. 1

Key Diagnostic Distinctions

Symptom Overlap and Clinical Challenges

Both cardiac and pulmonary conditions present with dyspnea, chest pain, and exercise intolerance, making clinical differentiation difficult. 1 The critical distinction lies in understanding that:

• Cardiac dyspnea typically results from cardiogenic pulmonary edema and pulmonary venous hypertension, often presenting as "cardiac asthma" with reflex bronchoconstriction 1
• Pulmonary dyspnea stems from airway obstruction, parenchymal disease, or ventilation-perfusion mismatch 1

Specific Clinical Features

Cardiac-predominant presentations:

• Dyspnea that improves with β-blockers suggests hypertrophic cardiomyopathy 1
• Peripheral edema in the context of dyspnea may indicate right ventricular failure from cardiac causes, though hypoxemia and hypercapnia from lung disease can also activate the renin-angiotensin-aldosterone system 1
• Syncope with dyspnea suggests complete heart block, cardiac dysrhythmias, or supraventricular tachycardia 1
• Chest pain with dyspnea that responds to β-blockers indicates cardiac origin 1

Pulmonary-predominant presentations:

• Wheezing with chronic cough may indicate true airway disease, though "out-of-proportion" pulmonary hypertension can compress mainstream bronchi and masquerade as asthma 1
• Bibasilar inspiratory crackles (velcro crackles) are characteristic of interstitial lung disease like idiopathic pulmonary fibrosis 2
• Significant exercise-induced desaturation (e.g., SpO2 dropping from 92% to 85% with minimal ambulation) is characteristic of pulmonary fibrosis 2

Diagnostic Algorithm

Initial Assessment

When symptoms are disproportionate to pulmonary function testing results, pursue cardiac evaluation with echocardiography. 1 This is critical because:

• Patients with COPD or asthma may have coexistent heart failure in up to 20-35% of cases 3
• Concomitant heart failure and COPD increases mortality by 39% and can exceed threefold the mortality of either disease alone 3

Definitive Testing Strategy

For distinguishing cardiac from pulmonary dyspnea, the most useful studies are: 1

1. B-natriuretic peptide (BNP) measurement - Elevated BNP indicates cardiac dysfunction and volume overload
2. Echocardiography - Assesses left ventricular function, valvular disease, and estimates pulmonary artery pressure 1
3. Cardiopulmonary exercise testing - Differentiates cardiac limitation from pulmonary limitation when the above are inconclusive 1

Specific Scenarios Requiring Specialist Referral

Refer to cardiologist or pulmonologist for cardiopulmonary testing when breathlessness with exercise, with or without chest pain, might be caused by heart disease or other conditions. 1

Specific red flags requiring urgent cardiac evaluation: 1

• Dyspnea with syncope, dizziness, or fatigue (suggests complete heart block or dysrhythmia)
• Chest pain improving with β-blockers (suggests hypertrophic cardiomyopathy)
• Exercise-induced symptoms in young athletes (1% annual mortality rate from sudden cardiac death)

Common Pitfalls and How to Avoid Them

Misdiagnosis of Pulmonary Hypertension

"Out-of-proportion" pulmonary hypertension (mean PAP >35-40 mmHg with relatively preserved lung function) can occur in COPD patients and requires distinction from primary pulmonary arterial hypertension. 4 Look for:

• Prominent dyspnea and fatigue disproportionate to spirometry results
• Low to normal arterial CO2 tension
• Mean pulmonary artery pressure >35-40 mmHg on right heart catheterization 4

Cardiac Conditions Masquerading as Asthma

Vascular rings of the aorta present as asthma but show: 1

• Decreased peak expiratory flow with truncated expiratory flow-volume loop
• Normal FVC, FEV1, and FEV1/FVC ratio
• Right aortic arch on chest radiograph

Idiopathic pulmonary arterial hypertension can present with wheezing and chronic cough due to central pulmonary artery dilation compressing mainstream bronchi. 1

Echocardiography Limitations

Echocardiography accuracy is low in patients with advanced respiratory disease. 1 When clinical or echocardiographic signs suggest severe pulmonary hypertension and/or severe right ventricular dysfunction, refer to a pulmonary hypertension center for right heart catheterization. 1

Spirometry Timing in Heart Failure

Perform spirometry only when patients have been stable and euvolemic for at least 3 months to avoid confounding effects of pulmonary congestion causing external obstruction of alveoli and bronchioles. 1 This prevents overdiagnosis of COPD in heart failure patients.

Management Implications

Beta-Blocker Use

COPD is not a contraindication to beta-blockers - use cardioselective agents (bisoprolol, metoprolol succinate, or nebivolol). 1 Beta-blocker use in COPD reduces risk of death by 31%, yet concurrent heart failure and COPD reduce beta-blocker prescription threefold. 3

In asthma, beta-blockers are only relatively contraindicated - start with low doses of cardioselective agents with close monitoring for wheezing and lengthening of expiration. 1

Oxygen Therapy

For patients with resting SpO2 of 92% and desaturation to 85% with minimal exertion (characteristic of pulmonary fibrosis), supplemental oxygen is indicated with target saturation of 94-98%. 2