What could be the cause of pulmonary arterial hypertension (PAH) in a patient with a dilated left atrium, elevated pulmonary artery systolic pressure (PASP), and impaired renal function following a computed tomography pulmonary angiogram (CTPA)?

Pulmonary Hypertension Due to Left Heart Disease with Contrast-Induced Nephropathy

This patient's pulmonary hypertension is most likely caused by left heart disease (Group 2 PH), specifically diastolic dysfunction, as evidenced by the dilated left atrium, and the acute kidney injury is contrast-induced nephropathy from the CTPA. 1

Etiology of Pulmonary Hypertension

The dilated left atrium is the key diagnostic clue pointing to elevated left-sided filling pressures as the cause of this patient's pulmonary hypertension. 1

• Left atrial enlargement indicates chronic elevation of left atrial pressure, which is transmitted backward to the pulmonary venous system, causing post-capillary pulmonary hypertension 1, 2
• The PASP of 70 mmHg represents severe pulmonary hypertension that developed secondary to sustained elevation of left ventricular filling pressures 2, 3
• Rhonchi without pedal edema suggests pulmonary venous congestion rather than systemic volume overload 4, 5
• Normal troponin I excludes acute myocardial infarction as a precipitant 1

Distinguishing Post-Capillary from Pre-Capillary PH

The clinical presentation strongly suggests post-capillary PH (Group 2) rather than pulmonary arterial hypertension (Group 1):

• Dilated left atrium is characteristic of left heart disease, not idiopathic PAH 1, 2
• A pulmonary capillary wedge pressure >15 mmHg would confirm post-capillary PH and exclude pre-capillary PAH 1
• Right heart catheterization with fluid challenge (500 mL saline over 10 minutes) can unmask diastolic left heart disease when resting wedge pressure appears normal 1
• The absence of pedal edema does not exclude left heart disease, as isolated pulmonary venous congestion can occur 4, 5

Acute Kidney Injury Management

The creatinine rise from 1.44 to 3.6 mg/dL following CTPA represents contrast-induced nephropathy, which requires immediate cessation of nephrotoxic agents and supportive care. 1

• Discontinue all nephrotoxic medications immediately, including NSAIDs, aminoglycosides, and ACE inhibitors/ARBs if hypotensive 1
• Ensure adequate hydration with isotonic saline to maintain urine output, but avoid volume overload given the pulmonary hypertension 1, 3
• Monitor daily creatinine, electrolytes, and urine output 1
• Consider nephrology consultation if creatinine continues to rise or oliguria develops 1

Recommended Medications for PH Due to Left Heart Disease

PAH-specific therapies are NOT recommended for pulmonary hypertension due to left heart disease and may cause harm. 1, 6

What NOT to Use

• Endothelin receptor antagonists (bosentan, macitentan) are contraindicated in PH due to left heart disease, as they have shown increased morbidity and mortality 1, 6
• Prostacyclin analogs are not recommended for Group 2 PH 1
• The ESC/ERS guidelines explicitly state that "the use of PAH specific drug therapy is not recommended in patients with PH due to left heart disease" (Class III recommendation) 1

Appropriate Treatment Strategy

Optimal treatment of the underlying left heart disease is the Class I recommendation for this patient. 1

• Diuretics (loop diuretics like furosemide) to reduce pulmonary venous congestion and left atrial pressure 1, 3
• ACE inhibitors or ARBs for afterload reduction once kidney function stabilizes 3
• Beta-blockers if there is systolic dysfunction or rate control is needed 3
• Aldosterone antagonists (spironolactone or eplerenone) for heart failure with reduced or preserved ejection fraction 3

Potential Exception: Combined Pre- and Post-Capillary PH

If hemodynamic assessment reveals combined pre- and post-capillary PH (transpulmonary gradient >12 mmHg, PVR >3 Wood units):

• Sildenafil may be considered to improve pulmonary hemodynamics and exercise capacity in highly selected patients with combined PH 6, 2
• Riociguat 2 mg three times daily may improve pulmonary hemodynamics in heart failure with reduced ejection fraction, but not preserved ejection fraction 6
• However, these agents should only be used after confirming combined PH with right heart catheterization and in consultation with a PH specialist 1, 6

Diagnostic Confirmation Required

Right heart catheterization is necessary to confirm the diagnosis and guide therapy. 1

• Measure pulmonary capillary wedge pressure (Ppcw) to differentiate post-capillary from pre-capillary PH 1
• Calculate transpulmonary gradient (mean PA pressure - Ppcw) and pulmonary vascular resistance 1
• Perform fluid challenge if Ppcw is borderline (12-15 mmHg) to unmask diastolic dysfunction 1
• Post-capillary PH is defined by mean PA pressure >20 mmHg, Ppcw >15 mmHg, and PVR <3 Wood units 2, 3

Critical Pitfalls to Avoid

• Do not initiate PAH-specific therapies without hemodynamic confirmation of the PH type, as this can worsen outcomes in Group 2 PH 1, 6
• Do not assume normal wedge pressure excludes left heart disease in patients on diuretics, as pressures can be "pseudo-normal" 1
• Avoid aggressive diuresis in the setting of acute kidney injury, but maintain adequate decongestion 3
• Do not overlook valvular heart disease as a contributor to left atrial enlargement and PH 7, 3