Right Heart Catheterization
The next best study is right heart catheterization (RHC) to confirm the diagnosis of pulmonary arterial hypertension and obtain definitive hemodynamic measurements. 1
Rationale for Right Heart Catheterization
This patient has completed the appropriate screening evaluation with echocardiography showing high probability of pulmonary hypertension (RVH, right atrial dilation, elevated estimated PA pressures), supported by ECG findings of RVH and chest X-ray showing enlarged pulmonary arteries. 1
All patients suspected of having PAH after noninvasive evaluation must undergo RHC prior to initiation of therapy. 1 The ACCF/AHA guidelines explicitly state that echocardiography alone is insufficient to confirm a diagnosis of PAH and initiate treatment. 2
Essential Hemodynamic Criteria to Establish
RHC is required to definitively establish PAH by documenting: 1, 3
- Mean pulmonary artery pressure (mPAP) ≥25 mmHg at rest
- Pulmonary capillary wedge pressure (PCWP) ≤15 mmHg to exclude left heart disease as the cause
- Pulmonary vascular resistance (PVR) >3 Wood units to confirm true pulmonary vascular disease rather than passive elevation from high cardiac output or left heart disease
Critical Diagnostic Distinction
The PVR measurement is particularly crucial because it distinguishes passive PH (elevated mPAP with normal PVR) from PH caused by pulmonary vascular disease (elevated mPAP with elevated PVR). 1 This distinction cannot be reliably made by echocardiography alone. 1
The transpulmonary gradient (PAP mean - wedge pressure) must be assessed to identify intrinsic pulmonary vascular changes versus passive increases from left heart dysfunction. 1 This is especially important in this patient given her elevated glucose tolerance, which raises concern for potential diastolic dysfunction that could masquerade as or coexist with PAH. 1
Additional Testing to Complete Before or Concurrent with RHC
While RHC is the definitive next step, the following pivotal tests should be completed if not already done: 1
- Ventilation-perfusion (V/Q) scan to exclude chronic thromboembolic pulmonary hypertension (CTEPH), which remains the screening method of choice with sensitivity >90% and specificity >94% 1, 3
- Pulmonary function tests with DLCO to assess for underlying obstructive or restrictive lung disease 1, 3
- HIV testing, ANA, and liver function tests to identify associated conditions (connective tissue disease, HIV, portopulmonary hypertension) 1
- Overnight oximetry or polysomnography if sleep-disordered breathing is suspected 1
Common Pitfalls to Avoid
Do not rely on echocardiographic estimates of pulmonary artery pressure to make treatment decisions. 1 Echocardiography may underestimate systolic PAP by a mean of 11 mmHg, with underestimation of 20 mmHg in up to 31% of patients. 2
Do not assume this is idiopathic PAH without excluding secondary causes. 1 PAH is a diagnosis of exclusion, and the diagnostic algorithm must systematically rule out left heart disease, lung disease, chronic thromboembolic disease, and associated conditions before concluding idiopathic PAH. 1
In patients with obesity (high BMI), be particularly vigilant about excluding obesity hypoventilation syndrome, sleep apnea, and left ventricular diastolic dysfunction as contributors to elevated pulmonary pressures. 1
Prognostic Importance
The hemodynamic profile obtained from RHC provides critical prognostic information and guides treatment decisions, including vasoreactivity testing which determines eligibility for calcium channel blocker therapy. 4 Right ventricular function assessed during catheterization is a critical determinant of outcomes in PAH. 4