Introduction
At the beginning of the diagnostic process for PAH, the clinician develops and works through an “index of suspicion” by using various tests and procedures. It is only through the use of right heart catheterization (RHC) that direct measurements of ventricular and arterial pressures can be made. The principal benefits that right heart catheterization can provide include:
- Confirm diagnosis (gold standard)
- Evaluate severity of PAH
- Assess congenital heart defects
- Exclude left-sided heart disease
- Assess response to vasodilator challenge
- Assess key hemodynamic parameters
RHC is the only technique that may accurately and directly measure pulmonary artery pressures, right ventricular pressures, and other important measures of right heart and pulmonary vascular functions. Other techniques, such as Doppler ECHO or cMRI, give algorithmic estimates of these values.
How RHC Testing is Performed
A Swan-Ganz catheter with a balloon tip is inserted into a large vein (either the subclavian or femoral veins). The catheter is attached to a pressure transducer so that blood pressures may be measured as the physician guides the catheter through the superior vena cava and into the right side of the heart. Using fluoroscopy to guide the physician’s positioning of the catheter, the Swan-Ganz is passed through the triscuspid valve, into the right ventricle, and into the pulmonary artery. The pressures measured as the catheter advances help determine its position. Once guided into the pulmonary artery, the balloon tip is inflated, allowing measurement of pulmonary artery pressure and pulmonary capillary wedge pressure (PCWP).
Reproduced with permission from A.D.A.M. Education.
If right heart pressures are found to be elevated above normal (>25 mmHg), a vasodilator challenge may be given to determine reactivity of the pulmonary vessels. The entire procedure takes 1-2 hours, after which the patient is returned to an observation room for 1-2 hours prior to discharge, assuming no
sequelae or complications arise.
The catheter may also be used to inject radiopaque dye into the pulmonary circulation. In this way, the presence and location of pulmonary thrombi can be ascertained.
Potential risks of RHC include:
- Bruising at the site of catheter insertion
- Bleeding at the venipuncture site of catheter insertion
- Pneumothorax if thoracic veins are used for the catheter placement
- Other, more rare complications can include arrhythmias, cardiac tamponade, hypotension, infection, air embolism, thrombus formation, and pulmonary artery rupture
Role of Right Heart Catheterization
The diagnosis of PAH/PH is a process of exclusion. Laboratory tests, exercise testing (6MWD), and ECHO serve to build an index of suspicion of PH, which can only be confirmed by RHC. Figure 2 depicts a simplified diagnostic algorithm for PAH.
Adapted from McLaughlin VV, et al. JACC 2009;53:1573-1619.
The essential aspects of an invasive hemodynamic assessment via right heart catheterization include:
- Oxygen saturation
- Right ventricular pressure
- Right atrial pressure
- Pulmonary arterial pressure, systolic, diastolic and mean
- PCWP, left atrial pressure or left ventricular end-diastolic pressure
- Cardiac output
- Pulmonary vascular resistance
- Systemic blood pressure
- Heart rate
- Response to vasodilator challenge
Vasodilator Challenge
A hemodynamic vasodilator challenge is a useful tool to determine which patients are responsive and hence have a better prognosis. Responders are more likely to have a sustained positive response to oral calcium channel blocking drugs as compared to non-responders.
Agents commonly used for vasodilator challenge include:
- Nitric oxide, inhaled (iNO) (dose range 10-80 ppm)*
- Epoprostenol intravenous infusion (2 ng/kg/min every 10-15 min; dose range 2-10 ng/kg/min)
- Adenosine intravenous infusion (50 μg/kg/min every 2 min, dose range 50-250 μg/kg/min)
* The 2009 JACC/AHA guidelines consensus is that iNO is the preferred vasodilator. Intravenous epoprostenol and adenosine are considered acceptable alternatives.
Ultimately the choice of vasodilator falls to operator preference, but calcium channel blockers, sodium nitroprusside, or nitrates should not be used as their safety and efficacy in PAH patients has not been established.
A positive vasoreactivity challenge is defined as a decrease in mPAP >10 mmHg reaching <40 mmHg, with an increase or no change in cardiac output.
Using RHC to Define PAH
The hemodynamic definition of pulmonary arterial hypertension is a mean pulmonary artery pressure (mPAP) of >25 mmHg at rest, AND a mean pulmonary capillary wedge pressure (PCWP) of <15 mmHg (no evidence of left heart disease).
According to WHO guidelines, pulmonary hypertension patients fall into 5 groups. Note that PAH patients fall into Group 1.
Adapted from McLaughlin VV, et al. JACC 2009;53(17):1573-1619.
The vast majority of PH cases fall outside of WHO Group I. PAH is characterized by increases in pulmonary vascular resistance (PVR) and transpulmonary pressure gradient (TPG) along with normal left-sided filling pressures. Pulmonary venous hypertension (PVH) is characterized by increased PCWP with normal TPG and PVR.
Summary
If a physician suspects the presence of pulmonary hypertension (PAH/PH), there are many diagnostic tools available to clinically assess a patient. The initial phases of diagnosis are non-invasive and can help exclude disease processes that can elicit symptoms similar to PH; these only serve to add or detract from the physician’s “index of suspicion” that pulmonary hypertension is at the root of the patient’s overt symptoms (e.g. dyspnea or dyspnea upon exertion). The culmination of this diagnostic testing strategy is the right heart catheterization. This procedure is a direct, accurate measure of pulmonary arterial pressure andright heart pressure. RHC is therefore recommended for all patients with a high suspicion of pulmonary hypertension.
References
1. McLaughlin VV, Archer SL, Badesch DB, et al. JACC 2009;53(17):1573-1619.
2. McLaughlin VV, Archer SL, Badesch DB, et al. Circulation 2009;119:2250-2294.
3. Tolle JJ, Waxman AB, Van Horn TL, et al. Circulation 2008;118:2183-2189.
4. Simmonneau G, Robbins IM, Beghetti M, et al. JACC 2009;54 (Suppl 1):S43-S54.
5. Barst RJ, et al. Circulation 2012;125:113-222.
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