Hipertensi Pulmonal

01Pathophysiology

Pulmonary hypertension is defined hemodynamically as a mean pulmonary artery pressure (mPAP) greater than 20 mmHg measured by right heart catheterization at rest. This threshold was revised downward from the older cutoff of 25 mmHg. The disease fundamentally results from increased resistance to blood flow through the pulmonary vasculature, which forces the right ventricle to generate progressively higher pressures to maintain cardiac output.

In Group 1 (Pulmonary Arterial Hypertension, PAH), the pathology centers on the small pulmonary arterioles. There is endothelial dysfunction leading to an imbalance between vasodilators (nitric oxide, prostacyclin) and vasoconstrictors (endothelin-1, thromboxane A2). The result is excessive vasoconstriction, in-situ thrombosis, and progressive vascular remodeling. Histologically, this manifests as intimal fibrosis, medial smooth muscle hypertrophy, and the formation of plexiform lesions, which are pathognomonic disorganized vascular proliferations that obliterate the arteriolar lumen. In heritable PAH, loss-of-function mutations in the BMPR2 gene (bone morphogenetic protein receptor type 2) impair the TGF-beta signaling pathway, promoting uncontrolled smooth muscle and endothelial proliferation.

In Group 2, the most common cause of PH overall, elevated left-sided filling pressures (from systolic heart failure, diastolic heart failure, or valvular disease) passively transmit backward into the pulmonary venous system. Over time, this passive congestion triggers reactive vasoconstriction and vascular remodeling in the pulmonary arterioles, converting initially "isolated post-capillary PH" into "combined pre- and post-capillary PH."

In Group 3, chronic hypoxia from parenchymal lung disease triggers hypoxic pulmonary vasoconstriction (HPV), an adaptive mechanism that diverts blood away from poorly ventilated alveoli. When hypoxia is global and sustained, HPV becomes maladaptive: chronic vasoconstriction leads to fixed vascular remodeling and a sustained rise in pulmonary vascular resistance.

In Group 4 (Chronic Thromboembolic Pulmonary Hypertension, CTEPH), the central problem is organized, fibrotic thrombus that fails to resolve after one or more episodes of pulmonary embolism. This organized material physically obstructs the pulmonary arteries. In addition, a secondary small-vessel arteriopathy develops in unobstructed territories due to shear stress redistribution.

The common downstream consequence across all groups is right ventricular (RV) pressure overload. The RV initially compensates through concentric hypertrophy, but because the RV wall is thin and evolved for a low-pressure system, it eventually dilates and fails. This progression explains the symptom trajectory: early disease produces only exertional dyspnea and fatigue (reduced cardiac output augmentation during exercise), while late disease produces signs of overt right heart failure including JVD, hepatomegaly, ascites, and peripheral edema. Exertional syncope is a particularly ominous symptom, indicating that the RV cannot increase cardiac output to meet systemic demand, resulting in transient cerebral hypoperfusion.

02Classification and Clinical Manifestation

WHO Classification of Pulmonary Hypertension

Functional Classification (WHO/NYHA Adapted)

Hemodynamic Classification

03Diagnostic Workup

When a patient presents with unexplained progressive exertional dyspnea or signs of right heart failure, the first step is transthoracic echocardiography. This is the best initial test because it is noninvasive, widely available, and provides both an estimate of pulmonary artery systolic pressure (derived from the tricuspid regurgitation jet velocity using the modified Bernoulli equation: $\text{RVSP}=4v^2+\text{RAP}\backslash text\{RVSP\}\; =\; 4v^2\; +\; \backslash text\{RAP\}$) and structural assessment of the right and left heart. An RVSP greater than 35 to 40 mmHg raises strong suspicion for pulmonary hypertension. Echocardiography also helps evaluate for left heart disease (Group 2) by assessing LV function, valvular abnormalities, and diastolic filling.

If echocardiography suggests PH, the next step is to identify the etiology before proceeding to right heart catheterization. This workup includes pulmonary function tests (to assess for Group 3 lung disease), a V/Q scan (to screen for Group 4 CTEPH), serologies (ANA for connective tissue disease, HIV testing), and liver assessment (for portopulmonary hypertension). The V/Q scan is critically important because it is the preferred screening test for CTEPH. It has superior sensitivity compared to CT pulmonary angiography for detecting chronic thromboembolic disease. A normal V/Q scan effectively rules out CTEPH.

Right heart catheterization is required to confirm the diagnosis and is mandatory before initiating pulmonary vasodilator therapy for Group 1 PAH. It provides definitive hemodynamic measurements: mPAP, PCWP, cardiac output, and calculated PVR. The PCWP value is the critical discriminator between pre-capillary PH (PCWP ≤ 15 mmHg, seen in Groups 1, 3, 4) and post-capillary PH (PCWP > 15 mmHg, seen in Group 2). During RHC for suspected Group 1 PAH, acute vasoreactivity testing is performed using short-acting vasodilators (inhaled nitric oxide is most commonly used, or IV epoprostenol, or IV adenosine). A positive response, defined as a decrease in mPAP of at least 10 mmHg to an absolute value of 40 mmHg or less with maintained or improved cardiac output, identifies the minority of PAH patients (~10%) who may respond to calcium channel blockers.

An isolated reduction in DLCO on pulmonary function testing, with otherwise preserved lung volumes and spirometry, should raise suspicion for pulmonary vascular disease rather than parenchymal lung disease.

04Management and Treatment

General supportive measures apply to all groups. Diuretics (loop diuretics such as furosemide, typically 20-80 mg daily adjusted to clinical euvolemia) are the mainstay of volume management in patients with right heart failure. Supplemental oxygen should be prescribed to maintain oxygen saturation above 90%, as hypoxia is a potent pulmonary vasoconstrictor that will worsen the hemodynamic burden.

For Group 1 PAH, the decision tree begins with the vasoreactivity test result. The small subset of vasoreactive patients receives high-dose calcium channel blockers. Verapamil must be avoided because its negative inotropic effect can precipitate RV failure. Patients must be reassessed at 3 to 6 months; if they do not maintain functional class I or II with near-normal hemodynamics, they should be transitioned to standard PAH-targeted therapy.

For non-vasoreactive Group 1 PAH in WHO functional class II or III, current guidelines recommend upfront dual combination therapy rather than sequential monotherapy. The preferred initial combination is a PDE-5 inhibitor plus an endothelin receptor antagonist. Sildenafil (20 mg three times daily) or tadalafil (40 mg once daily) increases cGMP-mediated vasodilation by preventing breakdown of nitric oxide signaling. Ambrisentan (5-10 mg daily) or macitentan (10 mg daily) blocks endothelin-1 receptors, reducing vasoconstriction and vascular remodeling. Bosentan (125 mg twice daily) is an older ERA that requires monthly liver function monitoring due to hepatotoxicity risk. All endothelin receptor antagonists are teratogenic and require pregnancy testing and reliable contraception.

Riociguat, a soluble guanylate cyclase (sGC) stimulator, is an alternative to PDE-5 inhibitors. It directly stimulates sGC independent of nitric oxide availability and also sensitizes sGC to endogenous NO. The critical drug interaction to remember is that riociguat must NEVER be combined with PDE-5 inhibitors because both act on the NO-cGMP pathway, and the combination causes severe systemic hypotension. Riociguat is also the approved pharmacologic therapy for inoperable CTEPH (Group 4).

If initial combination therapy is insufficient, a prostacyclin pathway agent is added as a third drug. Options include selexipag (oral, a selective IP receptor agonist, titrated from 200 mcg BID up to 1600 mcg BID), inhaled treprostinil or iloprost (6-9 inhalations daily for iloprost), subcutaneous treprostinil (continuous infusion starting at 1.25 ng/kg/min), or IV treprostinil.

For patients presenting in functional class IV or with rapidly deteriorating hemodynamics, IV epoprostenol is the cornerstone of treatment. Epoprostenol is the most potent pulmonary vasodilator available and remains the only PAH therapy with a demonstrated mortality benefit in a randomized trial. It is administered as a continuous intravenous infusion through a tunneled central venous catheter, starting at 2 ng/kg/min and uptitrated over weeks. Its extremely short half-life of approximately 3 to 5 minutes means that any interruption in the infusion, whether from pump malfunction, line occlusion, or running out of medication, can cause life-threatening rebound pulmonary hypertension and cardiovascular collapse. Patients and caregivers must be trained in emergency procedures for line or pump failure.

For Group 4 CTEPH, pulmonary thromboendarterectomy is the treatment of choice and should be evaluated at an experienced surgical center. Unlike embolectomy for acute PE, PTE involves a true endarterectomy through the organized, fibrotic intimal layer under deep hypothermia and circulatory arrest. Lifelong anticoagulation with warfarin is standard post-operatively and indefinitely. For patients deemed inoperable due to distal disease location or comorbidities, riociguat and balloon pulmonary angioplasty are therapeutic options.

Lung transplantation is reserved for patients with Group 1 PAH refractory to maximal medical therapy, typically those in functional class III or IV despite triple combination therapy including IV prostacyclin. Bilateral lung transplantation is preferred. Referral should occur early when patients show inadequate response to initial therapy.

05Differential Diagnosis and Distractors

06Traps and High-Yield Pearls

The most common way students lose points on pulmonary hypertension questions is by failing to classify PH into the correct WHO Group before selecting treatment. Exam vignettes frequently present a patient with dyspnea and elevated pulmonary pressures on echocardiography, then offer PAH-targeted vasodilators (such as bosentan or sildenafil) as answer choices. The trap is selecting these drugs for a patient whose PH is secondary to left heart disease (Group 2) or chronic lung disease (Group 3). PAH-targeted vasodilators are indicated only for Group 1 PAH and, in the case of riociguat, Group 4 CTEPH. For Group 2 PH, the correct answer is to optimize heart failure management. For Group 3 PH, the correct answer is to treat the underlying lung disease and provide supplemental oxygen.

Another frequently tested trap involves CTEPH screening. When a vignette describes a patient with persistent dyspnea and elevated pulmonary pressures months after a pulmonary embolism, students often select CT pulmonary angiography as the next step. The correct screening test is a V/Q scan, which has significantly higher sensitivity for detecting chronic thromboembolic disease than CTPA. A normal V/Q scan essentially rules out CTEPH.

Students must also remember that vasoreactivity testing is only performed for Group 1 PAH and only during right heart catheterization. It is not performed for Groups 2, 3, or 4. Calcium channel blockers are given only to vasoreactive Group 1 PAH patients, and verapamil is absolutely contraindicated due to its negative inotropic effect on an already compromised right ventricle.

A commonly tested clinical pearl is the danger of abrupt epoprostenol discontinuation. Any question describing a PAH patient on IV epoprostenol who develops sudden hemodynamic collapse should prompt consideration of pump malfunction or line disruption. The correct response is to restore the infusion immediately.

Finally, remember that pregnancy is contraindicated in PAH because it carries a maternal mortality rate of 30 to 50 percent. Exam questions may present a young woman with PAH asking about family planning or newly found to be pregnant. The core competency being tested is recognizing that the hemodynamic demands of pregnancy (increased blood volume, increased cardiac output, and the autotransfusion effect of uterine contraction during delivery) can overwhelm a right ventricle that is already at its compensatory limit, leading to RV failure and death.