ANSWER: C

Rationale:

The 2022 ESC/ERS guidelines define PAH hemodynamically as a resting mPAP greater than 20 mmHg by RHC, combined with a PAWP at or below 15 mmHg and a PVR greater than 2 Wood units. All three criteria must be met simultaneously. The mPAP threshold was lowered from the prior 25 mmHg cutoff based on outcome data demonstrating elevated mortality above 20 mmHg in otherwise healthy individuals; this 2022 revision is a high-yield distinction from the older definition. The PAWP criterion of 15 mmHg or below confirms the disease is precapillary rather than driven by elevated left-sided filling pressures. The PVR threshold of greater than 2 Wood units confirms intrinsic pulmonary vascular disease.

• Option A: Option A is incorrect because the mPAP threshold of 25 mmHg reflects the pre-2022 definition, which has been superseded; the current threshold is greater than 20 mmHg.
• Option B: Option B is incorrect because a PAWP greater than 15 mmHg defines postcapillary pulmonary hypertension (WHO Group 2, left heart disease), not PAH; this criterion explicitly excludes the diagnosis.
• Option D: Option D is incorrect because the PVR threshold is 2 Wood units, not 3; although a PVR of 3 Wood units was used in some older trial entry criteria, the current ESC/ERS diagnostic threshold is greater than 2 Wood units.
• Option E: Option E is incorrect because echocardiographic pressure estimation is a screening tool only and cannot establish the PAH diagnosis; RHC is mandatory, and systolic pressure alone does not satisfy the three-criterion definition.

ANSWER: D

Rationale:

Epoprostenol undergoes rapid non-enzymatic hydrolysis and enzymatic degradation at physiological pH, producing a plasma half-life of approximately 2 to 5 minutes. This extreme brevity of action makes any route other than continuous IV infusion pharmacokinetically impossible for maintaining steady-state pulmonary vasodilation. Delivery requires a tunneled central venous catheter and an ambulatory infusion pump; patients must carry backup cassettes and a battery-powered spare pump. Because circulating epoprostenol is eliminated within minutes of pump interruption, abrupt line disconnection or pump failure removes pulmonary vasodilation nearly instantaneously, triggering rebound severe vasoconstriction and right ventricular failure that can be fatal within minutes.

• Option A: Option A is incorrect because the 4-hour half-life describes treprostinil, not epoprostenol; treprostinil's longer half-life is precisely what permits subcutaneous and other non-continuous routes.
• Option B: Option B is incorrect because the 20- to 30-minute half-life and six-to-nine-times-daily inhalation schedule describe iloprost, not epoprostenol.
• Option C: Option C is incorrect because a 12-hour half-life does not apply to any approved prostacyclin-pathway agent, and epoprostenol cannot be given via peripheral IV or on a once-daily schedule.
• Option E: Option E is incorrect because tissue binding does not extend epoprostenol's effective duration; the 2- to 5-minute plasma half-life governs its pharmacodynamic duration, and subcutaneous bolus administration is not an approved or pharmacokinetically viable route for this agent.

ANSWER: E

Rationale:

Riociguat is a soluble guanylate cyclase (sGC) stimulator with two mechanistically complementary actions. First, it sensitizes sGC to endogenous NO, lowering the NO concentration required to shift the enzyme to its active conformation; this enhances cGMP production from residual NO signaling. Second, it independently activates sGC at an NO-independent allosteric binding site, producing cGMP even when endothelial NO synthesis is severely reduced — a state characteristic of advanced PAH endothelial dysfunction. This NO-independent component is the mechanistic rationale for its efficacy in patients with markedly impaired NO bioavailability.

• Option A: Option A is incorrect because riociguat does not inhibit PDE-5 or PDE-6; it acts upstream by stimulating sGC to produce more cGMP rather than preventing cGMP breakdown, and its mechanism includes an NO-independent component rather than requiring NO throughout.
• Option B: Option B is incorrect because riociguat does not supply exogenous NO and does not bypass sGC; sGC is the direct molecular target of riociguat, not a downstream element it circumvents.
• Option C: Option C is incorrect because riociguat does not block the ETA receptor or inhibit PDE-5; furthermore, co-administration of riociguat with any PDE-5 inhibitor is absolutely contraindicated because of additive cGMP accumulation causing severe hypotension.
• Option D: Option D is incorrect because riociguat does retain activity in NO-deficient states specifically because of its NO-independent binding site; the ability to generate cGMP without endogenous NO is a defining feature that distinguishes riociguat from PDE-5 inhibitors, which depend entirely on residual NO-driven cGMP production.

ANSWER: A

Rationale:

Bosentan is a potent inducer of both CYP3A4 and CYP2C9. CYP3A4 induction accelerates metabolism of cyclosporine, glyburide, and hormonal contraceptives, reducing their plasma concentrations substantially. CYP2C9 induction accelerates metabolism of the pharmacologically active S-enantiomer of warfarin, lowering anticoagulant effect and requiring INR monitoring and potential warfarin dose adjustment. Because bosentan induces CYP3A4, hormonal contraceptives undergo accelerated first-pass and systemic metabolism, making oral contraceptive pills unreliable for pregnancy prevention in patients on bosentan; this is one mechanistic reason the REMS program requires two reliable non-hormonal or hormonal-plus-barrier forms of contraception.

• Option B: Option B is incorrect because bosentan is an inducer rather than an inhibitor of CYP3A4 and CYP2C9; inhibition would raise substrate levels, whereas induction lowers them, and the clinical concern is subtherapeutic levels of co-medications, not toxicity from accumulation.
• Option C: Option C is incorrect because the relevant enzymes induced by bosentan are CYP3A4 and CYP2C9, not CYP2D6; bosentan does not have a clinically meaningful CYP2D6 induction effect, and warfarin is a CYP2C9 substrate squarely within bosentan's induction profile.
• Option D: Option D is incorrect because OATP1B1 inhibition raising ambrisentan levels is the mechanism of the cyclosporine-ambrisentan interaction, not the bosentan-warfarin interaction; bosentan's warfarin interaction is mediated by CYP2C9 induction.
• Option E: Option E is incorrect because bosentan induces both CYP3A4 and CYP2C9, not CYP3A4 alone; the CYP2C9 induction is specifically responsible for the warfarin interaction that requires INR monitoring throughout bosentan therapy.

ANSWER: B

Rationale:

Macitentan is distinguished from bosentan by three features. Structurally, macitentan is highly lipophilic, conferring enhanced tissue penetration into the pulmonary arterial wall and prolonged receptor occupancy compared with the less lipophilic bosentan and ambrisentan; this property is the mechanistic basis for macitentan's sustained efficacy in vivo. Clinically, it was studied in the SERAPHIN trial, which enrolled 742 patients in a randomized double-blind design with a median follow-up of 115 weeks and was the first PAH trial powered for a morbidity-mortality composite endpoint — death or worsening PAH — rather than a walk-test surrogate; macitentan 10 mg reduced this composite by approximately 45 percent. Safety-wise, macitentan carries a lower hepatotoxicity signal than bosentan; per its prescribing label it does not require mandatory monthly LFT monitoring, in contrast to bosentan's monthly LFT requirement, though baseline assessment remains standard practice.

• Option A: Option A is incorrect on all dimensions: macitentan is lipophilic not hydrophilic, BREATHE-1 was the bosentan trial not the macitentan trial, and macitentan has a lower not higher hepatotoxicity signal.
• Option C: Option C is incorrect because macitentan is a dual ETA/ETB antagonist like bosentan, not a selective ETA agent (that describes ambrisentan), and PATENT-1 was the riociguat trial.
• Option D: Option D is incorrect because macitentan and bosentan differ substantially in lipophilicity and hepatotoxicity profile, and the dosing comparison is reversed — both are dosed once daily in PAH.
• Option E: Option E is incorrect because ARIES-1 and ARIES-2 were the ambrisentan trials, not the macitentan trials, and macitentan has a lower not higher hepatotoxicity signal than bosentan.

ANSWER: C

Rationale:

Selexipag is an orally bioavailable, non-prostanoid compound that is chemically and pharmacologically distinct from prostacyclin analogues such as epoprostenol, treprostinil, and iloprost. It is hydrolyzed by carboxylesterases to its active metabolite ACT-333679, which binds the IP receptor (prostacyclin receptor) with high selectivity and raises cAMP in pulmonary arterial smooth muscle cells without the off-target prostanoid receptor binding that contributes to adverse effects of non-selective analogues. Selexipag is dosed twice daily and titrated upward in weekly increments to the maximum tolerated dose. The GRIPHON trial enrolled 1156 patients — the largest PAH outcomes trial — and demonstrated approximately a 40 percent reduction in the composite morbidity-mortality endpoint versus placebo.

• Option A: Option A is incorrect because selexipag is an oral non-prostanoid IP agonist, not a prostacyclin analogue; SUPER-1 was the sildenafil trial, and selexipag is not delivered subcutaneously.
• Option B: Option B is incorrect because the description of inhaled prostacyclin analogue with 20- to 30-minute half-life and six-to-nine daily inhalations describes iloprost; the INCREASE trial studied inhaled treprostinil in PH-ILD, not selexipag.
• Option D: Option D is incorrect because selexipag is a selective IP receptor agonist, not a dual IP/thromboxane agonist, and PATENT-1 was the riociguat trial, not the selexipag trial.
• Option E: Option E is incorrect because selexipag is not identical in receptor profile to epoprostenol, is not dosed once daily, and was not part of the AMBITION trial; AMBITION studied ambrisentan plus tadalafil as upfront combination.

ANSWER: D

Rationale:

Riociguat carries two distinct regulatory approvals. The PATENT-1 trial (Pulmonary Arterial Hypertension Soluble Guanylate Cyclase-Stimulator Trial 1) established its efficacy in WHO Group 1 PAH, demonstrating a 36-meter improvement in 6MWD and improvements in pulmonary hemodynamics and WHO functional class. The CHEST-1 trial (Chronic Thromboembolic Pulmonary Hypertension Soluble Guanylate Cyclase Stimulator Trial 1) established its efficacy in inoperable CTEPH and recurrent or persistent CTEPH after pulmonary endarterectomy (WHO Group 4), making riociguat the only PAH vasodilatory agent with a Group 4 approval. The mechanistic rationale for CTEPH efficacy is riociguat's NO-independent sGC activation, which generates cGMP even in the remodeled CTEPH vasculature where NO signaling is impaired.

• Option A: Option A is incorrect because riociguat is not approved for WHO Group 2 (left heart disease); prescribing vasodilators in Group 2 can be harmful, and CHEST-2 is the open-label extension of CHEST-1, not a Group 2 trial.
• Option B: Option B is incorrect because the INCREASE trial studied inhaled treprostinil in PH-ILD (WHO Group 3b), not riociguat; riociguat does not hold a Group 3 approval.
• Option C: Option C is incorrect because PATENT-1 was the PAH trial and CHEST-1 was the CTEPH trial; riociguat holds Group 1 and Group 4 approvals, not Group 1 and Group 3.
• Option E: Option E is incorrect because riociguat holds approvals for Group 1 and Group 4 only; approvals across all five groups do not exist for any PAH vasodilatory agent.

ANSWER: E

Rationale:

All three approved ERAs — bosentan, ambrisentan, and macitentan — carry an absolute contraindication in pregnancy based on severe teratogenicity demonstrated in animal studies at doses below the human therapeutic range. The required precautions are specific and non-negotiable: two reliable forms of contraception must be used throughout ERA therapy and for one month following discontinuation (covering the washout period during which the drug remains pharmacologically relevant). Monthly pregnancy testing is mandated under each agent's Risk Evaluation and Mitigation Strategy (REMS) program. If a pregnancy test is positive, the ERA must be discontinued immediately and urgent obstetric consultation obtained; there is no dose-reduction strategy or monitoring approach that renders ERA continuation permissible during pregnancy.

• Option A: Option A is incorrect because a single form of contraception does not meet the required standard, and annual pregnancy testing is far less frequent than the monthly testing mandated by the REMS programs.
• Option B: Option B is incorrect because two forms of contraception are required throughout therapy, not only during a defined trimester window, and the monthly testing requirement is independent of patient-reported contraceptive adherence.
• Option C: Option C is incorrect because formal pregnancy monitoring programs are mandatory for all three ERA REMS designations; patient self-reporting is not considered adequate in lieu of structured testing.
• Option D: Option D is incorrect because quarterly testing fails to meet the monthly REMS requirement, and ERA therapy cannot be continued at any dose once pregnancy is confirmed; immediate discontinuation is required with no dose-adjustment alternative.

ANSWER: A

Rationale:

The PDE-5 inhibitor plus riociguat combination is absolutely contraindicated because the two drug classes amplify cGMP signaling through mechanistically complementary and additive routes: PDE-5 inhibitors block phosphodiesterase-5 to prevent cGMP breakdown, while riociguat directly stimulates soluble guanylate cyclase (sGC) to increase cGMP production. Combined use produces additive cGMP accumulation in vascular smooth muscle causing severe symptomatic hypotension that has caused deaths in clinical trials. When switching from a PDE-5 inhibitor to riociguat, a washout period is mandatory. Sildenafil, with a shorter half-life, requires a minimum of 24 hours washout before initiating riociguat. Tadalafil, with a substantially longer half-life, requires a minimum of 48 hours washout. Careful hemodynamic monitoring during the transition period is essential.

• Option B: Option B is incorrect because riociguat does not inhibit PDE-5; it stimulates sGC to increase cGMP production — a distinct and complementary mechanism, not the same mechanism as PDE-5 inhibition. The washout periods also differ by agent, not uniformly 24 hours.
• Option C: Option C is incorrect because the contraindication is pharmacodynamic (additive cGMP signaling causing hypotension), not pharmacokinetic (riociguat inhibiting tadalafil metabolism); a 7-day washout is not the standard, and the required washout applies to the PDE-5 inhibitor before riociguat, not the reverse.
• Option D: Option D is incorrect because this is an absolute contraindication, not a relative one; dose reduction does not render the combination permissible, and the danger exists regardless of whether the patient is symptomatic at baseline.
• Option E: Option E is incorrect because the contraindication applies equally to all PDE-5 inhibitors combined with riociguat regardless of dosing schedule; once-daily tadalafil dosing does not create a pharmacodynamic safe window during which riociguat can be added.

ANSWER: B

Rationale:

Treprostinil is a stable prostacyclin analogue available in four routes: continuous subcutaneous infusion, continuous IV infusion, inhaled nebulization, and oral extended-release tablets. The subcutaneous route is the most commonly used. Its primary tolerability limitation is infusion site pain — erythema, swelling, and burning discomfort at the catheter insertion site — affecting the majority of patients and causing discontinuation in a subset; this is the most common reason for switching to the IV or inhaled route. The inhaled formulation (Tyvaso) was approved for Group 1 PAH and subsequently expanded to include WHO Group 3b PH-ILD based on the INCREASE trial, which demonstrated significant improvement in 6MWD and time to clinical worsening in patients with pulmonary hypertension associated with interstitial lung disease.

• Option A: Option A is incorrect because IV rather than SC infusion is associated with catheter-related infection risk, and the GRIPHON trial studied selexipag in PAH, not IV treprostinil in CTEPH.
• Option C: Option C is incorrect because six-to-nine daily inhalations describes iloprost, not treprostinil; inhaled treprostinil (Tyvaso) is administered four times daily, and PATENT-1 was the riociguat trial.
• Option D: Option D is incorrect because the oral formulation carries a higher gastrointestinal adverse effect burden than parenteral routes and is not the most widely used; CHEST-1 was the riociguat trial in CTEPH, not an oral treprostinil trial.
• Option E: Option E is incorrect because the four routes have meaningfully different tolerability profiles — site pain for SC, catheter infection for IV, bronchospasm/cough for inhaled, GI effects for oral — and BREATHE-1 was the bosentan PAH trial.

ANSWER: C

Rationale:

A positive acute vasodilator response requires the simultaneous fulfillment of three hemodynamic criteria: a reduction in mPAP of at least 10 mmHg, a resulting absolute mPAP below 40 mmHg, and maintenance or increase in cardiac output. All three must be met; meeting two of three is insufficient. The mPAP drop of at least 10 mmHg demonstrates genuine pulmonary vasodilatory reserve. The absolute mPAP threshold below 40 mmHg ensures the achieved pressure is within a clinically meaningful range. The requirement for preserved or increased CO is critical: it confirms that the mPAP fall reflects true vasodilation rather than a reduction in cardiac output that passively lowers pulmonary pressures while hemodynamic reserve deteriorates. A patient who meets all three criteria, typically a small minority with idiopathic PAH and WHO-FC I or II without features of right heart failure, can be treated with high-dose nifedipine, diltiazem, or amlodipine as first-line monotherapy with markedly better prognosis than non-vasoreactive patients.

• Option A: Option A is incorrect because the absolute mPAP threshold below 40 mmHg is a required criterion in addition to the 10-mmHg drop; any absolute value is insufficient and would misidentify patients who achieve a relative fall from a very high baseline without reaching a clinically meaningful level.
• Option B: Option B is incorrect because a decrease in cardiac output explicitly disqualifies the response; the CO criterion requires maintenance or increase, not decrease, to confirm that vasodilation rather than output reduction accounts for the mPAP fall.
• Option D: Option D is incorrect because systemic blood pressure response is not part of the vasoreactivity criteria; the criteria are entirely pulmonary hemodynamic — mPAP and CO — not systemic.
• Option E: Option E is incorrect because PVR normalization below 2 Wood units is not the defined criterion for a positive vasoreactivity response, and the direction of mPAP and CO changes are integral to the three-criterion definition.

ANSWER: D

Rationale:

The AMBITION trial enrolled 500 treatment-naive patients with WHO functional class II or III PAH and randomized them to the combination of ambrisentan (an ERA) plus tadalafil (a PDE-5 inhibitor) versus ambrisentan alone or tadalafil alone. The primary composite endpoint was time to first clinical failure event, defined as death, hospitalization for PAH, disease progression, or unsatisfactory long-term clinical response. The combination arm demonstrated approximately a 50 percent reduction in this composite compared with the pooled monotherapy arms, with a number needed to treat of approximately 6 to prevent one clinical failure event over the study period. This trial is the core evidence base for the current guideline recommendation of upfront dual oral combination therapy in treatment-naive patients with WHO-FC II or III PAH who are not at high risk.

• Option A: Option A is incorrect because these figures describe the SERAPHIN trial — 742 patients, macitentan versus placebo, 45 percent reduction in morbidity-mortality composite — not AMBITION.
• Option B: Option B is incorrect because these figures describe the GRIPHON trial — 1156 patients, selexipag versus placebo, 40 percent reduction — not AMBITION.
• Option C: Option C is incorrect because AMBITION compared ambrisentan plus tadalafil versus monotherapy with each agent, not riociguat combinations; furthermore, the PDE-5 inhibitor plus riociguat combination is absolutely contraindicated and would never be studied in this manner.
• Option E: Option E is incorrect because AMBITION enrolled WHO-FC II and III patients, not exclusively WHO-FC IV; the evidence for upfront triple therapy including parenteral prostacyclin in high-risk patients comes from other data and guideline consensus, not from AMBITION.

ANSWER: E

Rationale:

The ambrisentan-cyclosporine and bosentan-cyclosporine interactions are mechanistically distinct. For ambrisentan: cyclosporine inhibits the hepatic uptake transporter OATP1B1, which is responsible for ambrisentan's clearance into the liver; OATP1B1 inhibition impairs ambrisentan hepatic uptake, substantially raising ambrisentan plasma concentrations and increasing exposure-related adverse effects. Ambrisentan itself does not significantly induce or inhibit CYP enzymes, which is a pharmacokinetically favorable feature distinguishing it from bosentan. For bosentan: bosentan induces CYP3A4, which accelerates cyclosporine metabolism and reduces cyclosporine plasma levels — threatening immunosuppression efficacy. Concurrently, cyclosporine inhibits bosentan's clearance, raising bosentan levels. This bidirectional pharmacokinetic interaction, with each drug adversely affecting the other, is the basis for the formal contraindication of bosentan with cyclosporine.

• Option A: Option A is incorrect because ambrisentan does not induce CYP3A4 and its cyclosporine interaction is mediated by OATP1B1, not CYP induction; the two mechanisms are not identical.
• Option B: Option B is incorrect because it inverts the mechanisms: ambrisentan's interaction with cyclosporine involves OATP1B1, not CYP2C9 induction, and bosentan's interaction involves CYP3A4, not OATP1B1 inhibition.
• Option C: Option C is incorrect because ambrisentan does not inhibit CYP3A4 and bosentan does not inhibit OATP1B1; the mechanisms are swapped in this option.
• Option D: Option D is incorrect because clinically significant cyclosporine interactions exist for both ambrisentan (OATP1B1 mediated) and bosentan (CYP3A4/bidirectional); macitentan's lipophilicity does not explain these specific transporter interactions.

ANSWER: A

Rationale:

This patient meets high-risk criteria on every parameter of the 2022 ESC/ERS three-strata model: WHO-FC IV, 6MWD well below 165 meters, markedly elevated NT-proBNP, right atrial pressure above 14 mmHg, and cardiac index below 2.0 L/min/m². The treatment algorithm for newly diagnosed high-risk or WHO-FC IV vasoreactivity-negative PAH is upfront triple combination therapy comprising an ERA, a PDE-5 inhibitor, and a parenteral prostacyclin analogue. Continuous IV epoprostenol is the preferred parenteral agent in this setting because it is the only PAH therapy supported by randomized trial data demonstrating a survival benefit (the 1996 Barst trial in severe PAH). Deferring parenteral prostacyclin until deterioration leaves a high-risk patient on an inadequate regimen during the period of greatest clinical jeopardy.

• Option B: Option B is incorrect because upfront dual oral combination without parenteral prostacyclin is the recommended approach for low- or intermediate-risk patients (WHO-FC II/III); it is insufficient for a high-risk patient with this hemodynamic profile.
• Option C: Option C is incorrect because the patient is vasoreactivity-negative, and high-dose CCBs are not only ineffective but potentially dangerous in vasoreactivity-negative PAH; repeating the test with a second agent is not standard practice.
• Option D: Option D is incorrect because sequential monotherapy beginning with a single agent is the approach the AMBITION era has replaced; high-risk patients require the most intensive upfront regimen from the outset.
• Option E: Option E is incorrect because riociguat monotherapy is not the guideline-recommended first-line regimen for any risk stratum; in practice riociguat may be a component of a combination regimen (as the NO-pathway agent in combination with an ERA), but it is not used as sole initial therapy in high-risk disease.

ANSWER: B

Rationale:

Iloprost is a prostacyclin analogue with a plasma half-life of approximately 20 to 30 minutes. It is delivered exclusively by inhalation using a specialized nebulizer device (the I-neb Adaptive Aerosol Delivery system); no other administration route is approved for iloprost. Because of its short half-life, six to nine inhalations per day are required throughout waking hours to maintain sustained pulmonary vasodilation; the frequent dosing schedule is the principal barrier to patient adherence. The inhalation route preferentially delivers drug to ventilated lung units, reducing systemic vasodilatory adverse effects compared with parenteral prostacyclin therapy. Iloprost is used primarily as add-on therapy in patients already on a background oral regimen; its role has become more limited as inhaled treprostinil, which requires only four daily inhalations, has demonstrated longer-acting efficacy in the same inhalation niche.

• Option A: Option A is incorrect because the 4-hour half-life and SC/inhaled availability describe treprostinil, not iloprost; iloprost has no subcutaneous formulation and does not supplant epoprostenol in high-risk PAH.
• Option C: Option C is incorrect because iloprost has no IV formulation; it is available exclusively by inhalation, and IV prostacyclin options are epoprostenol and treprostinil.
• Option D: Option D is incorrect because iloprost's half-life is approximately 20 to 30 minutes, not 2 to 5 minutes; the 2- to 5-minute half-life is specific to epoprostenol; iloprost's longer duration allows inhalation every 2 to 3 hours rather than every 2 hours, and iloprost interruption does not carry the same acute rebound crisis risk as IV epoprostenol interruption.
• Option E: Option E is incorrect because iloprost is not an oral agent; GRIPHON was the selexipag trial, and iloprost's route is exclusively inhalation.

ANSWER: C

Rationale:

The 2022 ESC/ERS three-strata risk model categorizes patients as low, intermediate, or high risk of one-year mortality using a composite of five domains: WHO functional class (WHO-FC I/II = low, III = intermediate, IV = high); 6-minute walk distance (6MWD above 440 meters = low, 165 to 440 meters = intermediate, below 165 meters = high); N-terminal pro-B-type natriuretic peptide (NT-proBNP below 300 ng/L = low); right ventricular (RV) function on echocardiography; and invasive hemodynamics including right atrial pressure (RAP) and cardiac index (CI). All five domains contribute to the composite risk classification. The treatment target is explicit and proactive: achieving low-risk status, not merely stabilizing disease. A patient who remains at intermediate risk after 3 to 6 months of adequate combination therapy has not met the treatment target, and persistent intermediate risk is operationally defined as a treatment failure requiring escalation — regardless of whether the patient feels stable subjectively.

• Option A: Option A is incorrect because the model incorporates five domains, not two; WHO-FC and 6MWD are two of the five, not the complete parameter set.
• Option B: Option B is incorrect because stabilization is not the treatment target; the goal is low-risk status, and escalation is required for persistent intermediate risk rather than only for high-risk transition.
• Option D: Option D is incorrect because the model incorporates invasive hemodynamics (RAP and CI) as integral components, not a WHO-FC-IV-triggered escalation threshold.
• Option E: Option E is incorrect because the three-strata model is used at both initial diagnosis and at every reassessment — typically at 3 to 6 months after treatment initiation and every 3 to 6 months thereafter — and no separate binary tool replaces it; hospitalization prevention is one component of the composite endpoint, not the sole treatment target.