Diagnostic utility of sub-maximum cardiopulmonary exercise testing in the ambulatory setting for heart failure with preserved ejection fraction

Differential cardiopulmonary haemodynamic phenotypes in PASC-related exercise intolerance

Background

Post-acute sequelae of COVID-19 (PASC) affect a significant proportion of patients who have previously contracted SARS-CoV-2, with exertional intolerance being a prominent symptom. This study aimed to characterise the invasive haemodynamic abnormalities of PASC-related exertional intolerance using invasive cardiopulmonary exercise testing (iCPET).

Study design and intervention

55 patients were recruited from the Yale Post-COVID-19 Recovery Program, with most experiencing mild acute illness. Supine right heart catheterisation and iCPET were performed on all participants.

Main results

The majority (75%) of PASC patients exhibited impaired peak systemic oxygen extraction (pEO2) during iCPET in conjunction with supranormal cardiac output (CO) (i.e., PASC alone group). On average, the PASC alone group exhibited a "normal" peak exercise capacity, V'O2 (89±18% predicted). ∼25% of patients had evidence of central cardiopulmonary pathology (i.e., 12 with resting and exercise heart failure with preserved ejection fraction (HFpEF) and two with exercise pulmonary hypertension (PH)). PASC patients with HFpEF (i.e., PASC HFpEF group) exhibited similarly impaired pEO2 with well compensated PH (i.e., peak V'O2 and CO >80% respectively) despite aberrant central cardiopulmonary exercise haemodynamics. PASC patients with HFpEF also exhibited increased body mass index of 39±7 kg·m-2. To examine the relative contribution of obesity to exertional impairment in PASC HFpEF, a control group comprising obese non-PASC group (n=61) derived from a historical iCPET cohort was used. The non-PASC obese patients with preserved peak V'O2 (>80% predicted) exhibited a normal peak pulmonary artery wedge pressure (17±14 versus 25±6 mmHg; p=0.03) with similar maximal voluntary ventilation (90±12 versus 86±10% predicted; p=0.53) compared to PASC HFpEF patients. Impaired pEO2 was not significantly different between PASC patients who underwent supervised rehabilitation and those who did not (p=0.19).

Conclusions

This study highlights the importance of considering impaired pEO2 in PASC patients with persistent exertional intolerance unexplained by conventional investigative testing. Results of the current study also highlight the prevalence of a distinct high output HFpEF phenotype in PASC with a primary peripheral limitation to exercise.

Cognitive impairment in pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is characterized by progressive pulmonary vascular remodeling with resultant abnormal increase in pulmonary artery pressure and right heart dysfunction. There is evidence that PAH includes cognitive impairment. However, the cognitive impairment syndrome has not been well described, and both the underlying mechanism and the relationship between cardiopulmonary and cognitive dysfunction in PAH are unknown. We performed cognitive evaluations and same day sub-maximum cardiopulmonary exercise testing on adult subjects with PAH. A frontal-subcortical syndrome suggestive of vascular cognitive impairment was found in 26% of subjects and was associated with noninvasive markers of pulmonary vascular remodeling.

Diagnostic value of expired gas analysis in heart failure with preserved ejection fraction

Cardiopulmonary exercise testing (CPET) may potentially differentiate heart failure (HF) with preserved ejection fraction (HFpEF) from noncardiac causes of dyspnea (NCD). While contemporary guidelines for HF recommend using CPET for identifying causes of unexplained dyspnea, data supporting this practice are limited. This study aimed to determine the diagnostic value of expired gas analysis to distinguish HFpEF from NCD. Exercise stress echocardiography with simultaneous expired gas analysis was performed in patients with HFpEF (n = 116) and those with NCD (n = 112). Participants without dyspnea symptoms were also enrolled as controls (n = 26). Exercise capacity was impaired in patients with HFpEF than in controls and those with NCD, evidenced by lower oxygen consumption (VO₂), but there was a substantial overlap between HFpEF and NCD. Receiver operating characteristic curve analyses showed modest diagnostic abilities of expired gas analysis data in differentiating individuals with HFpEF from the controls; however, none of these variables clearly differentiated between HFpEF and NCD (all areas under the curve < 0.61). Expired gas analysis provided objective assessments of exercise capacity; however, its diagnostic value in identifying HFpEF among patients with symptoms of exertional dyspnea was modest.

Noninvasive determinants of pulmonary hypertension in interstitial lung disease

Pulmonary hypertension (PH) in interstitial lung disease (ILD) is associated with increased mortality and impaired exertional capacity. Right heart catheterization is the diagnostic standard for PH but is invasive and not readily available. Noninvasive physiologic evaluation may predict PH in ILD. Forty-four patients with PH and ILD (PH-ILD) were compared with 22 with ILD alone (non-PH ILD). Six-min walk distance (6MWD, 223 ± 131 vs. 331 ± 125 m, p = 0.02) and diffusing capacity for carbon monoxide (DLCO, 33 ± 14% vs. 55 ± 21%, p < 0.001) were lower in patients with PH-ILD. PH-ILD patients exhibited a lower gas-exchange derived pulmonary vascular capacitance (GXCAP, 251 ± 132 vs. 465 ± 282 mL × mmHg, p < 0.0001) and extrapolated maximum oxygen uptake (VO2max) (56 ± 32% vs. 84 ± 37%, p = 0.003). Multivariate analysis was performed to determine predictors of VO2 max. GXCAP was the only variable that predicted extrapolated VO2 max among PH-ILD and non-PH ILD patients. Receiver operating characteristic curve analysis assessed the ability of individual noninvasive variables to distinguish between PH-ILD and non-PH ILD patients. GXCAP (area under the curve [AUC] 0.85 ± 0.04, p < 0.0001) and delta ETCO2 (AUC 0.84 ± 0.04, p < 0.0001) were the strongest predictors of PH-ILD. A CART analysis selected GXCAP, estimated right ventricular systolic pressure (eRVSP) by echocardiogram, and FVC/DLCO ratio as predictive variables for PH-ILD. With this analysis, the AUC improved to 0.94 (sensitivity of 0.86 and sensitivity of 0.93). Patients with a GXCAP ≤ 416 mL × mmHg had an 82% probability of PH-ILD. Patients with GXCAP ≤ 416 mL × mmHg and high FVC/DLCO ratio >1.7 had an 80% probability of PH-ILD. Patients with GXCAP ≤ 416 mL × mmHg and an elevated eRVSP by echocardiogram >43 mmHg had 100% probability of PH-ILD. The incorporation of GXCAP with either eRVSP or FVC/DLCO ratio distinguishes between PH-ILD and non-PH-ILD with high probability and may therefore assist in determining the need to proceed with a diagnostic right heart catheterization and potential initiation of pulmonary arterial hypertension-directed therapy in PH-ILD patients.

Excess ventilation and exertional dyspnoea in heart failure and pulmonary hypertension

Increased ventilation relative to metabolic demands, indicating alveolar hyperventilation and/or increased physiological dead space (excess ventilation), is a key cause of exertional dyspnoea. Excess ventilation has assumed a prominent role in the functional assessment of patients with heart failure (HF) with reduced (HFrEF) or preserved (HFpEF) ejection fraction, pulmonary arterial hypertension (PAH) and chronic thromboembolic pulmonary hypertension (CTEPH). We herein provide the key pieces of information to the caring physician to 1) gain unique insights into the seeds of patients' shortness of breath and 2) develop a rationale for therapeutically lessening excess ventilation to mitigate this distressing symptom. Reduced bulk oxygen transfer induced by cardiac output limitation and/or right ventricle-pulmonary arterial uncoupling increase neurochemical afferent stimulation and (largely chemo-) receptor sensitivity, leading to alveolar hyperventilation in HFrEF, PAH and small-vessel, distal CTEPH. As such, interventions geared to improve central haemodynamics and/or reduce chemosensitivity have been particularly effective in lessening their excess ventilation. In contrast, 1) high filling pressures in HFpEF and 2) impaired lung perfusion leading to ventilation/perfusion mismatch in proximal CTEPH conspire to increase physiological dead space. Accordingly, 1) decreasing pulmonary capillary pressures and 2) mechanically unclogging larger pulmonary vessels (pulmonary endarterectomy and balloon pulmonary angioplasty) have been associated with larger decrements in excess ventilation. Exercise training has a strong beneficial effect across diseases. Addressing some major unanswered questions on the link of excess ventilation with exertional dyspnoea under the modulating influence of pharmacological and nonpharmacological interventions might prove instrumental to alleviate the devastating consequences of these prevalent diseases.

Clinical Relevance of Right Atrial Functional Response to Treatment in Pulmonary Arterial Hypertension

Background: Right atrial (RA) function has emerged as an important determinant of outcome in pulmonary arterial hypertension (PAH). However, studies exploring RA function after initiation of specific pulmonary vascular treatment and its association with outcome in patients with incident PAH are lacking. Methods: RA peak longitudinal strain (PLS), passive strain (PS), and peak active contraction strain (PACS) were retrospectively assessed in 56 treatment-naïve patients with PAH at baseline and during follow-up after initiation of specific monotherapy or combination therapy. Patients were grouped according to their individual RA functional response to treatment, based on change from baseline (Δ): worsened (first Δ-tertile), stable (second Δ-tertile), and improved (third Δ-tertile). The Spearman's rho correlation and linear regression analysis were used to determine associations. Time to clinical worsening (defined as deterioration of functional class or 6-min walking distance, disease-related hospital admission, or death) was measured from the follow-up assessment. The association of RA functional treatment response with time to clinical worsening was assessed using the Kaplan-Meier and the Cox regression analyses. Results: Median (interquartile range) time to echocardiographic follow-up was 11 (9-12) months. Of the 56 patients, 37 patients (66%) received specific dual or triple combination therapy. Δ RA PLS during follow-up was significantly associated with changes in key hemodynamic and echocardiographic parameters. The change of pulmonary vascular resistance, right ventricular (RV) end-systolic area, and global longitudinal strain were independently associated with Δ RA PLS. The median time to clinical worsening after echocardiographic follow-up was 6 (2-14) months [17 events (30%)]. In the multivariate Cox regression analysis, worsening of RA PLS was significantly associated with clinical deterioration (hazard ratio: 4.87; 95% CI: 1.26-18.76; p = 0.022). Patients with worsened RA PLS had a significantly poorer prognosis than those with stable or improved RA PLS (log-rank p = 0.012). By contrast, PS and PACS did not yield significant prognostic information. Conclusion: Treatment-naïve patients with PAH may show different RA functional response patterns to PAH therapy. These functional patterns are significantly associated with clinically relevant outcome measures. Improvements of RA function are driven by reductions of afterload, RV remodeling, and RV dysfunction.