Longitudinal trajectory of cardiac magnetic resonance and cardiopulmonary exercise testing findings in moderate to severe COVID-19 and association with symptoms

Background

Cardiac magnetic resonance (CMR) and cardiopulmonary exercise testing (CPET) have provided important insights into the prevalence of early cardiopulmonary abnormalities in COVID-19 patients. It is currently unknown whether such abnormalities persist over time and relate to ongoing symptoms.

Purpose

To describe the longitudinal trajectory of cardiopulmonary abnormalities on CMR and CPET in moderate to severe COVID-19 patients and assess their relationship with ongoing symptoms.

Methods

Fifty-eight previously hospitalised COVID-19 patients and 30 age, sex, body mass index, comorbidity-matched controls underwent CMR, CPET and a symptom-based questionnaire at 2–3 months (2–3m). Repeat assessments (including gas transfer) were performed in 46 patients at 6 months (6m).

Results

During admission, 1/3rd of patients needed ventilation or intensive care (Table 1) and three (5%) had a raised troponin.

On CMR, patients had preserved left (LV) and right ventricular (RV) volumes and function at 2–3m from infection. By 6m, LV function did not change but RV end diastolic volume decreased (mean difference −4.3 mls/m2, p=0.005) and RV function increased (mean difference +3.2%, p<0.001, Fig. 1A).

Patients had higher native T1 (a marker of fibroinflammation) at 2–3m compared to controls (Table 1, Fig. 1B), which normalised by 6m. Extracellular volume was normal and improved by 6m. Native T2, a marker of myocardial oedema, did not differ between patients and controls on serial CMR. At 2–3m, late gadolinium enhancement (LGE) was higher in patients (p=0.023) but became comparable to controls by 6m (p=0.62). Six (12%) patients had LGE in a myocarditis pattern and one (2%) had myocardial infarction. None had active myocarditis using the Modified Lake Louise Criteria.

Lung imaging (T2-weighted) revealed parenchymal abnormalities in 2/3rds of patients at 2–3 and 6 months. The extent of abnormalities improved on serial imaging (Table 1). Gas transfer (DLco) was worse in those with lung abnormalities (77% vs 91% of predicted, p=0.009).

CPET revealed reduced peak oxygen consumption (pVO2) in patients at 2–3m, which normalised by 6m (80.5% to 93.3% of predicted, p=0.001) (Table 1, Fig. 1C). At 2–3m, 49% of patients had submaximal tests (respiratory exchange ratio <1.1), reducing to 25% by 6m (p=0.057). VE/VCO2 slope, a marker of lung efficiency, was abnormal in patients but improved on serial CPET (Table 1, Fig. 1D).

Cardiac symptoms (chest pain, dyspnoea, palpitations, dizziness or syncope) were present in 83% of patients at 2–3m, reducing to 52% by 6m (p<0.001). There was no significant association between CMR or CPET parameters and persistent cardiac symptoms at 6m (Fig. 1E).

Conclusions

Cardiopulmonary parameters (on CMR and CPET) improved in moderate-severe COVID-19 patients from 2–3 to 6 months post infection. Despite this, patients continued to experience cardiac symptoms which had no relationship with measured parameters.

Funding Acknowledgement

Type of funding sources: Foundation. Main funding source(s): 1. NIHR Oxford and Oxford Health Biomedical Research Centre, Oxford British Heart Foundation (BHF) Centre of Research Excellence (RE/18/3/34214), United Kingdom Research Innovation and Wellcome Trust2. Medical Research Council and Department of Health and Social Care/National Institute for Health Research Grant (MR/V027859/1) ISRCTN number 10980107 Table 1Figure 1

Mutation of the von Hippel-Lindau gene alters human cardiopulmonary physiology

Intracellular responses to hypoxia are coordinated by the von Hippel-Lindau--hypoxia-inducible factor (VHL-HIF) transcriptional system. This study investigated the potential role of the VHL-HIF pathway in human systems-level physiology. Patients diagnosed with Chuvash polycythaemia, a rare disorder in which VHL signalling is specifically impaired, were studied during acute hypoxia and hypercapnia. Subjects breathed through a mouthpiece and ventilation was measured while pulmonary vascular tone was assessed echocardiographically. The patients were found to have elevated basal ventilation and pulmonary vascular tone, and ventilatory, pulmonary vasoconstrictive and heart rate responses to acute hypoxia were greatly increased, as were heart rate responses to hypercapnia. The patients also had abnormal pulmonary function on spirometry. This study's findings demonstrate that the VHL-HIF signalling pathway, which is so central to intracellular oxygen sensing, also regulates the organ systems upon which cellular oxygen delivery ultimately depends.

Human pulmonary vascular responses to hypoxia and hypercapnia

The ability of alveolar gas composition to influence pulmonary vascular tone has been appreciated for over 50 years. In particular, it has been proposed that both O2 and CO2 could play a role in the matching of perfusion to ventilation within the lung, improving the overall efficiency of gas exchange. A wide variety of experimental approaches has been used to investigate pulmonary vascular effects of the respiratory gases in a range of mammalian species. In this article, we review experiments performed in healthy humans, identify particular difficulties in the interpretation of such experiments, and discuss possible approaches to future study.

Release by hypoxia of a soluble vasoconstrictor from rabbit small pulmonary arteries

BACKGROUND

Soluble pulmonary vasoconstrictors released in response to hypoxia have been reported in pig and rat preparations, but not in rabbit preparations.

METHODS

We used myography to evaluate the contribution of a soluble factor to constriction in rabbit small pulmonary arteries (external diameter 300-475 microm) exposed to 45 min hypoxia (PO(2)=9 mm Hg).

RESULTS

Hypoxia produced gradually intensifying constriction. Return to euoxia (PO(2)=145 mm Hg) for 30 min relaxed only approximately 30% of the constriction, whereas elution of the myograph bath yielded full relaxation. Reapplication of the eluent gradually restored the constriction to its pre-elution level over a 30-min period.

CONCLUSIONS

In this closed system, a soluble factor contributes substantially to hypoxic pulmonary vasoconstriction.