Cardiovascular Risk in Young Patients Diagnosed With Obstructive Sleep Apnea.

BACKGROUND: In older adults, obstructive sleep apnea (OSA) has been associated with several cardiovascular complications. Whether young patients diagnosed with OSA also are at higher risk of developing subsequent cardiovascular disease is uncertain. We aimed to estimate the risk of developing an incident cardiovascular event among young patients diagnosed with OSA. METHODS AND RESULTS: We linked nationwide Danish health registries to identify a cohort of patients aged ≤50 years with OSA using data from 2010 through 2018. Cases without OSA from the general population were matched as controls (1:5). The main outcome was any cardiovascular event (including hypertension, diabetes, atrial fibrillation, ischemic heart disease, ischemic stroke, heart failure, and venous thromboembolism). All-cause mortality was a secondary outcome. The study included 20 240 patients aged ≤50 years with OSA (19.6% female; mean±SD age 39.9±7.7 years) and 80 314 controls. After 5-year follow-up, 31.8% of the patients with OSA developed any cardiovascular event compared with 16.5% of the controls, with a corresponding relative risk (RR) of 1.96 (95% CI, 1.90-2.02). At 5-year follow-up, 27.3% of patients with OSA developed incident hypertension compared with 15.0% of the controls (RR, 1.84 [95% CI, 1.78-1.90]). Incident diabetes occurred in 6.8% of the patients with OSA and 1.4% of controls (RR, 5.05 [95% CI, 4.60-5.54]). CONCLUSIONS: Similar to older adults, young adults with OSA demonstrate increased risk of developing cardiovascular events. To prevent cardiovascular disease progression, accumulation of cardiovascular risk factors, and mortality, risk stratification and prevention strategies should be considered for these patients.

Optimizing antithrombotic therapy in patients with coexisting cardiovascular and gastrointestinal disease.

Balancing the safety and efficacy of antithrombotic agents in patients with gastrointestinal disorders is challenging because of the potential for interference with the absorption of antithrombotic drugs and for an increased risk of bleeding. In this Review, we address considerations for enteral antithrombotic therapy in patients with cardiovascular disease and gastrointestinal comorbidities. For those with gastrointestinal bleeding (GIB), we summarize a general scheme for risk stratification and clinical evidence on risk reduction approaches, such as limiting the use of concomitant medications that increase the risk of GIB and the potential utility of gastrointestinal protection strategies (such as proton pump inhibitors or histamine type 2 receptor antagonists). Furthermore, we summarize the best available evidence and potential gaps in our knowledge on tailoring antithrombotic therapy in patients with active or recent GIB and in those at high risk of GIB but without active or recent GIB. Finally, we review the recommendations provided by major medical societies, highlighting the crucial role of teamwork and multidisciplinary discussions to customize the antithrombotic regimen in patients with coexisting cardiovascular and gastrointestinal diseases.

Fibrinolytic Agents in Thromboembolic Diseases: Historical Perspectives and Approved Indications.

Fibrinolytic agents catalyze the conversion of the inactive proenzyme plasminogen into the active protease plasmin, degrading fibrin within the thrombus and recanalizing occluded vessels. The history of these medications dates to the discovery of the first fibrinolytic compound, streptokinase, from bacterial cultures in 1933. Over time, researchers identified two other plasminogen activators in human samples, namely urokinase and tissue plasminogen activator (tPA). Subsequently, tPA was cloned using recombinant DNA methods to produce alteplase. Several additional derivatives of tPA, such as tenecteplase and reteplase, were developed to extend the plasma half-life of tPA. Over the past decades, fibrinolytic medications have been widely used to manage patients with venous and arterial thromboembolic events. Currently, alteplase is approved by the U.S. Food and Drug Administration (FDA) for use in patients with pulmonary embolism with hemodynamic compromise, ST-segment elevation myocardial infarction (STEMI), acute ischemic stroke, and central venous access device occlusion. Reteplase and tenecteplase have also received FDA approval for treating patients with STEMI. This review provides an overview of the historical background related to fibrinolytic agents and briefly summarizes their approved indications across various thromboembolic diseases.

Prospective Multicenter International Registry of Ultrasound-Facilitated Catheter-Directed Thrombolysis in Intermediate-High and High-Risk Pulmonary Embolism (KNOCOUT PE).

BACKGROUND: Prior clinical trials have demonstrated the efficacy of ultrasound-facilitated catheter-directed thrombolysis (USCDT) for the treatment of acute intermediate-risk pulmonary embolism (PE) using reduced thrombolytic doses and shorter infusion durations. However, utilization and safety of such strategies in broader PE populations remain unclear. The KNOCOUT PE (The EKoSoNic Registry of the Treatment and Clinical Outcomes of Patients With Pulmonary Embolism) registry is a multicenter international registry designed to study the treatment of acute PE with USCDT, with focus on safety outcomes. METHODS: The KNOCOUT PE prospective cohort included 489 patients (64 sites internationally) with acute intermediate-high or high-risk PE treated with USCDT between March 2018 and June 2020. Principal safety outcomes were independently adjudicated International Society on Thrombosis and Haemostasis major bleeding at 72 hours post-treatment and mortality within 12 months of treatment. Additional outcomes included change in right ventricular/left ventricular ratio and quality of life measures over 12 months. RESULTS: Mean alteplase (r-tPA [recombinant tissue-type plasminogen activator]) infusion duration was 10.5 hours. Mean total r-tPA dose was 18.1 mg, with 31.0% of patients receiving ≤12 mg. Major bleeding events within 72 hours occurred in 1.6% (8/489) of patients. One patient experienced worsening of a preexisting subdural hematoma after USCDT and therapeutic anticoagulation, which ultimately required surgery. All-cause mortality at 30 days was 1.0% (5/489). Improvement in PE quality of life score was observed with a 41.1% (243/489, 49.7%) and 44.2% (153/489, 31.3%) mean relative reduction by 3 and 12 months, respectively. CONCLUSIONS: In a prospective observational cohort study of patients with intermediate-high and high-risk PE undergoing USCDT, mean r-tPA dose was 18 mg, and the rates of major bleeding and mortality were low. REGISTRATION: URL: https://www.clinicaltrials.gov; Unique identifier: NCT03426124.

External validation of the PE-SARD risk score for predicting early bleeding in acute pulmonary embolism in the RIETE Registry.

INTRODUCTION: The PE-SARD score (syncope, anemia, renal dysfunction) was developed to predict the risk of major bleeding in the acute phase of pulmonary embolism (PE). METHODS: We analyzed data from 50,686 patients with acute PE included in the RIETE registry to externally validate the PE-SARD score. We calculated the overall reliability of the PE-SARD score, as well as discrimination and calibration for predicting the risk of major bleeding at 30 days. The performance of PE-SARD was compared to the BACS and PE-CH models. RESULTS: During the first 30 days, 640 patients (1.3 %) had a major bleeding event. The incidence of major bleeding within 30 days was 0.6 % in the PE-SARD-defined low-risk group, 1.5 % in the intermediate-risk group, and 2.5 % in the high-risk group, for an OR of 2.22 (95 % CI, 2.02-2.43) for the intermediate-risk group (vs low-risk group), and 3.94 for the high-risk group (vs low-risk group). The corresponding sensitivity was 81.1 % (intermediate/high vs low risk), and specificity was 85.9 % (95 % CI, 85.8-86.1) (low/intermediate vs high risk). The applicability of PE-SARD was consistent across clinically relevant patient subgroups and over shorter time periods of follow-up (i.e., 3 and 7 days). The C-index was 0.654 and calibration was excellent. The PE-SARD bleeding score improved the major bleeding risk prediction compared with the BACS and PE-CH scores. CONCLUSIONS: The PE-SARD score identifies PE patients with a higher risk of bleeding, which could assist providers for potentially adjusting PE management, in a framework of shared decision-making with individual patients.

When Direct Oral Anticoagulants Should Not Be Standard Treatment: JACC State-of-the-Art Review.

For most patients, direct oral anticoagulants (DOACs) are preferred over vitamin K antagonists for stroke prevention in atrial fibrillation and for venous thromboembolism treatment. However, randomized controlled trials suggest that DOACs may not be as efficacious or as safe as the current standard of care in conditions such as mechanical heart valves, thrombotic antiphospholipid syndrome, and atrial fibrillation associated with rheumatic heart disease. DOACs do not provide a net benefit in conditions such as embolic stroke of undetermined source. Their efficacy is uncertain for conditions such as left ventricular thrombus, catheter-associated deep vein thrombosis, cerebral venous sinus thrombosis, and for patients with atrial fibrillation or venous thrombosis who have end-stage renal disease. This paper provides an evidence-based review of randomized controlled trials on DOACs, detailing when they have demonstrated efficacy and safety, when DOACs should not be the standard of care, where their safety and efficacy are uncertain, and areas requiring further research.

Trends of Pulmonary Embolism-Related Sudden Cardiac Death in the United States, 1999-2019.

OBJECTIVES: Up-to-date population-based data on pulmonary embolism (PE)-related sudden cardiac death (SCD) mortality trends in the United States (US) are scant. We assess the current trends in PE-related SCD mortality in US over the past two decades and determine differences by sex, race, ethnicity, age, and census region. METHODS: We extracted PE-related SCD mortality rates from the Centers for Disease Control and Prevention Wide-Ranging Online Data for Epidemiologic Research (CDC WONDER) database from 1999 to 2019, in patients aged ≥ 15 years old. Age-adjusted mortality rates (AAMRs) were assessed using the Joinpoint regression modeling and expressed as estimated average annual percentage change (AAPC) with relative 95% confidence intervals (CIs). RESULTS: Between 1999 and 2019, the AAMR from acute PE-related SCD mortality in the US linearly increased [AAPC: +2.4% (95% CI: 2.2 to 2.6), p < 0.001)]. The AAMR increase was more pronounced in men [AAPC: +2.8% (95% CI: 2.6 to 2.9), p < 0.001], Whites [AAPC: +2.7% (95% CI: 2.3 to 3.1), p < 0.001], Latinx/Hispanic patients [AAPC:+2.0% (95% CI: 1.2 to 2.8), p < 0.001], subjects younger than 65 years [AAPC: +2.4% (95% CI: 2.1 to 2.6), p < 0.001] and in residents of rural areas [AAPC: +3.6% (95% CI: 3.3 to 3.9), p < 0.001]. Moreover, higher percentages of PE-related SCD and the relative absolute number of deaths were observed in the South compared with other geographical regions. CONCLUSIONS: PE-related SCD mortality in the US has increased over the last two decades. Stratification by race, ethnicity, urbanization, and census region demonstrates ethnoracial and regional disparities that require further investigation and remedy.

Developmental or Procedural Vena Cava Interruption and Venous Thromboembolism: A Review.

The inferior vena cava (IVC) and superior vena cava are the main conduits of the systemic venous circulation into the right atrium. Developmental or procedural interruptions of vena cava might predispose to stasis and deep vein thrombosis (DVT) distal to the anomaly and may impact the subsequent rate of pulmonary embolism (PE). This study aimed to review the various etiologies of developmental or procedural vena cava interruption and their impact on venous thromboembolism. A systematic search was performed in PubMed according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines per each clinical question. For management questions with no high-quality evidence and no mutual agreements between authors, Delphi methods were used. IVC agenesis is the most common form of congenital vena cava interruption, is associated with an increased risk of DVT, and should be suspected in young patients with unexpected extensive bilateral DVT. Surgical techniques for vena cava interruption (ligation, clipping, and plication) to prevent PE have been largely abandoned due to short-term procedural risks and long-term complications, although survivors of prior procedures are occasionally encountered. Vena cava filters are now the most commonly used method of procedural interruption, frequently placed in the infrarenal IVC. The most agreed-upon indication for vena cava filters is for patients with acute venous thromboembolism and coexisting contraindications to anticoagulation. Familiarity with different forms of vena cava interruption and their local and systemic adverse effects is important to minimize complications and thrombotic events.

Prognostic Role of Tricuspid Annular Plane Systolic Excursion to Systolic Pulmonary Artery Pressure Ratio for the Identification of Early Clinical Deterioration in Intermediate-High-Risk Pulmonary Embolism Patients.

The ratio of tricuspid annular plane systolic excursion (TAPSE) to echocardiographically measured systolic pulmonary artery pressure (PASP) has been proposed as a surrogate of RV-arterial coupling. In this analysis, we assess the prognostic role of TAPSE/PASP for early clinical deterioration and short-term mortality in an often clinically challenging population of intermediate-high-risk patients with pulmonary embolism (PE). A post hoc analysis of intermediate-high-risk patients with PE enrolled in the Italian Pulmonary Embolism Registry (ClinicalTrials.gov: NCT01604538) was performed. All patients underwent transthoracic echocardiography at admission. The primary and secondary outcomes were clinical deterioration within 48 hours from admission and 30-day all-cause mortality, respectively. In 422 intermediate-high-risk patients with PE (mean age 71.2 ± 5.3 years, 238 men), 37 (8.7%) experienced clinical deterioration within 48 hours of admission. The 30-day mortality rate was 6.6% (n = 28). The receiver operating characteristic analysis established 0.33 as the optimal cut-off value for the TAPSE/PASP in predicting 48-hour clinical deterioration (area under the curve 0.79 ± 0.1). The sensitivity, specificity, positive predictive value, and negative predictive value were 81%, 88.5%, 40.5%, and 97.9%, respectively. The multivariate Cox regression analysis showed that a TAPSE/PASP ≤0.33 was an independent predictor of 48-hour clinical deterioration (hazard ratio 2.06, 95% confidence interval 1.98 to 2.11, p <0.0001) and 30-day mortality (hazard ratio 2.28, 95% confidence interval 2.25 to 2.33, p <0.001). TAPSE/PASP shows promise as a noninvasive prognostic predictor to identify intermediate-high-risk patients with PE at a higher risk of early clinical deterioration and short-term mortality.

High-Sensitivity vs Conventional Troponin Cutoffs for Risk Stratification in Patients With Acute Pulmonary Embolism.

Importance: High-sensitivity troponin tests can detect even milder cardiac troponin elevations in plasma, beyond the threshold of conventional troponin tests. Whether detection of low-grade cardiac troponin elevation is associated with outcomes of patients with hemodynamically stable pulmonary embolism (PE) and helps with risk stratification is unknown. Objective: To determine the association between high-sensitivity cardiac troponin I (hs-cTnI) compared with conventional cardiac troponin I (cTnI) and PE risk designations according to the European Society of Cardiology (ESC) 2019 classification scheme and clinical outcomes in patients with hemodynamically stable PE. Design, Setting, and Participants: This is a post hoc analysis of data from the prospective Prognostic Value of Computed Tomography (PROTECT) multicenter cohort study enrolling patients from 12 hospital emergency departments in Spain. In this analysis, cTnI and hs-cTnI were compared with respect to ESC risk designation, and the association between troponin values and a complicated course after PE diagnosis was evaluated. Of 848 patients enrolled in PROTECT, 834 (98.3%) had hsTnI and cTnI values available and were included in the present analysis. Data were analyzed from May to December 2022. Exposures: Troponin blood testing with cTnI (threshold of >0.05 ng/mL) vs hs-cTnI (threshold of >0.029 ng/mL) assays at the time of PE diagnosis. Main Outcomes: Complicated course, defined as hemodynamic collapse, recurrent PE, or all-cause death, within 30 days after PE. Results: Of 834 patients (mean [SEM] age, 67.5 [0.6] years; 424 [50.8%] female), 139 (16.7%) had elevated cTnI and 264 (31.7%) elevated hs-TnI, respectively. During follow-up, 62 patients (7.4%; 95% CI, 5.7-9.4) had a complicated course. Analyzing troponin elevation as a binary variable, elevated cTnI (odds ratio [OR], 2.84; 95% CI, 1.62-4.98) but not hs-cTnI (OR, 1.12; 95% CI, 0.65-1.93) was associated with increased odds of a complicated course. Of 125 patients who had elevated hs-cTnI but normal cTnI, none (0; 95% CI, 0.0-2.9) developed a complicated course. Using the 2019 ESC risk stratification scheme, hs-TnI classified fewer patients as low risk compared with cTnI. Among 78 patients designated as ESC low risk when using cTnI but not with hsTnI, none (0; 95% CI, 0.0-4.6) had a complicated course. Conclusions and Relevance: In this study of patients with hemodynamically stable PE, hs-cTnI identified modest elevations in cardiac troponin levels. However, the results did not provide additive clinical value compared with cTnI. These findings suggest that use of hs-cTnI may result in overestimation of the risk in patients with stable PE.

High and intermediate risk pulmonary embolism in the ICU.

Pulmonary embolism (PE) is a common and important medical emergency, encountered by clinicians across all acute care specialties. PE is a relatively uncommon cause of direct admission to the intensive care unit (ICU), but these patients are at high risk of death. More commonly, patients admitted to ICU develop PE as a complication of an unrelated acute illness. This paper reviews the epidemiology, diagnosis, risk stratification, and particularly the management of PE from a critical care perspective. Issues around prevention, anticoagulation, fibrinolysis, catheter-based techniques, surgical embolectomy, and extracorporeal support are discussed.

Effect of Pharmacomechanical Catheter-Directed Thrombolysis on Segmental Artery Occlusions: Insights From the RESCUE Trial.

BACKGROUND: Reduction in distal vascular volume in acute pulmonary embolism (PE) is a significant predictor of 30- and 90-day mortality. The likely cause of this is pulmonary arterial obstruction. The effect of pharmacomechanical catheter-directed thrombolysis (PM-CDT) on the occlusions of these pulmonary artery (PA) branches is not known. OBJECTIVES: The RESCUE study evaluated PM-CDT with the Bashir endovascular catheter in patients with acute intermediate-risk PE. This analysis assessed PA occlusions using core laboratory data before and after PM-CDT therapy. METHODS: The baseline and 48-hour post-treatment contrast-enhanced chest computed tomography angiography of PE patients with right ventricular dilatation enrolled in the RESCUE trial were used. The primary analysis was the change in the number of segmental and proximal PA branches with total or subtotal (>65%) occlusions after 48 hours compared to baseline using McNemar's test. RESULTS: A total of 107 patients enrolled across 18 United States sites comprised this analysis. At 48 hours post-PM-CDT, the number of segmental PA branches with total or subtotal occlusions decreased from 40.5% to 11.7% (P < 0.0001). Proximal PA branch total or subtotal occlusions decreased from 28.7% to 11.0% (P < 0.0001). The reduction in segmental artery occlusions correlated significantly with the magnitude of reduction in right ventricular/left ventricular ratio (correlation coefficient of 0.287 [95% CI: 0.102-0.452]; P= 0.0026), whereas that in the proximal PA arteries did not (correlation coefficient of 0.132 [95% CI: 0.059-0.314] P= 0.173). CONCLUSIONS: PM-CDT with the Bashir catheter was associated with a significant reduction in total and subtotal occlusion of segmental and proximal PAs.

Antithrombotic Prophylaxis with Rivaroxaban in Patients with Prehospital COVID-19: A Meta-analysis of Two Placebo-Controlled Trials.

BACKGROUND: We conducted a prespecified meta-analysis of two randomized, placebo-controlled trials of rivaroxaban 10 mg daily in prehospital patients with acute coronavirus disease 2019 (COVID-19). Individually, the trials had limited power to detect a treatment effect due to recruitment stopping ahead of plan. MATERIAL AND METHODS: The statistical analysis plan for the meta-analysis was finalized before unblinding of PREVENT-HD, the larger of the two trials. Pooled risk ratios and pooled risk differences along with the two-sided 95% confidence intervals were calculated using random-effect models. RESULTS: Rivaroxaban did not reduce the occurrence of either the primary prespecified endpoint, a composite of symptomatic arterial and venous thromboembolism, myocardial infarction, ischemic stroke, acute limb ischemia, all-cause hospitalization, and all-cause mortality (risk difference: 0.0044; 95% confidence interval: -0.0263, 0.0175; p = 0.69 for pooled risk difference) or the secondary endpoint of all-cause hospitalization (p = 0.76). Although thrombotic events were infrequent, pooled analysis did reveal that rivaroxaban reduced arterial and venous thrombotic events (placebo 6 events, rivaroxaban 0 events; pooled risk difference: -0.0068; 95% confidence interval: -0.0132, -0.0006; p = 0.03). In the pooled studies, only one major bleeding event was observed in a rivaroxaban-allocated patient with no critical site or fatal bleeding events. CONCLUSION: Although this meta-analysis does not support antithrombotic prophylaxis with rivaroxaban in a broad prehospital population with acute COVID-19, the prevention of arterial and venous thrombotic events among rivaroxaban-allocated patients is consistent with the known thromboprophylactic effect of the drug in medically ill patients.

Early Predictors of Clinical Deterioration in Intermediate - High-Risk Pulmonary Embolism: Clinical Needs, Research Imperatives, and Pathways Forward.

A subset of intermediate-high-risk pulmonary embolism (PE) patients will suffer clinical deterioration in the early hours following the acute event. Current evidence-based guidelines for the management of acute PE have provided limited direction for identification of which intermediate-high-risk PE patients will go on to develop hemodynamic decompensation. Furthermore, a paucity of data further hampers guideline recommendations regarding the optimal approach and duration of intensive monitoring, best methods to assess the early response to anticoagulation, and the ideal window for reperfusion therapy, if decompensation threatens. The aim of the present article is to identify the current unmet needs related to the early identification of intermediate-high-risk PE patients at higher risk of clinical deterioration and mortality during the early hours after the acute cardiovascular event and suggest some potential strategies to further explore gaps in the literature.

Practical solutions for implementation of blood cholesterol guidelines in clinical practice.

Underutilization of lipid-lowering therapy (LLT) and failure to attain guideline-recommended low-density lipoprotein cholesterol (LDL-C) goals are important quality gaps in cardiovascular risk optimization, especially among patients with atherosclerotic cardiovascular disease (ASCVD). Large database analyses demonstrate an unmet need for improved LDL-C measurement, and that nearly 75% of patients with ASCVD have an LDL-C level above guideline-recommended levels, and greater than 50% are not treated with statins or ezetimibe. Proposed solutions for overcoming these obstacles to optimal lipid management include provider- and patient-facing educational interventions, health information technology strategies, implementation of incentive-based care, advocacy efforts, and systems-based process innovations. While individual interventions may not be enough to overcome the totality of barriers to optimal LLT, comprehensive multifaceted approaches that address barriers at the provider, patient, and healthcare delivery level are likely to offer the greatest likelihood of success and improved patient outcomes.

Trends in Pulmonary Embolism Deaths Among Young Adults Aged 25 to 44 Years in the United States, 1999 to 2019.

A concerning increase in mortality from acute pulmonary embolism (PE) in young adults in the United States has been reported. We extracted PE-related mortality rates (number of deaths per US population) from the Centers for Disease Control and Prevention Wide-Ranging Online Data for Epidemiologic Research database from 1999 to 2019, focusing on subjects aged 25 to 44 years. Age-adjusted mortality rates (AAMRs) were assessed using the Joinpoint regression modeling and expressed as the estimated average annual percentage change (AAPC) with relative 95% confidence intervals (95% CIs) and stratified by urbanization, gender, age, and race. Between 1999 and 2019, the AAMR from acute PE in US adults aged 25 to 44 years linearly increased without any difference between genders (AAPC +1.5%, 95% CI 1.2 to 1.8, p <0.001). AAMR increase was more pronounced in American-Indians/Alaska Natives and in Asian/Pacific Islanders (AAPC +2.5%, 95% CI 1.6 to 3.4, p <0.001), Whites (AAPC +1.7%, 95% CI 1.4 to 2.0, p <0.001), Latinx/Hispanic patients (AAPC +1.7%, 95% CI 0.6 to 3.0, p = 0.003), and residents of rural areas (AAPC +2.4%, 95% CI 1.9 to 2.8, p <0.001). A higher AAMR (4.02 per 100,000 residents, 95% CI 3.90 to 4.15) and absolute number of PE-related deaths were observed in the South. PE-related mortality in adults aged 25 to 44 years has increased over the last 2 decades in the United States. Stratification by race, ethnicity, urbanization, and census region showed ethnoracial and regional disparities that will require further evaluation and remedy.

Time-based reperfusion in haemodynamically unstable pulmonary embolism patients: does early reperfusion therapy improve survival?

High-risk pulmonary embolism (PE) is associated with significant morbidity and mortality. Systemic thrombolysis remains the most evidenced-based treatment for haemodynamically unstable PE, but in daily clinical practice, it remains largely underused. In addition, unlike acute myocardial infarction or stroke, a clear time window for reperfusion therapy, including fibrinolysis, for high-risk PE has not been defined either for fibrinolysis or for the more recently incorporated options of catheter-based thrombolysis or thrombectomy. The aim of the present article is to review the current evidence supporting the potential benefit of earlier administration of reperfusion in haemodynamically unstable PE patients and suggest some potential strategies to further explore this issue.