Open Access

Heart valve replacements are life-saving procedures essential for patients with dysfunctional heart valves. The global market for prosthetic heart valves is valued at approximately USD 8.71 billion in 2024, with devices available in various forms, including mechanical, transcatheter, and biological valves used for both replacement and repair procedures. While traditional prosthetic valves have improved survival, they present several limitations that contribute to postoperative complications over time. These include limited durability, the need for long-term anticoagulation due to clot formation linked to immune responses, mechanical valve noise (often described as clicking or squishing sounds), the inability to accommodate growth in pediatric patients, and suboptimal anatomical fit for certain individuals with complex health conditions. Moreover, common complications associated with these valves include stroke, bleeding, and leakage around valve flaps following surgery. In contrast, emerging 3D printed heart valves, fabricated from advanced co-polymers, show promise in early laboratory studies, demonstrating excellent tissue compatibility and the potential to reduce or eliminate the need for lifelong blood-thinning medications

Background: Tricuspid valve endocarditis (TVE) remains a significant cause of morbidity and mortality worldwide. Given the considerable variation in presentation and severity, as well as ongoing advances in percutaneous and operative interventions, the optimal treatment strategy remains undetermined. This study aims to report the outcomes of medical management (MM), percutaneous mechanical aspiration (PMA), and surgical intervention in isolated TVE patients. Methods: We conducted a single-centre retrospective review of consecutive patients with isolated TVE from June 2020 to January 2023. Diagnosis was based on the modified Duke criteria and confirmed with echocardiographic findings. Patients were categorized based on the intervention received: MM, PMA, or surgical intervention. The type of intervention received was determined by the consensus agreement of a multidisciplinary high-risk heart team. Primary outcomes included 30-day and 1-year survival rates. Secondary outcomes included length of hospital stay, degree of residual tricuspid regurgitation, and complications including septic emboli, pleural effusion, and stroke. Results: Overall, 20 patients were treated for TVE: 7 received MM, 4 underwent PMA, and 9 underwent surgical intervention. The 30-day survival rates were 57.1% for MM, 100% for PMA, and 100% for surgery (p=0.038). One-year survival rates were 57.1% for MM, 100% for PMA, and 88.9% for surgery (p=0.155). PMA patients had the longest median hospital stay (14.5 days), followed by surgical (13.5 days) and MM (5 days) groups. Post-intervention echocardiography showed a significant reduction in tricuspid regurgitation severity in the surgical group but an increase in the PMA group. Complications including septic emboli, reoperation, heart block and pleural effusion were insignificant between groups. Conclusion: This study suggests that intervention, either PMA or surgery, may offer superior short-term survival benefits compared to MM in surgically fit patients presenting with isolated TVE. The findings highlight the need for a multidisciplinary approach in managing TVE and suggest further prospective studies are warranted to establish definitive treatment guidelines,

Background: Eptifibatide is a known antiplatelet that is used in patients undergoing percutaneous coronary intervention for ACS, and it is proven to have a positive outcome. Despite thrombocytopenia not being reported in the pivotal trials, the emerging literature associated this link. We aim to further investigate this association and provide real-world data from a single centre. Methods: A retrospective study was conducted in Heart Hospital at Hamad Medical Corporation from 2016 to 2022. All patients admitted with ACS and received Eptifibatide were included in the study. Patients with confirmed secondary causes of thrombocytopenia were excluded. The data is reported in the form of mean, median, standard deviation, interquartile range, and percentage. Results: Twenty-six patients met the inclusion criteria, with an average age of 54 ± 11 years, and all patients were males. The baseline platelets count was 157 ± 80, and haemoglobin was 14 ± 2. Fourteen patients had platelets drop by more than 50% of their baseline. Thrombocytopenia developed after eptifibatide infusion by 36 ± 29. The average haemoglobin post-eptifibatide infusion was 13.5 ± 1.7 g/dL. Three patients required platelet transfusion, 23 patients were managed conservatively, and one patient died. Conclusion: Eptifibatide can cause life-threatening thrombocytopenia, which can be simply reversed by ceasing the infusion. However, platelet transfusion might be necessary in some patients. Neither the mechanism nor the risk factors are clear, and further studies are recommended to understand this association better.

Early detection of Congenital Hypothyroidism (CH) is crucial to prevent intellectual disability in affected neonates. Neonatal screening for CH typically involves measuring thyroid-stimulating hormone (TSH) and thyroxine (T4) levels, with methods varying between cord blood and venous blood sampling. This study aims to compare the efficacy and reliability of cord blood versus day 3 venous blood sampling in the screening for CH to inform best practices. Methods: This prospective comparative study involved 1,000 term neonates born at Springfield Children’s Hospital over an 18-month period. Cord blood and day 3 venous blood samples were analyzed for T3, T4, and TSH levels using competitive immunoassay techniques. The primary outcomes measured were the mean levels of T3, T4, and TSH, and the secondary outcome was the detection rate of CH based on these hormone levels. Statistical analyses included paired t-tests for continuous variables and sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) calculations for screening efficacy. Results: Significant differences were found in TSH levels between cord blood and day 3 venous samples (p<0.001), but not in T3 and T4 levels. CH was initially suspected in 25 neonates (2.5%) based on cord blood screening and confirmed in 15 neonates (1.5%) on day 3 venous blood screening. The sensitivity and specificity were 100% and 97.5% for cord blood screening, and 100% and 98.5% for day 3 venous blood screening, respectively. PPV and NPV were higher for day 3 venous blood screening compared to cord blood screening. Conclusions: Both cord blood and day 3 venous blood sampling are effective for neonatal CH screening, each with distinct advantages. Day 3 venous sampling, however, demonstrated slightly higher specificity and PPV, suggesting a more accurate reflection of persistent CH. These findings support the use of venous blood sampling on day 3 of life as a reliable method for CH screening, potentially reducing the number of false-positive results and enhancing the early detection and treatment of CH.

Infective endocarditis (IE) is a rare but life-threatening cardiac condition. Healthcare-associated infective endocarditis (HAIE) is an emerging subtype that occurs more than 48 hours after hospital admission, often following invasive procedures. Its occurrence in patients with end-stage kidney disease (ESKD) is not uncommon. Prosthetic valve endocarditis may also be healthcare-associated (HA-PVE) when it develops within one year of valve replacement. Antimicrobial-resistant Staphylococcus species are increasingly implicated in both forms. Amidst a paucity of data on HAIE in Nigeria, we report a case series involving both native valve HAIE in ESKD patients and prosthetic valve HAIE (HA-PVE). These cases were identified over one year in a 150-bed private tertiary healthcare institution in Southwest Nigeria. Patients were diagnosed based on the modified Duke’s criteria. HAIE was attributed to central-line cannulation in ESKD patients, while HA-PVE occurred within a year of valve surgery. Methicillin-resistant Staphylococcus species were the causative pathogens. Elevated erythrocyte sedimentation rates and neutrophilia were consistent findings. This study emphasizes the importance of early and thorough cardiovascular evaluation in ESKD patients with central-line access to facilitate early IE detection. Hemogram and sepsis biomarkers may serve as adjuncts to blood culture in confirming diagnosis. Glycopeptide antibiotics should be considered as first-line empirical therapy. Healthcare-associated IE involving native and prosthetic valves can present with diverse symptoms. The aforementioned diagnostic and management strategies are particularly relevant in resource-limited settings.

Background and aim of the study: During the COVID-19 pandemic in Bavaria, surgical ICU resources were reallocated, and elective procedures were postponed, impacting the management of infective endocarditis (IE). This study evaluated early surgical outcomes in patients with native valve endocarditis (NVE) and prosthetic valve endocarditis (PVE) before and during the pandemic. Methods: We retrospectively analyzed 94 patients (66% male) treated pre-pandemic (August 2018–March 21, 2020) and 84 patients (76% male) treated during the pandemic (March 22, 2020–November 2021). NVE cases comprised 78% pre-pandemic and 68% during the pandemic, while PVE cases increased from 22% to 32%. Preoperative characteristics, surgical urgency, postoperative complications, and in-hospital mortality were assessed. Explanted valves underwent histological, microbiological, and molecular analyses, including fluorescence in situ hybridization (FISH) with 16S rRNA PCR/sequencing. Results: During the pandemic, preoperative NYHA class III-IV increased significantly (NVE: 49% to 74%; PVE: 29% to 70%; all p<0.05). Urgent surgeries became more frequent (NVE: 27% to 49%, p=0.017; PVE: 20% to 52%, p=0.034), and the interval from diagnosis to surgery in PVE patients was prolonged (11 vs. 16 days, p=0.038). More complex procedures, including double-valve surgeries, were required (9.5% vs. 37%, p=0.022). Postoperatively, re-thoracotomy rates increased in NVE cases (OR: 9.106, p<0.001), while odds ratios for stroke, sepsis, and prolonged ICU stay in PVE patients trended higher but lacked statistical significance. Conclusion: The pandemic led to diagnostic delays, worsened preoperative conditions, and increased surgical urgency in IE patients, underscoring the need for resilient healthcare strategies to maintain timely surgical care during future crises.

Objective: Infective endocarditis requires prompt recognition and treatment due to its high mortality and morbidity rates. Few studies compare long-term patient outcomes after mitral and aortic valve endocarditis surgery. Hence, we aim to assess this in our cohort. Methods: We included adult patients aged 18 and above who underwent surgery between April 2011 and April 2021 for first-time native aortic or mitral valve endocarditis in our study. Patients were followed up until July 2024. Results: 94 patients were included in our study. Streptococcus was the most common bacterial species causing infective endocarditis and was more prevalent in the aortic group than the mitral group. Conversely, Staphylococci were more common in the mitral group. Patients undergoing mitral valve surgery had longer bypass and cross-clamp times compared to the aortic group. There was no statistical difference between aortic valve (AV) and mitral valve (MV) endocarditis in early post-operative re-exploration rates, post-operative cerebrovascular accidents (CVA), or post-operative dialysis. Patients with AV and MV endocarditis had comparable in-hospital and 1-year post-surgery mortality rates. Although the mortality rate for aortic valve endocarditis was higher at both 5-year and 8-year follow-ups, it was not statistically significant. Conclusions: Despite some differences in peri-operative variables, there was no significant difference in short- and long-term mortality rates after aortic and mitral valve endocarditis surgery.

Despite advances in the field of cardiology, cardiogenic shock (CS) remains a management dilemma with a high mortality rate. While most cases of CS are secondary to acute coronary syndrome (ACS), approximately one-fifth can be attributed to delayed mechanical complications of ACS, such as arrhythmia, cardiac tamponade, or valvular heart diseases. The coexistence of CS and mitral valve diseases (MVDs) further complicates clinical presentation, diagnosis, and management strategies. Surgical interventions are considered the gold standard for managing MVDs in the context of CS. However, these patients are often at extreme surgical risk and may not achieve favorable outcomes. Catheter-based interventions have garnered increasing interest, but despite their promising results, most trials have excluded patients in unstable or critical conditions. Pharmacological and mechanical circulatory support provide a bridge to definitive transcatheter or surgical intervention.

Background: Transcatheter edge-to-edge repair of the mitral valve (M-TEER) improves outcomes in patients with chronic severe symptomatic mitral valve regurgitation who are at high risk for surgical mitral valve repair or replacement. This systematic review and meta-analysis aimed to describe the outcomes of M-TEER in patients with moderate-to-severe (stage III; Group 1) chronic kidney diseases (CKD) and end-stage kidney disease (stages IV-V; Group 2) in comparison with those with normal kidney function or mild CKD (stages I-II; Group 3). Methods: A systematic literature search of PubMed, Scopus, and Embase was conducted from inception to December 10th, 2023. The odds ratio (OR) with a 95% confidence interval (CI) was pooled using the random-effects model. Results: We screened 6,090 articles of which 40 citations were reviewed in full texts. Eight cohort observational studies met the eligibility criteria. Group 1 versus Group 3: short-term and long-term mortality were significantly higher in Group 1 [(OR 1.73, CI: 1.30-2.29) and (OR 1.78, CI: 1.38-2.29), respectively]. The shock was significantly higher (OR 1.95, CI: 1.45-2.63), and vascular complications were significantly lower (OR 0.51, CI: 0.26-0.99) in Group 1. The incidence of stroke, cardiac tamponade, or conversion to open surgery did not differ between groups [OR 0.87, CI: 0.34-2.23), (OR 1.52, CI: 0.62-2.75), or (OR 0.53, 95% CI: 0.12-2.24), respectively]. Group 2 versus Group 3: long-term mortality was significantly higher in Group 2 (OR 3.56, CI: 2.53-5.02) without a difference in short-term mortality (OR 4.92, CI: 0.91-26.72) or conversion to open surgery (OR 0.92, CI: 0.45-1.91) between groups. Conclusion: In patients who are undergoing M-TEER, impaired kidney function may be associated with increased odds of mortality in comparison with absence or mild kidney impairment.

Objectives: This study aimed to examine whether the projected patient-prosthesis mismatch (PPM) rate calculated using the ideal body weight of patients can theoretically show a significant improvement compared to the actual rate of PPM conventionally calculated with the actual body weight of patients. Methods: We retrospectively analysed 2827 patients who underwent aortic valve replacement over 10 years. The rate of PPM was evaluated by measuring the iEOA using the body weight of the patients at the time of the operation and their ideal body weight. The difference in PPM rate was compared using the chi-square test; additionally, a P value < 0.05 was considered significant. Results: We observed a projected PPM rate of 50.2% with a moderate PPM of 45% and a severe PPM of 5.2% when the real body weight of the patients at the time of their operation was included in the calculus. Simulating a BMI of 22 for all patients, the rates of moderate and severe PPM decreased to 43.8% and 0.5%, respectively (P < 0.001). When simulating a lower BMI at 21, 20, and 19, there was a further significant reduction in moderate PPM at 38.8%, 33.4%, and 26.8%, respectively, and severe PPM at 0.2% and 0.1%, respectively (P < 0.001). Conclusions A significant reduction in post-aortic valve replacement PPM was predicted when the ideal body weight of the patient was used instead of actual body weight, suggesting that pre- and postoperative weight loss programmes should be part of the strategy to reduce PPM.

Background: Acute Aortic Syndrome’s (AAS) is a group of acute emergencies that include aortic dissection, intramural haematoma, penetrating atherosclerotic ulcer, and impending or ruptured aortic aneurysms. Various precipitating factors have been associated with the development of AAS, but it is unclear whether these factors are correlators or predictors of the disease. A clear understanding of these elements could improve the diagnosis, prevention, and treatment of AAS, with an accurate appreciation for risk stratification. Methods: A thorough literature search was conducted through several electronic databases to collate papers within the literature discussing precipitating factors leading to AAS. These results were discussed and analysed, grouping the individual factors into predictors or correlators of AAS. Results: The factors identified as correlators were age, certain chronobiological patterns, polycystic kidney disease and immunology. The factors identified as predictors included genetics, omics, and kidney markers. D-dimer, diabetes mellitus and aortic size were not implicated in the development of AAS, with diabetes mellitus found to be protective against AAS. Conclusion: Recognising the precipitating factors that increase the risk of disease empowers clinicians to be more diligent regarding methods of AAS diagnosis and prevention, as well as enables improved treatment techniques to be implemented. These results are key as they can both potentially help reduce the AAS incidence rate and uncover new potential avenues of research that can be explored in the future.

Background and aim of the study: Minimally invasive approaches for aortic valve replacement (AVR) are clinically beneficial for patients but are more technically demanding for surgeons. Sutureless AVR is a new and minimally invasive approach. The study aim was to evaluate initial AVR outcomes in patients aged >75 years after setting up a sutureless minimally invasive surgery program. Methods: Between January 2014 and December 2015, a total of 108 patients aged >75 years with indication of isolated elective AVR received a sutureless bioprosthesis using the minimally invasive approach (sutureless group). The latter group was compared with a second group of patients (n = 115) who received a stented valve through a full median sternotomy (stented group) at the authors’ institution between January 2012 and December 2013. After propensity score matching, 95 pairs of patients were available for analysis. Results: Preoperative demographic variables were similar between the matched groups. The aortic cross-clamp (ACC) and cardiopulmonary bypass (CPB) times were each shorter in the sutureless group (p <0.01). Perioperative mortality was 1% in the stented group, but no mortality occurred in the sutureless group (p = 0.32). Early postoperative extubation, intensive care unit and hospital stays, need for transfusion, and overall hospital stay were lower in the sutureless group. Frequency of pacemaker implantation was higher in the sutureless group than in the stented group (8.3% versus 1.9%; p = 0.05). Aortic transvalvular gradients were lower in the sutureless group (p = 0.01). Conclusion: In the authors’ experience, the sutureless aortic valve was a useful tool for establishing a minimally invasive AVR program. The technique was safe, and the shorter ACC and CPB times increased the likelihood of early extubation, reduced the need for blood transfusions, and demonstrated good hemodynamic performance. Patients who underwent sutureless AVR showed an increased need for pacemaker implantation.

Background and Aim of the Study: An incompetent bicuspid aortic valve (BAV) can be treated through valve replacement or repair using various surgical techniques. This study presents the outcomes of a 13-year single-surgeon experience in BAV repair and compares two annuloplasty techniques: external and subcommissural aortic annuloplasty. Materials and Methods: A total of 150 consecutive patients (111 males; mean age: 43.2 ± 17.5 years) with BAV insufficiency, with or without aortic dilatation, underwent valve repair at three institutions. Multivariable logistic regression was used to identify associations between risk factors and major adverse events. Among these, 50 patients were prospectively assigned to one of two groups based on the annular stabilization technique: Group EA received external annuloplasty, while Group SCA underwent subcommissural annuloplasty. All patients in both groups were evaluated by transthoracic echocardiography before surgery and two years postoperatively. Results: There was no in-hospital mortality, and all patients survived throughout the follow-up period. Nine patients (6%) developed moderate to severe postoperative insufficiency and required reoperation. The Kaplan–Meier estimated freedom from reoperation at eight years was 100% in patients who did not undergo subcommissural annuloplasty, compared to 81% in those who did (p = 0.037). External annuloplasty was associated with a significantly smaller postoperative aortic annulus diameter (24.1 ± 2.6 mm vs. 25.8 ± 2.1 mm, p < 0.05), and lower mean and peak transvalvular gradients (7 ± 4 mmHg vs. 13 ± 4 mmHg, p = 0.02; and 15.3 ± 9.7 mmHg vs. 20.7 ± 5.6 mmHg, p = 0.03, respectively). Aortic root or ascending aorta replacement was also found to be a predictor of repair durability (p = 0.0039). Conclusions: Bicuspid aortic valve repair provides favorable short- and midterm outcomes. External annuloplasty offers superior annular stabilization and hemodynamic performance compared to subcommissural annuloplasty. Additionally, concomitant aortic replacement further improves the long-term durability of the repair.

Background and Study Aims: Rheumatic heart disease (RHD) remains a leading cause of mitral valve disease globally, particularly in developing countries, where it poses a significant burden on cardiovascular health. Mitral valve repair (MVP) and replacement are the primary surgical interventions; however, the optimal selection between these procedures remains a subject of ongoing debate. This study aims to systematically review the clinical outcomes of MVP in patients with RHD and compare them with those of mitral valve replacement (MVR), thereby addressing a critical gap in the existing literature. Methods: This study adopts a systematic review methodology in accordance with PRISMA guidelines to screen relevant literature published between 2000 and 2024. The data sources for this study include PubMed, Embase, and the Cochrane Library. The key outcome measures include early mortality (defined as death from any cause within 30 days post-surgery), long-term survival, reoperation rates, and valve-related complications. Results: Five studies encompassing a total of 3,543 patients were analyzed. Compared with MVR, MVP demonstrated a non-significant trend toward lower 30-day mortality (OR 0.74, 95% CI 0.50–1.10; P = 0.14). Long-term survival appeared to favor MVP, with a hazard ratio (HR) of 0.63 (95% CI 0.35–1.11; P = 0.11), although without reaching statistical significance. MVP was associated with a significantly higher risk of reoperation (HR 3.85, 95 % CI 2.18–6.78; P < 0.00001), but a substantially lower incidence of valve-related complications, including thromboembolic events and infective endocarditis (HR 0.36, 95% CI 0.21–0.61; P < 0.001). Conclusions: MVP in patients with RHD reduces early mortality, improves long-term survival, and lowers the incidence of valve-related complications. However, it is associated with a higher risk of reoperation.

: Patients with repaired tetralogy of Fallot often have pulmonary valvar regurgitation with variable degrees of right ventricular dilatation, which may lead to dysfunction of both ventricles. Therefore, some patients may need pulmonary valve replacement. This calls for adequate patient selection, and there are ventricular volumetric guidelines to aid this. However, pulmonary valve replacement has caused a dilemma because: 1- It often does not reverse right ventricular dilatation back to normal nor prevent arrhythmias. 2- It is argued that right ventricular dilatation occurs early after repair of tetralogy of Fallot but remains stable thereafter. 3- The patient’ prognosis is said to be affected mainly by the function of the left ventricle rather than that of the right ventricle. 4- Prosthetic valves on the right side of the heart are more prone to infection as compared to the left side since bacteria can reach them easily. All these concerns are examined in this Opinion Article. Overall, this dilemma is justified but usually not sufficiently elaborated and often gives the incorrect message that this procedure is of no benefit. The reality is, however, that pulmonary valvar regurgitation is a harmful condition and deserves to be remedied on hemodynamic grounds. The dilemma arises because hemodynamic improvement after valve implantation may be partial, and many think that this is not enough to justify an intervention, especially with the added risk of endocarditis. However, if valve replacement is to be offered, this should be done in a timely fashion; waiting too long is associated with a worse outcome.

Calcific aortic stenosis (AS) is the most common valvular heart disease requiring invasive intervention. While the implantation of an artificial heart valve restores normal intracardiac hemodynamics, baseline left ventricular (LV) parameters can significantly influence both early and long-term postoperative outcomes. It is well-established that patients with LV dilation experience worse outcomes after surgical or transcatheter treatment of severe AS compared to those with normal LV dimensions. However, the impact of reduced LV volume remains insufficiently explored. This study aims to investigate the effect of small LV dimensions on clinical outcomes in the management of severe high-gradient AS, based on existing literature. We conducted a scoping review using PubMed, Google Scholar, and Elibrary databases. Articles published between 2015 and 2024 were included, though earlier publications were also referenced to support specific sections. Both original research articles and systematic reviews were examined. The central focus of this study is to investigate the impact of small LV size on clinical outcomes in patients undergoing treatment for severe high-gradient AS. According to the existing literature, small LV size is associated with significantly higher 30-day and 2-year all-cause mortality (20.8% vs. 14.3%; adjusted HR, 1.58 [95% CI, 1.20–2.09]; p = 0.0013) and cardiovascular mortality (8.8% vs. 5.5%; adjusted HR, 1.93 [95% CI, 1.25–2.98]; p = 0.0028). Furthermore, considerable emphasis has been placed on the low transvalvular flow (low flow–high gradient) pattern, which represents a critical predictor of clinical outcomes in severe AS. Notably, the 2-year cardiovascular event-free survival rate in patients exhibiting the low flow–high gradient pattern is 30 ± 12%. These findings underscore the importance of LV size and flow patterns in prognostic assessments and therapeutic decision-making for severe AS. The authors emphasize that these patterns require further investigation for early identification and minimization of perioperative risks, determination of optimal timing for surgical or transcatheter intervention, and improvement of prognosis for patients following treatment of severe aortic stenosis.

Multivalvular heart disease represents a less explored domain within cardiovascular surgery. In patients with aortic stenosis (AS) undergoing surgical or transcatheter aortic valve replacement (TAVR), the prevalence of moderate to severe mitral regurgitation (MR) ranges from 8% to 33%. Among the most common presentations are patients with severe AS and clinically significant functional MR. In instances of moderate surgical risk, open-heart surgery is typically performed, sometimes involving combined valve correction procedures. However, for patients deemed to be at high surgical risk or deemed inoperable, an interventional approach may be considered if the anatomy of both the aortic and mitral valves is conducive to such intervention. Careful analysis of each patient is essential in determining the appropriate treatment strategy, whether it involves isolated TAVR or if a staged intervention targeting the aortic and mitral valves is warranted. In the article, we present a review of the literature devoted to the strategy for bivalvular interventions in patients of high surgical risk and also a clinical case of a successful step-by-step interventional approach in an 83-year-old patient of high surgical risk with hemodynamically significant aortic and mitral valve disease, along with an analysis of the chosen approach.

Elderly patients with frailty and multiple comorbidities increasingly require mitral valve surgery. This includes patients who have previously undergone surgery with a tissue valve, which may deteriorate over time and require replacement. These cases are considered high-risk. There is growing interest in performing valve replacements using minimally invasive techniques, including access via the groin. However, such approaches are not always feasible. Here, we report the first case where innovative, "outside-the-box" thinking was employed to replace the valve using a non-conventional approach.