Back to Authors

Pereyra, Milagros

https://orcid.org/0000-0003-4695-8436

Mayo Clinic

Mayo Clinic in Arizona

Citations 56

Abstract 4142996: Controlled LDL levels can Attenuate the Lp(a) Cardiovascular Risk in Patients Who Underwent Percutaneous Coronary Intervention
Awad, Kamal , Baba, Nima, Abdalla, Hesham, Badr, Amro , Elahi, Mohammed M., Kamel, Moaz, Pereyra, Milagros , Arsanjani, Reza, Pereyra, Milagros , Awad, Kamal , Mahmoud, Ahmed , Farina, Juan M. , Abbas, Mohammed Tiseer , Baba, Nima, Elahi, Muhammed, Scalia, Isabel G. , Arsanjani, Reza

Circulation | November 14, 2024 | Volume: 150 | Issue: Suppl_1 | Pages: No page available

10.1161/circ.150.suppl_1.4142996 Get It

Background: Secondary prevention after percutaneous coronary interventions (PCIs) is still challenging and lipoprotein(a) [Lp(a)] is believed to be a residual risk factor in this setting. However, the effect of Lp(a) in case of well-controlled low-density lipoprotein cholesterol (LDL-C) is still unclear. The interaction between Lp(a) and LDL-C has been studied in primary prevention but still needs to be investigated in secondary prevention. Hypothesis: Achieving adequate LDL-C control after PCI may reduce the cardiovascular (CV) risk associated with Lp(a). Methods: A retrospective study of consecutive patients who underwent PCI and reached their LDL-C target levels (<70mg/dL) at three academic centers sites between 2006 and 2017. All included patients must have an Lp(a) measurement before the PCI intervention. Clinical outcomes on 10-year follow-up were collected by reviewing the electronic patients' records. The primary outcomes included all-cause mortality (ACM) and major adverse CV events (MACE) including non-fatal MI, ischemic stroke, coronary revascularization, and CV death. Kaplan-Meier curves were created to compare the survival probabilities among patients with high Lp(a) (≥50mg/dL) versus those with low Lp(a) (<50mg/dL). Univariate and multivariate Cox regression analyses were performed to quantify the association of elevated Lp(a) with outcomes and control for potential confounders. Results: In total, 878 patients (median age = 68 years, 74% males) were included in the analysis. Of them, 242 (27.6%) had high Lp(a) ≥50mg/dL. Kaplan Meier analyses did not reveal any significant difference in survival probabilities across the Lp(a) groups for any of the outcomes (Figure 1). The results were consistent in univariate (MACE, HR: 1.08 [95%CIs 0.85-1.35]; ACM, HR: 0.97 [95% CI 0.76-1.23]) and multivariate analyses (MACE, HR: 1.14, [95% CIs 0.90-1.45]; ACM, HR: 1.08 [95% CI 0.84-1.39]). Conclusion: These findings suggest that, in patients who underwent PCI and achieved an LDL-C target of <70 mg/dL, elevated Lp(a) levels were not associated with and increased risk of MACE or mortality. Controlling the LDL-C should still be the cornerstone in secondary prevention after PCI, however, larger prospective studies are still warranted to validate our results.
Abstract 4142044: The prognostic value of criteria for diagnosis of Immune Checkpoint Inhibitor Related Myocarditis: a comparison of the Bonaca et.al. criteria and European Society of Cardiology (ESC)-International Cardio-Oncology Society (ICOS) guidelines
Pereyra, Milagros , Mahmoud, Ahmed K., Tagle-Cornell, Maria Cecilia , Kenyon, Courtney , Baba, Nima, Herrmann, Joerg, Pereyra, Milagros , Farina, Juan M. , Mahmoud, Ahmed , Scalia, Isabel G. , Abbas, Mohammed Tiseer , Baba, Nima, Herrmann, Joerg, Arsanjani, Reza

Circulation | November 14, 2024 | Volume: 150 | Issue: Suppl_1 | Pages: No page available

10.1161/circ.150.suppl_1.4142044 Get It

Background: Myocarditis is a dreaded complication of immune-checkpoint inhibitor (ICI) therapy but challenging to diagnose. There are no published data comparing the two leading diagnostic criteria for ICI myocarditis and their association with cardiovascular events. Methods: Patients treated with ICI and cardiac Troponin (cTnT) measurements thereafter at a tertiary institution from 2011 to 2022 were identified. Charts were reviewed for ICI-related myocarditis according to the Bonaca et. al criteria and the ESC-ICOS guideline criteria. A propensity matched control group was identified of patients treated with ICI but without developing myocarditis. Medical records were reviewed for baseline characteristics and long-term outcomes, including cardiac death, MACE (myocardial infarction, TIA/stroke, new heart failure diagnosis), and arrhythmias (V-tach, A-fib, complete heart block). Results: A total of 59 patients were identified as having a diagnosis of ICI-related myocarditis per Bonaca criteria (16 having definite, 13 probable and 30 possible myocarditis), and 47 met the ESC-ICOS guideline criteria. Mean age was 73.1±10.2 years, 60.1% were male, median follow-up was 2.5 years. ICI-related myocarditis as diagnosed by both diagnostic criteria had prognostic value for cardiac death (HR 13.94, 95%CI 1.84-105.64, p=0.011 per Bonaca, HR 6.22, 95%CI 1.77-21.88, p=0.004 per ESC-ICOS), MACE, (HR 3.17, 95%CI 1.34-7.47, p=0.008 per Bonaca, HR 2.97, 95%CI 1.37-6.45, p=0.006 per ESC-ICOS), and arrhythmias (HR 1.93, 95%CI 1.10-3.38, p=0.022 per Bonaca, HR 2.09, 95%CI 1.21-3.60, p<0.001 per ESC-ICOS), (Figures 1 and 2). There was no significant difference for cardiac death (AUC 0.75 for Bonaca, AUC 0.74 for ESC, p=0.765) or MACE (AUC 0.66 for Bonaca, AUC 0.66 for ESC, p=0.916) when both criteria were compared with each other. Conclusion: The ESC-ICOS criteria were more restrictive than the Bonaca criteria for the diagnosis of ICI-related myocarditis but similar in terms of prognostic value.
Abstract 4139236: Artificial Intelligence–Electrocardiography to Predict Incident Atrial Fibrillation and Survival Following Kidney Transplant
Pereyra, Milagros , Awad, Kamal , Ali, Nima Baba , Steidley, D. Eric , Sorajja, Dan , Pereyra, Milagros , Awad, Kamal , Farina, Juan M. , Scalia, Isabel G. , Mahmoud, Ahmed , Abbas, Mohammed Tiseer , Alsidawi, Said , Masry, Hicham El , Mour, Girish , Arsanjani, Reza

Circulation | November 14, 2024 | Volume: 150 | Issue: Suppl_1 | Pages: No page available

10.1161/circ.150.suppl_1.4139236 Get It

Background: New-onset atrial fibrillation (AF) is common among kidney transplant (KTx) recipients and is associated with reduced patient survival. Predictors of AF after KTx are not well understood, although AF can be associated with traditional and non-traditional risk factors. While artificial intelligence-enabled electrocardiography (AI-ECG) has shown promise in predicting incident AF, its predictive and prognostic implications in the KTx population have not yet been evaluated. Hypothesis: AI-ECG can predict new-onset AF and carries prognostic implications in patients undergoing KTx. Aims: To evaluate the clinical implications of applying AI-ECG to the preoperative ECGs of recipients of a KTx. Methods: Patients without a history of AF who underwent KTx at three referral centers between 2011 and 2021, with at least one preoperative ECG, were included in this retrospective study. Preoperative ECGs were analyzed using a previously developed AI-ECG algorithm to estimate the probabilities of new-onset AF. Based on these probabilities, patients were categorized into two groups: high and low probability of incident AF. The optimal cut-off value for the AI-ECG tool was determined using ROC analysis. The incidence of new-onset AF and mortality at 5 years post KTx were compared between these two groups using univariate and multivariate Cox regression analyses. Results: In total, 6246 patients were included (mean age 52.9 ±14.3 years, 58.7% males). A pre-transplant AI-ECG probability of AF >10% was identified as the most accurate cutoff point to distinguish between patients at low risk and high risk of incident AF (ROC = 0.72). The study found that a preoperative AI-ECG high risk of AF demonstrated not only a strong association with new-onset AF (HR 2.54, 95%CI 2.02-3.19, p<0.001 on multivariable analysis, Figure 1A ) but was also associated with an increased risk of mortality both on univariate (HR 2.73, 95%CI 2.34-3.18, p<0.001) and multivariate (HR 1.57, 95%CI 1.29-1.91, p<0.001 ) analysis at 5-year follow-up ( Figure 1B ). Conclusion: The application of AI-ECG to a single widely available test may help assess the risk of new-onset AF and mortality in patients undergoing KTx. Accurate risk stratification may identify a high-risk subgroup of transplant recipients who can benefit from closer AF monitoring, risk factor modification, and early management.
Left Atrial Strain: State of the Art and Clinical Implications
Javadi, Niloofar , Bismee, Nadera N. , Abbas, Mohammed Tiseer , Scalia, Isabel G. , Pereyra, Milagros , Ali, Nima Baba , Esfahani, Sogol Attaripour , Awad, Kamal , Farina, Juan M. , Arsanjani, Reza , Baba Ali, Nima , Attaripour Esfahani, Sogol, Arsanjani, Reza , Farina, Juan M , Pereyra, Milagros , Scalia, Isabel G , Abbas, Mohammed Tiseer , Awad, Kamal

Journal of Personalized Medicine | November 5, 2024 | Volume: 14 | Issue: 11 | Pages: 1093

10.3390/jpm14111093 Get It

The assessment of left atrial strain (LAS) has emerged as an essential component in the evaluation of cardiac function, especially in pathologies such as heart failure and atrial fibrillation. This narrative review aims to outline the available methods for assessing LAS with a major emphasis on speckle-tracking echocardiography techniques. Other imaging modalities, including cardiac magnetic resonance and cardiac computed tomography, also provide important information on LA dynamics but have disadvantages with respect to cost and availability. The current narrative review underlines basic concepts such as the accurate assessment of LAS and discusses the clinical relevance of LAS by pointing out its significant diagnostic and prognostic role in several cardiovascular conditions. The aim of this article is to discuss the current integration of LAS into clinical practice with a view to further improving patient management and treatment strategies.
The impact of peptide receptor radionucleotide therapy with Lutetium-177 DOTATATE on cardiac metastases in neuroendocrine tumors
Sonbol, Bassam Bassam, Farina, J M, Connolly, Heidi M. , Halfdanarson, Thor R, Starr, Jason S. , Luís, A S , Pereyra, Milagros , Pereyra, Milagros , Scalia, Isabel G. , Wang, Yan , Bekaii‐Saab, Tanios , Yang, M, Pellikka, Patricia A. , Herrmann, J, Arsanjani, Reza , Ayoub, C

European Heart Journal | October 28, 2024 | Volume: 45 | Issue: Supplement_1 | Pages: No page available

10.1093/eurheartj/ehae666.3167 Get It

Abstract Background Cardiac metastasis from neuroendocrine tumors (NET) is rare and has been thought to potentially result in life threatening sequalae. Peptide receptor radionucleotide therapy (PRRT), such as Lutetium-177 (Lu-177) DOTATATE, has been validated as effective treatment for patients with NET who have progressed on somatostatin analogue (SSA) therapy and more recently suggested for use in SAA-naïve higher risk grade 2 and grade 3 NETs. However, Lu-177 DOTATATE therapy has been found to have potentially serious adverse effects both locally and systemically. Overall, the clinical significance of cardiac metastasis of NET, as well as the safety and efficacy of Lu-177 DOTATATE in this cohort, has not been thoroughly evaluated. Purpose This study assessed the outcomes and clinical consequences of cardiac metastatic involvement in patients with NET. Furthermore, this study investigated the safety of Lu-177 DOTATATE therapy in patients with cardiac metastases from NET. Methods All patients who underwent 68Ga-DOTATATE positron emission tomography for evaluation of NET across three tertiary centers between 2016 and 2022 were retrospectively evaluated. Patients with evidence of cardiac metastasis were further evaluated. Baseline characteristics, treatment modality, and clinical outcomes including mortality, arrhythmia or conduction disease, carcinoid heart disease, and heart failure admissions were recorded. Patients with cardiac metastases were grouped and compared based on therapeutic modality (conservative therapy with surveillance or SSA, Lu-177 DOTATATE therapy, or surgical resection of metastases). Results From 3253 patients with NET, 51 patients were identified to have cardiac metastases (mean age 66.7 ± 12.2 years, 54% male). Three patients underwent surgical resection of cardiac metastases, and in two of whom this was concomitant while undergoing valve surgery for carcinoid heart disease. Patients with cardiac metastasis had significantly higher mortality than patients without cardiac metastasis (HR 2.12, 95%CI 1.00 – 4.52, p = 0.049, Figure 1A). Median follow-up from diagnosis of cardiac metastasis was 3.64 years [IQR 1.59 – 5.64]. There was no significant difference in clinical outcomes between patients that received Lu-177 DOTATATE therapy (n = 27) and conservative therapy (n = 21). Specifically, there was no significant difference in mortality risk at five years post the diagnosis of cardiac metastasis between these groups (p = 0.47, Figure 1B). Conclusion Patients with cardiac metastasis from NETs have worse clinical outcomes than NET patients without cardiac metastatic involvement. Lu-177 DOTATATE therapy appears to be safe in patients with cardiac metastasis from NET.Figure 1AFigure 1B
Lipoprotein (a) as a Cardiovascular Risk Factor in Controversial Clinical Scenarios: A Narrative Review
Abdalla, Hesham, Mahmoud, Ahmed , Khedr, Ahmed E. , Farina, Juan M. , Scalia, Isabel G. , Abbas, Mohammed Tiseer , Awad, Kamal A., Ali, Nima Baba , Bismee, Nadera N. , Esfahani, Sogol Attaripour , Javadi, Niloofar , Pereyra, Milagros , Alsidawi, Said , Lester, Steven J., Ayoub, Chadi , Arsanjani, Reza , Abdalla, Hesham M, Mahmoud, Ahmed K , Baba Ali, Nima , Attaripour Esfahani, Sogol, Arsanjani, Reza , Farina, Juan M , Pereyra, Milagros , Alsidawi, Said , Scalia, Isabel G , Abbas, Mohammed Tiseer

International Journal of Molecular Sciences | October 14, 2024 | Volume: 25 | Issue: 20 | Pages: 11029

10.3390/ijms252011029 Get It

Lipoprotein (a) is a complex lipid molecule that has sparked immense interest in recent years, after studies demonstrated its significant association with several cardiovascular conditions. Lp(a) promotes cardiovascular disease through its combined proatherogenic, pro-inflammatory, and prothrombotic effects. While the measurement of Lp(a) has become widely available, effective methods to reduce its concentration are currently limited. However, emerging data from ongoing clinical trials involving antisense oligonucleotides have indicated promising outcomes in effectively reducing Lp(a) concentrations. This may serve as a potential therapeutic target in the management and prevention of myocardial infarction, calcific aortic stenosis, and cerebrovascular accidents. In contrast, the role of Lp(a) in atrial fibrillation, in-stent restenosis, cardiac allograft vasculopathy, and bioprosthetic aortic valve degeneration remains unclear. This review article aims to thoroughly review the existing literature and provide an updated overview of the evidence surrounding the association of Lp(a) and these cardiovascular diseases. We seek to highlight controversies in the existing literature and offer directions for future investigations to better understand Lp(a)’s precise role in these conditions, while providing a summary of its unique molecular characteristics.
The Role of Cardiovascular Imaging in the Diagnosis of Athlete’s Heart: Navigating the Shades of Grey
Ali, Nima Baba , Esfahani, Sogol Attaripour , Scalia, Isabel G. , Farina, Juan M. , Pereyra, Milagros , Barry, Timothy , Lester, Steven J., Alsidawi, Said , Steidley, D. Eric , Ayoub, Chadi , Palermi, Stefano , Arsanjani, Reza , Baba Ali, Nima , Attaripour Esfahani, Sogol, Steidley, David E, Arsanjani, Reza , Farina, Juan M , Pereyra, Milagros , Alsidawi, Said , Scalia, Isabel G

Journal of Imaging | September 16, 2024 | Volume: 10 | Issue: 9 | Pages: 230

10.3390/jimaging10090230 Get It

Athlete’s heart (AH) represents the heart’s remarkable ability to adapt structurally and functionally to prolonged and intensive athletic training. Characterized by increased left ventricular (LV) wall thickness, enlarged cardiac chambers, and augmented cardiac mass, AH typically maintains or enhances systolic and diastolic functions. Despite the positive health implications, these adaptations can obscure the difference between benign physiological changes and early manifestations of cardiac pathologies such as dilated cardiomyopathy (DCM), hypertrophic cardiomyopathy (HCM), and arrhythmogenic cardiomyopathy (ACM). This article reviews the imaging characteristics of AH across various modalities, emphasizing echocardiography, cardiac magnetic resonance (CMR), and cardiac computed tomography as primary tools for evaluating cardiac function and distinguishing physiological adaptations from pathological conditions. The findings highlight the need for precise diagnostic criteria and advanced imaging techniques to ensure accurate differentiation, preventing misdiagnosis and its associated risks, such as sudden cardiac death (SCD). Understanding these adaptations and employing the appropriate imaging methods are crucial for athletes’ effective management and health optimization.
Chemotherapy Related Cardiotoxicity Evaluation—A Contemporary Review with a Focus on Cardiac Imaging
Scalia, Isabel G. , Gheyath, Bashaer , Tamarappoo, Balaji , Moudgil, Rohit , Otton, James , Pereyra, Milagros , Narayanasamy, Hema, Herrmann, Joerg , Arsanjani, Reza , Larsen, Carolyn , Arsanjani, Reza , Pereyra, Milagros , Scalia, Isabel G

Journal of Clinical Medicine | June 26, 2024 | Volume: 13 | Issue: 13 | Pages: 3714

10.3390/jcm13133714 Get It

The long-term survivorship of patients diagnosed with cancer has improved due to accelerated detection and rapidly evolving cancer treatment strategies. As such, the evaluation and management of cancer therapy related complications has become increasingly important, including cardiovascular complications. These have been captured under the umbrella term “cardiotoxicity” and include left ventricular dysfunction and heart failure, acute coronary syndromes, valvular abnormalities, pericardial disease, arrhythmia, myocarditis, and vascular complications. These complications add to the burden of cardiovascular disease (CVD) or are risk factors patients with cancer treatment are presenting with. Of note, both pre- and newly developing CVD is of prognostic significance, not only from a cardiovascular perspective but also overall, potentially impacting the level of cancer therapy that is possible. Currently, there are varying recommendations and practices regarding CVD risk assessment and mitigating strategies throughout the cancer continuum. This article provides an overview on this topic, in particular, the role of cardiac imaging in the care of the patient with cancer. Furthermore, it summarizes the current evidence on the spectrum, prevention, and management of chemotherapy-related adverse cardiac effects.
Lipoprotein(a) and long-term in-stent restenosis after percutaneous coronary intervention
Mahmoud, Ahmed , Awad, Kamal , Ali, Nima Baba , Pereyra, Milagros , Scalia, Isabel G. , Allam, Mohamed, Kamel, Moaz, Rmilah, Anan Abu , Chao, Chieh-Ju, Barry, Timothy, Lester, Steven J., Pollak, Peter , Sweeney, John P., Fortuin, David, Arsanjani, Reza , Mahmoud, Ahmed K , Allam, Mohamed N , Kamel, Moaz A, Alsidawi, Said , Pollak, Peter M, Alkhouli, Mohamad A, Lee, Richard W, Fortuin, David F, Arsanjani, Reza , Pereyra, Milagros , Scalia, Isabel G , Awad, Kamal , Farina, Juan M. , Abbas, Mohammed Tiseer , Allam, Mohamed N, Chao, Chieh‐Ju , Alsidawi, Said , Alkhouli, Mohamad , Lee, Kwan , Yang, Eric H. , Lee, Richard

European Journal of Preventive Cardiology | June 20, 2024 | Volume: 31 | Issue: 15 | Pages: 1878-1887

10.1093/eurjpc/zwae212 Get It

Abstract Aims Lipoprotein(a) [Lp(a)] has demonstrated its association with atherosclerosis and myocardial infarction. However, its role in the development of in-stent restenosis (ISR) after percutaneous coronary intervention (PCI) is not clearly established. The aim of this study is to investigate the association between Lp(a) and ISR. Methods and results A retrospective study of adult patients who underwent successful PCI between January 2006 and December 2017 at the three Mayo Clinic sites and had a preprocedural Lp(a) measurement was conducted. Patients were divided into two groups according to the serum Lp(a) concentration [high Lp(a) ≥ 50 mg/dL and low Lp(a) &lt; 50 mg/dL]. Univariable and multivariable analyses were performed to compare risk of ISR between patients with high Lp(a) vs. those with low Lp(a). A total of 1209 patients were included, with mean age 65.9 ± 11.7 years and 71.8% were male. Median follow-up after baseline PCI was 8.8 [interquartile range (IQR) 7.4] years. Restenosis was observed in 162 (13.4%) patients. Median serum levels of Lp(a) were significantly higher in patients affected by ISR vs. non-affected cases: 27 (IQR 73.8) vs. 20 (IQR 57.5) mg/dL, P = 0.008. The rate of ISR was significantly higher among patients with high Lp(a) vs. patients with low Lp(a) values (17.0% vs. 11.6%, P = 0.010). High Lp(a) values were independently associated with ISR events (hazard ratio 1.67, 95% confidence interval 1.18–2.37, P = 0.004), and this association was more prominent after the first year following the PCI. Conclusion Lipoprotein(a) is an independent predictor for long-term ISR and should be considered in the evaluation of patients undergoing PCI.
High Lp(a) levels are a potential risk factor for aortic valve interventions in patients with bicuspid aortic valve
Farina, J M, Abbas, Moncef, Mahmoud, Ahmed K., Lester, S.C., Barry, Timothy, Marcotte, F, Pereyra, Milagros , Pereyra, Milagros , Arsanjani, Reza , Kamel, M A, Abbas, M T, Scalia, Isabel G. , Mahmoud, Ahmed , Ali, N Baba, Ayoub, C, Sell‐Dottin, Kristen , Alsidawi, Said , Lester, S, Majdalany, David S

European Journal of Preventive Cardiology | June 14, 2024 | Volume: 31 | Issue: Supplement_1 | Pages: No page available

10.1093/eurjpc/zwae175.359 Get It

Abstract Background Bicuspid aortic valve (BAv) is associated with increased oxidative stress and inflammation, resulting in valve fibrosis, calcification, and ultimately early degenerative valve disease, often necessitating premature aortic valve intervention. In recent years, growing evidence has been published supporting the role of lipoprotein(a) [Lp(a)], an important carrier of oxidized phospholipids, in the development of aortic valve disease in the general population. However, the specific influence of Lp(a) levels in patients with BAv remains to be firmly established. Purpose To assess the role of Lp(a) levels in the development of aortic valve disease and the necessity for aortic valve interventions among individuals with BAv. Methods This retrospective multicenter study encompassed consecutive patients diagnosed with BAv from January 1997 to December 2022, all of whom had undergone serum Lp(a) measurement. This study evaluated the association between Lp(a) concentrations and the occurrence of aortic valve interventions. A cutoff point of ≥30 mg/dl for high Lp(a) levels was established. Binary logistic regression was utilized to calculate the odds ratio (OR) for an aortic intervention according to high versus low Lp(a) levels. Additionally, Kaplan Meier curves were employed to estimate the cumulative requirement for an aortic valve replacement based on Lp(a) concentrations. Results A total of 452 patients with BAv and a Lp(a) measurement were included in the study, with a mean age of 37.2 ±10.5 years at the time of BAv diagnosis, with 71.2% being male. Among these, 101 (22.3%) patients underwent an aortic valve replacement. In 72 cases (71.3%) aortic stenosis was the primary indication for intervention, while aortic regurgitation accounted for 29 cases (28.7%). The presence of elevated Lp(a) levels (≥30 mg/dl) demonstrated a significant association with the requirement for an aortic valve intervention (OR 2.2, 95%CI 1.4-3.6, p&lt;0.001) in both the regression analysis and using the Kaplan-Meier estimator (Figure). High Lp(a) concentrations posed a risk factor for aortic valve replacements regardless of whether the primary indication for intervention was significant stenosis (OR 1.8, 95%CI 1.1-3.1, p=0.028) or regurgitation (OR 2.5, 95%CI 1.2-5.4, p=0.018). Conclusion Increased concentrations of Lp(a) may influence the clinical trajectory of patients with a BAv and may be a significant risk factor for aortic valve replacement, irrespective of the primary indication for intervention. Further investigations will be critical in unveiling the precise pathological mechanisms of Lp(a) in BAv. Confirming whether reducing Lp(a) levels could slow the progression of aortic disease in this demographic requires further exploration. Kaplan-Meier estimator.