Concentric Cardiac Remodeling and Hypertrophy in Pregnant Individuals with Chronic Hypertension.

OBJECTIVE: This study aimed to evaluate rates of superimposed preeclampsia in pregnant individuals with echocardiography-diagnosed cardiac geometric changes in the setting of chronic hypertension. STUDY DESIGN: This was a retrospective study of pregnant individuals with chronic hypertension who delivered singleton pregnancies at 20 weeks' gestation or greater at a tertiary care center. Analyses were limited to individuals who had an echocardiogram during any trimester. Cardiac changes were categorized as normal morphology, concentric remodeling, eccentric hypertrophy, and concentric hypertrophy according to the American Society of Echocardiography guidelines. Our primary outcome was early-onset superimposed preeclampsia defined as delivery at less than 34 weeks' gestation. Other secondary outcomes were also examined. Adjusted odds ratios (aORs) with 95% confidence intervals (95% CIs) were calculated, controlling for prespecified covariates. RESULTS: Of the 168 individuals who delivered from 2010 to 2020, 57 (33.9%) had normal morphology, 54 (32.1%) had concentric remodeling, 9 (5.4%) had eccentric hypertrophy, and 48 (28.6%) had concentric hypertrophy. Non-Hispanic black individuals presented over 76% of the cohort. Rates of the primary outcome in individuals with normal morphology, concentric remodeling, eccentric hypertrophy, and concentric hypertrophy were 15.8, 37.0, 22.2, and 41.7%, respectively (p = 0.01). Compared with individuals with normal morphology, individuals with concentric remodeling were more likely to have the primary outcome (aOR: 3.28; 95% CI: 1.28-8.39), fetal growth restriction (crude OR: 2.98; 95% CI: 1.05-8.43), and iatrogenic preterm delivery <34 weeks' gestation (aOR: 2.72; 95% CI: 1.15-6.40). Compared with individuals with normal morphology, individuals with concentric hypertrophy were more likely to have the primary outcome (aOR: 4.16; 95% CI: 1.57-10.97), superimposed preeclampsia with severe features at any gestational age (aOR: 4.75; 95% CI: 1.94-11.62), iatrogenic preterm delivery <34 weeks' gestation (aOR: 3.60; 95% CI: 1.47-8.81), and neonatal intensive care unit admission (aOR: 4.82; 95% CI: 1.90-12.21). CONCLUSION: Concentric remodeling and concentric hypertrophy were associated with increased odds of early-onset superimposed preeclampsia. KEY POINTS: · Concentric remodeling and concentric hypertrophy were associated with an increased risk of superimposed preeclampsia.. · Concentric hypertrophy was associated with an increased risk of delivery at less than 34 weeks.. · Two-thirds of the individuals in our study had concentric hypertrophy and concentric remodeling..

Perceived Stress After Acute Myocardial Infarction: A Comparison Between Young and Middle-Aged Women Versus Men.

OBJECTIVE: The aim of the study was to examine how psychological stress changes over time in young and middle-aged patients after experiencing an acute myocardial infarction (AMI) and whether these changes differ between men and women. METHODS: We analyzed data obtained from 2358 women and 1151 men aged 18 to 55 years hospitalized for AMI. Psychological stress was measured using the 14-item Perceived Stress Scale (PSS-14) at initial hospitalization and at 1 month and 12 months after AMI. We used linear mixed-effects models to examine changes in PSS-14 scores over time and sex differences in these changes, while adjusting for patient characteristics and accounting for correlation among repeated observations within patients. RESULTS: Overall, patients' perceived stress decreased over time, especially during the first month after AMI. Women had higher levels of perceived stress than men throughout the 12-month period (difference in PSS-14 score = 3.63, 95% confidence interval = 3.08 to 4.18, p < .001), but they did not differ in how stress changed over time. Adjustment for patient characteristics did not alter the overall pattern of sex difference in changes of perceived stress over time other than attenuating the magnitude of sex difference in PSS-14 score (difference between women and men = 1.74, 95% confidence interval = 1.32 to 2.16, p < .001). The magnitude of sex differences in perceived stress was similar in patients with versus without post-AMI angina, even though patients with angina experienced less improvement in PSS-14 score than those without angina. CONCLUSIONS: In young and middle-aged patients with AMI, women reported higher levels of perceived stress than men throughout the first 12 months of recovery. However, women and men had a similar pattern in how perceived stress changed over time.

Relation between door-to-balloon times and mortality after primary percutaneous coronary intervention over time: a retrospective study.

BACKGROUND: Recent reductions in average door-to-balloon (D2B) times have not been associated with decreases in mortality at the population level. We investigated this seemingly paradoxical finding by assessing components of this association at the individual and population levels simultaneously. We postulated that the changing population of patients undergoing primary percutaneous coronary intervention (pPCI) contributed to secular trends toward an increasing mortality risk, despite consistently decreased mortality in individual patients with shorter D2B times. METHODS: This was a retrospective study of ST-elevation myocardial infarction (STEMI) patients who underwent pPCI between Jan 1, 2005, and Dec 31, 2011, in the National Cardiovascular Data Registry (NCDR) CathPCI Registry. We looked for catheterisation laboratory visits associated with STEMI. We excluded patients not undergoing pPCI, transfer patients for pPCI, patients with D2B times less than 15 min or more than 3 h, and patients at hospitals that did not consistently report data across the study period. We assessed in-hospital mortality in the entire cohort and 6-month mortality in elderly patients aged 65 years or older matched to data from the Centers for Medicare and Medicaid Services. We built multilevel models to assess the relation between D2B time and in-hospital and 6-month mortality, including both individual and population-level components of this association after adjusting for patient and procedural factors. FINDINGS: 423 hospitals reported data on 150,116 procedures with a 55% increase in the number of patients undergoing pPCI at these facilities over time, as well as many changes in patient and procedural factors. Annual D2B times decreased significantly from a median of 86 min (IQR 65-109) in 2005 to 63 min (IQR 47-80) in 2011 (p<0·0001) with a concurrent rise in risk-adjusted in-hospital mortality (from 4·7% to 5·3%; p=0·06) and risk-adjusted 6-month mortality (from 12·9% to 14·4%; p=0·001). In multilevel models, shorter patient-specific D2B times were consistently associated at the individual level with lower in-hospital mortality (adjusted OR for each 10 min decrease 0·92; 95% CI 0·91-0·93; p<0·0001) and 6-month mortality (adjusted OR for each 10 min decrease, 0·94; 95% CI 0·93-0·95; p<0·0001). By contrast, risk-adjusted in-hospital and 6-month mortality at the population level, independent of patient-specific D2B times, rose in the growing and changing population of patients undergoing pPCI during the study period. INTERPRETATION: Shorter patient-specific D2B times were consistently associated with lower mortality over time, whereas secular trends suggest increased mortality risk in the growing and changing pPCI population. The absence of association of annual D2B time and changes in mortality at the population level should not be interpreted as an indication of its individual-level relation in patients with STEMI undergoing primary PCI. FUNDING: National Heart, Lung, and Blood Institute.

Comparison of clinical interpretation with visual assessment and quantitative coronary angiography in patients undergoing percutaneous coronary intervention in contemporary practice: the Assessing Angiography (A2) project.

BACKGROUND: Studies conducted decades ago described substantial disagreement and errors in physicians' angiographic interpretation of coronary stenosis severity. Despite the potential implications of such findings, no large-scale efforts to measure or improve clinical interpretation were subsequently undertaken. METHODS AND RESULTS: We compared clinical interpretation of stenosis severity in coronary lesions with an independent assessment using quantitative coronary angiography (QCA) in 175 randomly selected patients undergoing elective percutaneous coronary intervention at 7 US hospitals in 2011. To assess agreement, we calculated mean difference in percent diameter stenosis between clinical interpretation and QCA and a Cohen weighted κ statistic. Of 216 treated lesions, median percent diameter stenosis was 80.0% (quartiles 1 and 3, 80.0% and 90.0%), with 213 (98.6%) assessed as ≥70%. Mean difference in percent diameter stenosis between clinical interpretation and QCA was 8.2±8.4%, reflecting an average higher percent diameter stenosis by clinical interpretation (P<0.001). A weighted κ of 0.27 (95% confidence interval, 0.18-0.36) was found between the 2 measurements. Of 213 lesions considered ≥70% by clinical interpretation, 56 (26.3%) were <70% by QCA, although none were <50%. Differences between the 2 measurements were largest for intermediate lesions by QCA (50% to <70%), with variation existing across sites. CONCLUSIONS: Physicians tended to assess coronary lesions treated with percutaneous coronary intervention as more severe than measurements by QCA. Almost all treated lesions were ≥70% by clinical interpretation, whereas approximately one quarter were <70% by QCA. These findings suggest opportunities to improve clinical interpretation of coronary angiography.

New anticoagulants and antiplatelet agents: a primer for the clinical gastroenterologist.

The discovery of the first oral anticoagulant, warfarin, was a milestone in anticoagulation. Warfarin's well-known limitations, however, have led to the recent development of more effective anticoagulants. The rapidly growing list of these drugs, however, presents a challenge to endoscopists who must treat patients on these sundry medications. This review is intended to summarize the pharmacological highlights of new anticoagulants, with particular attention to suggested "best-practice" recommendations for the withholding of these drugs before endoscopic procedures.

Hypertension Trends and Disparities Over 12 Years in a Large Health System: Leveraging the Electronic Health Records.

BACKGROUND: The digital transformation of medical data enables health systems to leverage real-world data from electronic health records to gain actionable insights for improving hypertension care. METHODS AND RESULTS: We performed a serial cross-sectional analysis of outpatients of a large regional health system from 2010 to 2021. Hypertension was defined by systolic blood pressure ≥140 mm Hg, diastolic blood pressure ≥90 mm Hg, or recorded treatment with antihypertension medications. We evaluated 4 methods of using blood pressure measurements in the electronic health record to define hypertension. The primary outcomes were age-adjusted prevalence rates and age-adjusted control rates. Hypertension prevalence varied depending on the definition used, ranging from 36.5% to 50.9% initially and increasing over time by ≈5%, regardless of the definition used. Control rates ranged from 61.2% to 71.3% initially, increased during 2018 to 2019, and decreased during 2020 to 2021. The proportion of patients with a hypertension diagnosis ranged from 45.5% to 60.2% initially and improved during the study period. Non-Hispanic Black patients represented 25% of our regional population and consistently had higher prevalence rates, higher mean systolic and diastolic blood pressure, and lower control rates compared with other racial and ethnic groups. CONCLUSIONS: In a large regional health system, we leveraged the electronic health record to provide real-world insights. The findings largely reflected national trends but showed distinctive regional demographics and findings, with prevalence increasing, one-quarter of the patients not controlled, and marked disparities. This approach could be emulated by regional health systems seeking to improve hypertension care.

Sex Differences in Symptom Complexity and Door-to-Balloon Time in Patients With ST-Elevation Myocardial Infarction.

Greater symptom complexity in women than in men could slow acute ST-elevation myocardial infarction (STEMI) recognition and delay door-to-balloon (D2B) times. We sought to determine the sex differences in symptom complexity and their relation to D2B times in 1,677 young and older patients with STEMI using data from the VIRGO and SILVER-AMI studies. Symptom complexity was defined by the number of symptom patterns or phenotypes and average number of symptoms. The numbers of symptom phenotypes were compared in women and men using the Monte Carlo permutation testing. Groups were also compared using the generalized linear regression and logistic regression. The number of symptom phenotypes (244 vs 171, p = 0.02), mean number of symptoms (4.7 vs 4.2, p <0.001), and mean D2B time (114.6 vs 97.8 minutes, p = 0.004) were greater in young women than in young men but were not significantly different in older women compared with older men. The regression analysis did not show a relation between symptom complexity and D2B time overall; although, chest pain was a significant predictor of D2B times, and young women were more likely to report symptoms other than chest pain. Among patients with STEMI, 36% did not receive percutaneous coronary intervention (PCI), which was associated with presentation delay >6 hours. In patients with STEMI with either D2B time ≥90 minutes or no PCI, women had significantly more symptom phenotypes overall and in VIRGO but not in SILVER-AMI. In conclusion, the markers of symptom complexity were not associated with D2B time overall, but more symptom phenotypes in young women were associated with prolonged D2B time or no PCI. In addition, greater frequency of nonchest pain symptoms in young women may have also slowed the recognition of STEMI and D2B times in young women. Further research on symptoms clusters is needed to improve the recognition of STEMIs to improve the D2B times in young women.

Diagnostic reasoning in cardiovascular medicine.

Research in cognitive psychology shows that expert clinicians make a medical diagnosis through a two step process of hypothesis generation and hypothesis testing. Experts generate a list of possible diagnoses quickly and intuitively, drawing on previous experience. Experts remember specific examples of various disease categories as exemplars, which enables rapid access to diagnostic possibilities and gives them an intuitive sense of the base rates of various diagnoses. After generating diagnostic hypotheses, clinicians then test the hypotheses and subjectively estimate the probability of each diagnostic possibility by using a heuristic called anchoring and adjusting. Although both novices and experts use this two step diagnostic process, experts distinguish themselves as better diagnosticians through their ability to mobilize experiential knowledge in a manner that is content specific. Experience is clearly the best teacher, but some educational strategies have been shown to modestly improve diagnostic accuracy. Increased knowledge about the cognitive psychology of the diagnostic process and the pitfalls inherent in the process may inform clinical teachers and help learners and clinicians to improve the accuracy of diagnostic reasoning. This article reviews the literature on the cognitive psychology of diagnostic reasoning in the context of cardiovascular disease.

Sex Differences in Symptom Phenotypes Among Older Patients with Acute Myocardial Infarction.

BACKGROUND: Clinicians make a medical diagnosis by recognizing diagnostic possibilities, often using memories of prior examples. These memories, called "exemplars," reflect specific symptom combinations in individual patients, yet most clinical studies report how symptoms aggregate in populations. We studied how symptoms of acute myocardial infarction combine in individuals as symptom phenotypes and how symptom phenotypes are distributed in women and men. METHODS: In this analysis of the SILVER-AMI Study, we studied 3041 patients (1346 women and 1645 men) 75 years of age or older with acute myocardial infarction. Each patient had a standardized in-person interview during the acute myocardial infarction admission to document the presenting symptoms, which enabled a thorough examination of symptom combinations in individuals. Specific symptom combinations defined symptom phenotypes and distributions of symptom phenotypes were compared in women and men using Monte Carlo permutation testing and repeated subsampling. RESULTS: There were 1469 unique symptom phenotypes in the entire SILVER-AMI cohort of patients with acute myocardial infarction. There were 831 unique symptom phenotypes in women, as compared with 819 in men, which was highly significant, given the larger number of men than women in the study (P < .0001). Women had significantly more symptom phenotypes than men in almost all acute myocardial infarction subgroups. CONCLUSIONS: Older patients with acute myocardial infarction have enormous variation in symptom phenotypes. Women reported more symptoms and had significantly more symptom phenotypes than men. Appreciation of the diversity of symptom phenotypes may help clinicians recognize the less common phenotypes that occur more often in women.

A statewide collaborative initiative to improve the quality of care for patients with acute myocardial infarction and heart failure.

BACKGROUND: To enhance quality improvement, we created a unique statewide collaboration among 3 organizations: the Virginia Health Quality Center (Virginia's Medicare Quality Improvement Organization), the American College of Cardiology, and the American Heart Association. The goal was to improve discharge measures for acute myocardial infarction and heart failure. METHODS AND RESULTS: In 2004, 29 hospitals participated in the collaborative initiative. Using Medicare data submitted from 2004 through the second quarter of 2006, we analyzed adherence to individual discharge measures and all-or-none appropriate care measures for acute myocardial infarction, heart failure, and both. To control for differences in hospital characteristics, we were able to match 21 of the participating hospitals with 21 similar nonparticipating hospitals. In this paired analysis, the total appropriate care measure increased from 61% to 77% in participating hospitals compared with an increase from 51% to 60% in nonparticipating hospitals (P<0.0001). A generalized linear mixed model examining the full data set at the patient level failed to show a clear advantage among participating hospitals. Participating hospitals had higher baseline rates for most quality measures, suggesting a possible effect of a prior collaborative. Further analysis of only hospitals that participated in a prior collaborative showed that participants in the current collaborative initiative had higher rates of improvement for 7 of 10 quality measures and appropriate care measures for heart failure, acute myocardial infarction, or both (all P<0.05). CONCLUSIONS: We report a unique collaboration of a Medicare Quality Improvement Organization and 2 national organizations to address quality of care for acute myocardial infarction and heart failure. A composite measure of quality (the total appropriate care measure) improved more in the participating hospitals during the timeframe of the intervention, although the greater improvement in this and other measures in the participating hospitals appeared to be dependent on participation in a prior collaborative initiative.

Blueprint for the dissemination of evidence-based practices in health care.

Aimed at fostering the broad adoption of effective health care interventions, this report proposes a blueprint for improving the dissemination of best practices by national quality improvement campaigns. The blueprint's eight key strategies are to: 1) highlight the evidence base and relative simplicity of recommended practices; 2) align campaigns with strategic goals of adopting organizations; 3) increase recruitment by integrating opinion leaders into the enrollment process; 4) form a coalition of credible campaign sponsors; 5) generate a threshold of participating organizations that maximizes network exchanges; 6) develop practical implementation tools and guides for key stakeholder groups; 7) create networks to foster learning opportunities; and 8) incorporate monitoring and evaluation of milestones and goals. The impact of quality campaigns also depends on contextual factors, including the nature of the innovation itself, external environmental incentives, and features of adopting organizations.

Maintenance of Competence in Cardiovascular Training and Practices: Worth the Effort?

Americans expect their doctors to have the competence to deliver high-quality care and expect safeguards to be in place that assure their doctors are competent. However, competence requires knowledge, and people have trouble assessing their own knowledge and level of competence. Because external assessment is required, several organizations have taken on the roles of defining and assuring medical competence. For example, professional organizations such as the American College of Cardiology (ACC) have developed consensus documents that define core competencies for cardiologists. External organizations such as the Accreditation Council for Graduate Medical Education and the American Board of Internal Medicine (ABIM) have defined training requirements for cardiologists, and the ABIM has developed a process to certify that physicians maintain their competence, although the process has generated considerable criticism from the profession. Recently, the ACC and ABIM have worked together to make the certification process less onerous and more meaningful. This paper provides a brief summary of the history and ongoing efforts to assure the competence of cardiologists.

Sex Differences in Symptom Phenotypes Among Patients With Acute Myocardial Infarction.

BACKGROUND: The diagnosis of acute myocardial infarction (AMI) is missed more frequently in young women than men, which may be related to the cognitive psychology of the diagnostic process. Physicians start the diagnostic process by intuitively recognizing familiar symptom phenotypes, but little is known about how symptoms combine in individuals as unique symptom phenotypes. We examined how symptoms of AMI combine as unique symptom phenotypes in individual patients to compare the distribution of symptom phenotypes in women versus men. METHODS AND RESULTS: The VIRGO study (Variation in Recovery: Role of Gender on Outcomes of Young AMI Patients) was a multicenter, observational cohort study of 3501 young adults hospitalized with AMI. Data were collected on presenting symptoms with standardized interviews and from medical record abstraction. The number and distribution of unique symptom phenotypes were compared between women and men. Because of the 2:1 female-to-male enrollment ratio, women and men were compared with permutation testing and repeated subsampling. There were 426 interview-symptom phenotypes in women and 280 in men. The observed difference between women and men of 146 phenotypes was significant, even allowing for the greater enrollment of women (permutation P=0.004, median difference 110 under the null hypothesis of no association between sex and phenotype). The repeated subsample analysis also showed significantly more interview-symptom phenotypes in women than men (206.8±7.3 versus 188.6±6.0, P<0.001). Women were more broadly distributed among symptom phenotype subgroups than men (P<0.001). Similar findings were observed in the analysis of symptoms abstracted from the medical record. CONCLUSIONS: Women exhibited substantially more variation in unique symptom phenotypes than men, regardless of whether the symptoms were derived from structured interviews or abstracted from the medical record. These findings may provide an explanation for the higher missed diagnosis rate in young women with AMI and may have important implications for teaching and improving clinicians' ability to recognize the diagnosis of AMI in women.

Risk Model for Decline in Activities of Daily Living Among Older Adults Hospitalized With Acute Myocardial Infarction: The SILVER-AMI Study.

Background Functional decline (ie, a decrement in ability to perform everyday activities necessary to live independently) is common after acute myocardial infarction (AMI) and associated with poor long-term outcomes; yet, we do not have a tool to identify older AMI survivors at risk for this important patient-centered outcome. Methods and Results We used data from the prospective SILVER-AMI (Comprehensive Evaluation of Risk Factors in Older Patients With Acute Myocardial Infarction) study of 3041 patients with AMI, aged ≥75 years, recruited from 94 US hospitals. Participants were assessed during hospitalization and at 6 months to collect data on demographics, geriatric impairments, psychosocial factors, and activities of daily living. Clinical variables were abstracted from the medical record. Functional decline was defined as a decrement in ability to independently perform essential activities of daily living (ie, bathing, dressing, transferring, and ambulation) from baseline to 6 months postdischarge. The mean age of the sample was 82±5 years; 57% were men, 90% were White, and 13% reported activity of daily living decline at 6 months postdischarge. The model identified older age, longer hospital stay, mobility impairment during hospitalization, preadmission physical activity, and depression as risk factors for decline. Revascularization during AMI hospitalization and ability to walk a quarter mile before AMI were associated with decreased risk. Model discrimination (c=0.78) and calibration were good. Conclusions We identified a parsimonious model that predicts risk of activity of daily living decline among older patients with AMI. This tool may aid in identifying older patients with AMI who may benefit from restorative therapies to optimize function after AMI.

Standards for measures used for public reporting of efficiency in health care: a scientific statement from the American Heart Association Interdisciplinary Council on Quality of Care and Outcomes Research and the American College of Cardiology Foundation.

The assessment of medical practice is evolving rapidly in the United States. An initial focus on structure and process performance measures assessing the quality of medical care is now being supplemented with efficiency measures to quantify the "value" of healthcare delivery. This statement, building on prior work that articulated standards for publicly reported outcomes measures, identifies preferred attributes for measures used to assess efficiency in the allocation of healthcare resources. The attributes identified in this document combined with the previously published standards are intended to serve as criteria for assessing the suitability of efficiency measures for public reporting. This statement identifies the following attributes to be considered for publicly reported efficiency measures: integration of the quality and cost; valid cost measurement and analysis; minimal incentive to provide poor quality care; and proper attribution of the measure. The attributes described in this statement are relevant to a wide range of efforts to profile the efficiency of various healthcare providers, including hospitals, healthcare systems, managed-care organizations, physicians, group practices, and others that deliver coordinated care.

The door-to-balloon alliance for quality: who joins national collaborative efforts and why?

BACKGROUND: The Door-to-Balloon (D2B) Alliance is a collaborative effort of more than 900 hospitals aimed at improving D2B times for ST-segment elevation myocardial infarction. Although such collaborative efforts are increasingly used to promote improvement, little is known about the types of health care organizations that enroll and their motivations to participate. METHODS: To examine the types of hospitals enrolled and reasons for enrollment, a cross-sectional study was conducted of 915 D2B Alliance hospitals and 654 hospitals that did not join the D2B Alliance. Data were obtained from the American Hospital Association's Annual Survey of Hospitals and a Web-based survey completed by 797 enrolled hospitals (response rate, 87%). Chi-square statistics were used to examine statistical associations, and qualitative data analysis was used to characterize reported reasons for enrolling. RESULTS: Hospitals that enrolled in the D2B Alliance were significantly (p values < .05) more likely to be larger, nonprofit (versus for-profit), and teaching (versus nonteaching) hospitals. Earlier- versus later-enrolling hospitals were more likely to have key recommended strategies already in place at the time of enrollment. Improving quality and "doing the right thing" were commonly reported reasons for enrolling; however, hospitals also reported improving market share, meeting regulatory and accreditation requirements, and enhancing reputation as primary reasons for joining. CONCLUSIONS: The findings highlight the underlying goals of organizations to improve their position in the external environment--including economic, regulatory, accreditation, and professional environments. Designing quality improvement collaborative efforts to appeal to these goals may be an important strategy for enhancing participation and, in turn, increasing the uptake of evidence-based innovations.

Effect of Teaching Bayesian Methods Using Learning by Concept vs Learning by Example on Medical Students' Ability to Estimate Probability of a Diagnosis: A Randomized Clinical Trial.

Importance: Clinicians use probability estimates to make a diagnosis. Teaching students to make more accurate probability estimates could improve the diagnostic process and, ultimately, the quality of medical care. Objective: To test whether novice clinicians can be taught to make more accurate bayesian revisions of diagnostic probabilities using teaching methods that apply either explicit conceptual instruction or repeated examples. Design, Setting, and Participants: A randomized clinical trial of 2 methods for teaching bayesian updating and diagnostic reasoning was performed. A web-based platform was used for consent, randomization, intervention, and testing of the effect of the intervention. Participants included 61 medical students at McMaster University and Eastern Virginia Medical School recruited from May 1 to September 30, 2018. Interventions: Students were randomized to (1) receive explicit conceptual instruction regarding diagnostic testing and bayesian revision (concept group), (2) exposure to repeated examples of cases with feedback regarding posttest probability (experience group), or (3) a control condition with no conceptual instruction or repeated examples. Main Outcomes and Measures: Students in all 3 groups were tested on their ability to update the probability of a diagnosis based on either negative or positive test results. Their probability revisions were compared with posttest probability revisions that were calculated using the Bayes rule and known test sensitivity and specificity. Results: Of the 61 participants, 22 were assigned to the concept group, 20 to the experience group, and 19 to the control group. Approximate age was 25 years. Two participants were first-year; 37, second-year; 12, third-year; and 10, fourth-year students. Mean (SE) probability estimates of students in the concept group were statistically significantly closer to calculated bayesian probability than the other 2 groups (concept, 0.4%; [0.7%]; experience, 3.5% [0.7%]; control, 4.3% [0.7%]; P < .001). Although statistically significant, the differences between groups were relatively modest, and students in all groups performed better than expected, based on prior reports in the literature. Conclusions and Relevance: The study showed a modest advantage for students who received theoretical instruction on bayesian concepts. All participants' probability estimates were, on average, close to the bayesian calculation. These findings have implications for how to teach diagnostic reasoning to novice clinicians. Trial Registration: ClinicalTrials.gov identifier: NCT04130607.