Evaluating Changes in del Nido Cardioplegia Practices in Adult Cardiac Surgery.

There has been a rapid adoption of the use of del Nido cardioplegia (DC) among adults undergoing cardiac surgery. We leveraged a multicenter database to evaluate differences over time in the choice and impact of cardioplegia type (DC vs. blood) among patients undergoing cardiac surgery. We evaluated 26,373 patients undergoing non-emergent coronary artery bypass and/or valve surgery between 2014-2015 (early period) and 2017-2018 (late period) at 31 centers. DC was compared with blood-based cardioplegia (BC: 1:1, 2:1, 4:1, 8:1, and variable ratio). We evaluated whether treatment choice differed across prespecified patient characteristics, procedure type, and perfusion practices by time period. We evaluated increased DC use with clinical outcomes (major morbidity and mortality, prolonged intubation, and renal failure), after adjusting for baseline characteristics, procedure type, center, and year. DC use increased from 19.6% in 2014-2015 to 41.5% in 2017-2018, p < .001. Increased DC use occurred among coronary artery bypass grafting (CABG), valve, and CABG + valve procedures, all p < .001. Differences in median procedural duration increased over time (DC vs. BC): 1) bypass duration was 11.0 minutes shorter with DC in the early period and 27.0 minutes shorter in the late period, and 2) cross-clamp duration was 7.0 minutes shorter with DC in the early period and 17.0 minutes shorter in the late period, all p < .001. There were no statistical differences in adjusted odds of major morbidity and mortality (odds ratio [OR]adj: 1.01), prolonged intubation (ORadj: .99), or renal failure (ORadj: .80) by DC use (p > .05). In this large multicenter experience, DC use increased over time and was associated with reduced bypass and ischemic time absent any significant differences in adjusted outcomes.

Net Prime Volume Is Associated with Increased Odds of Blood Transfusion.

Hemodilutional anemia has been cited as a contributing factor to red blood cell (RBC) transfusions in cardiac surgery patients. Accordingly, efforts have been made to minimize hemodilution by reducing cardiopulmonary bypass (CPB) prime volume. We sought to assess the impact of these efforts on intraoperative RBC transfusions. We evaluated 21,360 patients undergoing coronary artery bypass with or without aortic valve surgery between July 2011 through December 2016 at any of 42 centers participating in the Perfusion Measures and Outcomes registry. The primary exposure was net CPB prime volume (total prime volume minus retrograde autologous prime volume) indexed to body surface area (mL/m2), which was further divided into quartiles (Q1: <262 mL/m2, Q2: 262-377 mL/m2, Q3: 377-516 mL/m2, and Q4: >516 mL/m2). The primary outcome was intraoperative RBC transfusion. We modeled the effect of index net prime volume on transfusion, adjusting for patient (age, gender, race, diabetes, vascular disease, previous myocardial infarction, ejection fraction, creatinine, preoperative hematocrit (HCT), total albumin, status, aspirin, and antiplatelet agents), procedural (procedure types) characteristics, surgical year, and hospital. The median net prime volume was 378 mL/m2 (25th percentile: 262 mL/m2, 75th percentile: 516 mL/m2). Relative to patients in Q1, patients in Q4 were more likely to be older, female, nondiabetic, have higher ejection fraction, have more ultrafiltration volume removed, and undergo more elective and aortic valve procedures (all p < .05). Patients in Q4 relative to Q1 were exposed to lower nadir HCTs on bypass, p < .05. The net prime volume was associated with an increased risk of transfusion (8.9% in Q1 vs. 22.6% in Q4, p < .001). After adjustment, patients in Q4 (relative to Q1) had a 2.9-fold increased odds (ORadj = 2.9, 95% CI [2.4, 3.4]) of intraoperative RBC transfusion. In this large, multicenter experience, patients exposed to larger net prime volumes were associated with greater adjusted odds of receiving intraoperative transfusions. Our findings reinforce the importance of efforts to reduce the net CPB prime volume. Based on these findings and other supporting evidence, the net prime volume should be adopted as a national quality measure.

Is Conventional Bypass for Coronary Artery Bypass Graft Surgery a Misnomer?

Although recent trials comparing on vs. off-pump revascularization techniques describe cardiopulmonary bypass (CPB) as "conventional," inadequate description and evaluation of how CPB is managed often exist in the peer-reviewed literature. We identify and subsequently describe regional and center-level differences in the techniques and equipment used for conducting CPB in the setting of coronary artery bypass grafting (CABG) surgery. We accessed prospectively collected data among isolated CABG procedures submitted to either the Australian and New Zealand Collaborative Perfusion Registry (ANZCPR) or Perfusion Measures and outcomes (PERForm) Registry between January 1, 2014, and December 31, 2015. Variation in equipment and management practices reflecting key areas of CPB is described across 47 centers (ANZCPR: 9; PERForm: 38). We report average usage (categorical data) or median values (continuous data) at the center-level, along with the minimum and maximum across centers. Three thousand five hundred sixty-two patients were identified in the ANZCPR and 8,450 in PERForm. Substantial variation in equipment usage and CPB management practices existed (within and across registries). Open venous reservoirs were commonly used across both registries (nearly 100%), as were "all-but-cannula" biopassive surface coatings (>90%), whereas roller pumps were more commonly used in ANZCPR (ANZCPR: 85% vs. PERForm: 64%). ANZCPR participants had 640 mL absolute higher net prime volumes, attributed in part to higher total prime volume (1,462 mL vs. 1,217 mL) and lower adoption of retrograde autologous priming (20% vs. 81%). ANZCPR participants had higher nadir hematocrit on CPB (27 vs. 25). Minimal absolute differences existed in exposure to high arterial outflow temperatures (36.6°C vs. 37.0°C). We report substantial center and registry differences in both the type of equipment used and CPB management strategies. These findings suggest that the term "conventional bypass" may not adequately reflect real-world experiences. Instead of using this term, authors should provide key details of the CPB practices used in their patients.

A BMI >35 does not protect patients undergoing cardiac bypass surgery from red blood cell transfusion.

The effect of obesity on allogeneic intraoperative blood product transfusion in patients undergoing coronary artery bypass graft surgery (CABG) is poorly understood. We analyzed the influence of obesity on the risk of intraoperative red blood cell (RBC) transfusion among 45,200 consecutive non-reoperative CABG procedures from a multi-institutional perfusion database. A body mass index (BMI) in obese I category was associated with a 9.9% decrease in transfusion risk (p<0.05). Compared to patients with a normal BMI, obese I and obese III patients do not have any change in the relative risk of RBC transfusion. Overweight and mild obesity have a protective role in reducing intraoperative blood transfusion during cardiopulmonary bypass (CPB) surgery. However, logistic regression analysis showed that much of the observed reduction in transfusion rates for obese patients can be accounted for by other known confounds. The lack of a linear effect of increasing BMI on blood transfusion risk is a novel finding and warrants further investigation.

Blood Conservation-A Team Sport.

Cardiac surgery accounts for between 15% and 20% of all blood product utilization in the United States. A body of literature suggests that patients who are exposed to even small quantities of blood have an increased risk of morbidity and mortality, even after adjusting for pre-operative risk. Despite this body of literature supporting a restrictive blood management strategy, wide variability in transfusion rates exist across institutions. Recent blood management guidelines have shed light on a number of potentially promising blood management strategies, including acute normovolemic hemodilution (ANH) and retrograde autologous priming (RAP). We evaluated the literature concerning ANH and RAP, and the use of both techniques among centers participating in the Perfusion Measures and outcomes (PERForm) registry. We leveraged data concerning ANH and RAP among 10,203 patients undergoing isolated coronary artery bypass grafting (CABG) procedures from 2010 to 2014 at 27 medical centers. Meta-analyses have focused on the topic of ANH, with few studies focusing specifically on cardiac surgery. Two meta-analyses have been conducted to date on RAP, with many reporting higher intra-operative hematocrits and reduced transfusions. The rate of red blood cell transfusions in the setting of CABG surgery is 34.2%, although varied across institutions from 16.8% to 57.6%. Overall use of ANH was 11.6%, although the utilization varied from .0% to 75.7% across institutions. RAP use was 71.4%, although varied from .0% to 99.0% across institutions. A number of blood conservation strategies have been proposed, with varying levels of evidence from meta-analyses. This uncertainty has likely contributed to center-level differences in the utilization of these practices as evidenced by our multi-institutional database. Perfusion databases, including the PERForm registry, serve as a vehicle for perfusionist's to track their practice, and contribute to multidisciplinary team efforts aimed at assessing and improving the value of cardiac surgical care.

The Relationship between Intra-Operative Transfusions and Nadir Hematocrit on Post-Operative Outcomes after Cardiac Surgery.

Uncertainty exists regarding the optimal strategy for the management of anemia in the setting of cardiac surgery. We sought to improve our understanding of the role of intra-operative hematocrit (HCT) and transfusions on peri-operative outcomes following cardiac surgery. A total of 18,886 patients undergoing on-pump cardiac surgery were identified from a multi-institutional registry including surgical and perfusion data. Patients were divided into four groups based on their intra-operative nadir HCT (<21 or ≥21) and whether or not they received intra-operative red blood cell (+RBC or -RBC) transfusions. Outcomes were adjusted for the Society of Thoracic Surgeons predicted risk of mortality (PROM), pre-operative HCT, and medical center. Regardless of nadir HCT cohort, those who received a transfusion had higher PROM relative to patients who did not receive a transfusion. The mean PROM was significantly higher among those HCT ≥21 + RBC (5.3%) vs. HCT ≥ 21 - RBC (1.9%), p < .001. Similarly, the PROM was significantly higher among HCT <21 + RBC (5.1%) vs. those HCT <21 - RBC (3.1%), p < .001. Adjusted outcomes demonstrated an increased impact of RBC transfusions on adverse outcomes irrespective of nadir HCT including stroke (p < .001), renal failure (p < .001), prolonged ventilation (p < .001), and mortality (p < .001). This study demonstrates that transfusions have a more profound effect on post-operative cardiac surgery outcomes than anemia.

The Society of Thoracic Surgeons, The Society of Cardiovascular Anesthesiologists, and The American Society of ExtraCorporeal Technology: Clinical Practice Guidelines for Cardiopulmonary Bypass--Temperature Management During Cardiopulmonary Bypass.

UNLABELLED: In order to improve our understanding of the evidence-based literature supporting temperature management during adult cardiopulmonary bypass, The Society of Thoracic Surgeons, the Society of Cardiovascular Anesthesiology and the American Society of ExtraCorporeal Technology tasked the authors to conduct a review of the peer-reviewed literature, including: 1) optimal site for temperature monitoring, 2) avoidance of hyperthermia, 3) peak cooling temperature gradient and cooling rate, and 4) peak warming temperature gradient and rewarming rate. Authors adopted the American College of Cardiology/American Heart Association method for development clinical practice guidelines, and arrived at the following recommendations: CLASS I RECOMMENDATIONS: a)The oxygenator arterial outlet blood temperature is recommended to be utilized as a surrogate for cerebral temperature measurement during CPB. (Class I, Level C) b)To monitor cerebral perfusate temperature during warming, it should be assumed that the oxygenator arterial outlet blood temperature under-estimates cerebral perfusate temperature. (Class I, Level C) c)Surgical teams should limit arterial outlet blood temperature to<37°C to avoid cerebral hyperthermia. (Class 1, Level C) d)Temperature gradients between the arterial outlet and venous inflow on the oxygenator during CPB cooling should not exceed 10°C to avoid generation of gaseous emboli. (Class 1, Level C) e)Temperature gradients between the arterial outlet and venous inflow on the oxygenator during CPB rewarming should not exceed 10°C to avoid out-gassing when blood is returned to the patient. (Class 1, Level C) CLASS IIa RECOMMENDATIONS: a)Pulmonary artery or nasopharyngeal temperature recording is reasonable for weaning and immediate post-bypass temperature measurement. (Class IIa, Level C)b)Rewarming when arterial blood outlet temperature ≥30° C: i.To achieve the desired temperature for separation from bypass, it is reasonable to maintain a temperature gradient between arterial outlet temperature and the venous inflow of≤4°C. (Class IIa, Level B) ii.To achieve the desired temperature for separation from bypass, it is reasonable to maintain a rewarming rate≤0.5°C/min. (Class IIa, Level B) NO RECOMMENDATION: No recommendation for a guideline is provided concerning optimal temperature for weaning from CPB due to insufficient published evidence.

The Society of Thoracic Surgeons, The Society of Cardiovascular Anesthesiologists, and The American Society of ExtraCorporeal Technology: Clinical Practice Guidelines for Cardiopulmonary Bypass--Temperature Management during Cardiopulmonary Bypass.

To improve our understanding of the evidence-based literature supporting temperature management during adult cardiopulmonary bypass, The Society of Thoracic Surgeons, the Society of Cardiovascular Anesthesiology and the American Society of ExtraCorporeal Technology tasked the authors to conduct a review of the peer-reviewed literature, including 1) optimal site for temperature monitoring, 2) avoidance of hyperthermia, 3) peak cooling temperature gradient and cooling rate, and 4) peak warming temperature gradient and rewarming rate. Authors adopted the American College of Cardiology/American Heart Association method for development clinical practice guidelines, and arrived at the following recommendation.

Report from AmSECT's International Consortium for Evidence- Based Perfusion Consensus Statement: Minimal Criteria for Reporting Cardiopulmonary Bypass-Related Contributions to Red Blood Cell Transfusions Associated With Adult Cardiac Surgery.

Gaps remain in our understanding of the contribution of bypass-related practices associated with red blood cell (RBC) transfusions after cardiac surgery. Variability exists in the reporting of bypass-related practices in the peer-reviewed literature. In an effort to create uniformity in reporting, a draft statement outlining proposed minimal criteria for reporting cardiopulmonary bypass (CPB)- related contributions (i.e., RBC data collection/documentation, clinical considerations for transfusions, equipment details, and clinical endpoints) was presented in conjunction with the American Society of ExtraCorporeal Technology's (AmSECT's) 2014 Quality and Outcomes Meeting (Baltimore, MD). Based on presentations and feedback from the conference, coauthors (n = 14) developed and subsequently voted on each proposed data element. Data elements receiving a total of 4 votes were dropped from further consideration, 5-9 votes were considered as "Recommended," and elements receiving ≥10 votes were considered as "Mandatory." A total of 52 elements were classified as mandatory, 16 recommended, and 14 dropped. There are 8 mandatory data elements for RBC data collection/documentation, 24 for clinical considerations for transfusions, 13 for equipment details, and 7 for clinical endpoints. We present 52 mandatory data elements reflecting CPB-related contributions to RBC transfusions. Consistency of such reporting would offer our community an increased opportunity to shed light on the relationship between intra-operative practices and RBC transfusions.

Heart-Lung Transplantation From Donation After Circulatory Death Using Mobile Normothermic Regional Perfusion.

Combined heart-lung transplant (HTLx) is the most durable treatment available for end-stage heart and lung failure. Many patients are unable to receive combined organs due to organ availability and allocation policies prioritizing separate heart or lung transplantation. While an average of 45 HTLxs have been performed per year in the United States half the listed patients do not receive organs. Recently, donation after circulatory death (DCD) utilizing normothermic regional perfusion (NRP) has been utilized for heart allografts with excellent results, and here, we present a case utilizing mobile NRP to procure a heart and lung block from a circulatory death donor and successful implantation for a recipient in a separate center.

Perfusion Measures and Outcomes (PERForm) registry: First annual report.

BACKGROUND: The Perfusion Measures and Outcomes (PERForm) registry was established in 2010 to advance cardiopulmonary bypass (CPB) practices and outcomes. The registry is maintained through the Michigan Society of Thoracic and Cardiovascular Surgeons Quality Collaborative and is the official registry of the American Society of Extracorporeal Technology. METHODS: This first annual PERForm registry report summarizes patient characteristics as well as CPB-related practice patterns in adult (≥18 years of age) patients between 2019 and 2022 from 42 participating hospitals. Data from PERForm are probabilistically matched to institutional surgical registry data. Trends in myocardial protection, glucose, anticoagulation, temperature, anemia (hematocrit), and fluid management are summarized. Additionally, trends in equipment (hardware/disposables) utilization and employed patient safety practices are reported. RESULTS: A total of 40,777 adult patients undergoing CPB were matched to institutional surgical registry data from 42 hospitals. Among these patients, 54.9% underwent a CABG procedure, 71.6% were male, and the median (IQR) age was 66.0 [58.0, 73.0] years. Overall, 33.1% of the CPB procedures utilized a roller pump for the arterial pump device, and a perfusion checklist was employed 99.6% of the time. The use of conventional ultrafiltration decreased over the study period (2019 vs. 2022; 27.1% vs. 24.9%) while the median (IQR) last hematocrit on CPB has remained stable [27.0 (24.0, 30.0) vs. 27.0 (24.0, 30.0)]. Pump sucker termination before protamine administration increased over the study period: (54.8% vs. 75.9%). CONCLUSION: Few robust clinical registries exist to collect data regarding the practice of CPB. Although data submitted to the PERForm registry demonstrate overall compliance with published perfusion evidence-based guidelines, noted opportunities to advance patient safety and outcomes remain.

Advancing cardiotomy suction practices for coronary surgery via multidisciplinary collaborative learning.

Objective: Professional standards recommend stopping cardiotomy suction at the termination of cardiopulmonary bypass before protamine administration based on perceived safety concerns. This study evaluated a multidisciplinary collaborative quality-improvement intervention promoting this agreed-upon cardiotomy suction practice during coronary artery bypass grafting (CABG). Methods: A statewide intervention (eg, unblinded surgeon and perfusionist feedback, evidence-based lectures, evaluating barriers to change) involved 32 centers participating in the PERForm (ie, Perfusion Measures and Outcomes) Registry to standardize cardiotomy suction practices at cardiopulmonary bypass termination during CABG. Four non-Michigan registry participating centers were not exposed to collaborative learning. Cardiotomy suction practice was defined as the absence of or stopping cardiotomy suction before protamine administration. The practice changes attributed to the intervention, including Michigan and non-Michigan comparisons, were evaluated with the change of time effect modeled using splines. Multivariable regression was used to evaluate the intervention's associated impact (eg, mortality, reoperation, transfusion). Results: Among 10,394 patients undergoing CABG at Michigan centers, 80.7% achieved agreed-upon cardiotomy suction practices. The Michigan centers had nonsignificant changes in agreed-upon cardiotomy suction practices during the preintervention period (P = .24), with significant increased monthly change in practice thereafter, absent adjusted morbidity and mortality increases. The Michigan centers achieved a significantly greater adjusted monthly improvement in agreed-upon practices relative to non-Michigan centers within 7 months after the intervention (adjusted odds ratio for change of trends: 2.53, P < .001). Conclusions: This initiative demonstrates the effectiveness of multidisciplinary collaborative quality improvement in advancing agreed-upon cardiotomy suction practices without negatively impacting clinical outcomes.

Report from AmSECT's International Consortium for Evidence-Based Perfusion: American Society of Extracorporeal Technology Standards and Guidelines for Perfusion Practice: 2013.

UNLABELLED: One of the roles of a professional society is to develop standards and guidelines of practice as an instrument to guide safe and effective patient care. The American Society of Extracorporeal Technology (AmSECT) first published its Essentials for Perfusion Practice, Clinical Function: Conduct of Extracorporeal Circulation in 1993. The International Consortium for Evidence-Based Perfusion (ICEBP), a committee within AmSECT, was tasked with updating this document in 2010. The aim of this report is to describe the method of development and content of AmSECT's new professional standards and guidelines. The ICEBP committee independently evaluated and provided input regarding the current "Essentials and Guidelines." Structural changes were made to the entire document, and a draft document was developed, presented, and circulated to the AmSECT Board of Directors and broader membership for comment. Informed by these reviews, a revised document was then presented to the Society for a membership vote. The final document consists of 15 areas of practice covered by 50 Standards and 38 Guidelines (see Appendix 1) with the first standard focusing on the development of institutional protocols to support their implementation and use. A majority of the membership voted to accept the document (81.2% of the voting membership accepting, 18.8% rejecting). After an audit of the balloting process by AmSECT's Ethics Committee, the results were reported to the membership and the document was officially adopted on July 24, 2013. The Standards and Guidelines will serve as a useful guide for cardiac surgical teams that wish to develop institution-specific standards and guidelines to improve the reliability, safety, and effectiveness of adult cardiopulmonary bypass. The ICEBP recognizes that the development of a Standards and Guidelines statement alone will not change care. Safe, reliable, and effective care will be best served through the development and implementation of institutional protocols based on these standards. AmSECT's Standards and Guidelines for Perfusion Practice reflect the changing landscape of our profession as we work toward a safer and optimal provision of cardiopulmonary bypass for all our patients as well as a work environment that is supportive of delivering this care. KEYWORDS: standards, guidelines, cardiopulmonary bypass, perfusion, cardiac surgery.

Validation of a perfusion registry: methodological approach and initial findings.

Although regional and national registries exist to measure and report performance of cardiac surgical programs, few registries exist dedicated to the practice of cardiopulmonary bypass (CPB). We developed and implemented a cardiovascular perfusion registry (Perfusion Measures and outcomes [PERForm] Registry) within the structure of the Michigan Society of Thoracic and Cardiovascular Surgeons (MSTCVS) to improve our understanding of the practice of CPB. The PERForm Registry comprises data elements describing the practice of CPB. Fourteen medical centers within MSTCVS have voluntarily reported these data on procedures in which CPB is used. We validated the case count among procedures performed between January 1, 2011 to December 31, 2011, and validated the values among 20 fields at three medical centers. We queried database managers at all 14 medical centers to identify the infrastructure that contributed to best overall data collection performance. We found that 98% of all records submitted to the PERForm and 95% of those submitted to the Society of Thoracic Surgeons (STS) matched. We found quite favorable agreement in our audit of select fields (95.8%). Those centers with the most favorable performance in this validation study were more likely to use electronic data capture, have a perfusionist as the STS database manager, and have involvement of the STS database manager in the PERForm or STS databases. We successfully and accurately collected data concerning cardiovascular perfusion among 14 institutions in conjunction with the MSTCVS. Future efforts will focus on expanding data collection to all MSTCVS participating institutions as well as more broadly outside of Michigan.

Phylogeny of Crataegus (Rosaceae) based on 257 nuclear loci and chloroplast genomes: evaluating the impact of hybridization.

BACKGROUND: Hawthorn species (Crataegus L.; Rosaceae tribe Maleae) form a well-defined clade comprising five subgeneric groups readily distinguished using either molecular or morphological data. While multiple subsidiary groups (taxonomic sections, series) are recognized within some subgenera, the number of and relationships among species in these groups are subject to disagreement. Gametophytic apomixis and polyploidy are prevalent in the genus, and disagreement concerns whether and how apomictic genotypes should be recognized taxonomically. Recent studies suggest that many polyploids arise from hybridization between members of different infrageneric groups. METHODS: We used target capture and high throughput sequencing to obtain nucleotide sequences for 257 nuclear loci and nearly complete chloroplast genomes from a sample of hawthorns representing all five currently recognized subgenera. Our sample is structured to include two examples of intersubgeneric hybrids and their putative diploid and tetraploid parents. We queried the alignment of nuclear loci directly for evidence of hybridization, and compared individual gene trees with each other, and with both the maximum likelihood plastome tree and the nuclear concatenated and multilocus coalescent-based trees. Tree comparisons provided a promising, if challenging (because of the number of comparisons involved) method for visualizing variation in tree topology. We found it useful to deploy comparisons based not only on tree-tree distances but also on a metric of tree-tree concordance that uses extrinsic information about the relatedness of the terminals in comparing tree topologies. RESULTS: We obtained well-supported phylogenies from plastome sequences and from a minimum of 244 low copy-number nuclear loci. These are consistent with a previous morphology-based subgeneric classification of the genus. Despite the high heterogeneity of individual gene trees, we corroborate earlier evidence for the importance of hybridization in the evolution of Crataegus. Hybridization between subgenus Americanae and subgenus Sanguineae was documented for the origin of Sanguineae tetraploids, but not for a tetraploid Americanae species. This is also the first application of target capture probes designed with apple genome sequence. We successfully assembled 95% of 257 loci in Crataegus, indicating their potential utility across the genera of the apple tribe.

Population genetic structure of diploid sexual and polyploid apomictic hawthorns (Crataegus; Rosaceae) in the Pacific Northwest.

Polyploidy and gametophytic apomixis are two important and associated processes in plants. Many hawthorn species are polyploids and can reproduce both sexually and apomictically. However, the population genetic structure of these species is poorly understood. Crataegus douglasii is represented exclusively by self-compatible tetraploid pseudogamous apomicts across North America, whereas Crataegus suksdorfii found in the Pacific Northwest is known to include self-incompatible diploid sexuals as well as polyploid apomicts. We compare population structure and genetic variability in these two closely related taxa using microsatellite and chloroplast sequence markers. Using 13 microsatellite loci located on four linkage groups, 251 alleles were detected in 239 individuals sampled from 15 localities. Within-population multilocus genotypic variation and molecular diversity are greatest in diploid sexuals and lowest in triploid apomicts. Apart from the isolation of eastern North American populations of C. douglasii, there is little evidence of isolation by distance in this taxon. Genetic diversity in western populations of C. douglasii suggests that gene flow is frequent, and that colonization and establishment are often successful. In contrast, local populations of C. suksdorfii are more markedly differentiated. Gene flow appears to be limited primarily by distance in diploids and by apomixis and self-compatibility in polyploids. We infer that apomixis and reproductive barriers between cytotypes are factors that reduce the frequency of gene flow among populations, and may ultimately lead to allopatric speciation in C. suksdorfii. Our findings shed light on evolution in woody plants that show heterogeneous ploidy levels and reproductive systems.

Evidence for genetic association between East Asian and western North American Crataegus L. (Rosaceae) and rapid divergence of the eastern North American lineages based on multiple DNA sequences.

Phylogeographic relationships were constructed for 72 Old and New World Crataegus species using combinations of four chloroplast and up to five nuclear regions. Maximum parsimony, maximum likelihood, and Bayesian results yield consistent relationships among major lineages. The close associations of the East Asian and western North American species point toward ancient trans-Beringian migrations. Relationships among eastern North American species are poorly resolved and few groups are identified that are congruent with existing classifications. Scant variation and short internal branches among these species suggest rapid divergence associated with polyploidy and hybridization. Incongruence between the chloroplast and nuclear data, and morphology suggest hybrid origins of three species from an extinct European lineage (the male parent) and three different North American female parents. Europe and eastern North America are suggested as the most recent common areas for Crataegus; at least four dispersal events are inferred to explain the present distribution of the genus.