The field of heart transplantation continues to evolve, with major changes in allocation systems and the increasing use of extended-criteria donor hearts, including hearts from donation after circulatory death donors, hearts supported with ex-vivo perfusion, and hearts from hepatitis C viremic donors. The use of such non-traditional donor hearts has made transplantation available to a larger number of recipients, but the demand continues to outpace the supply. Given this persistent donor heart shortage, much attention has been paid to the topic of donor-recipient size matching. Prior studies have challenged traditional criteria for size matching, 1-3 while others have attempted to identify the optimal metric for matching donor and recipient heart size by comparing criteria, such as height, weight, body mass index (BMI), body surface area (BSA), and predicted heart mass (PHM). [4][5][6][7] This 36th annual adult heart transplant report is based on data submitted to the International Society for Heart and Lung Transplantation (ISHLT) Thoracic Organ Transplant Registry on 146,975 heart transplants in recipients of all ages (including 131,249 adult heart transplants)

This year marks the 50th anniversary of the first heart transplant, performed in 1967. Since then, and in particular since the introduction of cyclosporine immunosuppression in the 1970s, heart transplantation has grown worldwide. This 34th adult heart transplant report is based on data submitted to the International Society for Heart and Lung Transplantation (ISHLT) Registry on 135,387 heart transplants in recipients of all ages (including 120,991 adult heart transplants) through June 30, 2016. With each year's report we now also provide more detailed analyses on a particular focus theme. Since 2013, these have been donor and recipient age, retransplantation, early graft failure, indication for transplant, and in 2017, allograft ischemic time. Statistical methods Data collection, conventions and statistical methods National and multinational organ/data exchange organizations and individual centers submit data to the ISHLT

This 36 th adult lung and heart-lung transplant report summarizes data from 69,200 adult lung and 4,128 adult heart-lung transplants performed through June 30, 2018 and reported to the International Thoracic Organ Transplant Registry. With each year's report, we now provide more detailed analyses on a particular focus theme important to patient outcomes. Since 2013, these have been donor and recipient age; retransplantation; early graft failure; indication for transplant; allograft ischemic time; and multiorgan transplantation. Although widely accepted as critical to decision making at the time of receipt of an organ donor offer, there is surprisingly little literature outlining current practice and the impact of size (mis-)matching on outcomes. Hence, this year's report focuses on an overall theme of donor and recipient size matching. In addition to reporting donor and recipient height and weight difference for all adult lung and heart-lung transplant recipients stratified by transplant type (bilateral or single) and indication, we report historical trends and associations between size match and survival. The Registry's online slide sets include results from additional analyses and complementary information not included in this publication (see https:// ishltregistries.org/registries/slides.asp).

and reported to the Registry. In addition to reporting key data for donor and recipient characteristics, transplant events and recipient treatments and outcomes, this year's report focuses on an overall theme of primary diagnostic indications for transplant. We present data on the distribution of diagnostic categories (see Figure 1), demographics of patients with the different lung disorders leading to the need for transplant, associations of the diagnoses with outcomes, and other data of interest related to this topic. The Registry's online slide sets show results from additional analyses and complementary information not included in this publication (see http:// ishlt.org/registries/slides.asp?slides=heartLungRegistry/). Data collection, conventions and statistical methods National and multinational organ/data exchange organizations and individual centers submit data to the ISHLT Registry. Since the Registry's inception, 457 heart transplant centers, 1,2 253 lung transplant centers 3 and 177 heart-lung transplant centers have reported data to the Registry. In our estimation, data submission to the Registry represents approximately two thirds of the worldwide thoracic transplant activity. This report presents an overview of donor and recipient characteristics and outcomes. Additional and extended analyses are presented in the aforementioned online slide sets (5 separate slide sets supplement the report data, including: "Introduction"; "Overall Lung Transplant"; "Overall Heart-Lung Transplant"; "Adult Lung Transplant"; and "Adult Heart-Lung Transplant"). The ISHLT website also contains slide sets for previous annual reports. This article refers to specific online eSlides when particular data are discussed but not presented due to space limitations; eSlide numbers refer to the online Adult Lung Transplant slides (e.g., eSlide LU 3) or Adult Heart-Lung Transplant slides (e.g., eSlide HL 3), unless otherwise specified. The Registry website also provides spreadsheets of the data elements collected in the Registry. Registry data quality depends on center reporting accuracy and completeness. The Registry uses various quality control measures to ensure acceptable data quality and completeness before including the data in the main data set and using the data for analyses. Analytical conventions Unless otherwise specified, analyses of lung transplants do not include heart-lung transplants. Retransplant includes those with a previously reported transplant of the same

, and reported to the International Society for Heart and Lung Transplantation (ISHLT) Registry. In addition to reporting key data for donor and recipient characteristics, transplant events, and recipient treatments and outcomes, this year's report focuses on an overall theme of allograft ischemic time. We report geographic, center, donor, and recipient factors associated with variations in allograft ischemic time, associations of allograft ischemic time with outcomes, and other data of interest related to this topic. The Registry's online slide sets show results from additional analyses and complementary information not included in this publication (see http://ishlt. org/registries/slides.asp?slides=heartLungRegistry/). Statistical methods Data collection, conventions, and statistical methods National and multinational organ/data exchange organizations and individual centers submitted data to the ISHLT Registry. Since the Registry's inception, 472 heart transplant centers, 256 lung transplant centers, and 180 heartlung transplant centers have reported data to the Registry. 1-3 We estimate that data submission to the Registry represents approximately 75% of the worldwide thoracic transplant activity. This report presents an overview of donor and recipient characteristics and outcomes. Additional and extended analyses presented in 5 separate online slide sets ("Introduction," " Lung Overall," "Adult Lung Transplant," "Heart-Lung Overall," and "Adult Heart-Lung Transplant" http://ishlt.org/registries/slides.asp?slides=heartLungRegistry) supplement the report. The ISHLT Web site also contains slide sets for previous annual reports. This report references specific online e-slides when particular data are discussed but not shown because of space limitations. The e-slide numbers refer to the online adult lung, shortened to L(a), and adult heart-lung, noted as HL(a) transplant slides. The Registry Web site (http://ishlt.org/registries/heart LungRegistry.asp) provides detailed spreadsheets of the data elements collected in the Registry. The Registry requires submission of core donor, recipient, and transplant proce dure variables at baseline (i.e., around the time of transplantation) and at yearly follow-up, and these variables therefore have low rates of missingness. Nevertheless, data quality depends on the accuracy and completeness of reporting. Rates of missingness may significantly increase for Registry variables that depend on voluntary reporting.