Abstract
The development of models for risk stratification in cardiac surgery goes back a number of years. In 1989, the Society of Thoracic Surgeons (STS) created the first database version for use in the USA. In the year 2005 alone, the data from 234,532 operations were recorded in a structured way by 654 participating institutes. The value of these collected data is described by Ferguson (Ferguson, Dziuban, Edwards, Eiken, Shroyer, & Pairolero, 2000): “Because of their collective efforts, the goal to establish the STS National Data Base as a ‘gold standard’ worldwide for process and outcomes analysis related to cardiothoracic surgery is becoming a reality.” The number of research projects deriving from this is correspondingly large (The Society of Thoracic Surgeons National Database Access and Publications Task Force, 2006).
Key Terms in this Chapter
Scoring Model: A scoring model is a mathematical model that forms the basis for risk stratification. Scoring models generally arise from clinical studies in which statistical methods (e.g., chi square test, ROC curve) are applied to the data of a relevant population in order to identify parameters with a significant influence on the particular issue. Scoring models are either logistic models, in which the coincidence of several parameters leads to a higher risk, or summary models, in which the risks are simply added together. Commonly used risk models are EuroSCORE, Parsonnet, Ontario Province Score, and STS.
Cardiac Register: Database for gathering and evaluating structured data about cardiac surgical interventions. Cardiac registers are operated by private and public organisations, and serve as a basis for the determination of outcome data and for scientific studies (clinical trials), and for the construction of scoring models.
Risk Stratification: The estimation based on significant risk factors of the risk of a disease progressing or of a disease or operation leading to complications or death. One or several endpoints can be estimated (morbidity).
VLAD (Variable life adjusted display or variable life adjusted diagram): The VLAD is a graphical representation of the result quality for a selected number of cardiac surgical interventions. The interventions are listed chronologically on the x-axis (1 – n). The result quality of the interventions is added together on the y-axis, a positive outcome causes the curve to rise by the risk-adapted expected mortality and a negative outcome causes it to fall by (1 – risk-adapted expected mortality). In this way, the expected risk of the intervention is taken into account. If there is a high degree of uniformity regarding the average risk, the graph can be expected to oscillate about the zero axis. Better results than predicted are recognised as a climbing graph.
Result Quality: The result quality is defined as the ratio of the outcome to the risk-adapted expected mortality. The observed mortality, as a given (observed) value within a sample, is constant. Since different scoring models calculate different predicted values for the same population, the result quality may be observed and compared only in the context of the underlying scoring model. result quality = observed mortality [%] / risk-adapted expected mortality [%]
The Austrian Cardiac Project: The Austrian Cardiac Project had the task of creating an Austria-wide heart register system consisting of a central database and distributed clients that would gather and analyse the data. Under the leadership of the corresponding author, the basis for this was constructed during the period November 2004 to February 2006. Since March 2007, the system is in use in 2/3 of all the Austrian hospitals where cardiac surgical interventions are performed. The Cardiac Project was carried out with the financial support of the Austrian Research Promotion Agency (FFG) and the Tyrolean Future Foundation, supported under the competence centre hitt – health information technologies tirol.
Outcome: The outcome is the result of an intervention, either referred to an individual intervention or to a number of interventions. In cardiac surgery, the 30-day mortality is the predominant characteristic for the outcome. This is independent of the individual risk of the intervention and states whether the patient is alive or not on the 30 th day after the operation. In addition to the simple 30-day mortality, the in-house mortality is frequently used as an outcome characteristic: in contrast to the simple 30-day mortality, it is determined whether the patient has already left the facility on the 30 th day or is in an intensive care unit. In the latter case, monitoring of the mortality is prolonged until the patient has left the facility or the ICU.