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PRACTICUM LIBRARY. Dual process thinking for clinicians

Contextualizing formal knowledge to particular clinical situations improves diagnostic accuracy

Clinicians tackle clinical reasoning by using intuition (heuristics) and analytical thinking in a two step decision-making process.

Cognitive psychology shows that expert clinicians make a medical diagnosis through a two-step process: 1) generating a list of possible diagnoses quickly and intuitively, drawing on previous experience; 2) testing the hypotheses and estimating the probability of each possibility by anchoring and adjusting. Experts distinguish themselves through their ability to mobilize experiential knowledge in a manner that is content specific. American article Diagnostic reasoning in cardiovascular medicine points out vertical integration of formal knowledge with clinical experience as the best strategy to improve diagnostic accuracy".

Madrid - February 24, 2022. Experience is clearly the best teacher, but some educational approaches have been shown to make a difference when it comes to clinical reasoning and medical error. A recent article signed by the US cardiologist John E Brush, along with award-winning teachers Jonathan Serbino and Geoffrey R Norman, both from McMaster University (Canada), explores the evidence base about diagnostic reasoning in the context of cardiovascular disease. "An accurate and timely diagnosis —the authors state— is of paramount importance for patients with heart disease".  Yet the process of diagnostic reasoning is underemphasized in cardiology training and continuing medical education.

Very few studies have examined how cardiovascular diagnostic strategies affect decisions about patients’ management, outcomes, and even costs. One challenge could be an ST elevation myocardial infarction, for which a correct and prompt diagnosis is critical for triggering emergency life saving interventions. For the purpose of this review, Dr Brush and his colleagues performed a broad, systematic search using the term “diagnostic reasoning” in Google Scholar and PubMed in all date ranges and with preference to experimental studies. This led them to confirm the double process theory as the most solid theory to explain clinical reasoning. They also questioned heuristics to be the most frequent cause of biases. 

Clinicians tackle clinical ambiguity and diagnostic uncertainty by using intuition and analytical reasoning. They first rapidly generate hypotheses and then they test them. According to the dual process theory, system 1 thinking is triggered by an automatic and effortless association between the patient information and an example stored in long term memory. System 2, on the other hand, is based on analysis, reflection and logical rules. Some authors have promoted the idea that errors occur because of shortcuts, which are used by system 1 thinking and not corrected by system 2, but Dr Brush maintains most of the evidence suggests that relying less on system 1 and more on system 2 does not lead to better outcomes.

Actually, in one observational study cited in this paper, if the clinician had the diagnosis in mind early on, the diagnostic accuracy was 95%; if not, the diagnostic accuracy fell to 25%. The defining feature of the master diagnostician is not possession of a generalizable diagnostic skill, but rather it is his or her ability to mobilize and use content specific knowledge from past experience. According to the article, “intuition would be nothing more and nothing less than recognition”. Expert clinicians know intuitively that an acute myocardial infarction is more common than an aortic dissection on the basis of an intuitive sense of the prevalence of a diagnosis based on the number of past encounters.

The accuracy of the diagnostic process is dependent on the clinician’s experiential knowledge. Students lack experience and rely on biomedical knowledge to make causal connections to formulate diagnostic hypotheses. As trainees gain experience, their diagnostic competence matures. This means, with clinical experience (real or simulated) the ability of a novice to mobilize appropriate knowledge improves, which might be explained by the development of illness scripts, prototypes, phenotypes, exemplars, and other possible knowledge structures. An optimum experiential knowledge base is analogous to a large file cabinet filled with many examples, filed according to diagnostic category.

When the patient’s presentation is ambiguous, experienced clinicians generate a differential diagnosis. Several studies have found that expert diagnosticians have between three and five diagnoses in mind very quickly during the initial encounter with a patient. Then, they begin testing hypotheses, starting with the most likely ones. Bayesian reasoning provides a mathematical method for updating a baseline probability estimate on the basis of the strength of new information, but people also use learned rapid mental shortcuts, such as anchoring and adjusting, which describes how someone subjectively estimates the baseline probability of an event and then adjusts the probability estimate.

How to improve diagnostic accuracy

Effective educational strategies are those that focus on the acquisition and mobilization of knowledge, both experiential and formal. Rather than attributing diagnostic error to biases or flawed cognitive processes, some cognitive psychologists have argued that diagnostic error is more commonly due to a problem to mobilize necessary knowledge, or due to knowledge deficits, and this ability improves with experience. Rapid and intuitive recognition of patterns is an important part of the diagnostic process, particularly in cardiology, and constraining this activity does not seem to be a good strategy. The diagnostic process, however, does allow the opportunity to reflect on the particular features of the diagnostic encounter.

Reflecting on the concordant and discordant features between the patient and the various diagnostic hypotheses offers an opportunity for mid-course correction. Deliberate reflection enables clinicians to overcome distracting and misleading features of a case but requires that the clinician have adequate experience and sufficient clinical knowledge about the diversity of diagnostic features. Other remedies? Checklist and computerized decision support programs tend to be more effective for junior clinicians and cognitive forcing strategies seem to the authors as nonsense because “humans are not capable of consciously recognizing unconscious biases”.

True expertise in cardiovascular diagnosis, however, resides in an ability that is learnt through experience and years of deliberate practice and reflection. The diagnostic expert uses experiential knowledge gained in the context of training in clinical rotations and specialized practice. Vertical integration of the basic sciences with clinical experience can create cognitive conceptual coherence that seems to improve diagnostic reasoning. This strategy may facilitate the formation of illness scripts and make knowledge more accessible at the time of a diagnostic encounter. 

Greater awareness of the diagnostic process and attention to the sources of diagnostic error could help clinicians to make the most of their experience, purposefully seek feedback, and be more intentional about avoiding diagnostic error. 



Brush JE Jr, Sherbino J, Norman GR. Diagnostic reasoning in cardiovascular medicine. BMJ. 2022 Jan 5;376:e064389. 

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