A multicenter study using stress echocardiograms from six institutions found an average kappa coefficient of 0.48 between institutions and percentage agreement was highest in cases of three-vessel disease or left anterior descending artery disease \cite{Peteiro_2006} (agreement lower when blinded? Go back and read the discussion).
In a small prospective study, interpretation of dobutamine stress echocardiography has been found to be affected by low image quality, a wall motion abnormality which is not severe, and a low peak rate-pressure product resulting in low inter-rater agreement \cite{Hoffmann1998}.
Previous studies have found a suggestive clinical history to significantly bias interpretation of electrocardiograms among physicians (van den Berge). Multiple previous studies have shown that cognitive bias is associated with therapeutic or management errors (Saposnik).
Harmonic imaging has also improved interpreter agreement and studies with poor image quality have previously been noted to have more inter-observer variability \cite{Hoffmann_2002}.
Other refs to look up:
Croskerry P. The importance of cognitive errors in diagnosis and strategies to minimize them. Acad Med. 2003;78(8):775–80. doi: 10.1097/00001888-200308000-00003.
Redelmeier DA, Shafir E. Medical decision making in situations that offer multiple alternatives. JAMA. 1995;273(4):302–5. doi: 10.1001/jama.1995.03520280048038.