Clinicians explain the electrocardiographic findings of a patient by formulating hypothesis on the anatomical and physiopathological changes in the myocardium, and on how these changes lead to the sequence of depolarisation/repolarisation which produces the observed surface electrocardiogram.
This explanation, which we call the clinical model of the arrhythmia is formulated in qualitative and semiquantitative terms, such as ``refractory period is much increased in the ischemic area, thus leading to a region of function block, thus to reentry and to the ventricular tachycardia during the ischemic periods''. Whether refractory for a theoretically possible increase in refractory period, on the assumed or theoretically possible size of the ischemic region in the actual patient, given his (patient's) actual anatomic sizes of the heart structures, reentry would in fact take place is not known.