International registries have identified the NYHA/WHO functional class as the fundamental prognostic factor for risk stratification in Pulmonary Arterial Hypertension (PAH).
Indeed, which class a clinician decides to assign a patient to will depend on the clinicians interpretation of what construes "ordinary physical activity" and "slight" and "marked" limitations. The widely accepted criteria of the NYHA/WHO classification, when have been subjected to the systematic validity testing demonstrated low reproducibility and low discrimination. However, simple modifications to this scale, by introducing more objective measures, such as direct measurement of oxygen consumption, may increase reproducibility while maintaining the strong prognostic relevance. The aim of the present study is to make a reliable, reproducible assessment of functional capacity in a PAH derivation cohort relative to "ordinary physical activity" to standardize daily activities according to the expected METS (metabolic equivalent) required for each specific class.
Ordinary activities considered will be measured by oxygen consumption with K5 Wearable Metabolic Technology and used to classify the patients in the four ranks. This will allow us to build an Ordinary Activity Metabolic Scale. For every given "ordinary physical activity" provided for NYHA/WHO classification, the measured METS from the derivation cohort will be reported.
To test the hypothesis that such a standardized NYHA/WHO functional assessment will improve the prediction of clinical worsening, we will evaluate both the new standardized NYHA/WHO classification and the commonly used one in a validation cohort of 150 PAH patients from 3 different referral centers. The prognostic relevance of the two NYHA/WHO classification methods will be compared by the c-statistic.
We believe that our Ordinary Activity Metabolic Scale for PAH patients may represent an acceptable tradeoff between precision and complexity.
Transforming clinical data into useful clinical scales is one of the most challenging problems in clinical research and daily practice. For a measurement scale to be valuable, it should be reproducible from one observer to another, and it should be reasonably well correlated with a relatively objective standard. Several systems have been proposed for categorizing the degree of cardiovascular disability so that one patient can be compared with another and so that one patient's status can be monitored over time.
The most often used classification system, formulated by the Criteria Committee of the New York Heart Association and endorsed by the WHO, is routinely applied in PAH and classifies patients according to the degree of symptoms resulting from ordinary or less-than-ordinary activity.
As already noted by Goldman L. in early 80¿s (Comparative reproducibility and validity of systems for assessing cardiovascular functional class; advantages of a new specific activity scale. Circulation 1981;64:1227), the widely accepted criteria of the New York Heart Association, when have been subjected to the systematic reproducibility and validity testing that would normally be required of any clinical assay or diagnostic test, demonstrated low reproducibility and low discrimination and calibration.
However, this widely adopted system has been used to categorize the functional status of patients in all PAH clinical trials and in daily clinical practice, despite several information are nowadays available concerning how often clinicians would disagree in their definitions of "ordinary" or in their assessments of a patient's functional classification.
The popularity of the New York Heart Association classification system is at least partly based on its simplicity. Any system that might replace this standard should be more accurate without being appreciably more complex. We believe that our Ordinary Activity Metabolic Scale for PAH patients, which is based on the metabolic requirements of the same types of activities that are included in the NYHA/WHO routine assessments, may represent an acceptable tradeoff between precision and complexity. The Ordinary Activity Metabolic Scale may also be administered by a non physician, and its questions will be no more time consuming than those used to estimate the traditional NYHA/WHO classification.
Considering the important role of the NYHA/WHO classification for patients prognostic evaluation and treatment prescription, if further trials at other institutions substantiate our experience, the Ordinary Activity Metabolic Scale or its future modifications might appropriately replace the NYHA/WHO system for PAH patients in both clinical practice and clinical trials, improving precision and accuracy in patients¿ management and in research findings.