Abstract-Extensive evidence is available that cardiovascular structure and function, along with other biological properties that span the range of organism size and speciation, scale with body size. Although appreciation of such factors is commonplace in pediatrics, cardiovascular measurements in the adult population, with similarly wide variation in body size, are rarely corrected for body size. The patient is a very tall 23-yearold competitive rower with a height of 203 cm and weight of 100 kg referred to the clinic for preparticipation athletic screening. He has never experienced syncope, palpitations, or chest pain during exertion and has no significant past medical history, but he occasionally feels "light-headed" at the end of an exhaustive competitive workout. He has no family history of sudden cardiac death or of premature cardiovascular disease. He is actively training 5 to 6 hours per day, 6 days per week in preparation for the upcoming Olympic Games. The examination is remarkable only for a soft systolic ejection murmur, cardiomegaly, and a third heart sound. An ECG is ordered, which is remarkable for sinus bradycardia, a 15-mV R wave in lead aVL, and R-wave voltage in lead V 5 plus S-wave voltage in lead V 1 totaling 46 mV. On a follow-up echocardiogram, septal and posterior wall thicknesses of 14.5 mm are observed with a left ventricular (LV) internal dimension in diastole of 53 mm. No significant obstructive LV outflow pattern is present, and wall thickness appears symmetrical. On the basis of current echocardiographic criteria, this patient is in the "gray zone" between physiological and pathological hypertrophy. His nonspecific symptoms and lack of other contributing history add to the ambiguity in diagnosis.
Clinical Vignette No. 2:The patient is a 66-year-old woman who has a height of 155 cm and a body mass of 49 kg.She has a history of hyperlipidemia and abdominal aortic aneurysm. She comes to the clinic for her yearly ultrasound follow-up, which shows a maximum aneurysm diameter of 50 mm. She is in a "gray zone" in which neither surgical correction nor watchful waiting is definitively indicated.Considerable evidence is available that biological processes from metabolic enzyme activity 1 to plant and animal metabolic rates 2-4 to cancer metastasis 5 scale with body size over the entire range of organism size and speciation. Cardiovascular structural and functional variables also scale with body size. Compare, for instance, the blue whale, which has a heart mass of 600 kg and a resting heart rate of 6 bpm, with the smallest mammal, the shrew, which has a heart mass of 12 mg and a resting heart rate of up to 1200 bpm. 6 Despite the clear relationship between body size and cardiovascular dimensions and functional parameters, the practice of scaling cardiovascular measurements is poorly applied in adult clinical cardiology. This contrasts with pediatric medicine, in which measurements are universally indexed to body size. The intuitive idea that body growth implies a greater need for scaling in pe...