Body Weight and Mortality
The relationship of body weight to mortality has been clouded by inclusion in some studies of large numbers of smokers, whose relatively lower body weight and higher mortality dampen the otherwise direct linear relationship between overweight and mortality.
The current report examines the relationship between body mass index (BMI) and mortality across age groups. The population studied were participants in the American Cancer Society's Cancer Prevention Study, consisting of 62,116 men and 262,019 women who had never smoked, had no history of stroke, heart disease, or systemic cancer, and had no history of recent unintentional weight loss. Follow-up extended for 12 years.
There was a direct relationship between BMI and cardiovascular disease mortality, as well as overall mortality in both men and women. In the 30-44 age group, women and men sustained an 8-10% increased mortality, respectively, for each increased BMI increment of 1. The deleterious effect extends over the age range 30-74, although with advancing age, the effect of increased BMI wanes. There was a slightly lower risk for women than men at the same BMI. The authors conclude that their data analysis is supportive of the healthy weight ranges as proposed in the 1995 Dietary Guidelines for Americans (Government Printing Office Publication #1996-402-519).
Stevens J, et al. N Engl J Med 1998; 338:1-7.
Clinical Scenario: The ECG in the figure was obtained from a 50-year-old man who presented to the office for evaluation of atypical chest "tightness" over the preceding few months. In view of the fact that the serum potassium was normal at the time this ECG was recorded, how would you interpret this tracing?
Interpretation: The rhythm is sinus at a rate of about 65 beats/min. All intervals are normal. The mean QRS axis is approximately +45°. There is no evidence of chamber en-largement. The finding of note on this tracing relates to assessment of ST segments and T wave appearance. Specifically, ST segments are flattened in many leads and T waves are peaked. The point to emphasize is that this tracing should not be interpreted as a normal ECG. Admittedly, the abnormalities are subtle-yet they are definitely present.
Normally, ST segments in most leads manifest a slightly rounded and upward sloping concavity, blending almost imperceptibly into an upright T wave. This is not the case in the figure. Instead, there is straightening of ST segments--especially in leads II, III, aVF, V3, V4, and V5. This subtle finding may be a nonspecific indicator of underlying coronary disease. Unfortunately, many other entities also produce a similar ECG appearance (ergo designation of ST segment flattening as a "nonspecific" change).
T wave peaking is seen in virtually the same leads on this tracing that show ST segment flattening. The presence of T wave peaking should always suggest the possibility of hyperkalemia. However, serum potassium is normal in this case. T wave peaking is also commonly seen as a normal repolarization variant in otherwise healthy individuals. Distinction from the T wave of hyperkalemia is usually suggested by history (that the patient is healthy and asymptomatic) and the findings that with a repolarization variant the peak of the T wave tends to be rounded, the ascending and descending limbs of the T wave are not as symmetric, and the base of the T wave is wider. A serum potassium level should always be checked if the diagnosis is in doubt.
Not nearly as well appreciated is the fact that T wave peaking may sometimes reflect ischemia. None of the standard leads on a 12-lead tracing directly view the posterior wall of the left ventricle. Posterior wall involvement must, therefore, be viewed indirectly on the ECG--by assessing for changes that occur in anterior leads (i.e., leads V1, V2, and V3) that reflect a "mirror image" view of electrical events in the posterior wall. Instead of the usual manifestation of ischemia (i.e., deep symmetric T wave inversion), posterior ischemia may, therefore, produce symmetric T wave peaking.
Thus, in this patient with a history of chest discomfort, the finding of ST segment flattening in many leads in conjunction with T wave peaking should suggest the possibility of ischemia. The presence of coronary disease was confirmed with further testing.
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