Letiters to the Editor

To the Editor: This letter is a plea to curators of rat colonies to supply us with a basic description of the resting heart rates and body weights of animals within your colonies. The urgency of this request is briefly summarized as follows. The results of recent studies of colonies of animals specially bred to become hypertensive have suggested that increased heart rate is an important factor in the genesis of the observed hypertension. The animals with spontaneous hypertension have resting heart rates which are significantly greater than the resting heart rates seen in other colonies of rats that do not become hypertensive. The observations are complicated, however, by the fact that normotensive control animals have body weights that are greater than the spontaneously hypertensive animals, and the results must be interpreted according to the dictum that heart rate increases with decreasing body size. There are little data available that describe resting heart rates in rats as a function of age and mature body size. This is a request, then, to all scientists currently using rat colonies to send to us information describing: (1) the genetic background of their colony; (2) resting heart rate, body weight, and age of an mal when the data were collected, for as many different ages as possible; (3) an estimate of the normal systolic blood pressure in the mature animal; and (4) comments on any extenuating circumstances that might prevent the data from being typical, such as environmental stress, unusual temperatures, or malnutrition. This information is greatly appreciated and will hopefully be used to maximum advantage. Two final comments: (1) Readers interested in helping but not having active colonies, please pass this request along to those who can respond. (2) All responders will be sent copies of any final compilations. THOMAS G. COLEMAN, PHi.D. Associate Professor The University of Mississippi Medical Center 2500 North State Street Jackson, Mississippi 39216 I believe that some of the "intermediate" H-V intervals (measured to the onset of the QRS complex in at least three surface leads) do not necessarily indicate an associated conduction delay through the right branch. We have recently been evaluating the usefulness of close (1 mm apart) bipolar (filtered) electrograms from a stable position in the right ventricular apex (RVA).5 When bundle-branch block was not present, the H-RVA interval gave a measure of conduction time through His bundle, right branch, and that part of the ordinary ventricular