A Totally Noninvasive Method for Obtaining Systolic Time Intervals in the Dog

SUMMARY Dogs (n = 21) were allotted to 3 groups for the purpose of obtaining and comparing systolic time intervals by conventional and echocardiographic procedures. The 1st group (n = 8 dogs) was anesthetized and catheterized in order to obtain aortic pressure pulses, and ultimately systolic time intervals, at different heart rates (hr) induced by the administration of small quantities (0.25 mg) of atropine. The dogs in the 2nd group (n = 8) were not anesthetized and were placed in left lateral recumbency for the purpose of acquiring echograms from which systolic time intervals were calculated. In the dogs in the 3rd group (n = 5), the 2 methods of acquiring the intervals, invasive and noninvasive, were performed simultaneously for purposes of comparison. In comparison of the 2 methods simultaneously, ejection times (et) differed on the average about 1.4% or 3.5 ms. Electromechanical systole (Q-S2) average differences were 1% or 0.5 ms, and the preejection period (pep) varied the most, with an average difference of 7% or 5 ms. Since some of the systolic time intervals are hr-dependent, systolic time indices were calculated for both the anesthetized and the unanesthetized groups. The anesthetized indices (I) were as follows: eti 290 (ms) — 0.70 (hr) [r = −0.95, P < 0.01]; Q-S2I = 346 (ms) — 0.75 (hr) [r = −0.88, P < 0.01]; and pepi = 65 (ms) — 0.03 (hr) [r = −0.23, P < 0.01]. Whereas the indices for the unanesthetized group were: eti = 222 (ms) — 0.55 (hr) [r = −0.93, P < 0.01]; Q-S2I = 282 (ms) −0.51 (hr) [r = −0.93, P < 0.01]; and pepi = 70 (ms) — 0.02 (hr) [r = −0.07, P < 0.01]. This noninvasive method utilizing echocardiography has been shown to provide a reliable means of acquiring systolic time intervals in the dog. These intervals have been shown to be useful in the assessment of ventricular function in man, and demonstrated differences between anesthetized and unanesthetized dogs, implying a similar potential in the canine species.