Technical Aspects for Acquisition of Systolic Time Intervals Especially for Determination of the Pre-ejection Index

In numerous publications in the last two decades it has been demonstrated that systolic time intervals (STI) could be of use in evaluating cardiovascular function and observing trends by a relatively simple procedure. The prior investigations were, in the main, by Blumberger, Weissler, and Spodick. The task, now, is to smooth the way for the general introduction of STI to routine cardiovascular examinations, which require: 1) A simple technique for obtaining good carotid pulse tracings; and 2) Concentration on the comparison of two or more measurements and evaluation of differences in the trends of these measurements. This is to be done mainly by determination of the preejection index (PI). PI is a comparative measure of the preejection period (PEP) at different preloads resulting from upright and supine postures (1, 2). PI, the ratio of PEP (upright) and PEP (supine), can diminish the influence of systematic errors: $${\rm{PI = }}{{{\rm{PEP}}\,\left( {{\rm{upright}}\,{\rm{posture}}} \right)} \over {{\rm{PEP}}\,\left( {{\rm{supine}}\,{\rm{posture}}} \right)}}$$ With an electrocardiogram (ECG), only the recording of the onset of the carotid pulse is necessary. Recording the second heart sound may be avoided because there is generally no difference in the pulse wave transmission time (PTT) in the upright and supine postures. It is not necessary to select the exact Q of the ECG. The point of reference may be a well-defined peak or zero passage of the QRS complex because, by the above ratio, equal differences in nominator and denominator are virtually eliminated.