New criteria to increase the reliability of systolic time intervals in left bundle branch block and right ventricular pacing.

We measured the systolic time intervals (STI) in 14 patients (pts) with intermittent left bundle branch block (LBBB) in order to find correlations and comparisons in their values which might pertain to the individual patients, with (b) and without (a) LBBB. QS2I, PEP and the PEP/LVET ratio increased significantly (b) while the LVET I did not change. STI correlation was significant and improved further when the QS2 (b) was corrected by subtracting from it the QRS prolongation (b) in msec. All 7 pts with a PEP/LVET ratio (b) greater than 0.65 had an (a) ratio greater than 0.42 (normal limits for our laboratory), sensitivity 100%. Six of 7 patients with a PEP/LVET (b) less than 0.65 had an (a) ratio less than 0.42 (specificity 87.5%). For the individual patient with LBBB his STI can be quite accurately assessed by subtracting from his QS2 (b) the prolongation of the QRS (b) greater than 80 msec the length of the normal QRS duration. The above data were prospectively evaluated in 10 pts to whom intermittent right ventricular pacing was applied. We found that the correction of the QS2 interval for QRS prolongation permitted a very reliable calculation of the STI.

The QS2/QT ratio as an index of appropriate left ventricular response to autonomic and inotropic stimuli.

Dissociation between duration of electrical and mechanical systole has been seen with increase of myocardial shortening velocity or adrenergic activity. We found a decrease of the QS2/QT ratio after exercise in 10 pts with semisitting bicycle maximal exercise test and a normal radionuclide angiogram. No change was seen in 9 patients with a normal study with beta blockade, and in pts with a abnormal radionuclide test, without beta blockade (11 pts). In 19 normal active individuals, a significant QS2/QT decrease (p less than 0.001) was seen after a submaximal exercise treadmill test, which was inhibited by beta blockade. We believe that QS2/QT diminution is suggestive of an increase of the inotropic state of the left ventricle with exercise, produced through adrenergic stimulation. It is not seen either when an ischemic left ventricle cannot adequately respond to exercise or after beta blockade.

Cardiac function at treadmill exercise in various age groups.

We compared the response to a modified Bruce treadmill exercise (EX) protocol lasting 7 min in 5 groups of male individuals free of clinical heart disease: I (age less than 35 years, N = 12), II (age 35-44 years, N = 10), III (age 45-54 years, N = 13), IV (age 55-64 years, N = 13) and V (age greater than 65, mean 70.35 +/- 4.67 years, N = 20). The following data were compared: (a) Heart rate (HR), systolic (SBP) and diastolic blood pressure (DBP); resting (R) and their % changes at pre-EX standing and at 3, 6, 7 min, immediately and 2 and 4 min after EX (where EX is a relatively low grade of exercise). (b) The R QS2/QT and PEP/LVET ratios and their % change immediately and 4 min after EX. Resting and peak SBP was higher in groups IV and V. The various groups responded in a similar way to EX. The only significant difference was that the older age group (V) showed on the whole an increase in DBP with EX while groups I-III showed a decrease and group IV no change. This finding may reflect a lesser diminution in vascular resistance with EX in old age. However, inotropic and chronotropic reserves appear similar to those of younger individuals.