Early Lengthening Research Articles

Temporal pattern of regional left ventricular wall motion in patients with segmental early relaxation

AbstractThe purpose of this investigation was to describe the temporal pattern of regional left ventricular (LV) wall motion in patients with segmental early relaxation (SER). Segmental early relaxation was demonstrated angiographically in seven patients undergoing diagnostic cardiac catheterization because of chest pain. In all patients, early relaxation of only the anterolateral wall was observed. The temporal pattern of regional wall motion was assessed from ventriculograms, obtained in the right anterior oblique projection, by measuring the lengths of the anterolateral minor axis chord and the corresponding diaphragmatic minor axis chord. The onset of lengthening of the anterolateral chord preceded that of the diaphragmatic chord by 110 ± 10 msec. Maximal shortening of the anterolateral chord during systole was 43 ± 4% and was coincident with a 32 ± 4% shortening of the diaphragmatic chord. During early relaxation, shortening of the anterolateral chord diminished to 17 ± 4% (P <.01); and was coincident with a 35 ± 4% shortening of the diaphragmatic chord (P <.05). Early relaxation of the anterolateral wall was followed by a transient augmentation of shortening of the anterolateral chord to 29 ± 3% (P <.001), whereas shortening of the diaphragmatic chord diminished to 32 ± 4%. Subsequently both chords returned to their initial end‐diastolic lengths. These preliminary observations indicate that early lengthening of the anterolateral segment is followed by a transient rebound of shortening which was only present in the segment that manifested early relaxation.

Ionic and electrical effects of ouabain on isolated rabbit hearts

The effects of ouabain (0.5 × 10 −6 m) on the intracellular ionic concentrations and the transmembrane potential were studied. Isolated rabbit hearts were perfused at 33°C and constant coronary flow. Krebs solution containing [ 14C]inulin was used to measure the extracellular space (ECS). The cell Na and K content were determined after 10 and 60 min perfusion with ouabain. The membrane potential was measured throughout the experiment. Ouabain produced a decrease in ECS and cell potassium ([K] i) and an increase in intracellular sodium ([Na] i) and water. There was a time lag between the change in [Na] i and the change in [K] i. A positive inotropic effect occurred during the first 10 to 20 min of perfusion with ouabain. The resting potential (RP) and action potential amplitude (APA) decreased with a similar time course, reaching values of 63 and 55% of the control by the end of the 60 min period. The maximum rate of depolarization ( V ̇ max ) decreased after 10 min, levelling off at about 50% of the control at 30 min. An early lengthening of the plateau was followed by progressive shortening of the action potential. It is postulated that the depolarization is due to inhibition of an electrogenic ionic pump, that the changes in APA are due to ionic shifts and depolarization, and that the values of V ̇ max are largely determined by shifts in the h ∞ curve.