Enhancement of left ventricular contractility after opening of an arteriovenous fistula in dogs

The effect of opening and closing the infrarenal arteriovenous (A-V) fistula on left ventricular (LV) function was analysed in 12 anaesthetised dogs, instrumented with a micromano-meter and a pair of ultrasonic crystals for measurement of LV diameter (D). Plasma noradrenaline (NA) levels sampled from the right ventricular cavity were determined using a high-performance liquid chromatographic method. Immediately after opening of the A-V fistula, the peak LV pressure (P) decreased by 4.3 kPa from the control value of 14.4 kPa and returned to the control level within 30 s. End-diastolic diameter did not significantly change immediately after opening the fistula but then gradually augmented to 28.3 mm, at the stable stage 5 min later. End-systolic diameter was significantly reduced from 22.0 to 20.8 mm immediately after opening and remained reduced until the fistula was closed. The percentage shortening of the LVD increased from 17.1 to 20.1% with the initial fall in LVP, and continued to increase to 26.6% with subsequent enlargement of diameter. With closure of the fistula, a directionally opposite response was observed. The end-systolic P-D relation, obtained by superimposing the series of loops and plotting end-systolic pressure against end-systolic diameter, fell on the single function curve during the initial pressure change, and clearly shifted to the left during the stable stage of volume loading and returned to the control relation with closure of the A-V fistula. The plasma NA levels were not significantly altered immediately after opening of the fistula (389 vs 417 pg·ml−1), but were significantly increased to 608 pg·ml−1 in association with a leftward shift of the end-systolic P-D relation during the stable stage of volume loading. These findings indicate that there is an augmented adrenergic activity, along with the maximal use of the Frank-Starling mechanism, which acts as a fundamental compensation for the acute volume overload associated with A-V fistula.