Left Ventricular Mechanics and Myocardial Blood Flow: Pressure-Volume Loops
Measurements were made during DDD pacing (ie, the mode that was programmed for the long term) and 5 min after a change of pacing mode to AAI, preserving the same pacing frequency. All drugs with a possible negative inotropic and/or chronotropic effect were stopped five half-lives before the study.
All patients provided written, informed consent, and the experimental protocol was approved by the hospital ethics committee.
The study was performed at least 15 min after the performance of routine coronary angiography. All patients were awake and mildly sedated with diazepam, 10 mg orally. itat on
In all cases, a Swan-Ganz catheter was used for the continuous measurement of cardiac output (the thermodilution method). Subsequently, a conductance catheter with a micromanometer on its tip (7F, Millar 572-7; Millar Instruments; Houston, TX) was inserted into the LV via the right femoral artery and was utilized to estimate possible alterations in LV mechanics in the short term after the restoration of a normal LV activation sequence. We documented the proper placement of the catheter at the top of the LV radiologically and by inspecting its five segmental volume signs. The parallel conductance was calculated at least twice using the hypertonic saline solution method.
To achieve pressure-volume loops under variable preload conditions, we transiently occluded the inferior vena cava for 6 to 8 s, in the end-expiratory position, using a vascular occlusion catheter system inserted through the left femoral vein (8F, STOPFLOW catheter system; PfM; Cologne, Germany). Measurements were recorded during long-term DDD pacing and 5 min after switching the pacing mode to AAI, preserving the closest possible pacing rate.
We used a special adapter (Leycom CFL 512; Cardio-dynamics BV; Zoetermeer, the Netherlands) to compute the LV total volume and to draw the LV pressure-volume loops. Data recordings were stored in the usual magnetic media and were analyzed off-line with special software (C0NDUCT2000; Cardiodynamics BV).