PO-02-206 A MECHANISM FOR PACING-INDUCED REGIONAL CONTRACTILE DYSFUNCTION MEDIATED BY RELEASED CATECHOLAMINES

We have previously shown that non-excitatory epicardial stimulation (NES) increases measures of cardiac function mediated by local release norepinephrine. In this further investigation we focused on the effects NES myocardial contractile pattern. Farm pigs were anesthetized and instrumented with a LV high-fidelity pressure/volume conductance transducer, thoracic aortic pressure left atrial (LA)/ electrodes, sonomicrometer segment length (SL) gauges placed proximal (lateral base) distal (posterior mid LV) to site. During constant LA pacing, pulses (0.8ms, 2-3x threshold volts) applied during absolute refractory period before after β-receptor blockade (BB, metoprolol). Regional was analyzed constructing LVP vs. SL loops in beat-by-beat fashion thus allowing characterization relation over entire cycle. resulted dysfunction characterized an early shortening, subsequent lengthening, re-shortening pattern cycle gauge (middle tracing), but not remote site (bottom tracing). The onset lengthening coincided peak generation, followed as fell. loop markedly altered. This effect rapidly waned within 10-15 seconds cessation electrical abolished BB. induced developed average 5-10 accompanied several global indices (dP/dt, LVP, valve opening) which also abrogated B-blockade. These findings demonstrate pacing elicits catecholamine may cause dyssynergy mimic regional pacing-induced seen at sites man.