Hemodynamic findings during sinus rhythm, atrial and AV sequential pacing compared to ventricular pacing in a dog...

The hemodynamic responses of atrial (AP), atrioventricular sequential (AVP) and ventricular pacing (VP) were compared to sinus rhythm (SR) in seventeen anesthetized dogs with intact AV conduction. The atrium and/or ventricle were paced at fixed rates above the control sinus rate. An AV interval shorter than normal conduction was selected to capture the ventricle. The changes of pulmonary capillary wedge pressure (PCWP, mmHg), mean aortic pressure (MAP, mmHg), cardiac output (CO, L/min), systemic vascular resistance (SVR, dynes/s/cm-5), left ventricular stroke work index (SWI) and mean systolic ejection rate (MSER, ml/s) during sinus rhythm, atrial pacing and atrioventricular sequential pacing (expressed in percentages of the individual values during ventricular pacing) were: (Chart: See text) The importance of atrial systole for cardiac performance was clearly demonstrated in dogs with normally compliant hearts. In both atrial and atrioventricular sequential pacing compared to ventricular pacing there was a reduction of pulmonary capillary wedge pressure (PCWP) (p less than 0.01) and systemic vascular resistance (SVR) (p less than 0.01) despite an increase in cardiac output (CO). The lesser mean systolic ejection rate (MSER) found during atrioventricular sequential pacing compared to sinus rhythm and atrial pacing may be explained by the abnormal ventricular depolarization in this pacing mode; nevertheless, the mean systolic ejection rate was still greater than that found during ventricular pacing (p less than 0.05).