Compensatory hemodynamic variations for cardiovascular stabilization in complete atrioventricular block before and after pacemaker implantation

Objectives: Stabilization of the cardiovascular system is maintained by variations in hemodynamic and hormonal parameters in complete atrioventricular (AV) block. We investigated the variations in hemodynamic parameters and brain natriuretic peptide (BNP) levels before and after permanent pacemaker implantation for complete AV block. Study design: We evaluated 25 patients (14 men, 11 women; mean age 72 +/- 10 years; range 39 to 83 years) who presented with a complaint of syncope due to complete AV block. All the patients were hemodynamically stable on presentation and were monitored in the coronary care unit until permanent pacemaker implantation. Variations in the cardiovascular system were determined before and two weeks after pacemaker implantation, including mean arterial pressure (MAP), stroke volume (SV), cardiac output (CO), systemic vascular resistance (SVR), systemic aortic compliance (SAC), and BNP levels. Results: The mean heart rates were 36 +/- 6 beat/min and 65 +/- 10 beat/min before and after pacing, respectively. Compared to the pacing period, CO was significantly lower (p<0.001) and SVR was significantly higher (p=0.001) before pacemaker implantation, suggesting a compensatory rise in SVR. The mean arterial pressure did not show a significant difference and remained within normal ranges before and after pacing. There were no significant differences in SV, SAC, and BNP levels before and after pacemaker implantation, with BNP exhibiting increased levels in both periods. Conclusion: While no compensatory alterations occur in SV, SAC, and BNP before and after pacemaker implantation, decreased CO in complete AV block seems to be balanced by increased SVR, which results in maintenance of MAP within the normal range.