The atrioventricular blocks (AVB) of II—III degree occupy a special place among the causes of death from cardiovascular diseases. The treatment of this type of conduction abnormality is the implantation of a two-chamber pacemaker (PM), which allows to maintain atrioventricular (AV) synchronization. The impact of AV-conduction abnormality on endothelial function has not been described to this day.
OBJECTIVE
To determine the dynamics of endothelial function and hemodynamics indices depending on the localization of the ventricular electrode during implantation of two-chamber PM.
MATERIAL AND METHODS
The study involved 91 patients with atrioventricular conduction abnormality of II—III degree. Among them 37 patients were implanted with a two-chamber PM with the localization of the ventricular electrode in the region of the interventricular septum (IVS) (1st group), 46 patients were implanted with a two-chamber PM with the localization of the ventricular electrode at the apex (apical section) of right ventricle (ARV) (2nd group). All patients were tested with endothelium dependent vasodilation (EDV) of the brachial artery according to the standard method, as well as determined the blood flow velocity parameters. The parameters of intracardiac hemodynamics and left atrial (LA) function were estimated. The noted investigations were carried out on patients while admission to the hospital and after two months from PM implantation.
RESULTS
In patients of the 1st group with electrode localization in the IVS region, EDV was initially 3.12 [1.85; 6.27]%, and after 2 months it increased to 6.38 [2.25; 8.19]% (p=0.014). In the 2nd group patients with electrode localization at the apex of RV the indicator, that initially had been equal 3.25 [2.25; 6.15]% improved, and after 2 months from surgery it was 5.79 [2.68; 9.76]% (p=0.02). At the same time, a comparative analysis of EDV results proved that in patients with interventricular electrode localization IVS stimulation leads to an improvement in endothelial function compared to patients with ARV electrode localization (p=0.04). According to the echocardiography, patients in the 1st group had a slight decrease in the ejection fraction (EF) to 64.75 [51.80; 67.57]% (p=0.042). The LA volume index decreased to 32.84 [24.59; 36.96] ml/m2 (p=0.017), indicating a decrease in the overload of LA volume and pressure. At the same time, patients in the 2nd group had a decrease in EF to 54.1 [43.3; 66.3]% (p=0.01). The tendency to a decrease of LA volume index to 31.78 [25.05; 45.01] ml/m2 (p=0.097) was noted. In the examination of peripheral hemodynamics in patients of both groups a decrease in vascular tone was observed, reflecting the state of microcirculatory bloodstream (peripheral vascular resistance (PVR), specific peripheral vascular resistance (SPVR)). The dynamics of these parameters had a tendency to decrease. Patients with IVS stimulation had a negative correlation between maximal blood flow velocity and PVR (r= –0.376, p=0.02). This means that while the blood flow velocity was improving, there was a decrease in arterial wall tone associated with the improvement of microcirculatory supply of vascular wall and myocardium stroma against the background of improved endothelial function. At the same time, patients with apical stimulation didn’t have such association (r= –0.001, p=0.99).
CONCLUSION
Implantation of a two-chamber pacemaker with the interventricular septum stimulation is the preferred treatment for improving endothelial function. The two-chamber stimulation with apical localization of the ventricular electrode is accompanied by more pronounced structural and functional changes of the left ventricular myocardium due to its hypocontractility. Electrical stimulation of the interventricular septum is a priority, as it improves endothelial function, caused by a change in shear stress and an increase in basal secretion of nitrogen oxide by endothelium, moderately improves left ventricle function due to a shorter electric systole of left ventricle and its more physiological activation.
