The electrical axis of the heart in patients with atrial fibrillation before and after radiofrequency ablation

Материалы и методы. Представлены данные изучения изменения положения электрической оси сердца (ЭОС) у 40 пациентов (24 мужчины и 16 женщин) с фибрилляцией предсердий до и в острый послеоперационный период (3–7 сутки) после перенесенной радиочастотной аблации с изоляцией легочных вен (РЧА ЛВ). Определяли значения вектора угла α ЭОС (αF QRS) и его проекций на фронтальную (αQRS max F), сагиттальную (αQRS max Si) и горизонтальную плоскости (αQRS max H) по усредненному комплексу за 5 секунд. Пациенты разделены на 3 группы: группа 1 – нормального положения ЭОС α = 30–70 (n = 10), группа 2 – отклонения ЭОС влево α < 30 (n = 23), группа 3 – отклонения ЭОС вправо – α > 70 (n = 7). Анализ достоверности изменений после операции проводили с использованием теста Вилкоксона.


Introduction
Atrial fibrillation (AF) -one of the most common arrhythmias in clinical practice, it is a significant cause of strokes, heart failure and cardiovascular death in the world [1][2][3]. The leading method of AF treatment in view of conservative therapy ineffectiveness is radiofrequency catheter ablation (RFA) with the pulmonary veins isolation (PVI) [2,4]. One of the RFA PVI effects is the change in the heart electrical axis (HEA), which, however, has been studied extremely little, mainly relating only atria [5][6][7][8][9].

Aim
To study changes of the electrical axis of the heart in patients with atrial fibrillation before and after radiofrequency ablation with pulmonary veins isolation.

Materials and methods
40 patients aged 58.0 ± 9.7 years (M ± sd) (16 -female, 24 -male) with AF were examined in the Department of Ultrasound and Instrumental Diagnostics with Miniinvasive Interventions of SI "Zaycev V. T. Institute of General and Urgent Surgery of NAMS of Ukraine". All patients had been undergone RFA PVI in period from 2015 to 2017.
The α angle values were measured in projections to the frontal (αQRS max F), the sagittal (αQRS max Si) and the horizontal plane (αQRS max H), as well as the resulting vector of HEA (αF QRS) before and during the acute postoperative period (3-7 days) after RFA PVI on the averaged complex for a period of 5 seconds in 12 leads of the standard ECG, recorded on the computer cardiograph of HAI Medica "Cardiolab +" (Kharkiv, Ukraine).
In the generated database in Microsoft Excel, Statistica 10, the obtained data were processed in programs using standard statistical procedures. Calculations for nonparametric data: absolute -n (number) and p (%, units). Parametric data mean (M, units) and standard deviation (sd, units). The analysis of distribution was performed using asymmetry, kurtosis and median (γ, units). A statistical significance analysis of the differences in α angle changes before and after RFA PVI was performed using the Wilcoxon test, the significance level was set at P < 0.05.

Results and discussion
The αF QRS angle distribution among all patients was bimodal with maxima in the groups 1 and 2 before performing RFA PVI (Fig. 1). After RFA PVI the αF QRS angle distribution became asymmetric unimodal (asymmetry γ = -0.79, excess γ = -0.2) with the displacement of the values peak to the right, into the region of the group 2 (change of median from 25.5 to 38) ( Figure 1). The median value of αF QRS angle in the groups 1 and 3 was slightly decreased, but in the group 2 it was significantly reduced.
Distributions of aQRS max angle for the frontal (A), horizontal (B) and sagittal (C) planes projections are shown in Fig. 2. In each plane the original form of aQRS max values distribution was preserved. In the frontal and horizontal planes there was a decrease in the median value for each group. In the sagittal plane the order of medians positions before RFA on the graph was different from the other planes: the group 3 has a more left-handed position than the groups 2 and 1, and medians positions changed after RFA to the ordinary order in the other planes -for the groups 2, 1 and 3.
In the frontal and horizontal planes the median value for each group decreased; in the sagittal plane the decrease occurred in the group 1 and increase -in the groups 2 and 3.
Statistically significant changes in the αF QRS angle and its projections on planes were revealed in the horizontal plane in the general group with a change in the mean αF QRS towards the HEA deviation to the left (from 36.02° to 30.53°) (P < 0.05). Similarly, in the horizontal plane a marked decrease in the mean αF QRS angle value in the group 2 (from 21.21° to 8.78°) was statistically significant (P < 0.05). In the sagittal plane there was an increase in the mean αF QRS in the general group (from 40.97° to 47.53°) (P < 0.05).
In the other planes no statistically significant changes were detected. Data on transitions of patients from one to another group after RFA PVI are presented in Table. 1.
Before RFA PVI the group 1 accounted 25.0 %, the group 2 -57.5 % and the group 3 -17.5 % of patients. After RFA PVI in the group 1 was 52.5 %, in the group 2 -35.0 %, in the group 3 -12.5 % of patients. In 37.5 % (n = 15) of patients α angle deviation with change of group after RFA occurred. At the same time, 32.5 % (n = 13) of Changes of aF QRS angle in patients with AF after RFA PVI have not been studied previously. Variety of aF QRS angles, we found in the early postoperative period with the HEA deviation to the right, can not be explained from the point of view of existing mechanisms known today, because it is acute, not long-term [6,[10][11][12]. The possible cause of its change may be PVI during RFA. The evidence for this argument is the transitions of patients from one to another group after RFA, when their maximum number is concentrated in the group 1 from the group 2.
The obtained data also shows the diagnostic significance of aF QRS angle against values of its projections on the planes due to the significant change in the first relatively non-significant changes of the others after the RFA PVI in the acute postoperative period.

Conclusions
1. In patients with AF in the acute postoperative period a significant transformation of aF QRS angle distribution from bimodal with maxima in the groups 1 and 2 in a single-modal one occurs with a maximum displacement to the right in the region of the HEA normal position.
2. For the HEA position in patients with AF after RFA PVI the resultant vector aF QRS angle is informative but its projections on the planes are low informative.
Prospects for further research. It seems advisable to compare aF QRS angle changes with the atrial vector changes in patients with AF undergoing RFA PVI.

Funding
The investigation was carried out within the framework of the research work «Pharmacological and intervention approaches to the therapy of patients with cardiac rhythm disturbances and arterial hypertension» (state registration number 0116U000973).