Right ventricular pacing group
The indication for permanent pacemaker implantation in six patients (50%) was sick sinus syndrome (sinus rate was consistently below 45 beats per minute, so the pacemaker was active in RV pacing more than 90% of the time). In comparison, in three patients (25%), the indication was acquired AV block. In two patients (16.7%), the indication was post-operative AV block; in one patient (8.3%), the indication was congenital third-degree AV block.
During the post-implantation period, the distance of the 6-MWT ranged from 329 to 705 m with a median of 493.5 m. During the following period, at one month, it went from 376 to 705 m with a median of 493.5 m; at three and six months, it ranged from 423 to 705 m with a median of 540.5 m.
After pacing, the QOL score ranged from 0 to 39, with a median of 0 during the study period. During the follow-up period of one, three, and six months, QOL scores ranged from 0 to 20, from 0 to 8, and from 0 to 5, respectively. During the preimplantation period, nine patients (75%) had no dyspnea, or other symptoms of heart failure, the other three patients (25%) were in NYHA class II. Ten patients (83.3%) had no dyspnea in a six-month follow-up period, and two (16.7%) became in NYHA class I.
Twelve lead resting electrocardiogram
As regards the QRS width, all patients had QRS width < 120 ms before pacemaker implantation. During the post-implantation and follow-up periods, five patients (41.6%) had a QRS width of 120 ms, five patients (41.6%) had a QRS width > 120-≤ 140 ms and two patients (16.7%) had a QRS width > 140 ms. Seven patients (58.3%) had complete left bundle branch blocks, and five patients (41.6%) had incomplete left bundle branch blocks after pacemaker implantation and during the follow-up period
By comparing the RVP group and the LVP group, a significant difference in the 6-MWT distance in favor of the RVP group, i.e., a longer length during the post-implant and the follow-up periods. In our study, the female gender was 25% in the RVP group and 50% in the LVP group. The prevalence of the female gender was the predictor of poor 6-MWT performance in the LVP group.
By comparing patients in the same group during the pre and post-implantation periods and at six months follow-up, a significant difference was found in the 6-MWT between the post-implantation period and at six months follow-up in the RVP and LVP groups which indicates that pacing improves the physical fitness and activity of patients, p = 0.01.
Echocardiographic study
A- Conventional echo-Doppler: Two-dimensional and M-mode measurements: The LV dimensions and ejection fraction are shown in Table 1
Table 1
Echo Doppler data: Left ventricular dimensions and ejection fraction
| RVP | LVP | P-value |
EDD | Post | 49.0 (33.0–68.0) | 49.5 (38.0–76.0) | 0.931 |
6 | 46.5 (34.0–67.0) | 51.0 (38.0–75.0) | 0.297 |
ESD | Post | 29.5 (19.0–55.0) | 31.5 (25.0–57.0) | 0.885 |
6 | 29.0 (17.0–56.0) | 32.5 (24.0–56.0) | 0.685 |
EF | Post | 62.0 (40.0–73.0) | 57.0 (41.0–64.0) | 0.099 |
6 | 60.5 (47.0–70.0) | 56.5 (46.0–69.0) | 0.203 |
* = significant P-value < 0.05 |
This shows that there was no deterioration of RV or LV function from RV or LV pacing
2) Pulsed-wave Doppler measurements: The DT, the AR, and the AT during the pre and post-implantation periods and the follow-up period are shown in Table 2 shows the ICT and the IRT before and after pacemaker implantation and during the follow-up period.
Table 2
Echo Doppler Hemodynamics: pulmonary wedge pressure, right atrial pressure, means pulmonary artery pressure, myocardial performance index, total isovolumic time, and Z ratio
| RVP | LVP | P-value |
PWP | Post | 17.0 (9.0–20.0) | 13.0 (9.0–25.0) | 0.090 |
6 | 17.0 (9.0–25.0) | 12.0 (9.0–18.0) | 0.061 |
RAP | Post | 3.0 (1.0–5.0) | 3.0 (1.0–5.0) | 0.179 |
6 | 3.0 (1.0–7.0) | 3.0 (2.0–4.0) | 0.809 |
MPAP | Post | 18.0 (6.0–28.0) | 18.0 (6.0–22.0) | 0.976 |
6 | 14.0 (6.0–22.0) | 14.0 (8.0–22.0) | 0.460 |
MPI | Post | 0.365 (0.32–0.38) | 0.365 (0.32–0.38) | 0.700 |
6 | 0.370 (0.34–0.39) | 0.365 (0.32–0.38) | 0.459 |
t-IVT | Post | 11.30 (10.3–20.1) | 11.60 (11.4–16.2) | 0.271 |
3 | 11.75 (10.3–21.1) | 15.00 (10.6–17.3) | 0.052 |
6 | 12.85 (10.3–21.9) | 14.40 (11.6–17.0) | 0.133 |
Z ratio | Post | 80.0 (66.0–82.0) | 80.0 (73.0–81.0) | 0.277 |
6 | 78.0 (64.0–82.0) | 75.5 (71.0–80.0) | 0.124 |
MPAP = Mean pulmonary artery pressure |
MPI = Myocardial performance index |
t-IVT = Total isovolumic time = 60- (total ejection time + total filling time). |
Z ratio = sum of the left ventricular ejection and filling times divided by RR interval. |
* = significant P value < 0.05 |
Table 2 shows no RV or LV function deterioration in both RV or LV pacing groups.
Echo Doppler data: Regional peak systolic velocities by pulsed-wave TDI in the RV pacing group and LV pacing group are shown in Table 3. Again, this indicates no significant dyssynchrony in both RV or LV pacing groups.
Table 3
Echo Doppler data. Regional peak systolic velocities by pulsed-wave TDI
| RVP | LVP | P-value |
Lateral | Post | 5.62 (3.75–6.25) | 5.50 (3.90–6.70) | 0.339 |
6 | 5.77 (5.00-6.75) | 5.50 (3.90-6.00) | 0.054 |
Septum | Post | 5.47 (4.00-6.50) | 5.52 (3.95–6.25) | 0.603 |
6 | 5.27 (4.50–6.25) | 5.45 (3.65–6.25) | 0.795 |
Anterior | Post | 5.55 (3.25–6.50) | 5.10 (3.90–6.70) | 0.355 |
6 | 5.45 (3.60-6.00) | 5.05 (3.75–6.10) | 0.165 |
Inferior | Post | 5.47 (3.75–6.20) | 5.35 (3.80–6.75) | 0.247 |
6 | 5.47 (3.85–6.20) | 5.15 (2.90–6.10) | 0.157 |
Right ventricular free wall | Post | 5.70 (3.75–6.50) | 5.25 (4.40–6.85) | 0.603 |
6 | 5.70 (5.15–6.25) | 5.47 (4.30–6.25) | 0.052 |
* = significant P value < 0.05 |
Table 3 shows no significant dyssynchrony in both RV or LV pacing groups.
Comparison between RV pacing group and LV pacing group: Qualitative assessment of intraventricular mechanical dyssynchrony by color M-mode TDI in the four walls of the left ventricle is shown in Table 4. It shows no significant dyssynchrony in both RV or LV pacing groups.
Table 4
Echo Doppler data: Qualitative assessment of intraventricular mechanical dyssynchrony by color M-mode TDI in the 4 walls of the left ventricle
| Color M-mode pattern | RVP | LVP | P-value |
No. | % | No. | % |
Lateral | Post | I | 4 | 33.3 | 12 | 100 | 0.001* |
II | 8 | 66.7 | 0 | 0.0 |
6 | I | 4 | 33.3 | 12 | 100 | 0.000* |
II | 8 | 66.7 | 0 | 0.0 |
Septum | Post | I | 1 | 8.3 | 12 | 100 | 0.000* |
II | 11 | 91.7 | 0 | 0.0 |
6 | I | 1 | 8.3 | 12 | 100 | 0.000* |
II | 11 | 91.7 | 0 | 0.0 |
Anterior | Post | I | 4 | 33.3 | 12 | 100 | 0.001* |
II | 8 | 66.7 | 0 | 0.0 |
6 | I | 4 | 33.3 | 12 | 100 | 0.000* |
II | 8 | 66.7 | 0 | 0.0 |
Inferior | Post | I | 1 | 8.3 | 12 | 100 | 0.000* |
II | 11 | 91.7 | 0 | 0.0 |
6 | I | 1 | 8.3 | 12 | 100 | 0.000* |
II | 11 | 91.7 | 0 | 0.0 |
* = significant P value < 0.05. |
Clinical data in Table 5: 6-minute walk test and quality of life score are shown in Table 5, which reveals no significant difference in RVP and LVP.
Table 5
Clinical data: 6-minute walk test and quality of life score
| RVP | LVP | RVP > 6 months | P-value |
6-MWT | 540.5 (423–705) | 446.5 (329–564) | 552 (188–634) | 0.015* |
QOL Score | 0.0 (0.0–5) | 0.0 (0.0–5) | 0.0 (0.0–10) | 0.404 |
NYHA functional class-- | 10 (83.3%) | 12 (100%) | 10 (83.3%) | 0.519 |
NYHA functional class–I | 2 (16.7%) | 0 | 2 (16.7%) |
* = significant P value < 0.05 |
B-Tissue Doppler imaging: The regional EMD in the lateral, septum, anterior, inferior, and right ventricular free walls are shown in Table 5.
The interventricular mechanical dyssynchrony assessed by conventional pulsed-wave and Tissue Doppler imaging is shown in Table 6.
Table 6
Echocardiographic data: Comparison of hemodynamics in the RV pacing group at the preimplantation period, post-implantation period, and six-month follow-up
Variable | Preimplantation | Post- implantation | 6 months | P-value |
PWP | 16.1 (9.0–22.0) | 17 (9.0–20.0) | 17 (9.0–25.0) | 0.472 |
RAP | 3 (1–5) | 3 (1.0–5.0) | 3 (1.0–7.0) | 0.639 |
MPAP | 19 (6.-28) | 18 (6–28) | 14 (6–22) | 0.264 |
COP | 3.2 (1.7–6.3) | 4.45 (2.8–7.1) | 4.8 (3.3–6.3) | 0.000* |
MPI | 0.35 (0.31–0.4) | 0.365 (0.32–0.38) | 0.37 (0.29–0.39) | 0.469 |
t-IVT | 27.9 (12.4–37.2) | 11.30 (10.3–20.1) | 12.85 (10.3–21.9) | 0.003* |
Z ratio | 55 (40–79) | 80(66–82) | 78 (64–82) | 0.004* |
MPI = Myocardial performance index |
t-IVT = Total isovolumic time = 60- (total ejection time + total filling time). |
Z ratio = sum of the left ventricular ejection and filling times divided by RR interval. |
* = Significant P value < 0.05 |
Table 6 shows no significant dyssynchrony in both RV or LV pacing groups.
Comparison of intraventricular and interventricular mechanical dyssynchrony in the right ventricular pacing group during the preimplantation period, post-implantation period, and six-month follow-up are shown in Table 7
Table 7
Echocardiographic data. Comparison of intraventricular and interventricular mechanical dyssynchrony in the right ventricular pacing group at the pre-implantation period, post-implantation period, and six-month follow-up
Variable | Preimplantation | Post- implantation | 6 months | P-value |
LVPEI (conventional) | 90 (80–110) | 107.5 (93–135) | 127.5 (115–130) | 0.001* |
RVPEI | 67.0 (60–85) | 87.3 (70–100) | 93.5 (90–95) | 0.01* |
EMD-4 (TDI) | 7.5 (2–20) | 10 (0.0–40) | 14 (4–25 | 0.042* |
IVMD (conventional) | 20.0 (10–30) | 18.5 (10–35) | 31 (20–35) | 0.146 |
Difference between EMD of the lateral wall and right ventricular free wall (TDI) | 10 (2–20) | 11.5 (5–30) | 10 (2–30) | 0.976 |
Difference between EMD of septum and right ventricular free wall (TDI) | 9 (2–25) | 10 (2.0–25) | 6.5 (50 − 15) | 0.766 |
* = Significant P value < 0.05 |
In the critical evaluation, by comparing RVP to LVP in group A, no significant difference was found between the groups for all the variables, including left ventricular dimensions and EF, isovolumic relaxation time (IRT), MR score, aortic flow-velocity integral (FVIAo), maximum protodiastolic mitral flow (Emax), mitral flow-velocity integral (FVIMi), deceleration time (DT), diastolic filling time (DFT) and QRS width except for two variables (ESD and MR score) where LVP was superior to RVP.
Thus these results show that RVP seems to have less detrimental effects on LV synchrony
Right ventricular pacing more than six months group: The duration of pacemaker implantation ranged from 3 to 9 years with a median of 6 years. The 6-MWT, the QOL score, the systolic and diastolic blood pressures, and NYHA functional class all improved.
Intragroup comparison: left ventricular pacing group
Intragroup comparisons
Intragroup comparisons were made in the RVP group and the LVP group. In addition, we] made a comparison between the pre and post-implantation variables and variables during the six-month follow-up period.
This significant difference was detected between the COP during the pre-and post-implantation periods (P = 0.002) and the preimplantation period and at the six-month follow-up (P = 0.003) Fig. 3
A highly significant difference was also found between the IVT variables at the pre and post-implantation periods and six months (P = 0.003), as shown in Table 2, 6. Furthermore, this significant difference was found between the pre-and post-implantation periods (P = 0.005), preimplantation periods, and six-month follow-up (P = 0.005).
A highly significant difference was demonstrated between the Z ratio at the pre and post-implantation periods and six months (P = 0.004). This significant difference was found between the pre-and post-implantation periods (P = 0.005), the preimplantation period, and the six-month follow-up (P = 0.006). For all the other hemodynamics, no significant difference was found between variables during the pre and post-implantation periods or six-month follow-up.
By comparing RVP, LVP, RVP > six months, and the control group, no significant difference was found in all variables except for 6-MWT, LVPEI, IVMD, and color M-mode TDI patterns.
By comparing patients in the same group, in the RVP group, a significant difference was found in 6-MWT, COP, IVT, Z ratio, LVPEI, EMD-4, and color M-mode TDI patterns.
On the other hand, in the LVP group, a significant difference was found in the 6-MWT, QOL, NYHA functional class, COP, IVT, Z ratio, LVPEI, and EMD-4.
Regarding the intragroup comparison, in the RVP, a significant improvement was shown in only four variables: EF, FVIAo, DFT, and QRS width. On the other hand, in the LVP, the considerable improvement was nearly in the same variables. Therefore, by comparing LVP versus RVP, the significant difference was demonstrated only in the EF, MR score, and QRS width.
Left ventricular pacing group
1-Clinical data: The comparison of the 6-MWT distance and the QOL score in the post-implantation period and at six months revealed a highly significant difference in the median values (P = 0.004, P = 0.026, respectively)
2-Echo Doppler data: Comparison of the left ventricular dimensions and ejection fraction. An insignificant difference was found between the LV dimensions and EF during the pre and post-implantation periods and between the pre and six-month follow-up.
Intragroup comparison: LV pacing group:
A highly significant difference between the median values of the mean PAP, COP, MPI, IVT, and Z ratio was found during the pre and post-implantation periods and at six months (P = 0.003, P = 0.000, P = 0.000, P = 0.000 and P = 0.000 respectively),