1. Patient Characteristics: The demographic data of these 135 patients are summarized in Table-1 below.
1.1. Clinical outcome: Out of 135 patients RV-RP uncoupling was identified in 90 patients (66.7%), 45 patients have coupled RV-RP on basis of CMRI examinations. Both groups were compared in terms of gender, weight, height, age at TOF repair, age at PVR, type of TOF repair, method of PVR, Hb, Hct, QRS duration, blood pressure and Pro-BNP were measured in both coupled and uncoupled group of patients. (Table-2) In our study males predominates females (55%). In our study the gender, weight, height, age at TOF and age at PVR, Hb , HCT and blood pressure did not appear as a significant factor for RV-RP uncoupling. We measured Pro-BNP just before PVR in all patients and Pro-BNP emerges as a strong predictor for uncoupling with a significant p-vale 0.001.
1.2. CMRI Correlations between coupling and uncoupling:
The hemodynamic data measured at each state are presented in Table 3. In uncoupling patients, the RV end-systolic volume was greater than coupling patients with a significant p-value0.001. (Table-3).The hemodynamic data also shows a greater indexed RV end systolic volume in uncoupling patients compare with coupling patients with a significant p-value 0.001. A reduced mean RVEF was found in uncoupling patients than coupling patients with a significant p-value 0.001. Most of LV hemodynamic shows no or less change between coupling and uncoupling patients except LV ejection fraction with a significant p-value of 0.001, so the LV hemodynamic shows a weak correlation with RV-PA coupling. Ea/Emax ratio was 0.81±0.15 in coupling patients which was almost double in uncoupling patients which was 1.55±0.46 with a significant p-value of< 0.001.
1.3. Factors affecting RV-PA coupling:
a) Pro-BNP and Pearson’s correlation: When we correlated Pro-BNP with Ea/Emax by Pearson’s correlation it shows a linear correlation with r value 0.16 and p-value 0.005 (Figure-1).
b) Right ventricular volumetric correlations: The Ea/Emax showed a significant relationship with RVEDVi, RVESVi, RVSVi and RVEF when we correlate these data with Pearson’s correlation equation. The Ea/Emax shown a positive linear relationship with CMRI-derived RVEDVi with r =0.35 and p-valve <0.005. Correlation with RVESVi with Ea/Emax was positive linear expression with r value 0.41 and a significant p-valve of 0.001. The Ea/Emax showed a significant inverse relationship with RVSVi and RVEF. The r value for RVSVi was 0.22 and p-valve was <0.05 which was found significant. For RVEF the r value was 0.78 and a significant p-value of <0.05. An increase in Ea/Emax thus describes the relative uncoupling of the RV-PA interaction, where afterload exceeds the ability of the RV to adapt. Thus, Ea/Emax is inversely related to RV ejection fraction (Figure-2).
1.4. Effect of Surgical Strategy
To evaluate whether the surgical procedure at the primary repair at TOF affects RV-PA coupling, we compared the 75 patients who had TAP repair with 18 patients who have RVOT repair, 21 patients with the Transatrial/Transpulmonary (TA/TP) repair, and 15 patients with RV-PA conduit repair. Out of 75 TAP repaired patients 60 patients were uncoupled, in 24 RVOT patients 12 patients were uncoupled, in 21 TA/TP patients 9 patients were uncoupled and in 15 patients with RV-PA conduit 9 patients were uncoupled (Figure-3). There was no significant difference of age, weight, and height in TAP, RVOT, RV-PA conduit and TA/TP group of patients.
1.5. RV-PA coupling and its correlation in TOF:
From CMRI data we calculated Ea/Emax ratio for all 135 patients and from Ea/Emax ratio the patients were divided in two groups coupling and uncoupling respectively. Ea/Emax ≤1 was considered for coupling patients and Ea/Emax >1 for uncoupling patients. On the basis of Ea/Emax ration the patient’s distribution is shown in (Figure-4) below. For coupling patients 3 patients Ea/Emax was between 0-0.5 and 42 patients ranges between Ea/Emax >0.5-1. In uncoupling patients majority of patients (n=51) the Ea/Emax ration was between >1-1.15. 21 patient’s Ea/Emax ranges between >1.5-2 and 15 patients were between Ea/Emax >2-2.5. Only 3 uncoupled patient Ea/Emax was >2.5.
2. Impact of PVR on ventricular performance (Follow up)
CMRI: After six months of PVR all 135 patients were followed up with CMRI. We compared 90 uncoupled RV-RP patients with their previous CMRI data to check out either their ventricular performance have been improved or not. Their follow up MRI data is below in the Table-4