Atrial Septal Defect (ASD) is the most common form of congenital heart disease (CHD) found in adults. The slow progression of the disease is the unique characteristic of ASD so it remains undiagnosed until young adulthood [1].In patients of atrial septal defect, severe pulmonary hypertension is contraindication to surgical or trans-catheter device closure. After detection of significant pulmonary arterial hypertension on transthoracic echocardiography, patients of ASD often undergo cardiac catheterization for determination of pulmonary artery pressure and pulmonary vascular resistance (PVR).

It is important to differentiate whether pulmonary hypertension in ASD is secondary to increased pulmonary flow or due to obliterative changes in pulmonary arterioles as the former is amenable to surgical or device closure.Elevated PVR differentiates raised pulmonary artery pressure due to vascular disease from that due to high blood flow.

The classification of PH has evolved over the years from the 1973 World Health Organization symposium[2] to the 6th World Symposium on Pulmonary Hypertension (WSPH)[3] in 2018 and the European Society of Cardiology/European Respiratory Society guidelines for the diagnosis and treatment of PH,[4] which decreased the PH threshold from an mean pulmonary artery pressure (mPAP ) ≥25 mm Hg to an mPAP >20 mm Hg (2 SDs above the mPAP of a healthy patient at rest, 14.0±3.3 mm Hg[5], differentiated PH on the basis of PVR >2 Wood units (instead of ≥3 Wood units).

The gold standard method for determining PVR is right heart catheterisation (RHC).Doppler Echocardiography can be used to determine PVR using the Abbas formula [6].PVR determined by echocardiography has been shown to correlate well with PVR determined by catheterisation. However, some studies have reported less correlation at PVR >6 WU in patients of CHD [12,13]. Abbas et al., have shown that squaring the TRV(tricuspid regurgitation velocity) improves the reliability of PVRecho even at values >6 WU[6].So we conducted a retrospective observational study to compare PVRecho using modified Abbas formula with PVRcath in patients of ostium secundum ASD.

This retrospective observational study was conducted in 25 patients of Ostium secundum ASD from the Cardiology Department of ABVIMS and Dr RML Hospital, New Delhi from 2022 to 2024

Inclusion criteria were

1. Uncorrected Ostium secundum ASD
2. Normal Left ventricular systolic function
3. Patients who underwent RHC

Exclusion criteria were

1. Left sided valvular abnormalities
2. Anomalous pulmonary venous drainage
3. RVOT or pulmonary valve stenosis
4. Left ventricular diastolic dysfunction of any grade

Echocardiography

Echocardiography was performed using The Philips EPIQ CVx machine. The agitated saline contrast echocardiography was carried out if the TTE study did not reveal conclusive result. Transoesophageal echocardiography was carried out for better assessment of defect size, rims of septal defect and any anomalous venous drainage. Guidelines from the ASE and the European Association of Echocardiography (EAE) were followed in the acquisition, validation, and confirmation of the images.

PVR was calculated using regression equation given by Abbas et al. [6]

PVR=5.19 × TRV2/TVIRVOT - 0.4

TRV: Tricuspid regurgitation velocity

TVIRVOT: Velocity time integral Right ventricular outflow tract

Right Heart Catheterisation

RHC was performed in all patients via trans-femoral venous approach. Oximetry and pressure recording were done as per standardized protocol. Left ventricular end diastolic pressure (LVEDP) was used as a surrogate for pulmonary capillary wedge pressure (PCWP). The indirect Fick method was employed to determine the cardiac output by hospital protocol. Using the equation: pulmonary blood flow (Qp)/systemic blood flow (Qs) = (aorta saturation − mixed vein (MV) saturation)/pulmonary vein (PV) saturation-pulmonary artery (PA) saturation, the flow ratio was obtained. Cardiac output (CO) and MV saturation were determined to be as following:

CO = O2 consumption (ml / min)/A-V O2 difference (ml O2/ 100 ml blood) × 10

MVsaturation = (3×SVCsaturation) +IVCsaturation/4

Systemic flow Qs (L/min) = O2 consumption (ml/min) / (arterial -mixed venous) O2 content Pulmonary flow Qp (L/min) = O2 consumption (ml/min)/ (pulmonary venous - pulmonary arterial) O2 content

The pulmonary vascular resistance index (PVRi) was determined using the following formula:

PVR=mPAP−mLAP/Qp    

PVRi=mPAP−mLAP/Qp × BSA

Qp=O2 consumption (mL/min) 1.36×10×Hemoglobin×(PVO2−PAO2) ×100

Qs=O2 consumption (mL/min) 1.36×10×Hemoglobin× (SAO2−MVO2) ×100

SVC: Superior vena cava

IVC: Inferior vena cava

mPAP: Mean pulmonary artery pressure

mLAP: Mean left atrial pressure

BSA: Body surface area

Left to right shunt = Qp -Qs

Statistical Analysis

Statistical analysis was performed using GraphPad Prism 10.0 version. Continuous variables were expressed as mean and standard deviation (SD). Linear correlation between two continuous variables was examined using Pearson's correlation method. Bland–Altman analysis was used to see the agreement between PVREcho and PVRcath. ROC plot was constructed to test the applicability of PVRecho across different cutoff values of PVR.

Study was conducted on 25 patients of Ostium secundum ASD.Amongt the study population 72% were female. The mean age of study population was 36 ±11 years.] Baseline Characteristics: Mean body mass index was 23±2.5 Kg/m².Mean tricuspid regurgitation velocity was 3.7±0.57 m/s.Right ventricular outflow tract VTI was 24±3.4. PVR as derived by echocardiography was found to be 2.6±0.78 WU.(Table 1) Right heart catheterisation yielded mean pulmonary blood flow and systemic blood flow as 6.9±0.84 and 4.0±0.46 L/min respectively. Left to right shunt was 2.9±0.87 L/min. PVR as calculated by RHC was found to be 2.7±0.74 WU.

Table 1: Baseline Characteristics

PVR Estimated by Echocardiography and by Right Heart Catheterization: In the correlation test, echocardiographic PVR (PVRecho) was significantly correlated with RHC PVR (PVRcath ) (r = 0.6203, p :0.0009).

 Table 2: Histological grading of pulmonary vascular disease

The gold standard method for estimation of PVR is RHC. However PVR can also be estimated non- invasively by echocardiography. Invasive PVR is measured by calculating pressure gradient across pulmonary circulation and pulmonary blood flow (Qp). In echocardiography, pressure gradient across pulmonary circulation is substituted by tricuspid regurgitation velocity (TRV), whereas Qp is quantified using TVIRVOT.

The ratio of tricuspid regurgitation velocity (TRV) to the time-velocity integral of the right ventricular outflow tract (TVIRVOT) has been studied as a reliable measure to distinguish hyperkinetic vs hypertensive PAH. The equation (TRV/TVIRVOT × 10 + 0.16) for PVRecho has been shown to provide a good noninvasive estimate of PVR [9].Modified equation by Abbas et al. (PVR=5.19 × TRV (2)/TVIRVOT - 0.4) provides better estimate in cases where PVR >6 WU [6].

A study by Bech-Hensen et al. showed that PVR calculated using Abbas formula showed a larger limit of agreement compared with PVRdoppler which was calculated using the stroke volume formula [10].

In our study, PVRecho significantly correlated with PVRcath. Bland-altman analysis also showed good agreement between the two. However, PVR should be evaluated on the basis of cardiac output, pulmonary artery mean pressure (mPAP), and pulmonary capillary wedge pressure (PCWP) instead of using Abbas’s formula.

The Abbas method does not take into account the right and left filling pressure of the heart. [10,11].Doppler method has limitations in the form of good  Window and appropriate ultrasound beam alignment. Comparison of PVRecho and PVRcath has showed varying results previously. However, previous studies have not examined uncorrected secundum ASD. We propose a cut-off value of PVRecho to determine high PVR. The cut-off value of PVRecho for high PVR is 2.16 WU, with a good discriminatory power. Given this finding, patients having PVRecho less than the cut-off value can safely undergo device/surgical closure without the need of RHC. Patients with PVRecho higher than the cut-off value should undergo RHC for confirmation. However, PVRecho should not be considered as a substitute of right heart catheterisation.

We conclude that PVRecho is reliable in predicting high PVR in uncorrected ostium secundum ASD. PVR measured by echocardiography according to Abbas formula is well correlated with PVRcath. We propose using a PVRecho cut-off value of 2.16 WU to identify individuals in high pulmonary vascular resistance group in whom right heart catheterisation is to be performed.

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