Patient 1 (AVSD)
(XMR)
Patient 2 (PDA)
(conventional catheter)
PA pressure at baseline
Systemic
Systemic
Qp:QS at baseline
1.9:1
1.8:1
PVR at baseline
10 WU.m2
8.1–12.4 wu.m2 (based on estimated oxygen consumption values of 100–150 ml/min/m2)
PA pressure with iNO & 100 % oxygen
Systemic
Systemic
Qp:Qs with iNO & 100 % oxygen
1.9:1
2.1:1
PVR with iNO & 100 % oxygen
9.7 wu.m2
6.0–9.0 wu.m2 (based on estimated oxygen consumption values of 100–150 ml/min/m2)
Case Description 2
A 7-year-old female with trisomy 21 was recently discovered to have a murmur on auscultation. She was asymptomatic with transcutaneous oxygen saturations of 98 % in air. Her haemoglobin measured 13 g/dL. A transthoracic echocardiogram showed a large 8-mm patent ductus arteriosus (PDA) with bidirectional shunting. Flow was right to left in early systole and left to right through diastole. In addition there was a very small 2-mm VSD with a gradient of 35 mmHg across the defect. This child proceeded to conventional cardiac catheterisation for haemodynamic assessment and potential device closure of the PDA if PVR was found to be suitable.
Venous and arterial access was achieved; pressures, blood gas and saturations were measured in the right atrium, the pulmonary artery and the aorta. Measurements were taken at baseline and after administration of 100 % oxygen and inhaled nitric oxide at 20 parts per million. Additional selective angiography of the duct was performed. PVR was calculated; results are illustrated in Table 22.1.
In view of the relatively high PVR which displayed some variability, the patient was referred to the ear, nose and throat (ENT) and respiratory teams for assessment of her airway. She was also commenced on sildenafil. A repeat PVR study was planned 3 months later to reassess suitability for PDA closure.
Discussion
Clearly in both cases accurate measurement of PVR was crucial. The presence of large left to right shunts is commonplace in the setting of congenital heart disease. If the shunt is large, early diagnosis leads to surgical closure once the patient is of an appropriate size or earlier if the patient develops symptoms that cannot be controlled with medication. Occasionally late diagnosis of large left to right shunt is made and in such circumstances this can result in pulmonary vascular changes (increased resistance), elevation of right ventricular pressures and irreversible pulmonary hypertension. Accurate assessment of the PVR and whether it is reversible is essential to determine whether the shunt can be repaired. If there is irreversible high PVR, repairing the shunt may have a detrimental effect resulting in right heart failure due to the increased afterload.
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