A Comparison of Echocardiogram Screening for Pulmonary Hypertension in Asymptomatic and Symptomatic Patients with Sickle Cell Disease

Background: Pulmonary hypertension (PHT) is an increasingly recognised complication of sickle cell disease (SCD), even in asymptomatic patients. Studies from the US have shown a prevalence of PHT of between 20–30% and this has been associated with an increased mortality. The prevalence of PHT in the UK sickle cell disease population is unknown.

Method: We identified adult patients with a diagnosis of SCD (HbSS, HbSC, HbSB0thalassaemia and HbSB+ thalassaemia) who had screening for PHT using transthoracic echocardiography over a one year period. We compared the echocardiographic findings of symptomatic and asymptomatic patients. Direct measurements of tricuspid regurgitant jet velocity (TRV_max) were recorded, as has been done in previous similar studies with a peak TRV of ≥ 2.5m/s indicating risk of PHT. In order to increase specificity and sensitivity of the echocardiogram recording and as TRV_max is not always measurable other indirect indicators of PHT were also recorded, including ‘time from start of flow to peak velocity’ which is measured by placing the pulsed sample in the centre of the main PA or pulmonary valve annulus; a time of >105ms excluded PHT while a time <80ms made PHT highly likely. Systolic function of the right ventricle was quantified using long-axis measurements: TAPSE (tricuspid annular plane systolic excursion) using a TAPSE <18mmHg as an abnormal threshold and ‘Doppler tissue S velocity’ was measured by placing the Doppler tissue sample in the RV free wall at the tricuspid annulus and recording the peak systolic velocity. A velocity of <10m/s was consistent with a reduced RV ejection fraction or PHT.

Results: 32 asymptomatic patients and 40 symptomatic patients had echocardiogram screening for PHT. The asymptomatic group had a mean age (± SD) 36.5 years(± 10.2), 17 patients were men, 20 patients had HbSS, 10 patients had HbSC, 1 patient had HbSB0thalassaemia and 1 patient had HbSB+ thalassaemia. 3/32 (9.4%) of patients had abnormal echocardiograms with a TRV of 2.5, 2.5 and 2.6 m/s respectively. One patient with a TRV = 2.5m/s had a history of chest crisis and was on hydroxyurea. The symptomatic group had a mean age (± SD) 35.8 years (± 11.2), 13 patients were men, 31 patients had HbSS, 8 patients had HbSC, 1 patient had HbSB0thalassaemia. 2 patients who had TRV ≥ 2.5m/s were excluded from analysis as had pulmonary stenosis. 7/38 (18.4%) patients had TRV ≥ 2.5m/s (range 2.5 to 2.7m/s). Of these 7 patients, 6 had HbSS, 1 had HbSC, only one was on hydroxyurea, and only one had a history of chest crisis. In 2 further patients in whom TRV was not measurable, other echocardiographic features were used to identify PHT; 1 patient had a ‘time to peak velocity’ of 58ms and 1 patient had a TAPSE of 17mmHg and a ‘time to peak velocity’ of 80ms. Both patients had HbSS, 1 had a history of chest crisis and none were on hydroxyurea.

Conclusion: In the asymptomatic group, 9.4% of patients had abnormal echocardiograms, which were suggestive of PHT. In the symptomatic group, 24% patients had echocardiograms suggestive of PHT with 7 patients having a peak TRV ≥ 2.5m/s and a further 2 patients being identified using other echocardiogram criteria. We conclude that the prevalence of PHT in the asymptomatic group was low but in the symptomatic group, the prevalence of PHT was comparable to figures in the US. In addition, transthoracic doppler echocardiographic screening for PHT should include other criteria apart from TRV.