T. Karu

Paediatric sickle cell disease: pulmonary hypertension but normal vascular resistance

Background Adults with sickle cell disease (SCD) and pulmonary hypertension have high mortality but death in SCD children with pulmonary hypertension is rare. The authors hypothesised that pulmonary hypertension in SCD children may be secondary to anaemia-induced high cardiac output rather than pulmonary vascular disease. Methods Two independent, validated techniques were used to estimate pulmonary vascular resistance (PVR) in 50 SCD children and 50 matched controls. Tricuspid regurgitant jet velocity (TRV) and right ventricular outflow tract velocity time integral were measured using Doppler echocardiography; PVR was calculated from their ratio. Acetylene rebreathing technique using respiratory mass spectrometry was also performed to calculate pulmonary blood flow and stroke index, an estimate of PVR. Results TRV was higher in SCD children compared with controls (2.28 vs 2.14 m/s, p=0.02). Fifteen of 34 (44%) children with haemoglobin of the SS genotype (HbSS) versus 1/16 (6%) children with haemoglobin of the SC genotype (HbSC) had pulmonary hypertension (TRV≥2.5 m/s) (p=0.009). Right ventricular stroke volume was higher (p<0.05) and Doppler PVR lower (1.20 (0.19) vs 1.31 (0.20) Wood units, p=0.04) in SCD children with pulmonary hypertension compared with controls. Qpeff and stroke index were higher in SCD children compared with controls (p<0.001 for both) and correlated with anaemia (p<0.001) and TRV (p=0.03). There was no correlation between TRV and history of asthma or acute chest syndrome. Conclusions Pulmonary hypertension due to raised cardiac output is common in HbSS SCD children and is associated with normal PVR. PVR should be measured before therapy with agents such as sildenafil or bosentan is contemplated.

Usefulness of Changes in Left Ventricular Wall Thickness to Predict Full or Partial Pressure Reperfusion in ST-Elevation Acute Myocardial Infarction

Experimental studies have shown that if an acute transmural myocardial infarction is reperfused at full pressure there is an immediate and persisting increase in end-diastolic wall thickness (EDWT) due to massive intramural edema, with the amount of edema inversely related to the residual stenosis in the infarct-related artery. This study investigated if these findings are paralleled in the clinical setting and whether the resultant myocardial substrate differs after percutaneous coronary intervention (PCI) versus thrombolysis (the latter having a higher incidence of residual flow limiting stenosis in the culprit vessel). Eighty-eight consecutive patients with ST-elevation myocardial infarction were enrolled. Twenty-seven patients underwent primary PCI, 23 had rescue PCI, and 38 had thrombolysis. Standard M-mode and 2-dimensional echocardiographies were performed within 12 hours. Regional EDWT was measured in 904 infarct-related segments after the different reperfusion strategies and compared with 504 remote noninfarcted segments. EDWT of infarct-related segments after primary PCI was significantly increased compared with normal segments. At follow-up, after 6 months, EDWT of these segments was significantly decreased, indicating transmural infarction. EDWT of infarct-related segments after thrombolysis did not differ from that of normal segments. After rescue PCI, EDWT of infarct-related segments was significantly decreased compared with that of normal segments. In conclusion, full-pressure restoration of epicardial blood flow after transmural myocardial infarction causes an immediate increase in EDWT, easily detected by echocardiography. In contrast, pressure-limiting reperfusion (typical for thrombolysis) resultsin normal EDWT. This confirms experimental data that PCI and thrombolysis can differ in their resultant myocardial substrate.