Transpulmonary gradient and diastolic pressure gradient
Transpulmonary gradient (TPG) is defined as the difference between the mean pulmonary arterial pressure and the left atrial pressure, which is usually equal to pulmonary capillary wedge pressure (PCWP) . When transpulmonary gradient is >12 mm Hg in left heart disease, it is considered as out of proportion pulmonary hypertension indicating pulmonary vascular disease. Diastolic pulmonary gradient (DPG) is the difference between the pulmonary artery diastolic pressure and pulmonary capillary wedge pressure.
Diastolic pulmonary gradient is important in patients with out of proportion pulmonary hypertension in left heart disease . Those with elevated DPG have significant pulmonary vascular disease and increased mortality. A study evaluated 1094 patients with post capillary pulmonary hypertension due to left heart disease. In those with transpulmonary gradient >12 mmHg, worse median survival was associated with a DPG ≥ 7 mm Hg (78 months) compared with a DPG < 7 mm Hg (101 months, P = .010) .
Preoperative transpulmonary gradient is an important predictor of nonrejection-related early mortality after orthotopic cardiac transplantation . Transpulmonary gradient was higher in those who died after cardiac transplantation. The study assessed the effect of transpulmonary gradient and pulmonary vascular resistance on post-transplant 30 day mortality. 718 adult patients undergoing primary cardiac transplantation were evaluated. A combination of transpulmonary gradient and pulmonary vascular resistance was a more reliable predictor of early post-transplant survival than pulmonary vascular resistance alone.
Another study of 109 recipients who underwent orthotopic cardiac transplantation also showed similar results . In this study, elevated preoperative transpulmonary gradient was associated with significant increase in mortality at 6 months and 12 months after orthotopic heart transplantation.
Elevated transpulmonary gradient is a risk factor for right heart failure after heart transplantation. Jahanyar J et al queried the UNOS (United Network for Organ Sharing) database from 1987 to 2017 and included adults who had complete transpulmonary gradient data. Those who underwent retransplant were excluded. Their sample consisted of 38,243 patients. It was found that median survival was higher in low transpulmonary gradient group (145 months vs 133 months in the high transpulmonary gradient group p<0.0001). Longer length of hospital stay was noted in high transpulmonary gradient group.