Ventricular T2 Ratio by Cardiac MRI as a Non-Invasive Indicator of Exercise Tolerance in Pulmonary Arterial Hypertension

Background: Cardiac magnetic resonance (CMR) T2 mapping is sensitive to blood oxygenation and offers a non-invasive means to assess cardiopulmonary status. In pulmonary arterial hypertension (PAH), oxygen imbalance between the right and left heart may manifest as inter-ventricular differences in blood pool T2 values. We hypothesize that the diastolic RV/LV T2 ratio reflects impaired exercise capacity and holds prognostic potential in PAH.

Methods: We retrospectively analyzed 127 PAH patients and 64 matched healthy controls who underwent cardiac MRI with T2 mapping and 6-minute walk tests (6MWT). RV and LV blood pool T2 times were measured, and the RV/LV T2 ratio was calculated. Risk stratification followed WSPH criteria, supported by right heart catheterization data. Associations with 6MWT and mortality were assessed using regression and Cox proportional hazards models.

Results: Compared to healthy controls, PAH patients demonstrated significantly reduced exercise capacity as measured by the 6-minute walk test (6MWT), alongside marked alterations in right and left ventricular blood pool T2 relaxation times. The RV/LV T2 ratio showed a significant negative correlation with 6MWT distance (r = -0.29, p < 0.001), indicating that higher ratios were associated with worse functional capacity. Furthermore, multivariable Cox regression identified the RV/LV T2 ratio as an independent predictor of all-cause mortality, with an approximately fivefold increased risk (HR ≈ 5.0, p = 0.023). Elevated RV/LV T2 ratios were also linked to deteriorated right ventricular systolic function and increased pulmonary vascular resistance, reflecting progressive cardiopulmonary impairment.

Conclusion: The diastolic RV/LV blood pool T2 ratio derived from cardiac magnetic resonance imaging represents a sensitive and non-invasive biomarker that captures the extent of right ventricular dysfunction and oxygenation imbalance in PAH patients. Its strong association with exercise capacity and mortality risk highlights its potential utility for risk stratification and prognostic evaluation in clinical practice.

Correlation of ventricular blood pool T2 ratio with parameters in PAH patients

	RVT2/LVT2 ratio  R (p)
Demographics
Distance (m)	-0.294( < 0.001*)
BNP(ng/ml)	0.252(0.005*)
Tapse/pasp	-0.196(0.156)
CMR parameters
RVEDVi	0.175(0.053)
RVESVi	0.216(0.017*)
RVEF	-0.248(0.006*)
RVmassi	0.196(0.077)
Pulmonary hemodynamic parameters
SVO2	-0.336( < 0.001*)
mpap	0.215(0.018*)
CI	-0.171(0.067)
CO	-0.127(0.172)
PVR	0.186(0.043*)
QP/QS	-0.174(0.180)
RP/RS	0.241(0.009*)
Qep	-0.194(0.035*)
QepI	-0.202(0.029*)

Table 3. PAH Patient Groups and Parameters Based on WSPH Risk Stratification

	low risk (n=10)	medium risk(n=88)	high risk(n=29)	P value
Demographics
Females(%)				0.798
Age(years ± SD)	31.80±9.89	38.97±14.73	42.17±15.34	0.154
BMI (kg/m2 ± SD)	19.64±2.70	22.32±4.34	21.56±3.56	0.129
BSA  (m2 ± SD)	1.57±0.14	1.62±0.22	1.61±0.18	0.759
BNP (pg/ml)	140.50±131.60	1033.41±1413.59	3066.18±2883.13	< 0.001*
Distance (m ± SD)	526.20±85.76	393.80±100.05	320.31±110.67	< 0.001
CMR parameters
LVEDVi (ml/m2±SD)	83.64±20.24	66.31±20.43	57.40±29.44	0.009*
LVESVi (ml/m2±SD)	33.97±12.75	30.67±15.49	29.70±26.04	0.816
LVEF (% ± SD)	59.99±8.37	55.30±9.90	52.35±13.18	0.141
RVEDVi (ml/m2±SD)	101.39±25.30	137.30±177.52	135.20±54.11	0.779
RVESVi (ml/m2±SD)	54.53±18.98	78.73±49.70	105.38±44.85	0.007*
RVEF (% ± SD)	47.11±9.04	36.93±12.96	26.96±10.94	< 0.001
LV T2(ms± SD)	123.08±15.30	110.32±20.50	106.7±18.32	0.079
RV T2(ms± SD)	57.20±13.23	71.26±19.71	76.86±17.29	0.019*
RVT2/LV T2 ratio(± SD)	0.48±0.16	0.67±0.24	0.75±0.24	0.010*
Pulmonary hemodynamic parameters
Mean PAP (mmHg)	53.20±22.31	50.12±21.23	54.07±19.55	0.658
PVR (Wood)	8.11±5.22	12.67±7.71	22.30±11.69	< 0.001*
PAWP (mmHg)	6.00±4.69	8.89±5.00	10.58±5.24	0.072
CI (L/min/m2)	2.82±0.41	2.36±1.04	1.40±0.31	< 0.001*
CO(L/min)	4.38±0.64	3.64±1.74	2.22±0.62	< 0.001*
SVC  SO2 (%)	72.70±5.72	67.55±7.54	53.38±9.51	< 0.001*

Association Between Blood Pool T2 Ratio and Exercise Capacity