Multiparametric evaluation of coronary flow predicts long-term outcome in heart transplantation: from coronary flow velocity reserve to its newly introduced companion

Background

Coronary microvascular dysfunction (CMD) leads to a worse prognosis in heart transplantation (HT) patients. Coronary flow velocity reserve (CFVR) estimates the physiologic impact of allograft disease on the coronary circulation.

Purpose

Our aim was to determine the prognostic role of CFVR and its companion (CFVRC) on long-term survival of HT patients with a follow-up of 28 years.

Methods

134 HT patients, surviving at least 5 years after HT, with normal systolic ventricular function and no evidence of angiographic allograft vasculopathy or symptoms/signs of rejection were included. The enrolled population underwent echocardiographic evaluation of microvascular function by the assessment of both the ratio of hyperemic to rest diastolic peak velocity (DPVh and DPVr). These measurements yield CFVR and its associated companion, defined as CFVRC = √{(DPVr)2 + (DPVh)2}, as well as basal and hyperemic coronary microvascular resistance (BMR and HMR). A CFVR≤2.5 was considered abnormal; the median value of DPVh (75 cm/s) and CFVRC (80 cm/s) were utilized to dichotomize the population.

Results

Based on CFVR and DPVh, HT patients can be assigned to four groups: group 1 (n=32), discordant with preserved CFVR (3.1±0.4); group 2 (n=60), concordant with preserved CFVR (3.4±0.5); group 3 (n=31), concordant with impaired CFVR (1.8±0.3) and group 4 (n=11), discordant with impaired CFVR (2.0±0.2). Survival for each patient group is presented in the Figure (panel A). Specifically, survival was similar in group 1 when compared to group 3 (p=0.8), but significantly lower when compared to group 2 (p=0.03). Therefore, a normal CFVR (>2.5) may not be able to predict the unfavourable long-term outcome. CFVR in fact is an incomplete dimensionless ratio; if the paired velocities are low with high BMR and HMR (group 1), the use of CFVR alone may miss some events, that are yet captured by CFVRC. Differences between survivors and no survivors are presented in the Table. At multivariable survival analysis, CMD, DPVh<75 cm/s, CFVRC<80 cm/s were independent predictors of mortality in HT patients. Consequently, we evaluated the added role of the CMD, DPVh<75 cm/s and CFVRC<80 cm/s to prognostic models including the clinical (Figure, panel B) predictors of mortality. The inclusion of CFVRC<80 cm/s to model with clinical predictors of mortality permitted better prediction of survival in HT patients, compared to only adding CMD or DPVh<75 cm/s.

Conclusions

This study is the first to demonstrate that the CFVR alone, even representing a determinant of survival in long-term HT patients, is not sufficient to completely predict long-term survival in HT patients. In comparison to CMD and DPVh, the CFVRC provides a significant improvement in survival prediction in long-term HT patients. Thus, the proposed multiparametric approach offers a more comprehensive evaluation of prognosis in HT patients, just by applying available data without the need to perform additional measurements.

Funding Acknowledgement

Type of funding source: None

Coronary flow evaluation in heart transplant patients compared to healthy controls documents the inadequacy of the coronary flow velocity reserve metric

Background

Coronary microvasculopathy has impact on prognosis in heart transplantation (HT). Distinct contributions by functional or structural alterations of coronary microcirculation in HT and their prognostic role have not been fully elucidated.

Purpose

We aimed to identify the mechanisms of coronary microvascular impairment in HT and their possible prognostic implications by applying a comprehensive analysis in a comparative study.

Methods

Included were 134 patients, surviving at least 5 years, with normal systolic function and no evidence of allograft vasculopathy or symptoms/signs of rejection. To permit comparison, 50 healthy volunteers without cardiovascular diseases, and matched for age and sex, served as controls. All underwent echocardiographic evaluation of microvascular function by the assessment of rest and hyperemic diastolic peak blood velocity (DPVr and DPVh). These paired data enable calculation of coronary flow velocity reserve (CFVR) and its inherent companion that is based on the quadratic mean: CFVRC = √{(DPVr)2 + (DPVh)2}. Additionally, basal and hyperemic coronary microvascular resistance (BMR and HMR) were estimated. A CFVR ≤2.5 was considered abnormal; the median value of DPVh (75 cm/s) and CFVRC (80 cm/s) were selected as cut-offs to classify patients.

Results

HT patients can be assigned to four groups, based on their CFVR and DPVh (Figure A): group 1 (n=32), discordant with preserved CFVR (3.1±0.4); group 2 (n=60), concordant with preserved CFVR (3.4±0.5); group 3 (n=31), concordant with impaired CFVR (1.8±0.3) and group 4 (n=11), discordant with impaired CFVR (2.0±0.2). Group 3 represents the structural microvascular remodeling with high HMR, while group 4 represents the functional remodeling with low BMR. Intriguingly, group 1 showed lower DPVr (p<0.0001) and lower DPVh (p<0.0001) than controls (Figure B, upper panel) with lower CFVR (p<0.0001), even if normal, and lower CFVRC (p<0.0001) than controls (Figure B, lower panel). Moreover, both BMR and HMR were higher in group 1 than in controls (5.3±1 vs 4.4±1.2, p=0.001 and 1.5±0.3 vs 1.1±0.2, p<0.0001, respectively), suggesting structural microvascular remodeling. Conversely, group 2 was comparable with controls (Figure B). Clinical characteristics of the different groups are shown in the Table. 13/32 (40.6%) patients in group 1 died in a follow up of 28 years and mortality rate was comparable to group 3 (14/31, 45.2%). However, CFVRC was <80 cm/s in all 13 deaths in group 1, yet being characterized by preserved CFVR (Figure C).

Conclusions

A normal CFVR could hide detection of microvascular damage with high flow resistance and low flow velocities at rest. This microvasculopathy seems to be secondary to factors unrelated to HT (i.e., less rejections and more often diabetes). Being a dimensionless ratio, CFVR may miss some deaths, yet captured by CFVRC. Thus, the combined use of CFVR and CFVRC provides more complete clinical information on coronary microvasculopathy in HT.

Funding Acknowledgement

Type of funding source: None