Results
This study included a total of 22,450 OHT recipients. Of these, 13,389
(59.6%) were male and received a heart from a male donor (MtoM), 3,660
(16.3%) were female and received a heart from a female donor (FtoF). A
total of 2,292 (10.2%) recipients were female and received a heart from
a male donor (MtoF), and 3,019 (13.4%) were male and received a heart
from a female donor (FtoM). Baseline recipient, donor, and transplant
characteristics are presented in Table 1 . Median age was
highest in the FtoM cohort, and this cohort had both the highest
percentage of patients with ischemic cardiomyopathy and lowest
percentage of patients with nonischemic cardiomyopathy (all
P<0.001).
Distributions of donor-to-recipient sizing are presented inTable 2 . For the weight and BMI metrics, a cutoff of
> 20% donor-to-recipient discrepancy, or a
donor-to-recipient ratio < 0.8 were used to define
“undersized”. A > 15% donor-to-recipient discrepancy, or
a donor-to-recipient ratio < 0.85 were used to define
undersizing using the pHM metric. These thresholds were based on prior
publications6,8,9. FtoM recipients were least commonly
undersized based on weight and BMI sizing metrics (both
P<0.001). When using the pHM sizing metric, FtoM recipients
were most commonly undersized (48.1% undersized, P<0.001).
Following OHT, the FtoM cohort experienced the highest incidence of
renal failure requiring dialysis (Table 3 ) (P=0.039). Rates of
posttransplant stroke and pacemaker placement were equivalent.
Thirty-day mortality was highest in the FtoM cohort and lowest in the
MtoF cohort (4.6% vs 2.9%, P=0.003). Drug-treated acute graft
rejection within the first year of transplantation was highest in the
FtoF cohort and lowest in the MtoM cohort (16.5% vs 9.7%,
P<0.001).
Median follow up time was 2.98 years (IQR 1.00 to 5.63 years). At one
year, actuarial survival was greatest in the MtoF cohort (92.0%).
Actuarial survival was lowest in the FtoM cohort (90.0%, P=0.0169).
Kaplan Meier survival comparison of all donor-recipient sex pairs are
displayed in Figure 1 .
A multivariable analysis was performed to identify independent
risk-adjusted predictors of one-year mortality following OHT. This
analysis adjusted for multiple independent predictors of mortality
including race, heart failure etiology, body mass index, pretransplant
mechanical ventilation or use of intra-aortic balloon pump, ventricular
assist device, donor age, and graft cold ischemia time. Predictors are
presented in Table 4 . In this analysis, both FtoF (HR 1.29,
95% CI 1.14 to 1.62, P=0.001) and FtoM (OR 1.17, 95% CI 1.01 to 1.36,
P=0.034) donation were associated with increased odds for mortality (in
relation to MtoM).
Because the FtoM cohort was found to have the lowest unadjusted 30-day
and one-year mortality, we investigated the impact of various
donor-recipient sizing metrics on posttransplant outcomes. In a
univariable analysis, donor weight undersizing was associated with a 1%
increase in odds for one-year mortality for each 1% undersized in
relation to the recipient, though these findings did not reach
statistical significance (OR 1.01, 95% CI 1.00 to 1.01, P=0.055). This
relation was also observed with undersizing based on pHM, and did not
meet statistical significance (OR 1.01, 95% CI 1.00 to 1.02, P=0.170).
Undersizing by BMI was found to have a significant association with
one-year mortality (per 1% undersized, OR 1.01, 95% CI 1.00 to 1.01,
P=0.008).
Multivariable logistic regression was performed to identify independent
risk factors of one-year posttransplant mortality in the FtoM cohort. In
this model, donor-recipient sizing metrics were adjusted for recipient
age, year of transplantation, heart failure etiology, total bilirubin
and serum creatinine, pretransplant mechanical ventilation, ventricular
assist device, and waitlist time. Full models are displayed inSupplemental Tables 1 – 3 . In these models, donor heart
undersizing was significantly associated increased odds of mortality for
all three sizing metrics (Table 5 ). For each sizing metric, a
1% increase in the degree of undersizing was associated with a 1%
increase in odds of one-year mortality. A large change in
donor-recipient sizing ratio (50% reduction, or recipient value twice
that of the donor value) was associated with significant increases in
odds of mortality. Of sizing metrics, a 50% reduction in pHM ratio had
the highest odds of mortality (OR 3.74, 95 CI 1.25 to 11.16, P=0.018).
Donor sizing metrics were also analyzed as categorical variables with
weight and BMI ratios of < 0.8 considered undersized, and with
a pHM < 0.85 considered undersized. In these analyses after
risk adjustment, both undersizing based on weight (OR 1.40, 95% CI 0.94
to 2.07, P=0.095) and BMI (OR 1.47, 95% CI 0.84 to 2.58, P=0.180) were
not significantly associated with posttransplant mortality. Undersizing
using the pHM metric was associated with a significant increase in
mortality (OR 1.32, 95% CI 1.02 to 1.71, P=0.035).