Kai Lin1, Roberto Sarnari1, Ashitha Pathrose1, Daniel Gordon1, Michael Markl1, and James Carr1
1Radiology, Northwestern University, Chicago, IL, United States
Synopsis
The existence of pulmonary
hypertension (PH) can independently shorten the length of cardiac rest periods.
The length of cardiac rest periods can be used to discriminate PH patients from
healthy controls.
Background
Cardiac rest periods refer to time intervals in a cardiac cycle when the
cardiac motion is minimal, and the ventricles are nearly “frozen”. Cardiac rest periods serve as optimal acquisition windows for magnetic
resonance imaging (MRI) examinations that are
sensitive to cardiac motion. Typically located in the end-systole and the middle to late-diastole, cardiac
rest periods are formed during transition courses between adjacent contraction
and dilation modes of the ventricles. Therefore, changes of systolic and
diastolic properties are expected to disturb the temporary myocardial
“quiescence” and reshape the rest periods. Unfortunately, the length of cardiac rest
periods was traditionally used as a technical factor for adjusting imaging parameters. Its clinical
relevance has not been reported.Purpose
To test the hypothesis that
the existence of pulmonary hypertension (PH) alters the length of cardiac rest
periods.Materials and methods
With
the approval of institution review board (IRB), 51 consecutive PH patients (21
males, 33 – 83 years old, diagnosed with right heart catheterization [RHC]) and
24 healthy volunteers (15 males, 26 – 80 years old) were recruited to undergo
MRI scans. The length of cardiac rest fields was measured on cine MRI (at
four-chamber view) and expressed as relative/absolute lengths and rest ratios. Figure 1. The lengths of rest periods were compared between participant groups.
Multiple linear models (MLR) were used to find Influences of the length of cardiac
rest periods. Receiver operation curve (ROC) was used to estimate the
capability of the length of cardiac rest periods in predicting PH.Results
Compared to health controls,
PH patients were older (59.1 ± 13.6 years vs. 51.8 ± 13.8 years, p = 0.032) and
they had higher bodyweight (92.1 ± 23.2 Kg vs. 76.8 ± 17.3 Kg, p = 0.006), BMI
(32.2 ± 6.9 vs. 26 ± 4.9, p < 0.001), heart rates (76.5 ± 9.1 vs. 69.5 ± 9.3,
p = 0.021), RVESV (89.2 ± 41 vs. 67.6 ± 20.7, p = 0018), lower RVEF (47.1 ± 12.1
% vs. 56 ± 5.6 %, p = 0.001), shorter relative (3.6 ± 2.1 phases vs. 6 ± 1.3
phases, p < 0.001) and absolute (120.6 ± 77.2 ms vs. 212.5 ± 60.2 ms, p <
0.001) lengths of cardiac rest periods and lower rest ratios (0.21 ± 0.1 vs.
0.44 ± 0.1, p < 0.001 ) in diastole. While there was no difference on other
indices, including the length of rest periods in end-systole. Figure 2.
There were strong correlations among
relative and absolute lengths and rest ratios at diastole (r > 0.9, p <
0.05). However, only absolute length of rest periods at diastole had a moderate
correlation with heart rates (r = -0.571, p < 0.001). Using multi-variate
linear models, we found that the status of PH independently contributed to a
shorter cardiac rest period (relative and absolute) and rest ratio at diastole after
the adjustment of age, heart rate, body weight, BMI, RVESF and RVEF. Table 1.
ROC
curves showed that relative (AUC = 0.838, 95% CI = 0.747 – 0.929) and absolute
(AUC = 0.851, 95% CI = 0.764 – 0.939) lengths of rest periods and rest ratios
(AUC = 0.845, 95% CI = 0.755 – 0.939) at diastole had better performance (Z
tests, p < 0.05) than the heart rate (AUC = 0.643, 95%CI = 0.513 – 0.773) in
discriminating PH patients from controls. Figure 3.Discussion
In the
present study, we demonstrated that the existence of PH independently resulted
in a significant reduction of cine MRI-derived cardiac rest periods in diastole
after the adjustment of prominent covariates, including age and heart rates. The
length of cardiac rest periods could effectively discriminate PH patients from controls.
As such, a shorter cardiac rest period was found no longer just an adverse
physical condition for cardiac imaging. It has the potential to become a novel imaging
biomarker of CVDs.
In
addition to establishing the role of the length of cardiac rest periods in the assessment
of CVDs, our results might also draw attentions from developers of cardiac imaging
techniques. Since CVDs could be another prominent source of a short rest
period, it should be caution that some imaging techniques which are originally
developed on healthy volunteers may encounter extra difficulties in CVDs patients
with shorter rest periods.
Our study has limitations. First, we only measured
cardiac rest periods on 4-chamber view cine MRI because both LV and RV were fully
visible on this standard view. Therefore, the motion perpendicular to the imaging
plane could be missed. Second, compared to clinical echocardiography, the
temporal resolution of cine MRI protocol in the present study was low. With 25
phases per cardiac cycle, we were unable to detect possible subtle differences
of rest periods, especially at the end-systole.
Conclusion
PH
is independently associated with shorter cardiac rest periods in diastole. The
length of cardiac rest periods has the potential to become a novel quantitative
imaging biomarker for presenting cardiovascular health.Acknowledgements
No acknowledgement found.References
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