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Cine MRI detects shorter cardiac rest periods in pulmonary hypertension
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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Figures

Figure 1 Four anchor points were set at septal and lateral sides of the LV and RV at base and apex (white circles) on four-chamber cine to track cardiac motion. The “rest status” was defined as motion of all 4 points < 1 mm on adjacent frames.

Figure 2 Compared to controls, PH patients had shorter rest periods at diastole ( 3.6 ± 2.1 phases vs. 6 ± 1.3 phases, p < 0.001). However, there was no differences on the length of rest periods at end-systole.

Figure 3 ROC curves showed that the relative length (AUC = 0.838), absolute length (AUC = 0.851) of rest periods and rest ratio (AUC = 0.845) were superior to heart rate (AUC = 0.643) in discriminating PH patients from controls.

Table 1 Multiple linear regressions showed that the existence of PH resulted in a shorter length of rest periods (represented by relative/absolute lengths of rest periods and rest ratios) after adjustment of various confounders (p < 0.05 at t tests)

Proc. Intl. Soc. Mag. Reson. Med. 30 (2022)
4915
DOI: https://doi.org/10.58530/2022/4915