Noninvasive pulmonary transit time: A new parameter for general cardiac performance

A new noninvasive evaluation method of pulmonary thromboembolism in rabbits-pulmonary transit time

BACKGROUND AND AIM

Pulmonary thromboembolism (PTE) is a common cause of cardiovascular death worldwide. Due to its nonspecific clinical symptoms, PTE is easy to be missed or misdiagnosed. Pulmonary transit time (PTT) is a noninvasive cardiopulmonary hemodynamic index, which is the time required for a blood sample to pass through pulmonary circulation. This study is aim to establish a rabbit PTE model using auto-thrombus, evaluating the dynamic changes in a rabbit's heart structure and function at multiple time points before and after modeling by echocardiography and exploring the application value of PTT obtained by contrast enhanced ultrasound (CEUS) in evaluating a PTE model.

METHODS

Twenty-four healthy rabbits were intubated by femoral vein puncture to establish the PTE model. Echocardiography was performed before embolization, 2 h, 24 h, 3 days, 5 days, and 7 days after embolization to obtain conventional ultrasonic parameters. Then, CEUS was performed to obtain the PTT.

RESULTS

Seventh day after modeling, nineteen rabbits were alive. Compared with pre-modeling, right heart parameters and heart rate in echocardiography were significantly impaired in the acute phase (2 and 24 h after modeling) and gradually returned to normal in the compensatory phase (3, 5, and 7 days after modeling). In contrast with conventional ultrasound parameters, PTT and nPTT revealed a gradually increasing trend at each time point. Receiver operating characteristic (ROC) curve analysis revealed with an extension of molding time, the area under the curve (AUC) of (n)PTT is larger and larger.

CONCLUSIONS

Right heart parameters obtained using conventional echocardiography can accurately indicate changes in the structure and function of the right heart during the acute phase of PTE, while (n)PTT measured by CEUS continues to extend during the acute and compensatory phases of PTE. Therefore, PTT (nPTT) obtained by CEUS is a useful clinical indicator for the diagnosis of PTE and can be utilized as a supplement to conventional echocardiography parameters.

Pulmonary Transit Time Derived from First-Pass Perfusion Cardiac MR Imaging: A Potential New Marker for Cardiac Involvement and Prognosis in Light-Chain Amyloidosis

BACKGROUND

First-pass perfusion cardiac MR imaging could reflect pulmonary hemodynamics. However, the clinical value of pulmonary transit time (PTT) derived from first-pass perfusion MRI in light-chain (AL) amyloidosis requires further evaluation.

PURPOSE

To assess the clinical and prognostic value of PTT in patients with AL amyloidosis.

STUDY TYPE

Prospective observational study.

POPULATION

226 biopsy-proven systemic AL amyloidosis patients (age 58.62 ± 10.10 years, 135 males) and 43 healthy controls (age 42 ± 16.2 years, 20 males).

FIELD STRENGTH/SEQUENCE

SSFP cine and phase sensitive inversion recovery late gadolinium enhancement (LGE) sequences, and multislice first-pass myocardial perfusion imaging with a saturation recovery turbo fast low-angle shot (SR-TurboFLASH) pulse sequence at 3.0T.

ASSESSMENT

PTT was measured as the time interval between the peaks of right and left ventricular cavity arterial input function curves on first-pass perfusion MR images.

STATISTICAL TESTS

Independent-sample t test, Mann-Whitney U test, Chi-square test, Fisher's exact test, analysis of variance, or Kruskal-Wallis test, as appropriate; univariable and multivariable Cox proportional hazards models and Kaplan-Meier curves, area under receiver operating characteristic curve were used to determine statistical significance.

RESULTS

PTT could differentiate AL amyloidosis patients with (N = 188) and without (N = 38) cardiac involvement (area under the curve [AUC] = 0.839). During a median follow-up of 35 months, 160 patients (70.8%) demonstrated all-cause mortality. After adjustments for clinical (Hazard ratio [HR] 1.061, confidence interval [CI]: 1.021-1.102), biochemical (HR 1.055, CI: 1.014-1.097), cardiac MRI-derived (HR 1.077, CI: 1.034-1.123), and therapeutic (HR 1.063, CI: 1.024-1.103) factors, PTT predicted mortality independently in patients with AL amyloidosis. Finally, PTT could identify worse outcomes in patients demonstrating New York Heart Association class III, Mayo 2004 stage III, and transmural LGE pattern.

DATA CONCLUSION

PTT may serve as a new imaging predictor of cardiac involvement and prognosis in AL amyloidosis.

LEVEL OF EVIDENCE

2 TECHNICAL EFFICACY: Stage 2.

Stress and Rest Pulmonary Transit Times Assessed by Cardiovascular Magnetic Resonance

Acquiring pulmonary circulation parameters as a potential marker of cardiopulmonary function is not new. Methods to obtain these parameters have been developed over time, with the latest being first-pass perfusion sequences in cardiovascular magnetic resonance (CMR). Even though more data on these parameters has been recently published, different nomenclature and acquisition methods are used across studies; some works even reported conflicting data. The most commonly used circulation parameters obtained using CMR include pulmonary transit time (PTT) and pulmonary transit beats (PTB). PTT is the time needed for a contrast agent (typically gadolinium-based) to circulate from the right ventricle (RV) to the left ventricle (LV). PTB is the number of cardiac cycles the process takes. Some authors also include corrected heart rate (HR) versions along with standard PTT. Besides other methods, CMR offers an option to assess stress circulation parameters, but data are minimal. This review aims to summarize the up-to-date findings and provide an overview of the latest progress on this promising, dynamically evolving topic.

Pulmonary Transit Time Assessment by CEUS in Healthy Rabbits: Feasibility, and the Effects of UCAs Dilution Concentration

To evaluate the inter-observer variability and the intra-observer repeatability of pulmonary transit time (PTT) measurement using contrast-enhanced ultrasound (CEUS) in healthy rabbits, and assess the effects of dilution concentration of ultrasound contrast agents (UCAs) on PTT. Thirteen healthy rabbits were selected, and five concentrations UCAs of 1:200, 1:100, 1:50, 1:10, and 1:1 were injected into the right ear vein. Five digital loops were obtained from the apical 4-chamber view. Four sonographers obtained PTT by plotting the TIC of right atrium (RA) and left atrium (LA) at two time points (T1 and T2). The frame counts of the first appearance of UCAs in RA and LA had excellent inter-observer agreement, with intra-class correlations (ICC) of 0.996, 0.988, respectively. The agreement of PTT among four observers was all good at five different concentrations, with an ICC of 0.758-0.873. The reproducibility of PTT obtained by four observers at T1 and T2 was performed well, with ICC of 0.888-0.961. The median inter-observer variability across 13 rabbits was 6.5% and the median variability within 14 days for 4 observers was 1.9%, 1.7%, 2.2%, 1.9%, respectively; The PTT of 13 healthy rabbits is 1.01 ± 0.18 second. The difference of PTT between five concentrations is statistically significant. The PTT obtained by a concentration of 1:200 and 1:100 were higher than that of 1:1, while there were no significantly differences in PTT of a concentration of 1:1, 1:10, and 1:50. PTT measured by CEUS in rabbits is feasible, with excellent inter-observer and intra-observer reliability and reproducibility, and dilution concentration of UCAs influences PTT results.

Pulmonary transit time has close relation with pulmonary pulse wave transit time in normal subjects

BACKGROUND

Pulmonary transit time (PTT) and pulmonary pulse wave transit time (pPTT) are useful parameters for the evaluation of cardiopulmonary circulation and vascular alterations, but their relationship remains unknown. The aim of this study was to investigate the correlation between PTT and pPTT.

METHODS

A total of 60 healthy volunteers were involved in this study. They were divided into two groups (30 participants per group): <50 years and >50 years. They all underwent Doppler echocardiography of pulmonary vein flow and contrast echocardiography with the measurement of pPTT and PTT, respectively. The correlation between PTT and pPTT was deduced.

RESULTS

Compared with Group of <50 years, there was a significant increment in left atrial volume index, left atrial pressure and pulmonary artery stiffness but a significant reduction in acceleration times of pulmonary artery flow in Group of >50 years (p < 0.05). Group >50 years had longer PTT and but reduced normalized PTT by R-R interval (NPTT), reduced normalized pPTT by R-R interval (NpPTT) than Group <50 years (p < 0.05), while there was no significant difference in pPTT between the two groups (p > 0.05). PTT and NPTT were all negatively correlated with pPTT and NpPTT. The statistically significant strongest correlation was observed between PTT and NpPTT (r = -0.886, p < 0.0001). The regression equation for them was y = 7.4396-13.095x (R²  = 0.785; p < 0.001), where x and y represent NpPTT and PTT, respectively.

CONCLUSION

PTT had close relation with pPTT in normal subjects. From the regression equation for them, we can get the value of PTT simply and easily by non-invasively measured pPTT.

Pulmonary transit time of cardiovascular magnetic resonance perfusion scans for quantification of cardiopulmonary haemodynamics

AIMS

Pulmonary transit time (PTT) is the time blood takes to pass from the right ventricle to the left ventricle via pulmonary circulation. We aimed to quantify PTT in routine cardiovascular magnetic resonance imaging perfusion sequences. PTT may help in the diagnostic assessment and characterization of patients with unclear dyspnoea or heart failure (HF).

METHODS AND RESULTS

We evaluated routine stress perfusion cardiovascular magnetic resonance scans in 352 patients, including an assessment of PTT. Eighty-six of these patients also had simultaneous quantification of N-terminal pro-brain natriuretic peptide (NTproBNP). NT-proBNP is an established blood biomarker for quantifying ventricular filling pressure in patients with presumed HF. Manually assessed PTT demonstrated low inter-rater variability with a correlation between raters >0.98. PTT was obtained automatically and correctly in 266 patients using artificial intelligence. The median PTT of 182 patients with both left and right ventricular ejection fraction >50% amounted to 6.8 s (Pulmonary transit time: 5.9-7.9 s). PTT was significantly higher in patients with reduced left ventricular ejection fraction (<40%; P < 0.001) and right ventricular ejection fraction (<40%; P < 0.0001). The area under the receiver operating characteristics curve (AUC) of PTT for exclusion of HF (NT-proBNP <125 ng/L) was 0.73 (P < 0.001) with a specificity of 77% and sensitivity of 70%. The AUC of PTT for the inclusion of HF (NT-proBNP >600 ng/L) was 0.70 (P < 0.001) with a specificity of 78% and sensitivity of 61%.

CONCLUSION

PTT as an easily, even automatically obtainable and robust non-invasive biomarker of haemodynamics might help in the evaluation of patients with dyspnoea and HF.

Stress pulmonary circulation parameters assessed by a cardiovascular magnetic resonance in patients after a heart transplant

Rest pulmonary circulation parameters such as pulmonary transit time (PTT), heart rate corrected PTT (PTTc) and pulmonary transit beats (PTB) can be evaluated using several methods, including the first-pass perfusion from cardiovascular magnetic resonance. As previously published, up to 58% of patients after HTx have diastolic dysfunction detectable only in stress conditions. By using adenosine stress perfusion images, stress analogues of the mentioned parameters can be assessed. By dividing stress to rest biomarkers, potential new ratio parameters (PTT ratio and PTTc ratio) can be obtained. The objectives were to (1) provide more evidence about stress pulmonary circulation biomarkers, (2) present stress to rest ratio parameters, and (3) assess these biomarkers in patients with presumed diastolic dysfunction after heart transplant (HTx) and in childhood cancer survivors (CCS) without any signs of diastolic dysfunction. In this retrospective study, 48 patients after HTx, divided into subgroups based on echocardiographic signs of diastolic dysfunction (41 without, 7 with) and 39 CCS were enrolled. PTT was defined as the difference between the onset time of the signal intensity increase in the left and the right ventricle. PTT in rest conditions were without significant differences when comparing the CCS and HTx subgroup without diastolic dysfunction (4.96 ± 0.93 s vs. 5.51 ± 1.14 s, p = 0.063) or with diastolic dysfunction (4.96 ± 0.93 s vs. 6.04 ± 1.13 s, p = 0.13). However, in stress conditions, both PTT and PTTc were significantly lower in the CCS group than in the HTx subgroups, (PTT: 3.76 ± 0.78 s vs. 4.82 ± 1.03 s, p < 0.001; 5.52 ± 1.56 s, p = 0.002). PTT ratio and PTTc ratio were below 1 in all groups. In conclusion, stress pulmonary circulation parameters obtained from CMR showed prolonged PTT and PTTc in HTx groups compared to CCS, which corresponds with the presumption of underlying diastolic dysfunction. The ratio parameters were less than 1.

Prognostic Value of Pulmonary Transit Time by Cardiac Magnetic Resonance on Mortality and Heart Failure Hospitalization in Patients With Advanced Heart Failure and Reduced Ejection Fraction

BACKGROUND

Pulmonary transit time (PTT) from first-pass perfusion imaging is a novel parameter to evaluate hemodynamic congestion by cardiac magnetic resonance (cMR). We sought to evaluate the additional prognostic value of PTT in heart failure with reduced ejection fraction over other well-validated predictors of risk including the Meta-Analysis Global Group in Chronic Heart Failure risk score and ischemic cause.

METHODS

We prospectively followed 410 patients with chronic heart failure with reduced ejection fraction (61±13 years, left ventricular (LV) ejection fraction 24±7%) who underwent a clinical cMR to assess the prognostic value of PTT for a primary endpoint of overall mortality and secondary composite endpoint of cardiovascular death and heart failure hospitalization. Normal reference values of PTT were evaluated in a population of 40 asymptomatic volunteers free of cardiovascular disease. Results PTT was significantly increased in patients with heart failure with reduced ejection fraction as compared to controls (9±6 beats and 7±2 beats, respectively, P<0.001), and correlated not only with New York Heart Association class, cMR-LV and cMR-right ventricular (RV) volumes, cMR-RV and cMR-LV ejection fraction, and feature tracking global longitudinal strain, but also with cardiac output. Over 6-year median follow-up, 182 patients died and 200 reached the secondary endpoint. By multivariate Cox analysis, PTT was an independent and significant predictor of both endpoints after adjustment for Meta-Analysis Global Group in Chronic Heart Failure risk score and ischemic cause. Importantly in multivariable analysis, PTT in beats had significantly higher additional prognostic value to predict not only overall mortality (χ² to improve, 12.3; hazard ratio, 1.35 [95% CI, 1.16-1.58]; P<0.001) but also the secondary composite endpoints (χ² to improve=20.1; hazard ratio, 1.23 [95% CI, 1.21-1.60]; P<0.001) than cMR-LV ejection fraction, cMR-RV ejection fraction, LV-feature tracking global longitudinal strain, or RV-feature tracking global longitudinal strain. Importantly, PTT was independent and complementary to both pulmonary artery pressure and reduced RV ejection fraction<42% to predict overall mortality and secondary combined endpoints.

CONCLUSIONS

Despite limitations in temporal resolution, PTT derived from first-pass perfusion imaging provides higher and independent prognostic information in heart failure with reduced ejection fraction than clinical and other cMR parameters, including LV and RV ejection fraction or feature tracking global longitudinal strain. Registration: URL: https://www.clinicaltrials.gov; Unique identifier: NCT03969394.

A novel application of pulmonary transit time to differentiate between benign and malignant pulmonary nodules using myocardial contrast echocardiography

Malignant pulmonary nodules (PNs) are often accompanied by vascular dilatation and structural abnormalities. Pulmonary transit time (PTT) measurement by contrast echocardiograghy has used to assess the cardiopulmonary function and pulmonary vascular status, such as hepatopulmonary syndrome and pulmonary arteriovenous fistula, but has not yet been attempted in the diagnosis and differential diagnosis of PNs. The aim of this work was to evaluate the feasibility and performance of myocardial contrast echocardiography (MCE) for differentiating malignant PNs from benign ones. The study population consisted of 201 participant: 66 healthy participants, 65 patients with benign PNs and 70 patients with malignant PNs. Their clinical and conventional echocardiographic characteristics were collected. MCE with measurements of PTT were performed. There was no difference in age, sex, heart rate, blood pressure, smoking rate, background lung disease, pulmonary function, ECG, myocardial enzymes, cardiac size and function among the healthy participant, patients with benign and malignant PNs (P > 0.05). PTT did not differ significantly in patients with PNs of different sizes, nor did they differ in patients with PNs of different enhancement patterns (P > 0.05). However, the PTT were far shorter (about one half) in patients with malignant PNs than in patients with benign ones (1.88 ± 0.37 vs. 3.73 ± 0.35, P < 0.001). There was no significantly different between patients with benign PNs and healthy participant (3.73 ± 0.35 vs.3.89 ± 0.36, P > 0.05). The area under the receiver operating characteristics curve (AUC) of PTT was 0.99(0.978-1.009) in discriminating between benign and malignant PNs. The optimal cutoff value was 2.78 s, with a sensitivity of 98.52%, a specificity of 97.34%, and a accuracy of 97.69%. MCE had a powerful performance in differentiating between benign and malignant PNs, and a pulmonary circulation time of < 2.78 s indicated malignant PNs.

Pulmonary hypertension detection by computed tomography pulmonary transit time in heart failure with reduced ejection fraction

Aims

To evaluate the relationships between pulmonary transit time (PTT), cardiac function, and pulmonary haemodynamics in patients with heart failure with reduced ejection fraction (HFrEF) and to explore how PTT performs in detecting pulmonary hypertension (PH).

Methods and results

In this prospective study, 57 patients with advanced HFrEF [49 men, 51 years ± 8, mean left ventricular (LV) ejection fraction 26% ± 8] underwent echocardiography, right heart catheterization, and cardiac computed tomography (CT). PTT was measured as the time interval between peaks of attenuation in right ventricle (RV) and LV and was compared between patients with or without PH and 15 controls. PTT was significantly longer in HFrEF patients with PH (21 s) than in those without PH (11 s) and controls (8 s) (P &lt; 0.001) but not between patients without PH and controls (P = 0.109). PTT was positively correlated with pulmonary artery wedge pressure (PAWP) (r = 0.74), mean pulmonary artery pressure (r = 0.68), N-terminal pro-B-type natriuretic peptide (r = 0.60), mitral (r = 0.54), and tricuspid (r = 0.37) regurgitation grades, as well as with LV, RV, and left atrial volumes (r from 0.39 to 0.64) (P &lt; 0.01). PTT was negatively correlated with cardiac index (r = −0.63) as well as with LV (r = −0.66) and RV (r = −0.74) ejection fractions. PAWP, cardiac index, mitral regurgitation grade, and RV end-diastolic volume were all independent predictors of PTT. PTT value ≥14 s best-detected PH with 91% sensitivity and 88% specificity (area under the receiver operating characteristic curve: 0.95).

Conclusion

In patients with HFrEF, PTT correlates with cardiac function and pulmonary haemodynamics, is determined by four independent parameters, and performs well in detecting PH.

Cardiac Imaging in Liver Transplantation Candidates: Current Knowledge and Future Perspectives

Cardiovascular dysfunction in cirrhotic patients is a recognized clinical entity commonly referred to as cirrhotic cardiomyopathy. Systematic inflammation, autonomic dysfunction, and activation of vasodilatory factors lead to hyperdynamic circulation with high cardiac output and low peripheral vascular resistance. Counter acting mechanisms as well as direct effects on cardiac cells led to systolic or diastolic dysfunction and electromechanical abnormalities, which are usually masked at rest but exposed at stress situations. While cardiovascular complications and mortality are common in patients undergoing liver transplantation, they cannot be adequately predicted by conventional cardiac examination including transthoracic echocardiography. Newer echocardiography indices and other imaging modalities such as cardiac magnetic resonance have shown increased diagnostic accuracy with predictive implications in cardiovascular diseases. The scope of this review was to describe the role of cardiac imaging in the preoperative assessment of liver transplantation candidates with comprehensive analysis of the future perspectives anticipated by the use of newer echocardiography indices and cardiac magnetic resonance applications.

The relationship between pulmonary artery wedge pressure and pulmonary blood volume derived from contrast echocardiography: A proof-of-concept study

BACKGROUND

Pulmonary transit time (PTT) obtained from contrast echocardiography is a marker of global cardiopulmonary function. Pulmonary blood volume (PBV), derived from PTT, may be a noninvasive surrogate for left-sided filling pressures, such as pulmonary artery wedge pressure (PAWP). We sought to assess the relationship between PBV obtained from contrast echocardiography and PAWP.

METHODS

Participants were adult survivors of childhood cancer that had contrast echocardiography performed nearly simultaneously with right-heart catheterization. PTT was derived from time-intensity curves of contrast passage through the right ventricle (RV) and left atrium (LA). PBV relative to overall stroke volume (rPBV) was estimated from the product of PTT and heart rate during RV-LA transit. PAWP was obtained during standard right-heart catheterization. The Spearman correlation coefficient was used to assess the relationship between rPBV and PAWP.

RESULTS

The study population consisted of 7 individuals who had contrast echocardiography and right-heart catheterization within 3 hours of each other. There was a wide range of right atrial (1-17 mm Hg), mean pulmonary artery (18-42 mm Hg), and PAW pressures (4-26 mm Hg) as well as pulmonary vascular resistance (<1-6 Wood Units). We observed a statistically significant correlation between rPBV and PAWP (r = .85; P = .02).

CONCLUSION

Relative PBV derived from contrast echocardiography correlates with PAWP. If validated in larger studies, rPBV could potentially be used as an alternative to invasively determine left-sided filling pressure.