Right-to-left ventricular diastolic delay in chronic thromboembolic pulmonary hypertension is associated with activation delay and action potential prolongation in right ventricle

Repolarization Dispersion Is Associated With Diastolic Electromechanical Discoordination in Children With Pulmonary Arterial Hypertension

Background

Electromechanical dyssynchrony is a well described comorbidity in pulmonary arterial hypertension (PAH). ECG‐derived measurements reflective of diastolic dysfunction and electromechanical imaging markers are yet to be investigated. In this study we investigated the ECG‐ derived marker of repolarization dispersion, interval between the peak and end of T wave (TpTe), in pediatric patients with PAH and left ventricular (LV) diastolic dysfunction.

Methods and Results

We measured TpTe from a standard 12‐lead ECG and in 30 children with PAH and matched control subjects. All participants underwent same‐day echocardiography and myocardial strain analysis to calculate the diastolic electromechanical discoordination marker diastolic relaxation fraction. When compared with control subjects, patients with PAH had increased TpTe (93±15 versus 81±12 ms, P=0.001) and elevated diastolic relaxation fraction (0.33±0.10 versus 0.27±0.03, P=0.001). Patients with PAH with LV diastolic dysfunction had significantly increased TpTe when compared with patients with PAH without diastolic dysfunction (P=0.012) and when compared with control group (P<0.001). Similarly, patients with PAH with LV diastolic dysfunction had increased diastolic relaxation fraction when compared with PAH patients without diastolic dysfunction (P=0.007) and when compared with control group (P<0.001). A 10‐ms increase in TpTe was significantly associated with 0.023 increase in diastolic relaxation fraction (P=0.008) adjusting for body surface area, heart rate, right ventricular volumes, and function.

Conclusions

Prolonged myocardial repolarization and abnormal LV diastolic electromechanical discoordination exist in parallel in children with PAH and are associated with worse LV diastolic function and functional class.

Interventricular systolic asynchrony predicts prognosis in patients with systemic sclerosis-associated pulmonary arterial hypertension

OBJECTIVE

Pulmonary arterial hypertension (PAH) is a serious complication of systemic sclerosis (SSc) with high mortality. Interventricular systolic asynchrony (IVSA) is observed in PAH patients, but the effect of IVSA and its association with long-term mortality and clinical events in SSc-associated PAH are unclear. This study aimed to investigate the impact of IVSA on the prognosis of SSc-associated PAH.

METHODS

Between March 2010 and July 2018, a total of 60 consecutive patients with SSc-associated PAH were enrolled. The end point was a composite of all-cause mortality and clinical worsening. Asynchrony was assessed by colour-coded tissue Doppler imaging (TDI) echocardiography. The myocardial sustained systole curves (Sm) of the basal portion of the right ventricular (RV) free wall and left ventricular (LV) lateral wall were obtained. IVSA was defined as the time difference from the onset of the QRS complex to the end of Sm between LV and RV.

RESULTS

Patients with greater IVSA time differences presented with advanced pulmonary vascular resistance (PVR). The IVSA time difference was an independent predictive factor (HR = 1.018, 95% CI 1.005-1.031, p = 0.005) for the composite end point and was significantly associated with PVR (r = 0.399, R2=0.092, p = 0.002). Kaplan-Meier survival curves showed that patients with greater IVSA had worse prognoses (log-rank p = 0.001).

CONCLUSION

In conclusion, IVSA analyzed by colour-coded TDI echocardiography provided added value as a noninvasive, easy-to-use approach for assessing the prognosis of patients with SSc-associated PAH. A significant IVSA time difference identifies the subgroup of patients at high risk of a poor prognosis.

Preliminary Study of Right Ventricular Dyssynchrony Under High-Altitude Exposure: Determinants and Impacts

The aims of this study were to explore the effect of high-altitude (HA) exposure on the incidence, determinants, and impacts of right ventricular dyssynchrony (RVD). In our study, 108 healthy young men were enrolled, and physiological and echocardiographic variables were recorded at both sea level and 4,100 m. By using two-dimensional speckle-tracking echocardiography, RVD was evaluated by calculating the R–R interval-corrected standard deviation of the time-to-peak systolic strain for the four mid-basal RV segments (RVSD4) and defined by RVSD4 > 18.7 ms. After HA exposure, RVSD4 was significantly increased, and the incidence of RVD was approximately 32.4%. Subjects with RVD showed lower oxygen saturation (SaO₂) and RV global longitudinal strain and higher systolic pulmonary artery pressure than those without RVD. Moreover, myocardial acceleration during isovolumic contraction was increased in all subjects and those without RVD, but not in those with RVD. Multivariate logistic regression revealed that SaO₂ is an independent determinant of RVD at HA (odds ratio: 0.72, 95% CI: 0.56–0.92; P = 0.009). However, the mean pulmonary artery pressure was linearly correlated with the magnitude of RVD in the presence of Notch. No changes were found in RV fractional area change, tricuspid annular motion, or tricuspid s’ velocity between subjects with and without RVD. Collectively, we demonstrated for the first time that HA exposure could induce RVD in healthy subjects, which may be mainly attributed to the decline in SaO₂ as well as RV overload; the incidence of RVD was associated with reduced RV regional function and blunted myocardial acceleration.

First in human: the effects of biventricular pacing on cardiac output in severe pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) carries high morbidity and mortality despite available treatment options. In severe PAH, right ventricular (RV) diastolic pressure overload leads to interventricular septal bowing, hindering of left ventricular diastolic filling and reduced cardiac output (CO). Some animal studies suggest that pacing may mitigate this effect. We hypothesized that eliminating late diastole via ventricular pacing could improve CO in human subjects with severe PAH. Using minimal to no sedation, we performed transvenous acute biventricular (BiV) pacing and right heart catheterization in six patients with symptomatic PAH. Hemodynamic measurements were taken at baseline and during BiV pacing at various 20-ms intervals of V-V timing. We compared baseline CO to (1) CO while pacing the RV first by 80 ms (mimicking RV-only pacing), and then to (2) CO during pacing at the V-V timing that resulted in the highest CO. All participants were female, PASP 74 ± 14 mmHg, QRS duration 104 ± 20 ms. Compared with baseline, the CO decreased when the RV was paced first by 80 ms (7.2 ± 1.0 vs. 6.2 ± 1.1 L/min, p = 0.028). Pacing with optimal V-V timing produced CO similar to baseline (7.2 ± 1.0 vs. 7.4 ± 1.4, p = 0.92). Two patients (33%) met the predefined endpoint of a 15% increase in CO during pacing at the optimal V-V timing. In symptomatic PAH, V-V optimized acute BiV pacing does not consistently improve CO. However, acute BiV pacing did improve CO in a subset of this cohort. Further research is needed to identify predictors of response to cardiac resynchronization therapy in this population.

Adaptation to acute pulmonary hypertension in pigs

The extent of right ventricular compensation compared to the left ventricle is restricted and varies among individuals, which makes it difficult to define. While establishing a model of acute pulmonary hypertension in pigs we observed two different kinds of compensation in our animals. Looking deeper into the hemodynamic data we tried to delineate why some animals could compensate and others could not. Pulmonary hypertension (mean pressure 45 mmHg) was induced gradually by infusion of a stable thromboxane A₂ analogue U46619 in a porcine model (n = 22). Hemodynamic data (pressure‐volume loops, strain‐analysis of echocardiographic data and coronary flow measurements) were evaluated retrospectively for the short‐term right ventricular compensatory mechanisms and limits (Roehl et al. [2012] Acta Anaesthesiol. Scand., 56:449–58) 10 animals showed stable arterial blood pressures, whereas 12 pigs exhibited a significant drop of 16.4 ± 9.9 mmHg. Cardiac output and heart rate were comparable in both groups. In contrast, right ventricular contractility and coronary flow only rose in the stable group. The unchanging values in the decrease group correlated with an increasing ST‐segment depression and a loss of ventricular synchronism and resulted in a larger septum bulging to the right ventricle. Simultaneously, a reduced left‐ventricular end‐diastolic volume and a missing improvement in contractility in the posterior septal and inferior free wall of the left ventricle have been observed. Our findings suggest that right ventricular compensation during acute pulmonary hypertension is strongly dependent on the individual capability to increase coronary flow. The cause for inter‐individual variability could be the dimension and reactivity of the coronary system.

Role of abnormal repolarization in the mechanism of cardiac arrhythmia

In cardiac patients, life-threatening tachyarrhythmia is often precipitated by abnormal changes in ventricular repolarization and refractoriness. Repolarization abnormalities typically evolve as a consequence of impaired function of outward K⁺ currents in cardiac myocytes, which may be caused by genetic defects or result from various acquired pathophysiological conditions, including electrical remodelling in cardiac disease, ion channel modulation by clinically used pharmacological agents, and systemic electrolyte disorders seen in heart failure, such as hypokalaemia. Cardiac electrical instability attributed to abnormal repolarization relies on the complex interplay between a provocative arrhythmic trigger and vulnerable arrhythmic substrate, with a central role played by the excessive prolongation of ventricular action potential duration, impaired intracellular Ca²⁺ handling, and slowed impulse conduction. This review outlines the electrical activity of ventricular myocytes in normal conditions and cardiac disease, describes classical electrophysiological mechanisms of cardiac arrhythmia, and provides an update on repolarization-related surrogates currently used to assess arrhythmic propensity, including spatial dispersion of repolarization, activation-repolarization coupling, electrical restitution, TRIaD (triangulation, reverse use dependence, instability, and dispersion), and the electromechanical window. This is followed by a discussion of the mechanisms that account for the dependence of arrhythmic vulnerability on the location of the ventricular pacing site. Finally, the review clarifies the electrophysiological basis for cardiac arrhythmia produced by hypokalaemia, and gives insight into the clinical importance and pathophysiology of drug-induced arrhythmia, with particular focus on class Ia (quinidine, procainamide) and Ic (flecainide) Na⁺ channel blockers, and class III antiarrhythmic agents that block the delayed rectifier K⁺ channel (dofetilide).

Diastolic Dysfunction Increases the Risk of Primary Graft Dysfunction after Lung Transplant

RATIONALE

Primary graft dysfunction (PGD) is a significant cause of early morbidity and mortality after lung transplant and is characterized by severe hypoxemia and infiltrates in the allograft. The pathogenesis of PGD involves ischemia-reperfusion injury. However, subclinical increases in pulmonary venous pressure due to left ventricular diastolic dysfunction may contribute by exacerbating capillary leak.

OBJECTIVES

To determine whether a higher ratio of early mitral inflow velocity (E) to early diastolic mitral annular velocity (é), indicative of worse left ventricular diastolic function, is associated with a higher risk of PGD.

METHODS

We performed a retrospective cohort study of patients in the Lung Transplant Outcomes Group who underwent bilateral lung transplant at our institution between 2004 and 2014 for interstitial lung disease, chronic obstructive pulmonary disease, or pulmonary arterial hypertension. Transthoracic echocardiograms obtained during evaluation for transplant listing were analyzed for E/é and other measures of diastolic function. PGD was defined as PaO2/FiO2 less than or equal to 200 with allograft infiltrates at 48 or 72 hours after reperfusion. The association between E/é and PGD was assessed with multivariable logistic regression.

MEASUREMENTS AND MAIN RESULTS

After adjustment for recipient age, body mass index, mean pulmonary arterial pressure, and pretransplant diagnosis, higher E/é and E/é greater than 8 were associated with an increased risk of PGD (E/é odds ratio, 1.93; 95% confidence interval, 1.02-3.64; P = 0.04; E/é >8 odds ratio, 5.29; 95% confidence interval, 1.40-20.01; P = 0.01).

CONCLUSIONS

Differences in left ventricular diastolic function may contribute to the development of PGD. Future trials are needed to determine whether optimization of left ventricular diastolic function reduces the risk of PGD.

Why septal motion is a marker of right ventricular failure in pulmonary arterial hypertension: mechanistic analysis using a computer model

Rapid leftward septal motion (RLSM) during early left ventricular (LV) diastole is observed in patients with pulmonary arterial hypertension (PAH). RLSM exacerbates right ventricular (RV) systolic dysfunction and impairs LV filling. Increased RV wall tension caused by increased RV afterload has been suggested to cause interventricular relaxation dyssynchrony and RLSM in PAH. Simulations using the CircAdapt computational model were used to unravel the mechanism underlying RLSM by mechanistically linking myocardial tissue and pump function. Simulations of healthy circulation and mild, moderate, and severe PAH were performed. We also assessed the effects on RLSM when PAH coexists with RV or LV contractile dysfunction. Our results showed prolonged RV shortening in PAH causing interventricular relaxation dyssynchrony and RLSM. RLSM was observed in both moderate and severe PAH. A negative transseptal pressure gradient only occurred in severe PAH, demonstrating that negative pressure gradient does not entirely explain septal motion abnormalities. PAH coexisting with RV contractile dysfunction exacerbated both interventricular relaxation dyssynchrony and RLSM. LV contractile dysfunction reduced both interventricular relaxation dyssynchrony and RLSM. In conclusion, dyssynchrony in ventricular relaxation causes RLSM in PAH. Onset of RLSM in patients with PAH appears to indicate a worsening in RV function and hence can be used as a sign of RV failure. However, altered RLSM does not necessarily imply an altered RV afterload, but it can also indicate altered interplay of RV and LV contractile function. Reduction of RLSM can result from either improved RV function or a deterioration of LV function.NEW & NOTEWORTHY A novel approach describes the mechanism underlying abnormal septal dynamics in pulmonary arterial hypertension. Change in motion is not uniquely induced by altered right ventricular afterload, but also by altered ventricular relaxation dyssynchrony. Extension or change in motion is a marker reflecting interplay between right and left ventricular contractility.

Cardiac Body Surface Potentials in Rats with Experimental Pulmonary Hypertension during Ventricular Depolarization

The spatial and the amplitude-temporal parameters of cardiac body surface potentials were examined in female Wistar rats with experimental pulmonary hypertension during ventricular depolarization. The cardiac body surface potentials have been led from 64 subcutaneous electrodes evenly distributed across the chest surface prior to and 4 weeks after subcutaneous injection of a single dose of monocrotaline (60 mg/kg). Right ventricular hypertrophy and electrophysiological remodeling of the heart developed in rats with experimental pulmonary hypertension in 4 weeks after monocrotaline injection; these changes led to a significant increase in amplitude and temporal characteristics of the cardioelectric field on the body surface in comparison with the initial state.

Is cardiac resynchronization therapy for right ventricular failure in pulmonary arterial hypertension of benefit?

Pulmonary arterial hypertension is a manifestation of a group of disorders leading to pulmonary vascular remodeling and increased pulmonary pressures. The right ventricular (RV) response to chronic pressure overload consists of myocardial remodeling, which is in many ways similar to that seen in left ventricular (LV) failure. Maladaptive myocardial remodeling often leads to intraventricular and interventricular dyssychrony, an observation that has led to cardiac resynchronization therapy (CRT) for LV failure. CRT has proven to be an effective treatment strategy in subsets of patients with LV failure resulting in improvement in LV function, heart failure symptoms, and survival. Current therapy for pulmonary arterial hypertension is based on decreasing pulmonary vascular resistance, and there is currently no effective therapy targeting the right ventricle or maladaptive ventricular remodeling in these patients. This review focuses on the RV response to chronic pressure overload, its effect on electromechanical coupling and synchrony, and how lessons learned from left ventricular cardiac resynchronization might be applied as therapy for RV dysfunction in the context of pulmonary arterial hypertension.

Impaired epicardial activation-repolarization coupling contributes to the proarrhythmic effects of hypokalaemia and dofetilide in guinea pig ventricles

AIM

Activation-repolarization coupling refers to the inverse relationship between action potential duration and activation time in myocardial regions along the path of ventricular excitation. This study examined whether the activation-repolarization coupling plays a role in coordinating repolarization times between the right ventricular (RV) and left ventricular (LV) chambers, and if impaired coordination contributes to electrical instability produced by hypokalaemia or dofetilide, a blocker of the delayed rectifier K(+) current.

METHODS

In Langendorff-perfused, isolated guinea pig hearts, six monophasic action potential recording electrodes were attached to RV and LV epicardium. Local activation time and action potential duration (APD90 ) were determined during spontaneous beating, regular pacing and extrasystolic excitation.

RESULTS

In regularly beating hearts, the RV epicardial sites had longer APD90 , but exhibited earlier activation times, as compared to LV sites, which minimized the interventricular difference in repolarization time. Upon extrasystolic stimulation, the APD90 was reduced to a greater extent in RV compared with LV, which translated to a reversed slope of APD90 -to-activation time relationship, and increased spatial repolarization gradients. Hypokalaemia and dofetilide prolonged APD90 , with the effect being greater in LV compared with RV. In hypokalaemic hearts, LV activation was delayed. These changes contributed to increased asynchrony in repolarization times in the LV and RV in both regular and extrasystolic beats, and enhanced susceptibility to tachyarrhythmia.

CONCLUSION

Impaired RV-to-LV activation-repolarization coupling is an important determinant of electrical instability in the setting of non-uniformly prolonged epicardial APD90 or slowed interventricular conduction.

Impact of right ventricular dyssynchrony on left ventricular performance in patients with pulmonary hypertension

Pulmonary hypertension has been associated with right ventricular (RV) dyssynchrony which may induce left ventricular (LV) dysfunction and dyssynchrony through ventricular interdependence. The present study evaluated the influence of RV dyssynchrony on LV performance in patients with pulmonary hypertension. One hundred and seven patients with pulmonary hypertension (age 63 ± 14 years, systolic pulmonary arterial pressure 60 ± 19 mmHg) and LV ejection fraction (EF) >35% were evaluated. Ventricular dyssynchrony was assessed with speckle tracking echocardiography and defined as the standard deviation of the time to peak longitudinal strain of six segments of the RV (RV-SD) and the LV (LV-SD) in the apical 4-chamber view. Mean RV-SD and LV-SD assessed with longitudinal strain speckle tracking echocardiography were 51 ± 28 and 47 ± 21 ms, respectively. The patient population was divided according to the median RV-SD value of 49 ms. Patients with RV-SD ≥49 ms had significantly worse NYHA functional class (2.7 ± 0.7 vs. 2.3 ± 0.7, p = 0.004), RV function (tricuspid annular plane systolic excursion: 16 ± 4 vs. 19 ± 4 mm, p < 0.001), LVEF (50 ± 10 vs. 55 ± 8%, p = 0.001), and larger LV-SD (57 ± 18 vs. 36 ± 18 ms, p < 0.001). RV-SD significantly correlated with LV-SD (r = 0.55, p < 0.001) and LVEF (r = -0.23, p = 0.02). Multiple linear regression analysis showed an independent association between RV-SD and LV-SD (β = 0.35, 95%CI 0.21-0.49, p < 0.001). RV dyssynchrony is significantly associated with LV dyssynchrony and reduced LVEF in patients with pulmonary hypertension.

Impaired left ventricular mechanics in pulmonary arterial hypertension: identification of a cohort at high risk

BACKGROUND

Pulmonary arterial hypertension (PAH) is characterized by pulmonary vascular remodeling and right heart failure. The right (RV) and left ventricles (LV) do not function in isolation, sharing a common pericardial sac and interventricular septum. We sought to define the clinical and prognostic significance of ventricular interdependence in PAH and its association with LV filling patterns through speckle-tracking strain echocardiography.

METHODS AND RESULTS

Echocardiography was performed in 71 adults with a new diagnosis of PAH. To analyze LV and RV function separately, we measured peak systolic longitudinal and circumferential strain of the LV and RV. Survival was assessed >2 years. Patients had dilated right-sided chambers (right atrial volume index, 44 ± 19 mL/m(2); RV end-diastolic area, 34 ± 9 cm(2)), and reduced RV function (RV fractional area change, 28 ± 12%). Speckle-tracking echocardiography revealed significant reductions in RV free wall peak systolic strain (-15 ± 3%). Despite normal LV size and normal conventional measures of LV systolic function (end-diastolic dimension, 42 ± 6 mm; ejection fraction, 65 ± 8%; cardiac index, 2.6 ± 0.8 L/min per m(2)), patients had reduced LV free wall systolic strain (-15 ± 3%). Decreased LV free wall systolic strain was associated with a delayed relaxation mitral inflow Doppler pattern, P=0.0002. During 2-year follow-up, 19 patients (27%) died. LV strain was associated with increased mortality (unadjusted hazard ratio, 2.40 per 5% decrease in LV free wall strain, 1.22-4.68), which remained significant when adjusted for age, sex, World Health Organization functional class, and PAH pathogenesis (hazard ratio, 3.11, 1.38-7.20).

CONCLUSIONS

The pressure loading in PAH results in geometric alterations and functional decline of the RV, with marked reduction in RV systolic strain. Despite preservation of LV ejection fraction, LV systolic strain was also reduced and associated with early mortality, highlighting the significance of ventricular interdependence in PAH.

Electrophysiologic remodeling of the left ventricle in pressure overload-induced right ventricular failure

OBJECTIVES

The purpose of this study was to analyze the electrophysiologic remodeling of the atrophic left ventricle (LV) in right ventricular (RV) failure (RVF) after RV pressure overload.

BACKGROUND

The LV in pressure-induced RVF develops dysfunction, reduction in mass, and altered gene expression, due to atrophic remodeling. LV atrophy is associated with electrophysiologic remodeling.

METHODS

We conducted epicardial mapping in Langendorff-perfused hearts, patch-clamp studies, gene expression studies, and protein level studies of the LV in rats with pressure-induced RVF (monocrotaline [MCT] injection, n = 25; controls with saline injection, n = 18). We also performed epicardial mapping of the LV in patients with RVF after chronic thromboembolic pulmonary hypertension (CTEPH) (RVF, n = 10; no RVF, n = 16).

RESULTS

The LV of rats with MCT-induced RVF exhibited electrophysiologic remodeling: longer action potentials (APs) at 90% repolarization and effective refractory periods (ERPs) (60 ± 1 ms vs. 44 ± 1 ms; p < 0.001), and slower longitudinal conduction velocity (62 ± 2 cm/s vs. 70 ± 1 cm/s; p = 0.003). AP/ERP prolongation agreed with reduced Kcnip2 expression, which encodes the repolarizing potassium channel subunit KChIP2 (0.07 ± 0.01 vs. 0.11 ± 0.02; p < 0.05). Conduction slowing was not explained by impaired impulse formation, as AP maximum upstroke velocity, whole-cell sodium current magnitude/properties, and mRNA levels of Scn5a were unaltered. Instead, impulse transmission in RVF was hampered by reduction in cell length (111.6 ± 0.7 μm vs. 122.0 ± 0.4 μm; p = 0.02) and width (21.9 ± 0.2 μm vs. 25.3 ± 0.3 μm; p = 0.002), and impaired cell-to-cell impulse transmission (24% reduction in Connexin-43 levels). The LV of patients with CTEPH with RVF also exhibited ERP prolongation (306 ± 8 ms vs. 268 ± 5 ms; p = 0.001) and conduction slowing (53 ± 3 cm/s vs. 64 ± 3 cm/s; p = 0.005).

CONCLUSIONS

Pressure-induced RVF is associated with electrophysiologic remodeling of the atrophic LV.