Resynchronization of the left atrium may play an important role in cardiac resynchronization therapy

Introduction

Left atrial (LA) dyssynchrony is a predictor of response to cardiac resynchronization therapy (CRT). It is unknown, however, if LA resynchronization contributes to response to CRT. We hypothesize that there is a relationship between correction of LA dyssynchrony and response to CRT.

Purpose

To investigate the association between LA resynchronization and response to CRT.

Methods

In a prospective study of 171 heart failure patients with LBBB, myocardial strain was measured by speckle-tracking echocardiography, before and 6 months after CRT. As indicated by the white arrows in Figure 1, LA dyssynchrony was measured as the time delay between onset systolic stretch of the interatrial septum and the LA lateral wall. Response to CRT was defined as at least 15% reduction in left ventricular (LV) end systolic volume at 6 months follow up.

Results

119 (70%) patients responded to CRT. The panels in Figure 1 shows LA strain traces in a representative LBBB patient that did respond (upper panels), and a patient that did not respond (lower panels). The white arrows in the left panels indicate that both the responder and the non-responder had marked LA dyssynchrony before CRT (198 and 171 ms, respectively). However, after 6 months with CRT, there was recovery of LA synchrony only in the responder (time delay −40 ms), and still marked LA dyssynchrony of 191 ms in the non-responder (right panels).

Figure 2 confirms similar results for the whole study population: CRT response was associated with marked reduction of LA dyssynchrony (p=0.0001). In the CRT non-responders there was, however, only a modest, non-significant reduction of LA dyssynchrony.

Conclusions

Positive CRT response was associated with resynchronization of the left atrium. These findings suggest LA resynchronization as a potential additional target for CRT.

Funding Acknowledgement

Type of funding sources: Public hospital(s). Main funding source(s): Institute for Surgical Research, Oslo University HospitalThe Intervention Centre, Oslo University Hospital

Is left ventricular function reduced after ultra-endurance exercise?

Funding Acknowledgements

Type of funding sources: Foundation. Main funding source(s): Norwegian Health Association

Introduction

Ultra-endurance exercise can be harmful according to previous studies, indicated by reduction in functional parameters and increase in cardiac biomarkers. Changes in load and heart rate with exercise influence left ventricle systolic function, making assessment of standard echocardiographic examination difficult.

Purpose

We investigated the effect of ultra-endurance exercise on myocardial function acutely and at restitution.

Methods

We investigated 10 participants aged 46 ±7 years, before (baseline), within 142 ± 78 minutes after finish (post run) and 5-10 days after (restitution) an ultra-endurance race (3.8 km swimming, 180 km bicycling and 42 km running with a total elevation of 5200 m). Echocardiography was performed at the three time points, including cardiac morphology and -function. Ejection fraction (EF) and stroke volume (SV) were measured by Simpson biplane. Cardiac output was calculated from SV and heart rate (HR). Cardiac power was calculated as the product of CO, mean arterial blood pressure and the conversion factor to Watt (W) 0.00222. Global longitudinal strain (GLS) was calculated using speckle-tracking echocardiography, and myocardial work was calculated by non-invasive pressure-strain analysis.

Results

Acutely after exercise, myocardial function by GLS (p = 0.002), myocardial work (p < 0.001), mitral annular plane systolic excursion (MAPSE, p = 0.003) and EF (p = 0.004) were substantially reduced compared to baseline, whereas cardiac power and cardiac output (CO) were maintained (see table and figure). Heart rate was moderately increased (p < 0.001). End-diastolic volume (EDV) as an index of preload was numerically, but not significantly reduced. End systolic volume (ESV) was numerically increased (p = NS) even though systolic blood pressure (sBP) was reduced (p = 0.01) post race. After restitution all parameters returned to baseline levels.

Conclusions

The temporary reduced strain and EF may be a physiologic response due to the higher heart rate. However, despite reduced systolic pressure the heart did not contract to a lower end systolic volume. This suggests loss of contractile function compensated by increase in heart rate. The findings should be explored in further studies. Abstract Figure  Abstract Table

Left atrial mechanical dyssynchrony: an independent predictor of left ventricular reverse remodelling after cardiac resynchronization therapy

Funding Acknowledgements

Type of funding sources: Public hospital(s). Main funding source(s): Institute for Chirurgical Research - Oslo University Hospital

Introduction

Left bundle branch block (LBBB) leads to left ventricular (LV) mechanical dyssynchrony. Since the left atrium (LA) and the left ventricle (LV) are anatomically connected, dyssynchronous LV contractions may be transmitted to the LA causing LA dyssynchrony and disturbed LA function.

Purpose

To investigate if LA dyssynchrony induced by LBBB predicts LV reverse remodelling after cardiac resynchronization therapy (CRT).

Methods

In a prospective study, myocardial strain was measured by speckle-tracking echocardiography in 171 heart failure patients with LBBB, before and 6 months after CRT. LA dyssynchrony was measured as the time delay between onset systolic stretch of the interatrial septum and the LA lateral wall (white arrows in Figure), and LV dyssynchrony as the time from onset septal shortening to onset lateral wall shortening. Septal flash was assessed visually. Response to CRT was defined as at least 15 % reduction in LV end systolic volume at 6 months follow up.

Results

The figure shows a representative LBBB patient with LA and LV dyssynchrony which was abolished by CRT. For the whole study population, LA dyssynchrony was 104 ± 77 ms (mean ± SD) before CRT, and decreased to 43 ± 70 ms (p < 0.0001) after CRT. There was a significant correlation between LA and LV dyssynchrony (r = 0.68, p < 0.0001).

LA dyssynchrony correlated with LV reverse remodelling after CRT (p = 0.009), and multivariable analysis revealed that LA dyssynchrony was an independent predictor of CRT response (β=-0.046, p = 0.04) when combined with septal flash, QRS duration and QRS morphology (Table).

Conclusions

Patients with LBBB had marked LA dyssynchrony which was attributed to direct LV-LA mechanical interaction. Furthermore, LA dyssynchrony was an independent predictor of LV reverse remodelling after CRT. These findings suggest that assessment of LA dyssynchrony should be part of the echocardiographic evaluation in patients with dyssynchronous heart failure. Abstract Figure.

Myocardial work still reflect function while strain simply measure deformation when afterload increases

Introduction

Global longitudinal strain is recommended by the European Society of Cardiology to detect subclinical left ventricular (LV) dysfunction, but is markedly load-dependent. Myocardial work was recently introduced as a clinical tool to study LV function by pressure-strain analysis. Since myocardial work incorporates afterload, it is assumed to be less afterload-dependent than strain, but the relationship with afterload is incompletely understood.

Hypothesis

Myocardial work is a better tool than strain, to measure myocardial function during elevated afterload.

Methods

In eleven anesthetized dogs, LV volume and longitudinal strain were measured by sonomicrometry, and pressure by micromanometry. Myocardial work was calculated by pressure-strain analysis. Additionally, stroke work was calculated as the area of the pressure-volume loop. Afterload was instantly increased by aortic constriction using a pneumatic cuff around the ascending aorta. Measurements were performed at baseline, during moderate- and marked afterload elevations.

Results

Table 1 summarizes the results. LV pressure (LVP) successively increased with moderate and marked afterload elevation, while longitudinal strain was successively reduced. Myocardial work and stroke work, on the other hand, increased with moderate afterload elevation, but was then reduced at marked afterload increase (Figure 1 and Table 1). Stroke volume and ejection fraction corresponded to strain and were reduced with afterload elevation.

Conclusions

Longitudinal strain and myocardial work have qualitatively different responses to increased afterload. While moderate changes in afterload cause reductions in strain that can be falsely interpreted as reductions in contractility, myocardial work increases as it incorporates the increased workload at moderately elevated afterload.

Funding Acknowledgement

Type of funding sources: Public Institution(s). Main funding source(s): The Norwegian Health Association

Left bundle branch block causes left atrial dyssynchrony: a result of atrio-ventricular mechanical interaction

Introduction

Left bundle brach block (LBBB) leads to left ventricular (LV) mechanical dyssynchrony with septal flash and delayed lateral wall contractions. Since atrium and ventricle are anatomically connected, dyssynchronous LV contractions may be transmitted to the left atrium, thereby disturbing left (LA) function.

Purpose

To test the hypothesis that patients with LBBB have LA dyssynchrony induced by tethering to the dyssynchronous left ventricle.

Methods

Myocardial strain was measured by speckle-tracking echocardiography in 20 non-ischaemic heart failure patients with LBBB, before and 6 months after cardiac resynchronization therapy (CRT), and in 20 healthy controls. For the LA, dyssynchrony was measured as time delay between onset of the interatrial septum and the lateral wall, and for the LV, between onset septal flash and onset lateral wall contraction. White arrows in Figure indicate onset LA stretch.

Results

As shown in the Figure, patients with LBBB and HF had marked LA reservoir phase dyssynchrony. Before CRT time delay from onset LA septal stretch to onset lateral wall stretch was 125±71 ms (mean±SD), and decreased to 23±70 (p<0.0001) with CRT. In controls there was a small delay of 34±56 ms. The LA dyssynchrony correlated with LV dyssynchrony (r=0.50, p=0.033), supporting the hypothesis that LA dyssynchrony in LBBB represents mechanical interaction due to tethering between the respective walls.

Conclusions

Patients with LBBB had marked LA reservoir phase dyssynchrony, which was abolished with CRT. The LA dyssynchrony was attributed to direct LV-LA mechanical interaction. The observed LA resynchronization by CRT represent an additional benefit of CRT in patients with heart failure.

Funding Acknowledgement

Type of funding sources: None. Left atrial and ventricular dyssynchrony

Duration of the preejection phase is less preload dependent and therefore a better marker of acute response to cardiac resynchronization therapy than maximum pressure rise

Funding Acknowledgements

Type of funding sources: Public grant(s) – EU funding. Main funding source(s): EU’s Horizon 2020 research and innovation program under the Marie Sklodowska-Curie

Background

There is no consensus on which haemodynamic marker should be used to quantify acute response to cardiac resynchronization therapy (CRT) during implantation of the device. CRT has been shown to acutely reduce left ventricular (LV) end systolic as well as end-diastolic volume (EDV), precluding the use of preload dependent markers such as LV maximum pressure rise (dP/dtmax).

Purpose

As resynchronization will abolish the uncoordinated regional early systolic contractions of the LV, it will shorten the time to maximal pressure rise and aortic valve opening. For this reason, the purpose of this study was to investigate if duration from the time-point of ventricular pacing to dP/dtmax is less preload dependent and a better marker of acute response to CRT than dP/dtmax by comparing how the 2 markers reflected LV function during different CRT configurations.

Methods

LV pressure by micromanometer and volume by sonomicrometry were measured in 6 anaesthetized canines with left bundle branch block. Transient caval constrictions were performed to vary preload. Preload dependency of the 2 markers was compared by normalizing their values and calculating their relations to EDV. In 4 of the animals, biventricular pacing was performed at 3 different pacing sites with variations in atrioventricular delays that provided a range of response to CRT. To correct for acute

changes in preload by CRT, stroke volume (SV) at identical EDV found from transient caval constrictions, were assessed and used as reference to grade improved LV function. Linear regression analysis was used to assess the correlation of both the duration of the preejection phase and dP/dtmax with SV.

Results

The duration of the preejection phase varied less with changes in preload compared to dP/dtmax: the slopes of their relation to EDV were -0.6 ± 0.7 %/ml and 4.8 ± 2.1 %/ml (p = 0.004), respectively. Turning CRT on, acutely reduced EDV from 74 ± 16 to 69 ± 17 ml (p < 0.001) at the best pacing configuration. For the different pacing sites and settings, there was a consistent relation in all animals where the preejection phase shortened as SV increased (average r2 = 0.75) (Figure A). dP/dtmax showed no clear relation to SV (average r2 = 0.22) and included cases with both negative and positive slopes (Figure B).

Conclusions

The duration of the preejection phase correlated with changes in LV function induced by CRT while dP/dtmax performed poorly as preload was changed. Hence, the novel timing parameter was less preload dependent and may be a better marker for assessing acute response to CRT. Abstract Figure.

Myocardial work comes to rescue when afterload-dependency of strain cause false positives

Funding Acknowledgements

Type of funding sources: Public Institution(s). Main funding source(s): The Norwegian Health Association

Introduction

Global longitudinal strain (GLS) can detect subclinical left ventricular (LV) dysfunction. GLS measurement is therefore recommended when chemotherapy-induced cardiotoxicity can be suspected. A relative, percentage reduction in GLS ≥8% may indicate subclinical LV dysfunction induced by chemotherapy. Due to afterload-dependency, moderate increase in blood pressure has the potential to cause reductions in GLS beyond this threshold. However, myocardial work incorporates afterload, and may be used to omit false positive outcomes.

Purpose

To investigate if moderate increases in afterload cause clinically relevant changes in strain, and if myocardial work is more robust to such changes.

Methods

Twenty cancer patients (41 ± 14 years) undergoing chemotherapy and twenty healthy controls (49 ± 11 years, NS) were included. All participants were free from concomitant heart disease. GLS was measured by speckle-tracking echocardiography. Global myocardial work was calculated by pressure-strain analysis using a previously validated method to estimate LV pressure (LVP) non-invasively. Recordings were performed before and after 2 minute stress by handgrip.

Results

At baseline, patients had lower GLS (20.1 ± 1.1 vs 22.1 ± 2.5%, p < 0.01) and global myocardial work (1810 ± 203 vs 2051 ± 287 mmHg·%, p < 0.01) than controls. Stress test moderately increased systolic blood pressure, similar in both groups (116 ± 10 to 146 ± 17 mmHg in patients, and 118 ± 12 to 147 ± 21 mmHg in controls). This afterload-enhancement was associated with a decrease in GLS from 20.1 ± 1.1 to 18.4 ± 1.3% in patients, and from 22.1 ± 2.5 to 20.3 ± 2.5% in controls (both p < 0.01). Every second participant, eleven patients and nine controls, experienced a relative reduction in GLS >8%. In contrast, global myocardial work increased during the stress test from 1810 ± 203 to 2002 ± 281 mmHg·% in patients, and from 2051 ± 287 to 2292 ± 398 mmHg·% in controls (both p < 0.01). Figure 1 shows changes in GLS and myocardial work at moderate increase in afterload.

Conclusions

Moderate increase in afterload caused reductions in GLS sufficient to promote over-diagnosis of chemotherapy-induced cardiotoxicity. Global myocardial work has the potential to distinguish true subclinical LV dysfunction from afterload-induced decline in GLS.

Abstract Figure.

Regional myocardial work as determinant of heart failure in left bundle branch block

Funding Acknowledgements

Type of funding sources: Public Institution(s). Main funding source(s): The Norwegian Health Association

Background

Left bundle branch block (LBBB) worsen prognosis in heart failure patients. LBBB may also cause heart failure in otherwise healthy individuals. The mechanical changes induced by LBBB are potential determinants of heart failure in these patients, but their relation to left ventricular (LV) systolic function is incompletely understood.

Purpose

This study investigates the contribution of regional contractile function to heart failure in patients with LBBB.

Methods

In 76 patients with LBBB and 11 healthy controls, myocardial strain was measured by speckle-tracking echocardiography and myocardial work by pressure-strain analysis. Patients with ischemic heart disease or myocardial scarring were excluded. LBBB patients were stratified by LV ejection fraction (EF) >50% (EFpreserved), 36-50% (EFmid), and ≤35% (EFlow). 62 LBBB patients subsequently underwent cardiac resynchronization therapy (CRT) implantation and was re-examined at 6 months.

Results

Septal work was significantly and successively reduced from controls, EFpreserved, EFmid, to EFlow (1977 ± 506, 1025 ± 342, 601 ± 494 and -41 ± 303 mmHg·%, respectively, all p < 0.01) (Figure 1). There was a strong correlation (R = 0.84, p < 0.01) between septal work and LVEF. In contrast, work in the LV lateral wall was preserved in both EFpreserved (2367 ± 459 mmHg·%) and EFmid (2252 ± 449 mmHg·%) vs controls (2062 ± 459 mmHg·%, all NS). In the EFlow group, however, LV lateral wall work was reduced (1473 ± 568 mmHg·%, p < 0.01 vs controls). Thus, lateral wall function was not correlated with LVEF in patients with LVEF >35% (NS). At six month CRT septal work was markedly increased (165 ± 485 vs 1288 ± 523 mmHg·%, p < 0.01) and LV lateral wall work reduced (1730 ± 620 vs 1264 ± 490 mmHg·%, p < 0.01). LVEF increased from 32 ± 8 to 47 ± 10 % (p < 0.01).

Conclusions

Heart failure in LBBB patients is determined by degree of septal dysfunction. LV lateral wall function, on the other hand, is preserved in the early phase of heart failure and was only reduced in patients with severe heart failure. Further clinical studies should investigate if measuring LV lateral wall function can increase precision in patient selection for CRT.

Abstract Figure.

Elevated septal wall stress - a driver of left ventricular dysfunction in left bundle branch block?

Funding Acknowledgements

Type of funding sources: Public Institution(s). Main funding source(s): The Norwegian Health Association

Background

Septal dysfunction is a main feature of left bundle branch block (LBBB), and increasing wall stress is a proposed mechanism of heart failure development in LBBB patients. To try to reveal the pathophysiologic pathway from dyssynchrony to heart failure, we investigated the relationship between septal and left ventricular (LV) lateral wall stress in patients with LBBB.

Hypothesis

Increased septal wall stress causes septal dysfunction in LBBB.

Methods

We included 24 LBBB-patients (65 ± 11 years, 11 males) with LV ejection fraction (EF) ranging from 18 to 67%, and 8 healthy controls (58 ± 10 years, 4 males). Wall stress was calculated at peak LV pressure (LVP) according to the law of La Place ([LVP x radius]/[wall thickness]). Wall thickness was measured using M-mode, and regional curvature was measured in mid-ventricular shortaxis from 2D echocardiographic images. We used a previously validated non-invasive method to estimate LVP from brachial blood pressure and adjusted for valvular events. Myocardial scar was ruled out by late gadolinium enhancement cardiac magnetic resonance imaging.

Results

Wall stress was significantly higher in septum than LV lateral wall at peak LVP (48 ± 12 vs 37 ± 11 kPa, p < 0.01) in LBBB patients, while no difference was seen in the controls (Figure A). In patients, septal wall thickening showed a strong correlation with LVEF (r = 0.77, p < 0.01) (Figure B). Similar correlation was not significant for the LV lateral wall (r = 0.13, NS). Attenuation of septal wall thickening in LBBB-patients correlated well with increasing septal wall stress (r=-0.60, p < 0.01). Wall thickening and stress did not correlate in the LV lateral wall (r=-0.14, NS).

Conclusion

Increased septal wall stress is associated with reduced systolic thickening in patients with LBBB. Septal wall thickening, in contrast to LV lateral wall thickening, was correlated to global LV function. These findings suggest that septal remodeling which could have normalized septal wall stress, was not achieved and heart failure may develop.

Abstract Figure.

158 Myocardial work exposes afterload-dependent changes in strain

Funding Acknowledgements

Norwegian Health Association

Background

Global longitudinal strain (GLS) is used for detection of subclinical left ventricular (LV) dysfunction, for example when screening for chemotherapy-induced cardiotoxicity. A relative percentage reduction in GLS ≥8% is considered abnormal. However, as GLS is load-dependent, modest increases in afterload can potentially prove sufficient to cause clinical implication. In contrast, global myocardial work (GMW) which incorporates afterload, may be more accurate in detecting LV-dysfunction.

Purpose

We investigated the effect of increased afterload on GLS, and if GMW may be a more accurate parameter of myocardial function during increased afterload.

Methods

In 20 healthy individuals (age 49 ± 11 years (mean ± SD), 10 men), blood pressure was increased by a 3 minute arithmetic mental stress test. GLS was measured by speckle tracking echocardiography and LV ejection fraction (EF) by biplane Simpson. GMW was calculated from LV pressure-strain analysis using a non-invasive estimate for LV pressure (LVP).

Results

During the afterload-elevation, systolic blood pressure increased by 25 ± 16 mmHg (p < 0.01), and heart rate by 16 ± 13 bpm (p < 0.01). This was followed by a decrease in EF from 62 ± 5 to 59 ± 5% (p < 0.01) and GLS from 21.9 ± 2.2 to 20.8 ± 2.0% (p < 0.01). In contrast, GMW increased from 2052 ± 278 to 2382 ± 388 mmHg·% (p < 0.01). In 5 of 20 (25%) individuals, the relative percentage reduction of GLS was >8%, despite an increase in GMW. The figure shows an individual example during rest and afterload-elevation, where an increase in systolic blood pressure of 16 mmHg was associated with a 9% relative percentage reduction in GLS, but a small increase in GMW as illustrated by the loop areas.

Conclusions

This study demonstrated that a modest increase in afterload can result in significant reduction in GLS, that may lead to overdiagnosis of LV-dysfunction. GMW did not decrease, suggesting it has a better specificity in patients at risk for subclinical LV dysfunction. Future studies should investigate if GMW is more accurate than strain in detecting LV-dysfunction.

Abstract 158 Figure.