Impact of homeometric autoregulation using a stepwise change in heart rate on dP/dtmax and time to peak dP/dt with resynchronization therapy

Funding Acknowledgements

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Norwegian South East heath Authorities

Background

We investigated the homeometric autoregulation utilizing a stepwise change in heart rate on dP/dtmax and time to peak dP/dt (Td) with biventricular pacing (BIVP) and the LV lead positioned in the apical, anterior and lateral positions. Pacing at low HR (LHR) and high heart rates (HHR) changes contractility through homeometric autoregulation (Bowditch effect) without changing the resynchronization itself.

Purpose

To determine the effect of a change in contractility through homeometric autoregulation on two different effect measures of resynchronization therapy.

Methods

Twenty-nine patients in heart failure with LBBB underwent CRT implantation with continuous LV pressure registration. The LV lead was first placed in either apical or anterior position followed by a permanent placement in a lateral position. Sequential BIVP pacing was performed for one minute, at a rate 10% above intrinsic heart rate (LHR = 75 ± 9bpm), before dP/dtmax measurements were recorded, and the sequence was repeated with pacing rate increased by 30% (HHR = 98 ± 11bpm). Td was defined as the time from pacemaker stimuli to peak dP/dt. Mixed linear models were used for statistics, numbers are estimated marginal means ± SEM. Significance was set at p < 0.05.

Results

DP/dtmax was higher with HHR in lateral position (1036 ± 41mmHg/s) than with LHR (933mmHg/s). The same was observed for all other lead positions. However, there was no difference between lateral position with LHR and apical position with HHR (930 ± 44mmHg/s). There were no differences in Td between LHR and HHR, but Td was shorter with BIVP in lateral position at pacing LHR (158 ± 4ms) and HHR (155 ± 4ms) than in all other positions. Overall dP/dtmax increased by 10% from LHR to HHR (888 ± 41mmHg/s vs. 980 ± 41 mmHg/s), while overall Td decreased by 2.4% from 168 ± 4ms to 164 ± 4ms. We found a linear relationship between Td and dP/dtmax (R = 0.7) with β=-0.07 that would indicate a 6ms reduction in Td going from LHR to HHR. The overall change in Td from LHR to HHR could therefore be attributed to the change in dP/dtmax.

Conclusion

Homeometric regulation does not influence Td, but Td is sensitive to changes in resynchronization and pacing lead position. Td is shorter with BIVP in lateral position at both high and low HR as would be expected from a biomarker of resynchronization. HR influences dP/dtmax so distinction between optimal and non-optimal positions using dP/dtmax may be difficult without knowledge of homeometric state.

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.

Comparison of adaptive and non-adaptive pacing modes on time-to-peak dP/dt in multipoint pacing or standard biventricular pacing with different degrees of intraventricular fusion

Funding Acknowledgements

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Norwegian South-East Health Authorities

Background

We have investigated the timing of the peak left ventricular pressure rise, time to peak dP/dt (Td) as marker of resynchronization to be measured during implantation for detection of effective resynchronization. Td links the time domain (dyssynchrony) to the mechanical domain (pressure) as the dyssynergic muscular contractions resulting from electrical dyssynchrony delays pressure development and hence the timing of peak dP/dt, Td. Td shortens with resynchronization.

Purpose

In this study we investigated the acute changes in Td by comparing pacing the left ventricle (LV) with fusion of intrinsic right ventricular (RV) conduction (Adaptive, A) with pacing RV and LV (Non-Adaptive, NA), with and without multipoint pacing (MPP) and with different degrees of intraventricular pacing delays (RV-LV).

Methods

19 patients with sinus rhythm and LBBB undergoing CRT implantation were studied. We measured pressures with an indwelling LV pressure catheter. Td was calculated as the time from onset of pacing to peak dP/dt, and averaged in 10 subsequent beats at each stage of pacing. We used quadripolar LV pacing leads positioned in what was considered an optimal mid/basal posterolateral/ lateral branch of the coronary sinus and sequential pacing (DDD) was performed; Adaptive and Non-Adaptive pacing was performed at LV distal [LVdist], proximal electrode [LVprox] and at both electrodes as multipoint pacing [MPP]. VV-timing: LV pacing was performed relative to QRS onset (either as a result of intrinsic activation or RV pace, mean ± SD): 1. LV only -76 ± 21ms before QRS activation with minimal fusion with RV activation (LVonly); 2. -28 ± 14ms before QRS activation (Pre); 3. 12 ± 15ms after (Post) QRS activation. Linear mixed models were used for statistics of the pooled data. Results are estimated marginal means ±SEM, and only significant P < 0.05 changes are reported.

Results

Average Td (data pooled) with RVP was 173 ± 2ms, MPP 144 ± 0.4ms and BIVP 150 ± 0.4ms. When analyzing the interaction between pacingmode (A,NA), VV-timing (LVonly,Pre,Post) and electrode(LVdist,LVprox,MPP) in all interventions we found that Td was shorter (p < 0.01) with A(Post) for all electrode combinations [LVdist] 143 ± 4ms, [LVprox] 140 ± 4ms and [MPP] 134 ± 4ms, while Td with A(Pre) was shorter with [MPP] 139 ± 4ms only. A(post)[MPP] provided shorter Td than the other adaptive modes (p < 0.01). NA(Post)[MPP] at 145 ± 4ms and NA(Post)[LVdist] at 146 ± 4ms provided the shortest Td (p < 0.01) of the NA pacing modes, and Td with NA(Post)[MPP] was shorter (p < 0.01) than all NA pacing modes.

Conclusion

Td shortens the most with LV MPP timed to near simultaneous intrinsic RV activation, indicating a beneficial mechanical effect from Adaptive MPP compared to standard biventricular pacing.

The missing link- time to maximal rate of left ventricular pressure rise reflects resynchronization with biventricular pacing in patients with heart failure and left bundle branch block

Funding Acknowledgements

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Norwegian South East Health Authorities

Introduction

Resynchronization therapy effectively restores myocardial function. No measures exist that specifically quantifies resynchronization. A parameter that quantifies resynchronization should be able to detect effective resynchronization and should not respond to changes in contractility caused by heterometric regulation.  Left ventricular pacing (LVP) is associated with dyssynchronous contraction patterns, while biventricular pacing (BIVP) promotes resynchronization dependent on the pacing position of the LV electrode.

Purpose

We compared the acute differences between BIVP and LVP with regards to the preload dependent maximum rate of the LV pressure rise (dP/dtmax), and time to peak dP/dt (Td) to determine which better reflect dyssynchrony and resynchronization.

Methods

Twenty nine patients in heart failure with LBBB underwent CRT implantation with continuous LV pressure registration. The LV lead was first placed in either apical or anterior position followed by a permanent placement in a lateral position. Sequential LVP and BIVP pacing were performed for one minute, at a rate 10% above intrinsic heart rate, before dP/dtmax measurements were recorded. For LVP, BIVP and RVP a patient specific AV delay was used to avoid fusion with intrinsic conduction. Td was defined as the time from pacemaker stimuli to peak dP/dt. Mixed linear models were used for statistics, numbers are estimated marginal means ± SEM and are only reported when with significance set at p < 0.05.

Results

We found no differences in dP/dtmax between BIVP (899 ± 37mmHg/s) and LVP (910 ± 37mmHg/s), while RVP (799 ± 37mmHg/s) was lower. Td was lower with BIVP (165 ± 4ms) than LVP (178 ± 4ms) and RVP (184 ± 4ms).  We found no differences in dP/dtmax between lateral (890 ± 35mmHg/s) and anterior (874 ± 38mmHg/s) while apical (824 ± 38mmHg/s) was lower. Td was lower in lateral (171 ± 4ms) than in anterior (179 ± 4ms) and apical (182 ± 4ms) positions. BIVP in lateral position (158 ± 4ms) was lower than any other pacingmode*position, with BIVP*anterior at 173 ± 4ms) and LVP*lateral at 170 ± 2ms. No difference was seen in dP/dtmax between  (BIVP + LVP)*(lateral + anterior) that was higher than all other pacingmode*positions.

Conclusion

Td shortens with BIVP and lateral position, and even more so with BIVP in lateral position and thus reflects resynchronization compared to all other combinations tested. DP/dtmax did not reflect resynchronization as BIVP/LVP and lateral/anterior performs equally good. There are no differences between dP/dtmax with any combination of pacing mode (BIVP + LVP) with position (anterior + lateral). This suggests that Td reflects resynchronization while dP/dtmax does not. Resynchronization with biventricular pacing in lateral position translates into a shorter Td and hence links electrical and mechanical events. Td could be the missing link between electrical and mechanical dyssynchrony and may serve as a biomarker for cardiac resynchronization therapy.

Time delay to peak left ventricular pressure rise identifies the substrate for dyssynchronous heart failure and detects disease modification with resynchronization- an observational clinical study

Funding Acknowledgements

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Norwegian South East Health Authorities

Introduction

Identification of disease modification prior to implantation of Cardiac Resynchronization Therapy may help select the right patients, increase responder-rates and promote the utilization of CRT. We tested the hypothesis that shortening of time-to-peak left ventricular pressure rise (Td) with CRT is useful to predict long-term volumetric response (End-systolic volume (ESV) decrease >15%) to CRT.

Methods

Forty-five heart failure patients admitted for CRT implantation with a class I/IIa indication according to current ESC/AHA guidelines were included in the study. Td was measured from onset QRS at baseline and from onset of pacing with CRT.

Results

Baseline characteristics were mean age 63 ± 10 years , 71% males, NYHA class 2.5, 87% LBBB, QRS duration 173 ± 15ms, EF biplane 31 ± 1%, ESV 144 ± 12mL and end-diastolic volume 2044 ± 14mL. At 6-months follow-up six patients increased ESV by 5 ± 8%, while 37 responders (85%) had a mean ESV decrease of 40 ± 2%.  Responders presented with a higher Td at baseline compared to non-responders (163 ± 4ms vs 119 ± 9ms, p < 0.01). Td decreased to 156 ± 4ms (p = 0.02) with CRT in responders, while in non-responders Td increased to 147 ± 10ms (p < 0.01) with CRT. A decrease in Td of less than +3.5ms from baseline accurately identified responders to therapy (AUC 0.98, p < 0.01, sensitivity 97%, specificity 100%). AUC was 0.92 for baseline Td and a cut-off at 120ms yielded a sensitivity of 100% and specificity of 80% to identify volumetric responders. A linear relationship between the change in Td from baseline and ESV decrease on long term was found (β=-61, R = 0.58, P < 0.01).

Conclusions

Td at baseline and the shortening of Td with CRT accurately identifies responders to CRT, with incremental value on top of current guidelines, in a population with already high response rates. Td carries the potential to become the marker for prediction of long-term volumetric response in CRT candidates. Abstract Figure.

[Acute pyelonephritis in children with minimal or normal urine findings]

BACKGROUND

Over the past years we have seen several children with serious bacterial infections in whom the focus of the infection was found in the kidneys despite of normal or minimal urine findings.

MATERIAL AND METHODS

We review the cases of all children hospitalised at our paediatric department from 1995-2000 with normal or minimal urine findings, and in whom acute pyelonephritis was diagnosed by means of computerized tomographic imaging of the kidneys.

RESULTS

All 10 children (aged 9 months to 9 years) had focal areas of decreased enhancement in the kidney parenchyma. All received intravenous antibiotic treatment. Vesicouretheral reflux was detected in four patients and required surgical intervention in one. One patient had considerable renal scarring and decreased renal function on dimercaptosuccinic acid (DMSA) scintigraphy.

INTERPRETATION

In children with suspected serious bacterial infection, it is important to have the possibility of renal infection in mind in spite of normal urine findings. The importance of establishing the right diagnosis lies in the fact that patients with pyelonephritis need further investigation and follow-up.