Cost-Effectiveness of Cardiovascular Magnetic Resonance for Rejection Surveillance After Cardiac Transplantation in the Australian Health Care System

BACKGROUND

Heart transplantation is an effective treatment for end-stage congestive heart failure, however, achieving the right balance of immunosuppression to maintain graft function while minimising adverse effects is challenging. Serial endomyocardial biopsies (EMBs) are currently the standard for rejection surveillance, despite being invasive. Replacing EMB-based surveillance with cardiac magnetic resonance (CMR)-based surveillance for acute cardiac allograft rejection has shown feasibility. This study aimed to assess the cost-effectiveness of CMR-based surveillance in the first year after heart transplantation.

METHOD

A prospective clinical trial was conducted with 40 orthotopic heart transplant (OHT) recipients. Participants were randomly allocated into two surveillance groups: EMB-based, and CMR-based. The trial included economic evaluations, comparing the frequency and cost of surveillance modalities in relation to quality-adjusted life years (QALYs) within the first year post-transplantation. Sensitivity analysis encompassed modelled data from observed EMB and CMR arms, integrating two hypothetical models of expedited CMR-based surveillance.

RESULTS

In the CMR cohort, 238 CMR scans and 15 EMBs were conducted, versus (vs) 235 EMBs in the EMB group. CMR surveillance yielded comparable rejection rates (CMR 74 vs EMB 94 events, p=0.10) and did not increase hospitalisation risk (CMR 32 vs EMB 46 events, p=0.031). It significantly reduced the necessity for invasive EMBs by 94%, lowered costs by an average of AUD$32,878.61, and enhanced cumulative QALY by 0.588 compared with EMB. Sensitivity analysis showed that increased surveillance with expedited CMR Models 1 and 2 were more cost-effective than EMB (all p<0.01), with CMR Model 1 achieving the greatest cost savings (AUD$34,091.12±AUD$23,271.86 less) and utility increase (+0.62±1.49 QALYs, p=0.011), signifying an optimal cost-utility ratio. Model 2 showed comparable utility to the base CMR model (p=0.900) while offering the benefit of heightened surveillance frequency during periods of elevated rejection risk.

CONCLUSIONS

CMR-based rejection surveillance in orthotopic heart transplant recipients provides a cost-effective alternative to EMB-based surveillance. Furthermore, it reduces the need for invasive procedures, without increased risk of rejection or hospitalisation for patients, and can be incorporated economically for expedited surveillance. These findings have important implications for improving patient care and optimising resource allocation in post-transplant management.

Intra-cardiac motion detection catheter for the early identification of acute pericardial tamponade during invasive cardiac procedures

Objectives

To develop and test an intra-cardiac catheter fitted with accelerometers to detect acute pericardial effusion prior to the onset of hemodynamic compromise.

Background

Early detection of an evolving pericardial effusion is critical in ensuring timely treatment. We hypothesized that the reduction in movement of the lateral heart border present in developing pericardial effusions could be quantified by positioning an accelerometer in a lateral cardiac structure.

Methods

A "motion detection" catheter was created by implanting a 3-axis accelerometer at the distal tip of a cardiac catheter. The pericardial space of 5 adult sheep was percutaneously accessed, and pericardial tamponade was created by infusion of normal saline. The motion detection catheter was positioned in the coronary sinus. Intracardiac echocardiography was used to confirm successful creation of pericardial effusion and hemodynamic parameters were collected.

Results

Statistically significant reduction in acceleration from baseline was detected after infusion of only 40 ml of normal saline (p < 0.05, ANOVA). In comparison, clinically significant change in systolic blood pressure (defined as >10% drop in baseline systolic blood pressure) occurred after infusion of 80 ml of normal saline (107 ± 22 mmHg vs. 90 ± 12 mmHg p = 0.97, ANOVA), and statistically significant change was recorded only after infusion of 200 ml (107 ± 22 mmHg vs. 64 ± 5 mmHg, p < 0.05, ANOVA).

Conclusions

An intra-cardiac motion detection catheter is highly sensitive in identifying acute cardiac tamponade prior to clinically and statistically significant changes in systolic blood pressure, allowing for early detection and treatment of this potentially life-threatening complication of all modern percutaneous cardiac interventions.

Metabolic Sequelae of Everolimus Treatment After Cardiac Transplant: A Hypothesis-Generating Study

BACKGROUND

Although modern immunosuppressants improve survival post-transplant, they are associated with long-term metabolic complications, such as post-transplant diabetes mellitus (PTDM). Calcineurin inhibitor-sparing regimens using everolimus attenuate some complications such as left ventricular hypertrophy. However, the metabolic effects of everolimus following transplant are less clear.

METHODS

Post-hoc analysis to compare PTDM and other metabolic outcomes in participants of a randomised open-label clinical trial of low-dose everolimus and tacrolimus versus standard-dose tacrolimus in heart transplant recipients (RADTAC1 study).

RESULTS

There were 39 participants in the trial; mean follow-up was 6.4±1.5 years. There was a high rate of pre-existing diabetes (26%) and newly diagnosed PTDM (36%) during follow-up. Half the patients who developed PTDM in the everolimus-tacrolimus group (n=4/8) ceased diabetes medications during follow-up, which was not observed in patients on standard tacrolimus (n=0/6). In the first 12 months there was a higher use of non-insulin treatment for diabetes in the everolimus-tacrolimus group compared to the standard tacrolimus group.

CONCLUSIONS

This study suggests that treatment with everolimus may be associated with improved glycaemic control of PTDM relative to treatment with standard doses of calcineurin inhibitor. These findings should be further studied in prospective randomised trials.

Atrial cardiomyopathy: Current and future imaging methods for assessment of atrial structure and function

Changes in atrial size and function have historically been considered a surrogate marker of ventricular dysfunction. However, it is now recognized that atrial cardiomyopathy (ACM) may also occur as a primary myocardial disorder. Emerging evidence that ACM is a major risk factor for atrial fibrillation, heart failure, and thromboembolic stroke, has highlighted the significance of this disorder and the need for better assessment of atrial metrics in clinical practice. Key barriers in this regard include a lack of standardized criteria or hierarchy for the diagnosis of ACM and lack of consensus for the most accurate phenotyping methods. In this article we review existing literature on ACM, with a focus on current and future non-invasive imaging methods for detecting abnormalities of atrial structure and function. We discuss the relative advantages and disadvantages of transthoracic echocardiography and cardiac magnetic resonance imaging for assessing a range of parameters, including atrial size and contractile function, strain, tissue characteristics, and epicardial adipose tissue. We will also present the potential application of novel imaging methods such as sphericity index and four- or five-dimensional flow.

Cardiovascular Magnetic Resonance for Rejection Surveillance After Cardiac Transplantation

BACKGROUND

Endomyocardial biopsy (EMB) is the gold standard method for surveillance of acute cardiac allograft rejection (ACAR) despite its invasive nature. Cardiovascular magnetic resonance (CMR)-based myocardial tissue characterization allows detection of myocarditis. The feasibility of CMR-based surveillance for ACAR-induced myocarditis in the first year after heart transplantation is currently undescribed.

METHODS

CMR-based multiparametric mapping was initially assessed in a prospective cross-sectional fashion to establish agreement between CMR- and EMB-based ACAR and to determine CMR cutoff values between rejection grades. A prospective randomized noninferiority pilot study was then undertaken in adult orthotopic heart transplant recipients who were randomized at 4 weeks after orthotopic heart transplantation to either CMR- or EMB-based rejection surveillance. Clinical end points were assessed at 52 weeks.

RESULTS

Four hundred one CMR studies and 354 EMB procedures were performed in 106 participants. Forty heart transplant recipients were randomized. CMR-based multiparametric assessment was highly reproducible and reliable at detecting ACAR (area under the curve, 0.92; sensitivity, 93%; specificity, 92%; negative predictive value, 99%) with greater specificity and negative predictive value than either T1 or T2 parametric CMR mapping alone. High-grade rejection occurred in similar numbers of patients in each randomized group (CMR, n=7; EMB, n=8; P=0.74). Despite similarities in immunosuppression requirements, kidney function, and mortality between groups, the rates of hospitalization (9 of 20 [45%] versus 18 of 20 [90%]; odds ratio, 0.091; P=0.006) and infection (7 of 20 [35%] versus 14 of 20 [70%]; odds ratio, 0.192; P=0,019) were lower in the CMR group. On 15 occasions (6%), patients who were randomized to the CMR arm underwent EMB for clarification or logistic reasons, representing a 94% reduction in the requirement for EMB-based surveillance.

CONCLUSIONS

A noninvasive CMR-based surveillance strategy for ACAR in the first year after orthotopic heart transplantation is feasible compared with EMB-based surveillance.

REGISTRATION

HREC/13/SVH/66 and HREC/17/SVH/80.

AUSTRALIAN NEW ZEALAND CLINICAL TRIALS REGISTRY

ACTRN12618000672257.

Everolimus for the Prevention of Calcineurin-Inhibitor-Induced Left Ventricular Hypertrophy After Heart Transplantation (RADTAC Study)

OBJECTIVES

This study aimed to determine the safety and efficacy of combined low-dose everolimus and low-dose tacrolimus compared with standard-dose tacrolimus in attenuating left ventricular hypertrophy (LVH) after orthotopic heart transplantation (OHT).

BACKGROUND

Calcineurin inhibitors (CNIs) such as tactrolimus are important in preventing cardiac allograft rejection and reducing mortality after OHT. However CNIs are causatively linked to the development of LVH, and are associated with nephrotoxicity and vasculopathy. CNI-sparing agents such as everolimus have been hypothesized to inhibit adverse effects of CNIs.

METHODS

In this prospective, randomized, open-label study, OHT recipients were randomized at 12 weeks after OHT to a combination of low-dose everolimus and tacrolimus (the RADTAC group) or standard-dose tacrolimus (the TAC group), with both groups coadministered mycophenolate and prednisolone. The primary endpoint was LVH indexed as the change in left ventricular mass (ΔLVM) by cardiovascular magnetic resonance (CMR) imaging from 12 to 52 weeks. Secondary endpoints included CMR-based myocardial performance, T1 fibrosis mapping, blood pressure, and renal function. Safety endpoints included episodes of allograft rejection and infection.

RESULTS

Forty stable OHT recipients were randomized. Recipients in the RADTAC group had significantly lower tacrolimus levels compared with the TAC group (6.5 ± 3.5 μg/l vs. 8.6 ± 2.8 μg/l; p = 0.02). The mean everolimus level in the RADTAC group was 4.2 ± 1.7 μg/l. A significant reduction in LVM was observed in the RADTAC group compared with an increase in LVM in the TAC group (ΔLVM = -13.0 ± 16.8 g vs. 2.1 ± 8.4 g; p < 0.001). Significant differences were also noted in secondary endpoints measuring function and fibrosis (Δ circumferential strain = -2.9 ± 2.8 vs. 2.1 ± 2.3; p < 0.001; ΔT1 mapping values = -32.7 ± 51.3 ms vs. 26.3 ± 90.4 ms; p = 0.003). No significant differences were observed in blood pressure (Δ mean arterial pressure = 4.2 ± 18.8 mm Hg vs. 2.8 ± 13.8 mm Hg; p = 0.77), renal function (Δ creatinine = 3.1 ± 19.9 μmol/l vs. 9 ± 21.8 μmol/l; p = 0.31), frequency of rejection episodes (p = 0.69), or frequency of infections (p = 0.67) between groups.

CONCLUSIONS

The combination of low-dose everolimus and tacrolimus compared with standard-dose tacrolimus safely attenuates LVH in the first year after cardiac transplantation with an observed reduction in CMR-measured fibrosis and an improvement in myocardial strain.

Platelet-derived growth factor-AB improves scar mechanics and vascularity after myocardial infarction

Therapies that target scar formation after myocardial infarction (MI) could prevent ensuing heart failure or death from ventricular arrhythmias. We have previously shown that recombinant human platelet-derived growth factor-AB (rhPDGF-AB) improves cardiac function in a rodent model of MI. To progress clinical translation, we evaluated rhPDGF-AB treatment in a clinically relevant porcine model of myocardial ischemia-reperfusion. Thirty-six pigs were randomized to sham procedure or balloon occlusion of the proximal left anterior descending coronary artery with 7-day intravenous infusion of rhPDGF-AB or vehicle. One month after MI, rhPDGF-AB improved survival by 40% compared with vehicle, and cardiac magnetic resonance imaging showed left ventricular (LV) ejection fraction improved by 11.5%, driven by reduced LV end-systolic volumes. Pressure volume loop analyses revealed improved myocardial contractility and energetics after rhPDGF-AB treatment with minimal effect on ventricular compliance. rhPDGF-AB enhanced angiogenesis and increased scar anisotropy (high fiber alignment) without affecting overall scar size or stiffness. rhPDGF-AB reduced inducible ventricular tachycardia by decreasing heterogeneity of the ventricular scar that provides a substrate for reentrant circuits. In summary, we demonstrated that rhPDGF-AB promotes post-MI cardiac wound repair by altering the mechanics of the infarct scar, resulting in robust cardiac functional improvement, decreased ventricular arrhythmias, and improved survival. Our findings suggest a strong translational potential for rhPDGF-AB as an adjunct to current MI treatment and possibly to modulate scar in other organs.

1196Transvascular pace-capture of aorticorenal ganglia provides a testable procedural endpoint for transcatheter renal artery denervation and identifies a novel therapeutic ablation target for denervation

Background

Transcatheter renal denervation procedures often produces incomplete renal denervation and inconsistent antihypertensive effect. The lack of an intraprocedural method for renal sympathetic nerve function assessment has precluded a rational and physiologically based approach to ensure adequate denervation has been achieved at the time of the procedure.

Purpose

To demonstrate that it is possible to localise aorticorenal ganglia via transvascular pacing to provide: 1) a testable procedural endpoint for transcatheter renal denervation and, 2) a novel ablation target for renal denervation.

Methods

High frequency pacing in the inferior vena cava and aorta, invasive blood pressure measurements and renal angiography was performed in sheep (N=19) to identify ARG pace-capture sites by concurrent hypertensive and renal vasoconstrictive responses. Group A (N=5) underwent ink injection labelling at the ARG pace-capture site for histological verification; Group B (N=6) received unilateral irrigated radiofrequency ablation of ARG pace-capture sites and assessment of renal innervation at 1week post-procedure; and Group C (N=8) had ARG pacing performed prior to and 2–3 weeks after unilateral transcatheter microwave renal denervation.

Results

ARG pace-capture responses were observed at paired discrete sites in the posterior IVC and anterolateral aorta approximately 40mm above the ipsilateral renal artery. Pacing elicited a mean arterial blood pressure change of 22.2 [IQR 15.5–34.3] mmHg, p<0.001, together with ipsilateral renal vasoconstriction with main renal artery calibre change of −0.42mm [IQR −0.64mm to −0.24mm] measured with quantitative coronary analysis (QCA), p<0.0001, and branch renal artery median pixel density index change −10.4% [IQR −22.7% to −3.0%], p=0.003. Contralateral renal arterial vasoconstriction was not observed consistently at either the main or branch renal artery level. Sympathetic ganglionic tissue was observed at ARG pace-capture sites, and ganglion ablation caused significant ipsilateral renal denervation with a median hilar functional sympathetic nerve area reduction of 51% [IQR 24%–52%], p=0.043, and renal cortical norepinephrine reduction of 54% [IQR 36%–59%], p=0.043. Circumferential renal denervation resulted in immediate and sustained abolition of ARP pacing induced renal vasoconstriction and significant ipsilateral renal denervation.

Conclusion

Localisation of ARG using transvascular pacing is feasible with pace-capture demonstrated by concurrent hypertensive and ipsilateral renal arterial vasoconstrictive responses. Abolition of ARG pacing induced renal arterial vasoconstriction may indicate successful renal sympathetic denervation, providing a physiological procedural endpoint to guide transcatheter renal denervation. Additionally, ablation of ARG could provide an alternative or adjunctive method for renal denervation.

Acknowledgement/Funding

University of Sydney; Western Sydney Local health District; National Health and Medical Research Council of Australia; National Heart Foundation (Au)

1197The development and validation of a novel transcatheter microwave renal denervation system

Background

Clinical studies of transcatheter radiofrequency renal denervation for treating hypertension have been hampered by the lack of consistent denervation efficacy. Microwave energy is well suited to renal denervation due to its capacity to spare vascular structures due to cooling from adjacent blood flow while enabling deep perivascular heating.

Purpose

We aimed to: 1) develop a transcatheter microwave system capable of safely delivering deep and circumferential perivascular renal nerve ablation, and 2) demonstrate the feasibility, short-term efficacy and safety of transcatheter microwave renal denervation.

Method

A novel 7F transcatheter microwave denervation system was designed, built, and iteratively prototyped in vitro and in 15 sheep. A histological grading system for microwave induced renal arterial and renal nerve injury was devised. The microwave denervation system was validated in an additional 9 sheep, which underwent unilateral renal denervation. Up to 2 microwave ablations were delivered to each artery with maximum power at 100–110W for 480s. Sheep were euthanised at 2–3 weeks post procedure. Gross microscopic histological examination as well as renal tissue norepinephrine content was analysed.

Results

Catheter deployment and ablation was successful in all 19 targeted vessel segments and ablation produced substantial circumferential perivascular injury; median ablation lesion area >395 (IQR 251–437) mm2, depth 17.1 (IQR 15.8–18.4) mm, length 16 (IQR 12–20) mm, without collateral visceral injury. Limiting power to 100W minimised arterial injury, while maintaining a deep circumferential perivascular ablation. At microwave ablation sites, a total of 292 nerve fascicles were identified, median distance from the renal artery of 4.2mm (IQR 2.1–8.8mm), of which 249 (85%) had sustained thermal injury with 128/249 (51%) showing grade 3–4 (moderate to severe) injury. Microwave denervation reduced median functional sympathetic nerve surface area at the renal hilum on anti-tyrosine hydroxylase staining by 100% (IQR 87%-100%), p=0.0039, and median renal cortical norepinephrine content by 83% (IQR 76%–92%), p=0.0078, compared to the paired control kidney.

Conclusion

Transcatheter microwave ablation can produce deep circumferential perivascular ablations over a long segment of the renal artery without significant arterial or collateral visceral injury to provide effective renal denervation. Clinical translation may enable more consistent and complete transcatheter renal denervation and antihypertensive efficacy.

Acknowledgement/Funding

University of Sydney; Western Sydney Local health District; National Health and Medical Research Council of Australia; National Heart Foundation (Au)

Analysis of recombinant adeno-associated viral vector shedding in sheep following intracoronary delivery

Differences between mouse and human hearts pose a significant limitation to the value of small animal models when predicting vector behavior following recombinant adeno-associated viral (rAAV) vector-mediated cardiac gene therapy. Hence, sheep have been adopted as a preclinical animal, as they better model the anatomy and cardiac physiological processes of humans. There is, however, no comprehensive data on the shedding profile of rAAV in sheep following intracoronary delivery, so as to understand biosafety risks in future preclinical and clinical applications. In this study, sheep received intracoronary delivery of rAAV serotypes 2/6 (2 × 10¹² vg), 2/8, and 2/9 (1 × 10¹³ vg) at doses previously administered in preclinical and clinical trials. This was followed by assessment over 96 h to examine vector shedding in urine, feces, nasal mucus, and saliva samples. Vector genomes were detected via real-time quantitative PCR in urine and feces up to 48 and 72 h post vector delivery, respectively. Of these results, functional vector particles were only detected via a highly sensitive infectious replication assay in feces samples up to 48 h following vector delivery. We conclude that rAAV-mediated gene transfer into sheep hearts results in low-grade shedding of non-functional vector particles for all excreta samples, except in the case of feces, where functional vector particles are present up to 48 h following vector delivery. These results may be used to inform containment and decontamination guidelines for large animal dealings, and to understand the biosafety risks associated with future preclinical and clinical uses of rAAV.

Influence of Body Mass Index on Recurrence of Ventricular Arrhythmia, Mortality in Defibrillator Recipients With Ischaemic Cardiomyopathy

BACKGROUND

Obesity is associated with increased risk of cardiovascular disease. There is little known, however, about the influence of body mass index (BMI) on spontaneously occurring ventricular arrhythmias in patients with ischaemic heart disease. We sought to examine the effect of BMI on the ventricular arrhythmia (VA) recurrence and mortality in defibrillator recipients with ischaemic cardiomyopathy.

METHODS

Consecutive patients (n = 123) with ischaemic cardiomyopathy (left ventricular ejection fraction (LVEF) ≤ 40%) and a primary or secondary prevention defibrillator were included. Patients were classified according to their BMI as being normal (18.5-24.99, n = 54/ 43.9%), overweight (2 -29.99, n = 43/ 35%) or obese (>30, n = 26/20.3%).

RESULTS

The primary combined endpoint of VA recurrence and mortality occurred in 36%, 5.4% and 11.5% of patients with normal, overweight and obese BMI (p = 0.001). When adjusting for risk factors such as ejection fraction, age and triple vessel disease, on multivariable analysis, normal BMI remained a significant predictor for the primary outcome (Hazard Ratio, Normal vs Overweight = 7.1, 95% CI 1.8-25, p = 0.002: Hazard Ratio, Normal vs Obese = 5.5, 95% CI 1.11-25, p = 0.033). There was a non-significant trend towards reduced survival in patients with normal weight in comparison to overweight and obese patients (p = 0.08).

CONCLUSION

In defibrillator recipients with ischaemic cardiomyopathy, BMI appears to be a significant predictor for the combined primary outcome of spontaneously occurring ventricular arrhythmias and mortality. Normal BMI, compared to overweight and obese patients had worse outcomes, suggesting the presence of the obesity paradox in ventricular arrhythmogenesis late post infarction.

Comparison of two different radiofrequency ablation systems for renal artery denervation: Evaluation of short-term and long-term follow up

Objectives

To assess the clinical efficacy of renal artery denervation (RAD) in our center and to compare the efficacy of two different radiofrequency (RF) systems.

Background

Several systems are available for RF renal denervation. Whether there is a difference in clinical efficacy among various systems remains unknown.

Methods

Renal artery denervation was performed on 43 patients with resistant hypertension using either the single electrode Symplicity Flex (n = 20) or the multi‐electrode EnligHTN system (n = 23). Median post‐procedural follow‐up was 32.93 months. The primary outcome was post‐procedural change in office blood pressure (BP) within 1 year (short‐term follow‐up). Secondary outcomes were change in office BP between 1 and 4 years (long‐term follow‐up) and the difference in office BP reduction between the two systems at each follow‐up period.

Results

For the total cohort, mean baseline office BP (systolic/diastolic) was 174/94 mmHg. At follow‐up, mean changes in office BP from baseline were −19.70/−11.86 mmHg (P < 0.001) and −21.90/−13.94 mmHg (P < 0.001) for short‐term and long‐term follow‐up, respectively. The differences in office BP reduction between Symplicity and EnligHTN groups were 8.96/1.23 mmHg (P = 0.42 for systolic BP, P = 0.83 for diastolic BP) and 9.56/7.68 mmHg (P = 0.14 for systolic BP, P = 0.07 for diastolic BP) for short‐term and long‐term follow‐up, respectively.

Conclusions

In our cohort, there was a clinically significant office BP reduction after RAD, which persisted up to 4 years. No significant difference in office BP reduction between the two systems was found.

Quantitative spectral assessment of intracardiac electrogram characteristics associated with post infarct fibrosis and ventricular tachycardia

Background

Post-myocardial infarction (MI) remodeling contributes to increased electrophysiological and structural heterogeneity and arrhythmogenesis. Utilising the post-infarct ovine model our aim was to determine unipolar electrogram frequency characteristics consequent to this remodeling and the development of Ventricular Tachycardia (VT).

Methods and results

Mapping studies were performed on 14 sheep at >1 month post-MI induction. Sheep were divided into VT inducible (n = 7) and non-inducible (n = 7) groups. Multielectrode needles (n = 20) were deployed within and surrounding ventricular scar for electrophysiological assessment of electrogram amplitude and width. Spectral analysis of electrograms was undertaken using wavelet and fast fourier transformations (WFFT) to calculate root mean square (RMS) power intervals spanning 0-300Hz in 20Hz intervals. Quantitative assessment between electrophysiological and histological parameters including collagen density, and structural organization of the myocardium was performed.

Increasing myocardial scar density resulted in attenuation of electrogram amplitude and RMS values. (all p<0.01). Between groups there were no differences in electrogram amplitude (p = 0.37), however WFFT analysis revealed significantly higher RMS values in the VT group (p<0.05) in association with high frequency fractional components of the electrogram. As scar density increased, greater between-group differences in RMS were observed spanning this high frequency (200-280Hz) spectrum and which were proportionally dependent on the degree of structural disorganisation of the myocardium (p<0.001) and number of extrastimuli required to induce VT (p<0.05).

Conclusion

High frequency unipolar electrogram spectral characteristics were quantitatively co-influenced by the presence of fibrosis and degree of myocardial structural dissorganisation and were associated with the propensity for development of VT.

Five seconds of 50-60 W radio frequency atrial ablations were transmural and safe: an in vitro mechanistic assessment and force-controlled in vivo validation

Aims

Longer procedural time is associated with complications in radiofrequency atrial fibrillation ablation. We sought to reduce ablation time and thereby potentially reduce complications. The aim was to compare the dimensions and complications of 40 W/30 s setting to that of high-power ablations (50-80 W) for 5 s in the in vitro and in vivo models.

Methods and results

In vitro ablations-40 W/30 s were compared with 40-80 W powers for 5 s. In vivo ablations-40 W/30 s were compared with 50-80 W powers for 5 s. All in vivo ablations were performed with 10 g contact force and 30 mL/min irrigation rate. Steam pops and depth of lung lesions identified post-mortem were noted as complications. A total of 72 lesions on the non-trabeculated part of right atrium were performed in 10 Ovine. All in vitro ablations except for the 40 W/5 s setting achieved the critical lesion depth of 2 mm. For in vivo ablations, all lesions were transmural, and the lesion depths for the settings of 40 W/30 s, 50 W/5 s, 60 W/5 s, 70 W/5 s, and 80 W/5 s were 2.2 ± 0.5, 2.3 ± 0.5, 2.1 ± 0.4, 2.0 ± 0.3, and 2.3 ± 0.7 mm, respectively. The lesion depths of short-duration ablations were similar to that of the conventional ablation. Steam pops occurred in the ablation settings of 40 W/30 s and 80 W/5 s in 8 and 11% of ablations, respectively. Complications were absent in short-duration ablations of 50 and 60 W.

Conclusion

High-power, short-duration atrial ablation was as safe and effective as the conventional ablation. Compared with the conventional 40 W/30 s setting, 50 and 60 W ablation for 5 s achieved transmurality and had fewer complications.

Human Connexin40 Mutations Slow Conduction and Increase Propensity for Atrial Fibrillation

BACKGROUND

Patch clamping studies using non-cardiomyocytes revealed that the human connexin40 mutations P88S, G38D, and A96S are associated with reduced gap junction conductances compared to wild type connexin40 (wtCx40). Their effects within myocytes however are unclear. We aimed to characterise P88S, G38D, and A96S after expression in rat hearts and primary cardiomyocyte cultures.

METHODS

Adult Sprague-Dawley rat atria were transduced with a lentivector containing a transgene encoding wtCx40, P88S, G38D, A96S, or eGFP (n=6 per transgene). Electrophysiology studies (EPS) were performed just prior to and 7 days after surgery. Left atria were assessed for connexin expression, mRNA levels, inflammation and fibrosis. Primary cardiomyocyte cultures were also transduced with the abovementioned vectors (n=6 per transgene) and monolayer conduction velocities (CV) and protein expression were assessed at 96hours.

RESULTS

At day 7 EPS, P wave and induced atrial fibrillation (AF) durations were significantly longer in the mutant groups when compared to wtCx40 controls (p<0.05). There were no significant differences in inflammation, fibrosis, or heart to body weight ratios. Monolayer CV's were reduced in the A96S group compared to the wtCx40 group. While similar to wtCx40 controls, P88S velocities were reduced compared to eGFP controls. G38D monolayers possessed spontaneous fibrillatory activity and could not be paced. Immunofluorescence revealed that P88S and G38D reduced native connexin43 myocyte coupling while A96S appeared to co-localise with connexin43 in gap junctions. Connexin43 mRNA levels were similar between groups.

CONCLUSIONS

The A96S, G38D, and P88S Cx40 mutations slow conduction and increased the propensity for inducible AF.

Influence of Intramyocardial Adipose Tissue on the Accuracy of Endocardial Contact Mapping of the Chronic Myocardial Infarction Substrate

BACKGROUND

Recent studies have demonstrated that intramyocardial adipose tissue (IMAT) may contribute to ventricular electrophysiological remodeling in patients with chronic myocardial infarction. Using an ovine model of myocardial infarction, we aimed to determine the influence of IMAT on scar tissue identification during endocardial contact mapping and optimal voltage-based mapping criteria for defining IMAT dense regions.

METHOD AND RESULTS

In 7 sheep, left ventricular endocardial and transmural mapping was performed 84 weeks (15-111 weeks) post-myocardial infarction. Spearman rank correlation coefficient was used to assess the relationship between endocardial contact electrogram amplitude and histological composition of myocardium. Receiver operator characteristic curves were used to derive optimal electrogram thresholds for IMAT delineation during endocardial mapping and to describe the use of endocardial mapping for delineation of IMAT dense regions within scar. Endocardial electrogram amplitude correlated significantly with IMAT (unipolar r=-0.48±0.12, P<0.001; bipolar r=-0.45±0.22, P=0.04) but not collagen (unipolar r=-0.36±0.24, P=0.13; bipolar r=-0.43±0.31, P=0.16). IMAT dense regions of myocardium reliably identified using endocardial mapping with thresholds of <3.7 and <0.6 mV, respectively, for unipolar, bipolar, and combined modalities (single modality area under the curve=0.80, P<0.001; combined modality area under the curve=0.84, P<0.001). Unipolar mapping using optimal thresholding remained significantly reliable (area under the curve=0.76, P<0.001) during mapping of IMAT, confined to putative scar border zones (bipolar amplitude, 0.5-1.5 mV).

CONCLUSIONS

These novel findings enhance our understanding of the confounding influence of IMAT on endocardial scar mapping. Combined bipolar and unipolar voltage mapping using optimal thresholds may be useful for delineating IMAT dense regions of myocardium, in postinfarct cardiomyopathy.

Ninety Seconds Could be the Optimal Duration for Ventricular Radiofrequency Ablation - Results From a Myocardial Phantom Model

BACKGROUND

Shallow lesions could be the predominant factor affecting the efficacy of ventricular radiofrequency (RF) ablations. The objective of this study was to assess lesion dimensions and overheating in extended RF ablations up to 180seconds and compare with that of conventional 30seconds ablations.

METHODS

The Navistar Thermocool irrigated catheter (Biosense Webster, CA, USA) was used in a previously validated myocardial phantom. Ablations were performed with 20W, 30W, 40W and 50W powers for 180seconds. The volume of lesion and overheating were measured at 53⁰C and 80⁰C isotherms respectively.

RESULTS

A total of 110 RF lesions were analysed. The lesion depth increment when ablation was extended from the conventional 30seconds to 90seconds were 31.2±0.2, 33.6±0.6, 36.3±1.8% of that at 30seconds, respectively for powers 30W, 40W and 50W. During 30W ablations, at 90seconds the lesion width and depth were 95.4±1.2%, 91.8±1.6% respectively of the final dimensions at 180seconds. Similar proportions were observed for 40W and 50W. During 40W ablations, the volume of overheating was 113±6% and 184±11% higher at 90seconds and 180seconds respectively compared to that at 30seconds and was 142±9% and 194±9% for 50W ablations.

CONCLUSION

Extending RF ablations up to 90seconds significantly increased the lesion depth (30-40%), however, overheating was present at 40W and 50W powers. Ablations beyond 90seconds provided little incremental value.

Novel use of NavX three-dimensional mapping to guide renal artery denervation

AIMS

Renal artery denervation (RAD) is an effective treatment for resistant hypertension. The Navigation and Visualisation Technology (NavX) system creates three-dimensional (3-D) anatomical maps to guide catheter position and identify ablation sites. This first-in-human study assessed the utility of NavX 3-D mapping for RAD.

METHODS AND RESULTS

Consecutive patients who underwent RAD using fluoroscopy alone (control group, n=8) were compared to NavX-guided RAD (NavX group, n=10). Where NavX was utilised, orthogonally located skin patches were applied to the torso for acquisition of 3-D geometry of each renal artery. Baseline clinical characteristics and renal artery anatomy were similar between groups. Median contrast dose was significantly higher in the control versus NavX group (123 ml versus 78 ml, p=0.016). Median radiation dose was significantly higher in the control versus NavX group (166 Gy cm² versus 43 Gy cm², p=0.034). Mean changes in systolic and diastolic BP at three-month follow-up were -22/-9 mmHg and -23/-11 mmHg in the control and NavX group, respectively (p=0.99).

CONCLUSIONS

Use of NavX mapping as compared to standard renal artery denervation was found to correlate with a significant reduction in contrast load and radiation exposure. This study demonstrates both the feasibility and potential benefits of NavX 3-D mapping to guide renal artery denervation.

Investigating the utility of in vivo bio-impedance spectroscopy for the assessment of post-ischemic myocardial tissue

Increased myocardial structural heterogeneity in response to ischemic injury following myocardial infarction (MI) is purported as the mechanism of ventricular arrhythmogenesis. Current modalities for in vivo assessment of structural heterogeneity for identification of arrhythmogenic substrate are limited due to the complex nature of the structural microenvironment post-MI. We investigated the utility of in vivo bio-impedance spectroscopy (BIS) in a large post-infarct animal model for differentiation between normal and infarcted tissue. We also investigated the quantitative effects of adipose and collagen on BIS assessment of myocardium. The results indicate that the degree of myocardial injury following chronic post-infarction remodeling could be reliably quantified (performed in triplicates) using BIS. Furthermore, the presence of intramyocardial adipose tissue that develops in conjunction with collagen within the infarct zone had a greater and significant influence on BIS then collagen tissue alone. These preliminary results indicate a potential role of BIS for quantitative assessment and characterization of complex arrhythmogenic substrates in ischemic cardiomyopathy.

Electrogram-Gated Radiofrequency Ablations With Duty Cycle Power Delivery Negate Effects of Ablation Catheter Motion

Background—

Cardiac and respiratory movements cause catheter instability. Lateral catheter sliding over target endocardial surface can lead to poor tissue contact and unpredictable lesion formation. We describe a novel method of overcoming the effects of lateral catheter sliding movements using an electrogram-gated pulsed power ablation.

Methods and Results—

All ablations were performed on a thermochromic gel myocardial phantom. Ablation settings were randomized to conventional (nongated) 30 W versus electrogram-gated at 20% duty cycle (30 W average power) at 0-, 3-, 6-, and 9-mm lateral sliding distances. Forty-eight radiofrequency ablations were performed. Deeper lesions were created in electrogram-gated versus conventional ablations at 3 mm (4.36±0.08 versus 4.05±0.17 mm; P =0.009), 6 mm (4.39±0.10 versus 3.44±0.15 mm; P <0.001), and 9 mm (4.41±0.06 versus 2.94±0.16 mm; P <<0.001) sliding distances. Electrogram-gated ablations created consistent lesions at a quicker rate of growth in depth when compared with conventional ablations ( P <0.001).

Conclusions—

(1) Lesion depth decreases and length increases in conventional ablations with greater degrees of lateral catheter movements; (2) electrogram-gated pulsed radiofrequency delivery negated the effects from lateral catheter movement by creating consistently deeper lesions irrespective of the degree of catheter movement; and (3) target lesion depths were reached significantly faster in electrogram-gated than in conventional ablations.

Electrical impedance tomography for assessing ventilation/perfusion mismatch for pulmonary embolism detection without interruptions in respiration

Recent studies have shown high correlation between pulmonary perfusion mapping with impedance contrast enhanced Electrical Impedance Tomography (EIT) and standard perfusion imaging methods such as Computed Tomography (CT) and Single Photon Emission Computerized Tomography (SPECT). EIT has many advantages over standard imaging methods as it is highly portable and non-invasive. Contrast enhanced EIT uses hypertonic saline bolus instead of nephrotoxic contrast medium that are utilized by CT and nuclear Ventilation/Perfusion (V/Q) scans. However, current implementation of contrast enhanced EIT requires induction of an apnea period for perfusion measurement, rendering it disadvantageous compared with current gold standard imaging modalities. In the present paper, we propose the use of a wavelet denoising algorithm to separate perfusion signal from ventilation signal such that no interruption in patient's ventilation would be required. Furthermore, right lung to left lung perfusion ratio and ventilation ratio are proposed to assess the mismatch between ventilation and perfusion for detection of Pulmonary Embolism (PE). The proposed methodology was validated on an ovine model (n=3, 83.7±7.7 kg) with artificially induced PE in the right lung. The results showed a difference in right lung to left lung perfusion ratio between baseline and diseased states in all cases with all paired t-tests between baseline and PE yielding p <; 0.01, while the right lung to left lung ventilation ratio remained unchanged in two out of three experiments. Statistics were pooled from multiple repetitions of measurements per experiment.

Primary Radiofrequency Ablation of Ventricular Tachycardia Early After Myocardial Infarction

Background—

Ventricular tachycardia (VT) is a significant complication of myocardial infarction. Radiofrequency ablation for postinfarct VT is reserved for drug refractory VT or VT storms. Our hypothesis is that radiofrequency ablation in the early postinfarct period could abolish or diminish late recurrences of VT.

Methods and Results—

Myocardial infarct was induced by balloon occlusion of the left anterior descending artery in 35 sheep. The 25 survivors underwent programmed ventricular stimulation and electroanatomical mapping 8 days postinfarct. Animals with inducible VT (12 out of 25 animals) underwent immediate radiofrequency ablation. Further VT inductions were performed 100 and 200 days postinfarct. At day 8, 3.0±0.9 VT morphologies per animal were inducible. All were successfully ablated with 24±6 applications of radiofrequency energy. All had ablations on the left ventricular endocardium, and 67% had ablations on the right ventricular aspect of the interventricular septum. All targeted arrhythmias were successfully ablated acutely. One animal was euthanized because of hypotension from a serious pericardial effusion. The other 11 survived and remained arrhythmia free on subsequent inductions on the 100th and 200th days ( P <0.001). The 13 animals without inducible VT remained noninducible at the subsequent studies. A historical control arm of 9 animals with inducible VT at day 8 remained inducible at day 100.

Conclusions—

Radiofrequency ablation on the eighth day after infarction abolished inducibility of VT at late induction studies ≤200 days in an ovine model. Early identification and ablation of VT after infarction may prevent or reduce late ventricular arrhythmias but needs to be validated in clinical studies.