Focal But Not Diffuse Myocardial Fibrosis Burden Quantification Using Cardiac Magnetic Resonance Imaging Predicts Left Ventricular Reverse Modeling Following Cardiac Resynchronization Therapy.

INTRODUCTION: Many heart failure patients with dyssynchrony do not reverse remodel (RR) in response to cardiac resynchronization therapy (CRT). The presence of focal and diffuse interstitial myocardial fibrosis may explain this high nonresponse rate. T1 mapping is a new cardiac magnetic resonance imaging (CMR) technique that overcomes the limitations of conventional contrast CMR and provides reliable quantitative assessment of diffuse myocardial fibrosis. The study tested the hypothesis that focal and diffuse fibrosis quantification would correlate with a lack of left ventricular (LV) RR to CRT. METHODS AND RESULTS: In a prospective study of 48 consecutive patients (27 ischemic cardiomyopathy, 21 dilated cardiomyopathy) LV scar burdens were quantified (scar core and gray zone using late gadolinium enhancement LGE CMR; interstitial fibrosis using T1 mapping) before CRT implant. LV RR was defined by a ≥ 15% reduction in LV end-systolic volume 6 months postimplant. Twenty-seven (56%) patients were responders with RR. Association between scar quantification and LV RR was assessed using the Poisson regression model. Univariate analysis showed that QRS duration/morphology, scar core, and gray zone volumes expressed as % of LV mass and extracellular volume index (ECV) (a measure of interstitial fibrosis from T1 mapping) to be significant predictors of LV RR. Multivariable-adjusted analyses demonstrated scar core quantification (≥ 13.7% LV mass) to be the only independent predictor of LV RR (prevalence ratio 0.40, P = 0.038). CONCLUSIONS: Focal scar burden detected by LGE CMR is associated with a poor response to CRT. Diffuse interstitial fibrosis assessment by T1 mapping, however, is not independently predictive of CRT response.

A randomized prospective mechanistic cardiac magnetic resonance study correlating catheter stability, late gadolinium enhancement and 3 year clinical outcomes in robotically assisted vs. standard catheter ablation.

AIMS: To prospectively compare cardiac magnetic resonance late gadolinium enhancement (LGE) findings created by standard vs. robotically assisted catheter ablation lesions and correlate these with clinical outcomes. METHODS AND RESULTS: Forty paroxysmal atrial fibrillation patients (mean age 54 ± 13.8 years) undergoing first left atrial ablation were randomized to either robotic-assisted navigation (Hansen Sensei(®) X) or standard navigation. Pre-procedural, acute (24 h post-procedure) and late (beyond 3 months) scans were performed with LGE and T2W imaging sequences and percentage circumferential enhancement around the pulmonary vein (PV) antra were quantified. Baseline pre-procedural enhancements were similar in both groups. On acute imaging, mean % encirclements by LGE and T2W signal were 72% and 80% in the robotic group vs. 60% (P = 0.002) and 76%(P = 0.45) for standard ablation. On late imaging, the T2W signal resolved to baseline in both groups. Late gadolinium enhancement remained the predominant signal with 56% encirclement in the robotic group vs. 45% in the standard group (P = 0.04). At 6 months follow-up, arrhythmia-free patients had an almost similar mean LGE encirclement (robotic 64%, standard 60%, P = 0.45) but in recurrences, LGE was higher in the robotic group (43% vs. 30%, P = 0.001). At mean 3 years follow-up, 1.3 procedures were performed in the robotic group compared with 1.9 (P < 0.001) in the standard to achieve a success rate of 80% vs. 75%. CONCLUSION: Robotically assisted ablation results in greater LGE around the PV antrum. Effective lesions created through improved catheter stability and contact force during initial treatment may have a role in reducing subsequent re-do procedures.

A comparison of left ventricular endocardial, multisite, and multipolar epicardial cardiac resynchronization: an acute haemodynamic and electroanatomical study.

AIMS: Alternative forms of cardiac resynchronization therapy (CRT), including biventricular endocardial (BV-Endo) and multisite epicardial pacing (MSP), have been developed to improve response. It is unclear which form of stimulation is optimal. We aimed to compare the acute haemodynamic response (AHR) and electrophysiological effects of BV-Endo with MSP via two separate coronary sinus (CS) leads or a single-quadripolar CS lead. METHODS AND RESULTS: Fifteen patients with a previously implanted CRT system received a second temporary CS lead and left ventricular (LV) endocardial catheter. A pressure wire and non-contact mapping array were placed into the LV cavity to measure LVdP/dtmax and perform electroanatomical mapping. Conventional CRT, BV-Endo, and MSP were then performed (MSP-1 via two epicardial leads and MSP-2 via a single-quadripolar lead). The best overall AHR was found using BV-Endo pacing with a 19.6 ± 13.6% increase in AHR at the optimal endocardial site over baseline (P < 0.001). There was an increase in LVdP/dtmax with MSP-1 and MSP-2 compared with conventional CRT, but this was not statistically significant. Biventricular endocardial pacing from the optimal site was significantly superior to conventional CRT (P = 0.039). The AHR achieved when BV-Endo pacing was highly site specific. Within individuals, the best pacing modality varied and was affected by the underlying substrate. Left ventricular activation times did not predict the optimal haemodynamic configuration. CONCLUSION: Biventricular endocardial pacing and not MSP was superior to conventional CRT, but was highly site specific. Within individuals, however, different methods of stimulation are optimal and may need to be tailored to the underlying substrate.

Patient-specific modeling of atrial fibrosis increases the accuracy of sinus rhythm simulations and may explain maintenance of atrial fibrillation.

Left atrial fibrosis is thought to contribute to the manifestation of atrial fibrillation (AF). Late Gadolinium enhancement (LGE) MRI has the potential to image regions of low perfusion, which can be related to fibrosis. We show that a simulation with a patient-specific model including left atrial regional fibrosis derived from LGE-MRI reproduces local activation in the left atrium more precisely than the regular simulation without fibrosis. AF simulations showed a spontaneous termination of the arrhythmia in the absence of fibrosis and a stable rotor center in the presence of fibrosis. The methodology may provide a tool for a deeper understanding of the mechanisms maintaining AF and eventually also for the planning of substrate-guided ablation procedures in the future.

Acute effects of multisite left ventricular pacing on mechanical dyssynchrony in patients receiving cardiac resynchronization therapy.

BACKGROUND: A novel quadripolar left ventricular (LV) pacing lead has the ability to deliver multisite LV pacing (MSLV). We set out to characterize the safety and changes in acute mechanical dyssynchrony with MSLV in cardiac resynchronization therapy (CRT) patients. METHODS AND RESULTS: Prospective multicenter study in 52 patients receiving CRT. An acute pacing protocol comprising 8 MSLV configurations covering a range of delays was compared with conventional CRT (baseline). Transthoracic tissue Doppler imaging (TDI) was used to measure the standard deviation of time to peak contraction of 12 LV segments (Ts-SD) and delayed longitudinal contraction. No ventricular arrhythmia occurred in any of the 52 patients. Complete TDI datasets were collected in 41 patients. Compared with baseline: 1) The mean Ts-SD was significantly lower for the optimal MSLV configuration (35.3 ± 36.4 vs 50.2 ± 29.1 ms; P < .001); 2) at least 1 MSLV configuration exhibited a significant dyssynchrony improvement in 63% of patients; and 3) the mean number of LV segments with delayed longitudinal contractions was significantly reduced with the optimal MSLV configuration (0.37 ± 7.99 vs 2.20 ± 0.19; P < .001). CONCLUSIONS: Acute MSLV was acutely safe, and a proportion of MSLV vectors resulted in a significant reduction in echocardiographic dyssynchrony compared with conventional CRT.

Quad-site pacing using a quadripolar left ventricular pacing lead.

Pacing the left ventricle (LV) from multiple sites simultaneously may result in a better response to cardiac resynchronization therapy (CRT). We sought to assess whether multisite pacing using a quadripolar LV lead improves acute hemodynamic response (AHR) to CRT. We paced four ventricular sites simultaneously using two vectors of a Quartet lead, a right ventricular apical lead, and an additional LV lead temporarily placed in an anterior branch of the coronary sinus. Multisite pacing using the Quartet lead alone did not improve the AHR but "quad-site" pacing using an additional temporary LV lead did increase dP/dt(max).

Multi-site left ventricular pacing as a potential treatment for patients with postero-lateral scar: insights from cardiac magnetic resonance imaging and invasive haemodynamic assessment.

AIMS: Multi-site left ventricular (LV) pacing may be superior to single-site stimulation in correcting dyssynchrony and avoiding areas of myocardial scar. We sought to characterize myocardial scar using cardiac magnetic resonance imaging (CMR). We aimed to quantify the acute haemodynamic response to single-site and multi-site LV stimulation and to relate this to the position of the LV leads in relation to myocardial scar. METHODS: Twenty patients undergoing cardiac resynchronization therapy had implantation of two LV leads. One lead (LV1) was positioned in a postero-lateral vein, the second (LV2) in a separate coronary vein. LV dP/dtmax was recorded using a pressure wire during stimulation at LV1, LV2, and both sites simultaneously (LV1 + 2). Patients were deemed acute responders if ΔLV dP/dtmax was ≥ 10%. Cardiac magnetic resonance imaging was performed to assess dyssynchrony as well as location and burden of scar. Scar anatomy was registered with fluoroscopy to assess LV lead position in relation to scar. RESULTS: LV dP/dtmax increased from 726 ± 161 mmHg/s in intrinsic rhythm to 912 ± 234 mmHg/s with LV1, 837 ± 188 mmHg/s with LV2, and 932 ± 201 mmHg/s with LV1 and LV2. Nine of 19 (47%) were acute responders with LV1 vs. 6/19 (32%) with LV2. Twelve of 19 (63%) were acute responders with simultaneous LV1 + 2. Two of three patients benefitting with multi-site pacing had the LV1 lead positioned in postero-lateral scar. CONCLUSION: Multi-site LV pacing increased acute response by 16% vs. single-site pacing. This was particularly beneficial in patients with postero-lateral scar identified on CMR.

Relationship between endocardial activation sequences defined by high-density mapping to early septal contraction (septal flash) in patients with left bundle branch block undergoing cardiac resynchronization therapy.

AIMS: Early inward motion and thickening/thinning of the ventricular septum associated with left bundle branch block is known as the septal flash (SF). Correction of SF corresponds to response to cardiac resynchronization therapy (CRT). We hypothesized that SF was associated with a specific left ventricular (LV) activation pattern predicting a favourable response to CRT. We sought to characterize the spatio-temporal relationship between electrical and mechanical events by directly comparing non-contact mapping (NCM), acute haemodynamics, and echocardiography. METHODS AND RESULTS: Thirteen patients (63 ± 10 years, 10 men) with severe heart failure (ejection fraction 22.8 ± 5.8%) awaiting CRT underwent echocardiography and NCM pre-implant. Presence and extent of SF defined visually and with M-mode was fused with NCM bull's eye plots of endocardial activation patterns. LV-dP/dt(max) was measured during different pacing modes. Five patients had a large SF, four small SF, and four no SF. Large SF patients had areas of conduction block in non-infarcted regions, whereas those with small or no SF did not. Patients with large SF had greater acute response to LV and biventricular (BIV) pacing vs. those with small/no SF (% increase dP/dt 28 ± 14 vs. 11 ± 19% for LV pacing and 42 ± 28 vs. 22 ± 21% for BIV pacing) (P < 0.05). This translated into a more favourable chronic response to CRT. The lines of conduction block disappeared with LV/BIV pacing while remaining with right ventricle pacing. CONCLUSION: A strong association exists between electrical activation and mechanical deformation of the septum. Correction of both mechanical synchrony and the functional conduction block by CRT may explain the favourable response in patients with SF.

Cardiac implantable electronic device-related endocarditis: a 12-year single-centre experience.

BACKGROUND: The incidence of cardiac implantable electrical device endocarditis (CIEDE) is increasing, but CIEDE remains a relatively poorly described infection. This case series describes our experience of the condition at a tertiary referral centre in London over a 12-y period. METHODS: We identified cases using an endocarditis database containing prospectively collected clinical and microbiological information. We also used data recorded in an electronic database of all cardiac implantable electrical device-related procedures. RESULTS: Thirty cases of CIEDE were treated at our institution during the study period. Presentation was most commonly with fever, and 93% of our patients had positive blood cultures. Vegetations were identified on echocardiography in only 70% of patients, although a transoesophageal echocardiogram (TOE) was performed in only half of the cases. Sixty-seven percent of our cases were defined as definite endocarditis according to the modified Duke criteria for infective endocarditis. Twenty-three patients underwent percutaneous explantation of their infected CIED (including 6 patients with vegetations greater than 10 mm in diameter), while 5 underwent surgical explantation. The overall in-hospital mortality was 17%. CONCLUSIONS: Our data confirm the life-threatening nature of CIEDE in a UK population. In addition, our experience suggests that percutaneous extraction of devices with large adherent vegetations may be safe, and that the selective use of TOE may not compromise outcomes. Lastly, we show that the modified Duke criteria do not perform very well with this condition, suggesting a need for specific, validated criteria for diagnosing CIEDE.

Percutaneous extraction of cardiac implantable electronic devices (CIEDs) in octogenarians.

BACKGROUND: As the population receiving cardiac device therapy ages, the number of extraction procedures performed in octogenarians is increasing. This group has more comorbidities and may be at higher risk of such procedures. OBJECTIVES: Document the safety and success of percutaneous lead extraction in octogenarians. METHODS: All extraction cases performed between January 2001 and April 2011 entered into a computer database were analyzed for patient characteristics and indications, extraction technique, procedural success, and complications. Success and complications were classified according to the Heart Rhythm Society consensus statement. Outcomes in octogenarians were compared to younger patients undergoing extraction during the same period. RESULTS: Four hundred and six cases were performed: 72 procedures in octogenarians (mean age 84, range 80-95) and 334 in younger adults (mean age 62, range 20-79). Octogenarians had a greater number of comorbidities per case. Infection was the commonest indication for extraction in both groups. One hundred forty-one leads were extracted in octogenarians and 657 in younger patients. Laser assistance was required in 51.4% of octogenarians versus 49.7% of younger patients. Procedural success was achieved in 71/72 (98.6%) octogenarians versus 329/334 (98.5%) younger patients. No procedural mortality occurred in either group. Overall, complications were more frequent in octogenarians with major and minor complications occurring in 2.8 and 8.3% of octogenarians versus 0.6 and 3.0% of younger patients (P = 0.014). CONCLUSIONS: Procedural success was equally high in octogenarians and younger patients. Percutaneous lead extraction can be performed effectively and safely in octogenarians and is associated with a higher complication rate but no increased mortality.

The acute hemodynamic response to LV pacing within individual branches of the coronary sinus using a quadripolar lead.

BACKGROUND: It is not clear whether there is a large difference in acute hemodynamic response (AHR) to left ventricle (LV) pacing in different regions of the same coronary sinus (CS) vein. Using the four electrodes available on a Quartet LV lead, we evaluated the AHR to pacing within individual branches of the CS. METHODS: An acute hemodynamic study was attempted in 20 patients. In each patient, we assessed AHR in a number of CS veins and along a significant proportion of each CS branch using three different bipolar configurations. We compared the AHR achieved when pacing using each different vector and also the highest AHR achieved in any position within the same patient with the lowest achieved in that patient. RESULTS: Sixty-four different CS positions in 19 patients were successfully assessed. No significant difference in AHR was found overall between the three vectors tested. The mean percentage difference in AHR between the CS branch vectors with the lowest and highest dP/dt(max) was +6.5 ± 5.4% (P < 0.001). A much larger difference of +16.9 ± 6.1% (P < 0.001) was seen when comparing the highest and lowest AHR achieved using any vector in any position within the same patient. CONCLUSION: A small difference in AHR is seen when pacing within the same branch of the CS compared to pacing in different branches in the same patient. This suggests that although the site of LV lead placement is important, the position within a CS branch is less important than choosing the right vein.

Quadripolar left ventricular lead implantation through the anchor struts of a mitral valve annuloplasty device.

We describe cardiac resynchronization therapy in a patient with a mitral valve annuloplasty device in situ for functional mitral regurgitation. We successfully implanted a left ventricular lead through a mitral valve annuloplasty device anchor into the coronary sinus and then through the struts of the device's proximal anchor.

Use of a quadripolar left ventricular lead to achieve successful implantation in patients with previous failed attempts at cardiac resynchronization therapy.

AIMS: Problems with implanting a left ventricular (LV) lead during cardiac resynchronization therapy (CRT) procedures are not uncommon and may occur for a variety of reasons including phrenic nerve stimulation (PNS) and high capture thresholds. We aimed to perform successful CRT in patients with previous LV lead problems using the multiple pacing configurations available with the St Jude Quartet model 1458Q quadripolar LV lead to overcome PNS or high capture thresholds. METHODS AND RESULTS: Four patients with previous failed attempts at LV lead implantation underwent a further attempt at CRT using a Quartet lead. In all four cases, successful CRT was achieved using a Quartet lead placed in a branch of the coronary sinus. Problems with PNS or high capture thresholds were seen in all four patients but were successfully overcome. Satisfactory lead parameters were seen at implant, pre-discharge, and at short-term follow-up (8.5±5 weeks). CONCLUSION: The Quartet lead allows 10 different pacing vectors to be used and may overcome common pacing problems because of the multiple pacing configurations available. Problems with either PNS or unsatisfactory pacing parameters experienced during CRT may be resolved simply by changing the pacing configuration using this quadripolar lead system.

Relationship between intracardiac impedance and left ventricular contractility in patients undergoing cardiac resynchronization therapy.

AIMS: Cardiac resynchronization therapy (CRT) has dramatically improved the symptoms and prognosis of patients with heart failure in large randomized clinical trials. Optimization of device settings may maximize benefit on an individual basis, although the best method for this is not yet established. We evaluated the use of cardiogenic impedance measurements (derived from intracardiac impedance signals) in CRT device optimization, using invasive left ventricular (LV) dP/dtmax as the reference. METHODS AND RESULTS: Seventeen patients underwent invasive haemodynamic assessment using a pressure wire placed in the LV cavity at the time of CRT device implantation. Intracardiac impedance measurements were made at different atrioventricular (AV) and interventricular (VV) delays and compared with LV dP/dtmax. We assessed the performance of patient-specific and generic impedance-based models in predicting acute haemodynamic response to CRT. In two patients, LV catheterization with the pressure wire was unsuccessful and in two patients LV lead delivery was unsuccessful; therefore, data were acquired for 13 out of 17 patients. Left ventricular dP/dtmax was 919±182 mmHg/s at baseline and this increased acutely (by 24%) to 1121±226 mmHg/s as a result of CRT. The patient-specific impedance-based model correctly predicted the optimal haemodynamic response (to within 5% points) for AV and VV delays in 90 and 92% of patients, respectively. CONCLUSION: Cardiogenic impedance measurements are capable of correctly identifying the maximum achievable LV dP/dtmax as measured by invasive haemodynamic assessment. This study suggests that cardiogenic impedance can potentially be used for CRT optimization and may have a role in ambulatory assessment of haemodynamics.

Advanced image fusion to overlay coronary sinus anatomy with real-time fluoroscopy to facilitate left ventricular lead implantation in CRT.

BACKGROUND: Failure rate for left ventricular (LV) lead implantation in cardiac resynchronization therapy (CRT) is up to 12%. The use of segmentation tools, advanced image registration software, and high-fidelity images from computerized tomography (CT) and cardiac magnetic resonance (CMR) of the coronary sinus (CS) can guide LV lead implantation. We evaluated the feasibility of advanced image registration onto live fluoroscopic images to allow successful LV lead placement. METHODS: Twelve patients (11 male, 59 ± 16.8 years) undergoing CRT had three-dimensional (3D) whole-heart imaging (six CT, six CMR). Eight patients had at least one previously failed LV lead implant. Using segmentation software, anatomical models of the cardiac chambers, CS, and its branches were overlaid onto the live fluoroscopy using a prototype version of the Philips EP Navigator software to guide lead implantation. RESULTS: We achieved high-fidelity segmentations of cardiac chambers, coronary vein anatomy, and accurate registration between the 3D anatomical models and the live fluoroscopy in all 12 patients confirmed by balloon occlusion angiography. The CS was cannulated successfully in every patient and in 11, an LV lead was implanted successfully. (One patient had no acceptable lead values due to extensive myocardial scar). CONCLUSION: Using overlaid 3D segmentations of the CS and cardiac chambers, it is feasible to guide CRT implantation in real time by fusing advanced imaging and fluoroscopy. This enabled successful CRT in a group of patients with previously failed implants. This technology has the potential to facilitate CRT and improve implant success.

Percutaneous lead and system extraction in patients with cardiac resynchronization therapy (CRT) devices and coronary sinus leads.

BACKGROUND: Cardiac resynchronization therapy (CRT) device and coronary sinus (CS) lead extraction is required due to the occurrence of system infection, malfunction, or upgrade. Published series of CS lead extraction are limited by small sample sizes. We present a 10-year experience of CRT device and CS lead extraction. METHODS: All lead extractions between 2000 and 2010 were entered into a computer database. From these, a cohort of 71 cases involving a CRT device or CS lead was analyzed for procedural method, success, and complications. RESULTS: Sixty coronary sinus leads were extracted in 71 cases (median age 71 years; 90% male) by manual traction/locking stylets (n = 54) or using a laser sheath (n = 6). Procedural success was achieved in 98% of CS leads. A total of 143 non-CS leads were extracted, with laser required in 46% of cases. The mean duration of lead implantation was 35.8 months (range 1-116 months) and 2.86 ± 1.07 leads were extracted per case. CRT extraction case load increased significantly over time. Minor complications occurred in four (5.6%) cases and major complications in one (1.4%) case. There were no intraprocedural deaths, but two deaths occurred within 30 days of extraction. CONCLUSIONS: Our 10-year experience confirms that percutaneous removal of CS leads can be achieved with high procedural success. Our recorded complication rates are no higher than those of non-CS lead extraction series, and should be taken in the context of the frail nature of CRT patients. Ongoing audit of procedure success and complications will be required to further guide best practice in CS lead extraction.

A multicenter prospective randomized controlled trial of cardiac resynchronization therapy guided by invasive dP/dt.

BACKGROUND: No periprocedural metric has demonstrated improved cardiac resynchronization therapy (CRT) outcomes in a multicenter setting. OBJECTIVE: We sought to determine if left ventricular (LV) lead placement targeted to the coronary sinus (CS) branch generating the best acute hemodynamic response (AHR) results in improved outcomes at 6 months. METHODS: In this multicenter randomized controlled trial, patients were randomized to guided CRT or conventional CRT. Patients in the guided arm had LV dP/dtmax measured during biventricular (BIV) pacing. Target CS branches were identified and the final LV lead position was the branch with the best AHR and acceptable threshold values. The primary endpoint was the proportion of patients with a reduction in LV end-systolic volume (LVESV) of ≥15% at 6 months. RESULTS: A total of 281 patients were recruited across 12 centers. Mean age was 70.8 ± 10.9 years and 54% had ischemic etiology. Seventy-three percent of patients in the guided arm demonstrated a reduction in LVESV of ≥15% at 6 months vs 60% in the conventional arm (P = .02). Patients with AHR ≥ 10% were more likely to demonstrate a reduction of ESV ≥ 15% (84% of patients with an AHR ≥10% vs 28% with an AHR <10%; P < 0.001). Procedure duration and fluoroscopy times were longer in the pressure wire-guided arm (104 ± 39 minutes vs 142 ± 39 minutes; P < .001 and 20 ±16 minutes vs 28 ± 15 minutes; P = .002). CONCLUSIONS: AHR determined by invasively measuring LV dP/dtmax during BIV pacing predicts reverse remodeling 6 months after CRT. Patients in whom LV dP/dtmax was used to guide LV lead placement demonstrated better rates of reverse remodeling.

Echocardiography to magnetic resonance image registration for use in image-guided cardiac catheterization procedures.

We present a robust method to register three-dimensional echocardiography (echo) images to magnetic resonance images (MRI) based on anatomical features, which is designed to be used in the registration pipeline for overlaying MRI-derived roadmaps onto two-dimensional live x-ray images during cardiac catheterization procedures. The features used in image registration are the endocardial surface of the left ventricle and the centre line of the descending aorta. The MR-derived left ventricle surface is generated using a fully automated algorithm, and the echo-derived left ventricle surface is produced using a semi-automatic segmentation method provided by the QLab software (Philips Healthcare) that it is routinely used in clinical practice. We test our method on data from six volunteers and four patients. We validated registration accuracy using two methods: the first calculated a root mean square distance error using expert identified anatomical landmarks, and the second method used catheters as landmarks in two clinical electrophysiology procedures. Results show a mean error of 4.1 mm, which is acceptable for our clinical application, and no failed registrations were observed. In addition, our algorithm works on clinical data, is fast and only requires a small amount of manual input, and so it is applicable for use during cardiac catheterization procedures.

Improved identifiability of myocardial material parameters by an energy-based cost function.

Myocardial stiffness is a valuable clinical biomarker for the monitoring and stratification of heart failure (HF). Cardiac finite element models provide a biomechanical framework for the assessment of stiffness through the determination of the myocardial constitutive model parameters. The reported parameter intercorrelations in popular constitutive relations, however, obstruct the unique estimation of material parameters and limit the reliable translation of this stiffness metric to clinical practice. Focusing on the role of the cost function (CF) in parameter identifiability, we investigate the performance of a set of geometric indices (based on displacements, strains, cavity volume, wall thickness and apicobasal dimension of the ventricle) and a novel CF derived from energy conservation. Our results, with a commonly used transversely isotropic material model (proposed by Guccione et al.), demonstrate that a single geometry-based CF is unable to uniquely constrain the parameter space. The energy-based CF, conversely, isolates one of the parameters and in conjunction with one of the geometric metrics provides a unique estimation of the parameter set. This gives rise to a new methodology for estimating myocardial material parameters based on the combination of deformation and energetics analysis. The accuracy of the pipeline is demonstrated in silico, and its robustness in vivo, in a total of 8 clinical data sets (7 HF and one control). The mean identified parameters of the Guccione material law were [Formula: see text] and [Formula: see text] ([Formula: see text], [Formula: see text], [Formula: see text]) for the HF cases and [Formula: see text] and [Formula: see text] ([Formula: see text], [Formula: see text], [Formula: see text]) for the healthy case.