3D printed patient-specific aortic root models with internal sensors for minimally invasive applications.

Minimally invasive surgeries have numerous advantages, yet complications may arise from limited knowledge about the anatomical site targeted for the delivery of therapy. Transcatheter aortic valve replacement (TAVR) is a minimally invasive procedure for treating aortic stenosis. Here, we demonstrate multimaterial three-dimensional printing of patient-specific soft aortic root models with internally integrated electronic sensor arrays that can augment testing for TAVR preprocedural planning. We evaluated the efficacies of the models by comparing their geometric fidelities with postoperative data from patients, as well as their in vitro hemodynamic performances in cases with and without leaflet calcifications. Furthermore, we demonstrated that internal sensor arrays can facilitate the optimization of bioprosthetic valve selections and in vitro placements via mapping of the pressures applied on the critical regions of the aortic anatomies. These models may pave exciting avenues for mitigating the risks of postoperative complications and facilitating the development of next-generation medical devices.

Exit vs. entrance block testing for cardiac lesion assessment.

Cardiac lesions are created to act as barriers which prohibit the transmission of cardiac myocyte contractile activity from one side of the lesion to the other. Testing for conduction block is the main way to acutely confirm the effectiveness of this therapy. There are two general methods used to test for conduction block. These methods are called: 1) "exit block testing" and 2) "entrance block testing." In this study, two different devices were used on n = 5 swine to determine if the method of lesion assessment (exit vs. entrance block testing) affected the ability to correctly identify if acute conduction block was achieved. No significant difference was found between conclusions drawn from either method of lesion assessment. However, the most robust lesion assessment will occur when both methods are employed so that the physician has the most information available for analysis.

Novel visualization of intracardiac pacing lead extractions: methodologies performed within isolated canine hearts.

Several methodologies are typically employed to extract chronically-implanted pacing leads including: laser catheter systems, radio frequency catheters, mechanical cutting catheters, and/or direct traction. In the present study, Visible Heart(R) methodologies were employed to obtain novel internal and external views of such extractions. Utilizing standard cardioplegia procedures, canine hearts (n = 3) with chronically-implanted endocardial pacing leads were explanted to a unique isolated heart apparatus. Modified Krebs-Henseleit buffer allowed for clear endocardial imaging with endoscopic video cameras inserted into the cardiac chambers. Leads were extracted using: (1) laser system with sheath; (2) dissection sheath with incorporated bipolar tungsten electrode; (3) non-powered mechanical sheath; or (4) direct traction. Resultant images provide a novel perspective regarding lead extraction methodologies and the imposed force on an encapsulated lead and on the great vessels and/or heart itself; this understanding may improve the outcome and safety of future lead extractions.

Estimation of global ventricular activation sequences by noninvasive three-dimensional electrical imaging: validation studies in a Swine model during pacing.

BACKGROUND: A novel noninvasive imaging technique, the heart-model-based three-dimensional cardiac electrical imaging (3DCEI) approach was previously developed and validated to estimate the initiation site (IS) of cardiac activity and the activation sequence (AS) from body surface potential maps (BSPMs) in a rabbit model. The aim of the present study was to validate the 3DCEI in an intact large mammalian model (swine) during acute ventricular pacing. METHODS AND RESULTS: The heart-torso geometries were constructed from preoperative magnetic resonance (MR) images acquired from each animal. Body surface potential mapping and intracavitary noncontact mapping (NCM) were performed simultaneously during pacing from both right ventricular (RV) (intramural) and left ventricular (LV) sites (endocardial). Subsequent 3DCEI analyses were performed from the measured BSPMs. The estimated ISs were compared with the precise pacing locations and estimated ASs were compared with those recorded by the NCM system. In total, five RV and five LV sites from control and heart failure (HF) animals were paced and sequences of 100 paced beats were analyzed (10 for each site). The averaged localization error (LE) of the RV and LV sites were 7.3 +/- 1.8 mm (n = 50) and 7.0 +/- 2.2 mm (n = 50), respectively. The global 3D ASs throughout the ventricular myocardium were also derived. The endocardial ASs as a subset of the estimated 3D ASs were consistent with those reconstructed from the NCM system. CONCLUSION: The present experimental results demonstrate that the noninvasive 3DCEI approach can localize the IS and estimate AS with good accuracy in an in vivo setting under control, paced, and/or diseased conditions.

Noninvasive estimation of three-dimensional cardiac electrical activities from body surface potential maps.

A noninvasive three-dimensional (3D) cardiac electrical imaging (3DCEI) approach, which can estimate the location of the initiation site (IS) of activation and the resultant 3D activation sequence (AS) from body surface potential maps (BSPMs), was validated in an intact large mammalian model (swine) during acute ventricular pacing. Body surface potential mapping and intracavitary noncontact mapping (NCM) were performed simultaneously during pacing from both right ventricular (RV) sites (intramural) and left ventricular (LV) sites (endocardial). Subsequent 3DCEI analyses were performed on the measured BSPMs. In total, 5 RV and 5 LV sites from control and heart failure animals were paced. The averaged localization error of the RV and LV sites were 7.0+/-1.1 mm and 6.6+/-1.9 mm, respectively. The endocardial ASs as a subset of the estimated 3D ASs by 3DCEI were consistent with those reconstructed from the NCM system. The present experimental results demonstrate that the noninvasive 3DCEI approach can localize the initiation site and estimate cardiac activation sequence with good accuracy in an in vivo setting, under control, paced and/or diseased conditions.

Investigation of pacing site-related changes in global restitution dynamics by non-contact mapping.

AIMS: The determination of dynamic changes in ventricular repolarization may provide insight into arrhythmogenic mechanisms as a consequence of pacing site. This study investigated acute pacing site effects on global characteristics of electrical restitution using high resolution, non-contact mapping (NCM). METHODS AND RESULTS: Activation-recovery intervals (ARIs) were determined from reconstructed left ventricular electrograms by the NCM system and were analysed during pacing from the right atrial appendage (RAA, intrinsic), right ventricular apex (RVA), and right ventricular septum (RVS) with extrasystoles delivered at intermediate and short coupling intervals in anesthetized swine (n = 5). Electrical restitution curves were determined by the S1-S2 pacing protocol. Activation-recovery interval restitution slopes were determined by the overlapping linear segments regression method. Global distribution of repolarization was defined as the coefficient of variation of the ARIs during restitution. The maximum ARI slopes yielded by RVA pacing were significantly greater than RAA pacing (0.44 vs. 0.32; P < 0.05) and RVS pacing (0.44 vs. 0.37; P = 0.05). There was no significant difference between RAA and RVS pacing (0.32 vs. 0.37). The global distribution of ARIs during restitution from RVA pacing was significantly greater than RAA pacing (12.0 vs. 8.1%; P < 0.05). CONCLUSION: Right ventricular apex pacing is associated with impaired global repolarization patterns compared to RAA and RVS. These observations support the hypothesis that RVA pacing may be associated with increased risk of ventricular arrhythmias compared to RVS pacing.

Effect of pacing site on systolic mechanical restitution curves in the in vivo canine model.

INTRODUCTION: Pacing site is known to influence the contractile state of the ventricle. Non-physiologic pacing sites such as the right ventricular apex (RVA) or left ventricular freewall (LVFW) have been shown to decrease the contractile state of normal myocardium, due to abnormal electrical propagation. The impact of pacing at these sites may alter mechanical restitution (MR), a fundamental cardiac property involving the electro-mechanical regulation of contraction. This, in turn, may affect cardiac function. The present study was conducted to determine if pacing site alters the time constant of MR: tau. METHODS AND RESULTS: Anesthetized canines (n = 6) were acutely paced at four sites: right atrium (RA), RVA, right ventricular septum (RVS), and LVFW. MR data was captured by the S1-S2 pacing protocol and used to create MR curves, generating a restitution time constant, tau, at each site. No significant difference in tau was found between pacing sites. A linear regression analysis of MR curves revealed that there was no significant difference in slope between pacing sites. CONCLUSION: Although pacing site has been found to influence the contractile state of the ventricle, this is the first known study to demonstrate no change in tau in an in vivo preparation. This suggests that alteration of electro-mechanical coupling described by MR is not sufficiently robust to provide insight into pacing site and cardiac function in healthy hearts.

Novel means to monitor cardiac performance: the impact of the force-frequency and force-interval relationships on recirculation fraction and potentiation ratio.

Insights into intracellular calcium regulation and contractile state can be accomplished by changing pacing rate. Steady-state increases in heart rate (HR) (force-frequency relationship, FFR), and introduction of extrasystoles (ES) (force-interval relationship, FIR) have been used to investigate this relationship. This study focused on the recirculation fraction (RF) and potentiation ratio (PR), obtained from the recovery of the FFR and FIR. These parameters may provide insight on intracellular Ca(2+) regulation. Left ventricular (LV) pressures and HR were assessed in anesthetized canines (n = 7). Intrinsic data were collected prior to and following HR increases to 150, 180, and 200 bpm, as well as following delivery of an ES at 280 ms. The RF was calculated as the slope of dP/dt(max(n + 1)) vs. dP/dt(max(n)), where n = beat number. The PR was calculated by normalizing dP/dt(max) from the first beat following the ES (or the last paced beat) to the steady-state dP/dt(max). The RF due to an ES was not significantly different than that from a HR of 200 bpm. The PR from an ES was not significantly different than from a HR of 150 bpm. The impact of an ES delivered at an interval of 280 ms produces a PR similar to that from a HR of 150 bpm; yet, it recovers similarly to the termination of pacing at 200 bpm, eliciting a similar RF value. The method of measuring RF by an ES versus an increased HR may provide a safer and more feasible approach to collecting diagnostic information.

Effects of pacing rate on mechanical restitution within the in vivo canine heart: study of the force-frequency relationship.

INTRODUCTION: It is known that as stimulation frequency is increased in a healthy heart, a corresponding increase in LV contractile function (dP/dt(max)) is observed, i.e., force-frequency relationship. The impact of this relationship on systolic and diastolic mechanical restitution in an ejecting, in vivo preparation has yet to be explored. Understanding this relationship may lead to further insight on the cellular processes that govern the contraction and relaxation of the heart, in addition to providing a safer, more feasible clinical diagnostic tool. METHODS AND RESULTS: Anesthetized canines (n = 8) were paced from the RA at rates of 130, 150, and 180 bpm. At each rate, extrasystoles were delivered at varying intervals. The LV dP/dt(max) and dP/dt(min) associated with the extrasystolic beat were expressed as a percentage of steady-state levels and plotted as a function of the extrasystolic interval to obtain mechanical restitution curves. The systolic restitution time constant length decreased significantly with all increases in heart rate, P < 0.05. In the diastolic case, significant decreases in restitution time constants were seen when heart rate was increased from 130 bpm to 180 bpm, and from 150 bpm to 180 bpm, P < 0.05. CONCLUSION: This study was the first to quantify the finding that the time constant of restitution significantly and consistently decreased with a consistent increase in heart rate. The identification of such behavior may be employed to develop stimulation protocols and chronic diagnostic tools to more safely and sensitively identify and optimize the clinical status of patients receiving pacing therapy.