# Virtual Prototyping: Computational Device Placements within Detailed Human Heart Models
## 3 Results and Discussion  
Here we describe a set of 3D models generated from four distinct human hearts utilizing the aforementioned methodology. Relevant information about each patient is summarized in Table 1. These models are displayed in atititudinally correct anatomical orientation in Figure 3. A MicraTM transcatheter pacing system (TPS) (Medtronic, Minneapolis, MN, USA) was computationally implanted into the right ventricular apex of each patient's heart model. Each heart model was then sliced along the coronal plane to offer a clear view of the anterior half of the heart and the resultant computational implant locations of these MicraTM devices. Further, implanting this device in a variety of models allows for the characterization of device placement within varied human anatomy (Figure 4). Since the MicraTM TPS has only one size, it was originally imperative to understand how the device fit within a range of human heart sizes. Computational vasculature anatomies obtained from a cadaver CT scan were digitally added to the heart (Figure 5). This can then be utilized to model the delivery pathways, e.g., from implant into the vasculature upward from femoral veins and/or arteries up to the modeled heart. Further, we have been able to computationally add the delivery catheter for the MicraTM TPS into the modeled vascular pathway. In other words, we computationally modeled the MicraTM TPS implant along the entire delivery vascular pathway of the device, from the access point into the femoral vein, up through the inferior vena cava, right atrium, and finally into the right ventricular apex. This model, and other similar models, allow device designers to understand the anatomical constraints that affect the delivery of the MicraTM TPS to an ideal target location--a crucial step due to this large bore delivery catheter (23 French). Such insights should further enable design requirements to be established for a delivery catheter system, even before expensive animal and cadaver experiments are initiated. Additionally, these computational models can be used to help determine the constraints or boundary conditions of given anatomical sites, e.g., those that a catheter will be able to navigate and deploy a MicraTM TPS within, for patients with similar anatomy. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \begin{tabular}{c} **Heart** \\ **Number** \\ \end{tabular} & **Age** & **Gender** & \begin{tabular}{c} **Body Weight** \\ **(kg)** \\ \end{tabular} & \begin{tabular}{c} **Body Height** \\ **(cm)** \\ \end{tabular} & \
\begin{tabular}{c} **Heart Weight** \\ **(g)** \\ \end{tabular} &
\begin{tabular}{c} **Cardiac Medical** \\ **History** \\ \end{tabular} \\ \hline
102 & 14 & F & 79.8 & 142 & 333.1 & None known \\
229 & 44 & F & 83.8 & 163 & 394 & Hypertension \\
248 & 64 & F & 105.6 & 178 & 441.4 & Hypertension \\
311 & 20 & F & 38.6 & 142 & 161 & None known \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Human heart and patient information. Figure 3: Computational 3D models of four MRI scanned human hearts from the Visible Heart® Laboratories (left to right: HH229, HH248, HH102, and HH311). These models were used for subsequent computational implants of cardiac devices. Shown in Figure 6, this model was digitally sliced along the coronal plane to reveal the posterior half of the heart and the computationally placed MicraTM TPS and delivery catheter. This model was then 3D printed and hand painted to highlight the different anatomical features as well the implant system and MicraTM TPS (the implanted device). This printed and painted model offers a realistic representation of a device implanted in a human patient, and its interaction with the surrounding anatomical features. Figure 4: Anterior views of sliced human hearts depicting MicraTM transcatheter pacing system computationally implanted into each right ventricle (left to right: HH229, HH248, HH102, and HH311). Each heart model is depicted with no transparency (top) and high transparency (bottom).