In Vivo Mechanical Loading Conditions of Pectorally Implanted Cardiac Pacemakers - Cardiovascular and Cardiac Therapeutic Devices - page 233

A constraint of the current study was the small experimental sample size,
mainly demonstrating the feasibility of the developed approach for the assessment
of in vivo mechanical loading conditions of implantable pacemakers. Further
research with larger sample sizes will provide data to verify intra-species corre-
lation and inter-species transfer function established in this study. There may also
be potential to refine these relationships by quantifying and extending morpho-
metric parameters and implant dimensions. Additional morphometric parameters
can include the thickness of Pectoralis major and Pectoralis minor at the implant
site, the change in thickness of these muscles during contraction, Pectoralis major
attachment angles, optimal fibre length, pennation angle as well as parameters
relating to the compliance of skeletal structures surrounding the implant. While the
strength of the intra-species correlation was not affected by the estimation of the
muscle parameters L f /L f,opt and h [ 10 ], the quantification of these parameters can
contribute to the validation of the initial values of coefficients a i of the transfer
function. The consideration of repeated load cases at sub-maximum level and
potential fatigue, both of which exceeded the scope of the current study, may
constitute a further beneficial extension of the presented transfer function.
The inter-species transfer function serves as basis for the prediction of patient-
specific mechanical loadings, in particular maximum levels, on a sub-muscular
pectoral device implants, such as cardiac pacemakers. Such data will be beneficial
for the development of smaller implantable devices while ensuring mechanical
integrity and reliability of current designs. In verification studies, the transfer
function may be refined to provide additional information required to aid in the
design of such implantable devices.
Acknowledgments The authors thank Professor Stephen Beningfield, Petronella Samuels,
Sharon Heyne and Nazlea Behardien-Peters of the Department of Radiology, University of Cape
Town, for MRI and CT imaging.
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