Quantifying Cardiothoracic Variation with Posture and Respiration to Inform Cardiac Device Design.

PURPOSE: With extravascular implantable cardioverter defibrillator leads placed beneath the sternum, it is important to quantify heart motion relative to the rib cage with postural changes and respiration. METHODS: MRI scans from five males and five females were collected in upright and supine postures at end inspiration [n = 10 each]. Left and right decubitus [n = 8 each] and prone [n = 5] MRIs at end inspiration and supine MRIs at end expiration [n = 5] were collected on a subset. Four cardiothoracic measurements, six cardiac measurements, and six cardiac landmarks were collected to measure changes across different postures and stages of respiration. RESULTS: The relative location of the LV apex to the nearest intercostal space was significantly different between the supine and decubitus postures (average ± SD difference: - 15.7 ± 11.4 mm; p < 0.05). The heart centroid to xipho-sternal junction distance was 9.7 ± 7.9 mm greater in the supine posture when compared to the upright posture (p < 0.05). Cardiac landmark motion in the lateral direction was largest due to postural movement (range 23-50 mm) from the left decubitus to the right decubitus posture, and less influenced by respiration (5-17 mm). Caudal-cranial displacement was generally larger due to upright posture (13-23 mm caudal) and inspiration (7-20 mm cranial). CONCLUSIONS: This study demonstrates that the location of the heart with respect to the rib cage varies with posture and respiration. The gravitational effects of postural shifts on the heart position are roughly 2-3 times larger than the effects of normal respiration.

Cardiothoracic Morphology Measures in Heart Failure Patients to Inform Device Designs.

PURPOSE: Approximately 5.7 million people in the US are affected by congestive heart failure. This study aimed to quantitatively evaluate cardiothoracic morphology and variability within a cohort of heart failure patients for the purpose of optimally engineering cardiac devices for a variety of heart failure patients. METHODS: Co-registered cardiac-gated and non-gated chest computed tomography (CT) scans were analyzed from 20 heart failure patients (12 males; 8 females) who were primarily older adults (79.5 ± 8.8 years). Twelve cardiothoracic measurements were collected and compared to study sex and left ventricular (LV) ejection fraction (EF) type differences in cardiothoracic morphology. RESULTS: Four measures were significantly greater in males compared to females: LV long-axis length, LV end diastolic diameter (LVEDD) at 50% length of the LV long-axis, the minimal distance between the sternum and heart, and the angle between the LV long-axis and coronal plane. Four measures were significantly greater in patients with reduced EF compared to preserved LV: LV long-axis length, LVEDD at 50% length of the LV long-axis, left ventricular volume normalized by body surface area, and the angle between the mitral valve plane and LV long-axis. CONCLUSIONS: These cardiothoracic morphology measurements are important to consider in the design of cardiac devices for heart failure management (e.g. cardiac pacemakers, ventricular assist devices, and implantable defibrillators), since morphology differs by sex and ejection fraction.

Radiographic predictors of lead conductor fracture.

BACKGROUND: Lead fracture is a limiting factor in high voltage lead durability. Fractures noted with the Medtronic Fidelis leads provide an opportunity to examine factors captured on implant chest x-ray that correlate with risk for lead conductor fracture. We evaluated contributory factors in a large population of fractures. METHODS AND RESULTS: We conducted a retrospective case-control study at 8 Canadian centers that routinely capture anterior posterior and lateral chest x-rays within 2 weeks of implant. Cases were patients that experienced confirmed Medtronic Fidelis 6949 lead fracture based on standard definitions, matched one-to-one to controls for date of implant, sex, and age with normally functioning Fidelis leads from the same center. Select chart data and x-rays were collected for all patients. Radiographic measurements by ≥2 individuals per case/control were blinded to patient status. The data were analyzed using a time to failure multivariable Cox proportional hazards model with stratification for each matched pair. X-ray pairs from 111 fracture patients were compared with 111 controls (age 61.5±12.8 years, 75% male, 221 model 6949 leads). Six parameters included in the statistical analysis were significantly associated with risk of fracture, including slack/tortuosity measures, pulse generator and superior vena cava coil location, and angle of lead exit from the pocket. CONCLUSIONS: Pocket, intravascular and intracardiac lead characteristics on x-ray correlate with risk of lead conductor fracture. These observations may be useful to direct implant technique to optimize lead durability. Validation in larger populations and other lead models may inform the application of these results.

Physiologic responses during rest on a sleep system at varied degrees of firmness in a normal population.

This study explores the hypothesis that a high degree of sustained muscle activity associated with a sub-optimal spinal orientation may compromise an individual's ability to relax or initiate sleep. Data from 22 participants who were considered to be part of a normal, back-pain-free population were used in these studies. Participants laid down on a mattress in a foetal position (i.e. on their sides) at three varying bed pressures while EMG activities, heart rates, blood pressures, subjective comfort levels and spinal alignment data were recorded. Minor effects of mattress inflation pressures were associated with changes in EMG activity, heart rate, blood pressure and/or subjective comfort. In contrast, spinal alignment assessment revealed significant differences between the three different inflation pressures studied (827.4, 2413.2 and 3999.0 Pa). It was concluded that in a population of normal participants, although mattress inflation pressure induced significant changes in spinal alignment, these changes were of little physiological consequence. Nevertheless, this data provides baseline information needed to assess similar correlations in a symptomatic population (e.g. those with either acute or chronic neck or back pain).