Sample Research Paper On Monitor Integrated With Medical Stent

Advances in technology should be used to improve patient care. In acute and chronic illness, biomedical monitoring of indicators such as pulmonary artery pressure in COPD, right ventricle pressure in right-sided heart failure, and pressure in an aneurysm sac can aid clinicians in detecting real-time changes that require modifications in the treatment plan where doing so ensures optimum patient outcomes. One recent technology is the monitor integrated with medical stent (MIMS) that permits the continuous measurement of pressure in the heart and blood vessels. Knowing what the technology is, its indications and contraindications, its application, and the expected outcomes will assist nurses in patient education and optimizing the health benefits of this technology.

MIMS Defined

The MIMS is the integration of micro-electro-mechanical-systems (MEMS) with stent technology. The MEMS permits the creation of machines, including biomedical devices, at micro or nano scales using silicon (James, Mannoor & Ivanov, 2008). Examples of interventions that employ MEMS are drug discovery, screening, and delivery devices as well as immunochemistry and hematology tests. The versatility of silicon permits the patterning of a device’s operations on very small wafers or chips (James, Mannoor & Ivanov, 2008). Meanwhile, stents have been widely used particularly in percutaneous transluminal coronary angioplasty (PTCA) used to remove occlusions in the coronary arteries. They are approved by the US Food and Drug Administration.
The MIMS consists of a device with a wireless, miniature, and implantable pressure monitor integrated with a medical stent, the latter serving as support for the implant and also as antenna for real-time wireless telemetry and power transfer (Chow et al., 2010). The structural support provided by the stent is necessary to anchor the device and prevent dislodgment. MIMS devices can be implanted in the chambers of the heart or blood vessels through a surgical procedure. The cardiac pressure device is where the pressure transducer using MEMS technology is installed. An application-specific integrated circuit (ASIC) permits data communication from the MEMS to telemetry devices used to receive, present, and store readings.
The function of the MEMS sensor is to convert measurements of cardiac pressure into values which it then feeds into the ASIC (Chow et al., 2010). One technique of measurement is that the membrane sensor that bends or deflects with increased pressure and then goes back to its normal shape with baseline or normal pressure (Murphy et al., 2013). The changes in the sensor’s shape are what are converted into numerical values corresponding to units of measure of pressure that are useful to clinicians.
The ASIC in the device processes the data and modulates it for wireless transmission. The ASIC also functions as voltage regulator, control logic that controls the device’s software operations, and RF power harvester (Chow et al., 2010). The MIMS does not derive power from batteries but from alternative sources, namely radio frequencies transmitted by an external device. Another alternative source is acoustic energy that is converted into electric energy by a piezoelectric element (Murphy et al., 2013).
The device electronics are housed in liquid crystal polymer (LCP) which has been proven to be biocompatible with body tissues (Chow et al., 2010). The LCP was compared with co-fired ceramic, silicon, parylene, and alumina to determine biological tissue reactions to them that represent a significant safety issue. The in vivo studies conducted over 4 weeks showed that LCP caused the least damage to tissue and did not induce inflammation (Chow et al., 2010). In addition, LCP generated the least layer of tissue encapsulation thickness compared to the other materials.
Besides the electrical components, packaging, and biocompatibility, there are other factors taken into account in the development of a MIMS pressure monitor as well. Studies also consider the interaction of the device’s materials with the gases, electrolytes, compounds, and temperature of the body part targeted for insertion (James, Mannoor & Ivanov, 2008; Murphy et al., 2013). Specifically, tissues can exert electromagnetic effects on the device affecting the quality of data transmission and power consumption (Chow et al., 2010). The MIMS device must also have compensation circuits as well to make up for possible deterioration of accuracy or drift from the baseline values arising from mechanical fatigue, material aging, and changes in the tissue environment of the implant site exerting greater pressure on the monitor (James, Mannoor & Ivanov, 2008).
The entire device consisting of the MEMS sensor and ASIC encased in LCP is smaller compared with traditional cardiac implants with one product, namely the CardioMEMS, having dimensions as small as 3 mm x 6 mm with a thickness of 300 µm (Chow et al., 2010). Size is important as it determines the surgical approach, i.e. transcutaneous or thoracic surgery. The anatomic limitations of the implant site also impact the size of the device (James, Mannoor & Ivanov, 2008). For instance, MIMS too large for the pulmonary artery aneurysm sac cannot be implanted.
When implanted with the stent, this MIMS cardiac pressure device expands the blood vessel slightly by about 4.8% which has not been shown to result in injury. The surgical technique and the telemetry feature of the CardioMEMS was also tested in vivo in pigs to ensure the cardiac pressure monitor target placement site and procedure is feasible and there is reliable transmission of data despite its location from inside the body (Chow et al., 2010). The device’s ability to harvest radio frequency (RF) waves for power, the adequacy of power for the operations of the device, the amount of heat it gives off to surrounding tissues, and the effects of RF radiation were investigated as well. The pressure monitor was found to be functional and safe.

Indications for the Procedure

Implantation with a MIMS is necessary in patient conditions where the monitoring of pressure needs to be precise, spontaneous, and continuous to generate trends that facilitate disease diagnosis, the monitoring of treatment progress, the assessment of prognosis, and the early detection of adverse events (Yu, Kim & Meng, 2014). Because it allows ambulatory measurements, it eliminates the stress patients experience when they consult physicians that can contribute to increased blood pressure referred to as the white coat hypertension phenomenon (James, Mannoor & Ivanov, 2008; Yu, Kim & Meng, 2014). It also improves patient safety and quality of life as long-term catheterization limits ambulation, causes discomfort, and increases the risk of serious infection.
The MIMS is also useful for continuous blood pressure monitoring in hypertension and left arterial pressure in congestive heart failure (Murphy et al., 2013). Continuous ambulatory measurements provide pressure readings at various times of the day, e.g. waking, standing, and sleeping. Moreover, this type of close pressure monitoring provides accurate measurements that aid classification in situations where the criterion consists of 10-mmHg ranges or the frequency of readings required is at hourly or shorter intervals (Murphy et al., 2013). MIMS devices can transmit measurements every 5 to 10 seconds with high reliability as readings were shown to deviate for a maximum of 5 mmHg only.
A MIMS device also has benefits for patients who have undergone heart transplant. The device overcomes the challenges of external cuff monitoring as palpable pulses are sometimes absent in this group of patients owing to occlusions in the blood vessels (Murphy et al., 2013). It is also a more reliable option than external Doppler measurements. A MIMS device has also been developed for continuous pressure measurement within aneurysm sacs post endovascular aneurysm repair to monitor the effectiveness of treatment and detect pressures that threaten the integrity of the blood vessel (Yu, Kim & Meng, 2014). Hence, emergent complications can be mitigated.
The MIMS can detect not only the condition of the heart or blood vessel but also the condition of the stent that was placed to treat coronary artery blood flow obstruction. A common issue with stents is re-occlusion and restenosis with one study showing 15% and 33% rates, respectively, 6 months after placement (Chow et al., 2010). Newer versions of stents are now drug-eluting, meaning they are coated with a drug that prevents blockage from excessive tissue growth within or at the ends of the stent following angioplasty.
Nevertheless, this technology cannot guarantee that it can prevent most if not all incidents of restenosis or re-occlusion given that studies have yet to investigate stent performance in humans following implantation (Chow et al., 2010). Prior in vivo and in vitro studies do show a low risk for this complication. Pressure sensors built into the stent can, however, relay data related to its integrity so that signs of re-occlusion can be detected early leading to timely interventions.

Possible Indications in the Future

MIMS devices are being considered for the measurement of intracranial pressure (ICP) in conditions such as brain tumor, aneurysm, traumatic brain injury, stroke, meningitis, and hydrocephalus (Yu, Kim & Meng, 2014). Conventional treatment is shunting or craniotomy to relieve the pressure from fluid build-up or inflammation albeit these procedures are not always successful underscoring the need to monitor and regulate cerebrospinal fluid pressure.
While devices such as the Codman Microsensor ICP for the long-term monitoring of ICP are available, they require opening of the blood-brain barrier for extended periods of time (Yu, Kim & Meng, 2014) that also increase the risk of hospital-acquired infection while requiring the confinement of the patient in the hospital throughout the duration of the procedure. Implantable MEMS-based devices can generate precise measurements of pressure in the brain as long as the design is able to withstand the immune response mounted by the body of foreign objects penetrating the blood-brain barrier (Yu, Kim & Meng, 2014).
Moreover, microdevices using MEMS can be developed for the monitoring of intraocular pressure (IOP) in patients with glaucoma (Yu, Kim & Meng, 2014). Possible implantation techniques are needles or contact lenses. The present gold standard for diagnosis is tonometry that is efficient and non-invasive but because it is done only during the consultation, it cannot capture the dynamics of IOP variations useful in tracking the progression of disease. It is a useful technology in individualizing the treatment plan to fit the needs of the patient.
Another potential indication of MIMS technology is in the monitoring of urinary bladder pressure. Urinary incontinence is currently diagnosed through cystometry that involves the insertion of a catheter-based pressure sensor through the urethra and into the bladder for the purpose of evaluating variations in pressure (Yu, Kim & Meng, 2014). This procedure can be painful, however. Similar to other single-point diagnostic measurements, cystometry also generates a snapshot only of pressure in the bladder.
For this reason, there are concerns with reliability because of the lack of consideration of fluctuations in bladder pressure that present a more accurate clinical picture. Besides the risk of infection, long-term catheterization can also induce stone formation. Implantable sensors can overcome many of these barriers while also featuring neuromodulation as a rehabilitation intervention (Yu, Kim & Meng, 2014). The sensor can be operated to produce electrical stimulation that either promotes or inhibits urinary bladder activity.

Contraindications of the Procedure

Contraindications pertain to the patient’s unfitness for the surgical procedure. Without pre-operative clearance that considers the patient’s cardiopulmonary status, the procedure may cause more harm than good. MIMS implantation is also generally for adult patients at present because clinical trials have not been conducted on children or older adults. For patients who need to undergo magnetic resonance imaging or radiography, implantation with the device is also contraindicated as the diagnostic tests can cause dialectic heating of the pressure monitor constituting harm to the patient (James, Mannoor & Ivanov, 2008).
Known allergy to the medications used in drug eluting stents is also a contraindication. The common drugs employed are anti-neoplastics such as everolimus, dexamethasone, and cyclosporine. Anti-proliferatives such as actinomycin and methotrexate; migration inhibitors such as batimistat and probucol; and enhanced healing factors such as estradiols and EPC antibodies may also be used (Chow et al., 2010). While great care is taken to ensure the biocompatibility of the materials used in the MIMS monitor, the possibility of contact allergy with the monitor or the stent is another contraindication.

Procedure Technique

The procedure may vary for each MIMS device system and the purpose of monitoring. The use of the CardioMEMS device for pulmonary artery pressure monitoring involves a similar surgical procedure as percutaneous angioplasty wherein stent placement may be done (Chow et al., 2010). The PTCA is an established and safe procedure. A balloon catheter with the stent and the calibrated and sterilized pressure monitor is inserted into the artery. Subsequently, the device is activated and tested. The balloon catheter is then withdrawn leaving the stent and monitor in the artery. The patient is under general anesthesia during the surgery.
In left atrial pressure monitoring, a sensor was implanted via transseptal puncture and its antenna implanted in subcutaneous tissue (Murphy et al., 2013). The system is interrogated via externally applied radio frequency excitation by the patient at recommended times. The data was sent to telehealth personnel who conducted offline analysis. In open heart surgery patients, a hole was created in the apex of the left ventricle following sternotomy and controlled via a purse string suture (Murphy et al., 2013). The calibrated MIMS sensor and transducer were then inserted into the opening via a plastic rod holding the device and with a handle to guide the insertion. The sensor device was activated by placing an antenna near the surface of the chest and the beating heart. The suture is closed and subsequently the sternal incision.

Results for the Procedure

In a trial of heart failure patients, arterial pressure monitoring using the CardioMEMS system showed enhanced treatment and reduced rehospitalization rates (Murphy et al., 2013). As discussed above, the performance of MIMS monitoring devices are shown to be superior to external pressure monitoring devices and invasive catheter-tip transducers, needles, or shunts used for intermittent or long-term monitoring. The added benefits were real-time, reliable, accurate, and continuous monitoring with high clinical usefulness because the device is also compatible with telemetry systems. It is associated with a reduced risk of infection and other complications, increased patient comfort, reduced effect of the white coat phenomenon, patient ambulation throughout monitoring, and improved quality of life.

Conclusion

The monitor integrated with medical stent (MIMS) monitor is a recent advancement in biomedical device technology. It is useful in the diagnosis, treatment, and monitoring of patients with chronic conditions such as heart failure, hypertension, and aneurysm. It integrates FDA-approved stents with micro-electro-mechanical-systems (MEMS) as well as optimizes alternative energy harvesting thus precluding the need for batteries. The MEMS permits the collection, analysis, and transmission of pressure data. Many considerations are taken into account in MIMS device development including its size, biocompatibility, safety, and short- and long-term functionality.
The MIMS device is implanted via surgery, and studies demonstrate its safety and effectiveness among patients in whom the procedure is not contraindicated. MIMS devices allow patients to optimize the benefits of telemetry monitoring in the planning and delivery of treatment. Continuous monitoring can lead to the early detection of emergent conditions or disease progression permitting timely interventions and better outcomes. While MIMS use is more established in cardiac and blood vessel pressure monitoring, there are many other possible uses of MIMS technology that are currently being developed.

References

Chow, E.Y., Chlebowski, A.L., Chakraborty, S., Chappell, W.J., & Irazoqui, P.P. (2010). Fully wireless implantable cardiovascular pressure monitor integrated with a medical stent. IEEE Transactions on Biomedical Engineering, 57(6), 1487-1496. doi: 10.1109/TBME.2010.2041058.
James, T., Mannoor, M.S., & Ivanov, D.V. (2008). BioMEMS – Advancing the frontiers of medicine. Sensors, 8, 6077-6107. doi: 10.3390/s8096077.
Murphy, O.H., Bahmanyar, M.R., Borghi, A., McLeod, C.N., Navaratnarajah, M., Yacoub, M.H., & Toumazou, C. (2013). Continuous in vivo blood pressure measurements using a fully implantable wireless SAW sensor. Biomedical Microdevices, 15, 737- 749. doi:10.1007/s10544-013-9759-7.
Yu, L., Kim, B.J., & Meng, E. (2014). Chronically implanted pressure sensors: Challenges and state of the field. Sensors, 14, 20620-20644. doi:10.3390/s141120620.