the right atrium to facilitate synchrony with the atrial contraction. thus, the timing between the atrial and ventricular contractions, as well as between the septal and lateral walls of the left ventricle can be adjusted to achieve optimal cardiac function. crt devices have been shown to reduce mortality and improve quality of life in patients with heart failure symptoms; a lv ejection fraction less than or equal to 35% and qrs duration on ekg of 120 ms or greater. biventricular pacing alone is referred to as crt-p (for pacing). for selected patients at risk of arrhythmias, crt can be combined with an implantable cardioverter-defibrillator (icd): such devices, known as crt-d (for defibrillation), also provide effective protection against life-threatening arrhythmias. conduction system pacing conventional placement of ventricular leads in or around the tip or apex of the right ventricle, or rv apical pacing, can have negative effects on heart function. it has been associated with increased risk of atrial fibrillation, heart failure, weakening of the heart muscle and potentially shorter life expectancy. his bundle pacing (hbp) leads to a more natural or perfectly natural ventricular activation and has generated strong research and clinical interest. by stimulating the his–purkinje fiber network directly with a special lead and placement technique, hbp causes a synchronized and therefore more effective ventricular activation and avoids long-term heart muscle disease. hbp in some cases can also correct bundle branch block patterns. advancements in function posteroanterior and lateral chest radiographs of a pacemaker with normally located leads in the right atrium (white arrow) and right ventricle (black arrowhead), respectively. a major step forward in pacemaker function has been to attempt to mimic nature by utilizing various inputs to produce a rate-responsive pacemaker using parameters such as the qt interval, po2 – pco2 (dissolved oxygen or carbon dioxide levels) in the arterial-venous system, physical activity as determined by an accelerometer, body temperature, atp levels, adrenaline, etc. instead of producing a static, predetermined heart rate, or intermittent control, such a pacemaker, a 'dynamic pacemaker', could compensate for both actual respiratory loading and potentially anticipated respiratory loading. the first dynamic pacemaker was invented by anthony rickards of the national heart hospital, london, uk, in 1982. dynamic pacemaking technology could also be applied to future artificial hearts. advances in transitional tissue welding would support this and other artificial organ/joint/tissue replacement efforts. stem cells may be of interest in transitional tissue welding. many advancements have been made to improve the control of the pacemaker once implanted. many of these have been made possible by the transition to microprocessor controlled pacemakers. pacemakers that control not only the ventricles but the atria as well have become common. pacemakers that control both the atria and ventricles are called dual-chamber pacemakers. although these dual-chamber models are usually more expensive, timing the contractions of the atria to precede that of the ventricles improves the pumping efficiency of the heart and can be useful in congestive heart failure. rate responsive pacing allows the device to sense the physical activity of the patient and respond appropriately by increasing or decreasing the base pacing rate via rate response algorithms. the david trials have shown that unnecessary pacing of the right ventricle can exacerbate heart failure and increases the incidence of atrial fibrillation. the newer dual-chamber devices can keep the amount of right ventricle pacing to a minimum and thus prevent worsening of the heart disease. considerations insertion a pacemaker may be implanted whilst a person is awake using local anesthetic to numb the skin with or without sedation, or asleep using a general anesthetic. an antibiotic is usually given to reduce the risk of infection. pacemakers are generally implanted in the front of the chest in the region of the left or right shoulder. the skin is prepared by clipping or shaving any hair over the implant site before cleaning the skin with a disinfectant such as chlorhexidine. an incision is made below the collar bone and a space or pocket is created under the skin to house the pacemaker generator. this pocket is usually created just above the pectoralis major muscle (prepectoral), but in some cases the device may be inserted beneath the muscle (submuscular). the lead or leads are fed into the heart through a large vein guided by x-ray imaging (fluoroscopy). the tips of the leads may be positioned within the right ventricle, the right atrium, or the coronary sinus, depending on the type of pacemaker required. surgery is typically completed within 30 to 90 minutes. following implantation, the surgical wound should be kept clean and dry until it has healed. some movements of the shoulder within a few weeks of insertion carry a risk of dislodging the pacemaker leads. the batteries within a pacemaker generator typically last 5 to 10 years. when the batteries are nearing the end of life, the generator is replaced in a procedure that is usually simpler than a new implant. replacement involves making an incision to remove the existing device, disconnecting the leads from the old device and reconnecting them to a new generator, reinserting the new device and closing the skin. periodic pacemaker checkups two types of remote monitoring devices used by pacemaker patients once the pacemaker is implanted, it is periodically checked to ensure the device is operational and performing appropriately; the device can be checked as often as is deemed necessary. routine pacemaker checks are typically done in-office every six months, though will vary depending upon patient/device status and remote monitoring availability. newer pacemaker models can also be interrogated remotely, with the patient transmitting their pacemaker data using a transmitter at home connected to a cellular telephone network. during in-office follow-up, diagnostic tests may include: sensing: the ability of the device to "see" intrinsic cardiac activity (atrial and ventricular depolarization). impedance: a test to measure lead integrity. large and/or sudden increases in impedance can indicate a lead fracture, while large and/or sudden decreases in impedance can be caused by insulation failure. threshold amplitude: the minimum voltage (generally in hundredths of volts) required in order to pace the atrium or ventricle connected to the lead. threshold duration: the time that the device requires at the preset amplitude to reliably pace the atrium or ventricle connected to the lead. percentage of pacing: the percentage of time that the pacemaker has been actively pacing since the previous device interrogation, which shows how dependent the patient is on the device. estimated battery life at current rate: as modern pacemakers are "on-demand" and only pace when necessary, battery lifespan is affected by how much the pacemaker is utilized. other factors affecting battery life include programmed output and algorithms (features) that use battery power. any events that were stored since the last follow-up, in particular arrhythmias such as atrial fibrillation. these are typically stored based on specific criteria set by the physician and specific to the patient. some devices have the availability to display intracardiac electrograms showing the onset of an event as well as the event itself, which helps to diagnose its cause or origin. magnetic fields, mris, and other lifestyle issues a patient's lifestyle is usually not modified to any great degree after the insertion of a pacemaker. there are a few activities that are unwise, such as full-contact sports and exposure of the pacemaker to intense magnetic fields. the pacemaker patient may find that some types of everyday actions need to be modified. for instance, the shoulder harness of a vehicle seatbelt may be uncomfortable if it falls across the pacemaker insertion site. women will not be able to wear bras for a while after the operation, and later might have to wear bras with wide shoulder straps. for some sports and physical activities, special pacemaker protection can be worn to prevent possible injuries, or damage to the pacemaker leads. pacemakers may be affected by magnetic or electromagnetic fields, and ionising and acoustic radiation. however, a 2013 study found that "the overall risk of clinically significant adverse events related to emi (electromagnetic interference) in recipients of cieds (cardiovascular implantable electronic devices) is very low. therefore, no special precautions are needed when household appliances are used. environmental and industrial sources of emi are relatively safe when the exposure time is limited and distance from the cieds is maximized. the risk of emi-induced events is highest within the hospital environment." the study lists and tabulates (in table 2) many sources of interference, and many different potential effects: damage to circuitry, asynchronous pacing, etc. some sources of hazard in older devices have been eliminated in newer ones. activities involving strong magnetic fields should be avoided. this includes activities such as arc welding with certain types of equipment, and maintaining heavy equipment that may generate strong magnetic fields. some medical procedures, particularly magnetic resonance imaging (mri), involve very strong magnetic fields or other conditions that may damage pacemakers. however, many modern pacemakers are specified to be mr conditional or mri conditional, safe to use during mri subject to certain conditions. the first to be so specified was the medtronic revo mri surescan, approved by the us fda in february 2011, which was the first to be specified as mr conditional. there are several conditions to use of mr conditional pacemakers, including certain patients' qualifications and scan settings. an mri conditional device has to have mri settings enabled before a scan, and disabled afterwards. as of 2014 the five most commonly used cardiac pacing device manufacturers (covering more than 99% of the us market) made fda-approved mr-conditional pacemakers. the use of mri may be ruled out by the patient having an older, non-mri conditional pacemaker, or by having old pacing wires inside the heart, no longer connected to a pacemaker. a 2008 us study found that the magnetic field created by some headphones used with portable music players or cellphones may cause interference if placed very close to some pacemakers. in addition, according to the american heart association, some home devices have the potential to occasionally inhibit a single beat. cellphones do not seem to damage pulse generators or affect how the pacemaker works. it is recommended that objects containing magnets, or generating a significant magnetic field, should not be in close proximity to a pacemaker. induction cooktops, in particular, can pose a risk. before medical procedures, the patient should inform all medical personnel that they have a pacemaker. having a pacemaker does not imply that a patient requires the use of antibiotics to be administered before procedures such as dental work. end-of-life care and pacemaker deactivation a panel of the heart rhythm society, a us specialist organization based in washington, dc, deemed that it was legal and ethical to honor requests by patients, or by those with legal authority to make decisions for patients, to deactivate implanted cardiac devices. lawyers say that the legal situation is similar to removing a feeding tube, though as of 2010 there was no legal precedent involving pacemakers in the united states. a patient in many jurisdictions (including the us) is deemed to have a right to refuse or discontinue treatment, including a pacemaker that keeps them alive. physicians have a right to refuse to turn it off, but are advised by the hrs panel that they should refer the patient to a physician who will. some patients consider that hopeless, debilitating conditions, such as severe strokes or late-stage dementia, can cause so much suffering that they would prefer not to prolong their lives with supportive measures. privacy and security security and privacy concerns have been raised with pacemakers that allow wireless communication. unauthorized third parties may be able to read patient records contained in the pacemaker, or reprogram the devices, as has been demonstrated by a team of researchers. the demonstration worked at short range; they did not attempt to develop a long range antenna. the proof of concept exploit helps demonstrate the need for better security and patient alerting measures in remotely accessible medical implants. in response to this threat, purdue university and princeton university researchers have developed a prototype firewall device, called medmon, which is designed to protect wireless medical devices such as pacemakers and insulin pumps from attackers. complications complications from having surgery to implant a pacemaker are uncommon (each 1-3% approximately), but could include: infection where the pacemaker is implanted or in the bloodstream;