Revered in Canada as the father of biomedical engineering, John Hopps made many contributions to the field of medicine. He is perhaps best known for the invention that keeps hundreds of thousands of hearts beating around the world: the cardiac pacemaker.
 
John “Jack” Hopps (Figure 1 [12]) was born in 1919 in Winnipeg, where he spent most of his early life. After graduating with a degree in electrical engineering from the University of Manitoba in 1941, he was recruited to the Division of Radio and Electrical Engineering by the National Research Council, based in Ottawa. He would remain there for the duration of his career, working on a variety of innovations in the new field of biomedical engineering. As the head of the medical engineering section, he led a team in the development of devices designed to improve the quality of life for those affected by blindness and muscular disabilities, and to advance the diagnostic uses of ultrasound. He also furthered cardiovascular research by inventing machines for respiration, cathode-ray displays for cardiac operating rooms, cardioscopes for postoperative monitoring, heart rate monitors for sports medicine, and, of course, the cardiac pacemaker.[1]

Invention of the pacemaker
During the 1940s, Hopps studied the use of radiofrequency reheating for pasteurizing beer in Ottawa. Hopps was so dedicated to this project that he looked upon his assignment to the Banting Institute in Toronto in 1949 “as an annoying interruption to this vital task.”[1] Little did he know that this assignment would have groundbreaking implications for the lives of so many cardiac patients around the world. 

At the Banting Institute, cardiac surgeon Wilfred Bigelow and his research fellow John Callaghan were using hypothermia to slow the heart down enough to enable open-heart surgery. When cooled below a certain temperature, the perfectly functional heart became immobile due to lack of cardiac depolarization. Bigelow’s team was stymied by the problem of how to induce cardiac contraction during hypothermia.[2] Hopps serendipitously observed that an electrical impulse would cause the heart to contract and that repetitive stimuli, that is, pacing, would allow this to occur over a prolonged time.[3] Hopps and others went on to develop a series of experiments to refine this process for pacemaker-induced cardiac stimulation.[4] With the parameters derived from these initial experiments, Hopps returned to the National Research Council in 1950 to design and build the first pacemaker prototype (Figure 2 [13]).[1] Resembling a small table radio, the device measured 30 cm in length, used vacuum tubes to generate pulses, and was powered by a 60-Hz household current.[1,3,4] Hopps then developed transvenous catheter electrodes, which could be passed through the external jugular vein and eliminate the need to open the chest for heart stimulation. The same catheter electrodes that were part of the original pacemaker continue to be used in today’s modern implantable versions.[5] 

Implantation of first pacemaker
Hopps’ early work eventually led to the development of the implantable pacemaker. With the advent of transistor circuitry, the original vacuum tubes were replaced by transistors, which allowed the pacemaker battery to become small enough for implanting in the body. The first implantable pacemaker was developed by engineer Rune Elmqvist.[6,7] It consisted of two transistors and was assembled in a mold of an empty British Kiwi shoe polish tin (Figure 3 [14]).[2] On 8 October 1958, it was implanted by surgeon Ake Senning into the chest of Arne Larsson, a 43-year-old man who suffered from complete heart block and Stokes-Adams attacks.[2] Larsson’s first pacemaker failed within 3 hours of implantation and the second was no longer functional after 1 week. Larsson would eventually undergo a total of 26 pacemaker replacement procedures, until his death in 2001 from unrelated causes.[7,8] 

Leadership and legacy
In addition to his work in the laboratory, Hopps worked to advance the field of biomedical engineering. In 1965 he founded the Canadian Medical and Biological Engineering Society.[9] He took on a variety of leadership roles in the International Federation for Medical and Biological Engineering and in the International Union for Physical and Engineering Science in Medicine. Hopps was the recipient of countless awards and accolades throughout his illustrious career. He became an Officer of the Order of Canada in 1986, received an honorary doctorate from the University of Manitoba in 1976, and was inducted into the Canadian Science and Engineering Hall of Fame in 2006.[10]

Hopps took his life’s work quite literally to heart. Thirty years after inventing the pacemaker he found himself in need of the very device that he had spent his life perfecting. In 1984 he had his first pacemaker implanted at the National Defence Medical Centre in Ottawa. Thirteen years later when the battery started to wane, he underwent a second operation to have the pacemaker replaced. Although Hopps retired in 1979, he remained active in the field of biomedical engineering until his death in 1998 at the age of 79.[10]

Questions about pacemaker use 
While pacemaker use has become common, many questions must be addressed when considering implantation in a particular patient. These include questions about pacemaker function, indications for insertion, possible complications, and whether pacing devices are affected by electrocautery, electromagnetic fields, and MRI scanning. 

How is pacemaker function described?
The North American Society of Pacing and Electrophysiology (NASPE) and the British Pacing and Electrophysiology Group (BPEG) have created a five-position universal pacemaker code to describe various pacing modes. Table 1 [15] outlines this code and shows how letters are assigned to describe the heart chambers paced and sensed by the device, the response to sensing, and whether rate modulation or multisite pacing apply.[11]

What are the indications for permanent pacemaker implantation? 
Recommendations for permanent pacemaker implantation are evidence-based for the most part, and the most recent practice guideline can be found on the American College of Cardiology’s website.[12] Table 2 [16] summarizes the class I recommendations from the American College of Cardiology/American Heart Association/Heart Rhythm Society 2008 document.[12] The decision to implant a pacemaker, however, must not be based solely on published guidelines. Along with indications, physicians must consider comorbidities, surgical risks, quality of life, and patient preference.

What is a cardiac resynchronization therapy pacemaker? 
A device for cardiac resynchronization therapy (CRT) differs from a conventional pacemaker in having an additional third lead positioned in a vein or on the outer surface of the left ventricle. This allows the CRT pacemaker (CRT-P) to simultaneously stimulate both ventricles, which is why we often refer to the result as biventricular pacing. This action decreases electrical delay and results in a more coordinated contraction that improves left ventricular systolic performance, and ultimately leads to symptomatic improvement in patients with heart failure.[13] Recommendations for CRT-P implantation are based on the efficacy data available from clinical trials.[14-17] The current Canadian Cardiology Society (CCS) guidelines recommend CRT-P for patients in sinus rhythm with NYHA class III or ambulatory class IV heart failure symptoms, a left ventricular ejection fraction (LVEF) less than 35%, and QRS durations greater than 130 ms due to left bundle branch block (LBBB). If patients meet the above criteria but have NYHA II symptoms, a CRT-P is recommended only if they have an LVEF less than 30%. This patient population may also benefit from an implantable cardioverter defibrillator (ICD) and should be assessed for candidacy. A CRT-D refers to the device that serves as both an ICD and CRT-P. Patients with atrial fibrillation, right bundle branch block (RBBB), or nonspecific intraventricular conduction delay are less likely to derive as much benefit from CRT-P and should be evaluated on an individual basis.[17] The guidelines include a weak recommendation that patients with non-left bundle branch block QRS morphology be considered for CRT if they have NYHA II, III, or ambulatory IV heart failure, sinus rhythm, and an LVEF less than 35%. The 2013 CCS cardiac resynchronization therapy implementation guidelines also suggest that CRT be considered for patients with new-onset high-degree atrioventricular (AV) block requiring chronic right ventricular (RV) pacing, signs or symptoms of heart failure, and an LVEF less than 45%, as research has demonstrated chronic RV pacing is associated with worse outcomes in patients with heart failure and in patients with a reduced ejection fraction.[18] An algorithm for device selection in patients with a standard indication for pacing can be found in Figure 4 [17].[17] 

What are the risks and complications of permanent pacemaker implantation?
Pacemaker implantation requires surgery, and like any surgical procedure is associated with risks and complications, including lead dysfunction, pneumothorax, infection, and bleeding.  provides incidence rates for some adverse events from a number of clinical trials.[19-22] While data from these trials give us approximate rates for acute complications, the rates may not apply to the general population as patients included in the trials tended to be healthier.

What are some postoperative considerations after pacemaker insertion?
After a device is inserted, careful attention is needed to prevent pacemaker pocket or lead infection, as this will require removal of the device and adjuvant antibiotic therapy. Currently, there are no guidelines detailing proper postoperative care; however, good judgment and patient participation in the postoperative period are certainly required.

Recommendations for postoperative care differ depending on the institution. The following are used at Vancouver General Hospital:
•    Patients are asked to keep the incision dry for 7 days. They may sponge bathe but not shower.
•    Dressings should be changed daily. The use of antibiotic cream is optional.
•    Steri-Strips, sutures, or staples should be left in place for 1 to 2 weeks.
•    Patients are asked to watch for an increase in swelling, drainage, or bleeding at the insertion site.
•    Patients with a fever should have blood drawn for culturing and the insertion site should be inspected.
•    The pacemaker pocket should never be aspirated as this may introduce infection into a previously sterile pocket.
•    Patients are asked to refrain from lifting the affected arm over the head for 6 weeks.

How should infections involving the pacemaker insertion site be managed?
Perioperative contamination of the pacemaker pocket with skin flora appears to be the most common cause of infection.[22] Treatment involves antibiotic therapy as well as removal of the device and leads, followed by reimplantation of a new system. The duration and type of antibiotic treatment depend on the extent of infection and the suspected organism. For infections limited to the pocket and underlying tissue, as indicated by no evidence of endocarditis or bacteremia, vancomycin is recommended as the first-line agent given the prevalence of methicillin resistance. The recommended duration of antibiotic therapy after device removal is 7 to 10 days for patients without inflammatory changes and 10 to 14 days for patients with these changes. Patients with evidence of deeper infection, as indicated by endocarditis and pocket infection with bacteremia, should receive at least 2 weeks of parenteral antibiotic therapy after extraction of the device. If blood cultures are persistently positive after 24 hours of antibiotic therapy, treatment should be continued for at least 4 weeks.[23] Routine antibiotic prophylaxis is not recommended for patients with pacemakers unless they have another condition requiring this.[24]

What does a magnet do to the permanent pacemaker?
All pacemakers respond to a magnet by switching to an asynchronous pacing mode at a programmed atrioventicular delay with a fixed magnet rate. The specific rate depends on the device model, manufacturer, and battery life. DDD pacemakers switch to DOO, VVI pacemakers switch to VOO, and AAI pacemakers switch to AOO. Rate responsiveness is not active in the magnet mode. A magnet placed over an implantable cardioverter defibrillator suspends antitachycardia therapy without any effect on the pacing mode. This applies to ICDs with biventricular pacing functions as well.

There are two clinical scenarios when reprogramming is preferred over the use of a magnet: when patients undergo a surgical procedure that requires a nonsupine position, and when the magnet response mode in a device has been manually deactivated.

Patients who require pacing should have their devices reprogrammed to an asynchronous mode to prevent pacing inhibition from electrocautery used during surgical procedures. Several older Boston Scientific pacemaker models may not revert to original programming after magnet removal,[25] but programming in the majority of current devices will revert to previous parameters after the magnet is removed. 

How does electrocautery affect implanted pacemakers and defibrillators?
The high-frequency signals generated by electrocautery may interfere with implanted pacemakers and defibrillators. These signals can cause the pacemaker to pace incorrectly, which in rare circumstances may induce ventricular arrhythmias, inhibit pacing therapy, trigger the end-of-life indicator, cause electrical reset, or switch the device to an asynchronous mode. In patients with defibrillators, inappropriate antitachycardia therapy may occur. The risk for device malfunction is significantly reduced during electrocautery by using short, intermittent, and irregularly spaced bursts at the lowest feasible energy levels. Bipolar electrocautery systems also minimize the amount of current to which the pacing system is exposed. If electrocautery is performed closer than 15 cm to the generator, permanent damage may occur to the internal circuitry and the device will need to be interrogated. 

Preparing the pulse generator for electrocautery with a magnet is important. Alternatives to magnet use are reprogramming the device to an asynchronous mode or turning on the electrocautery protection mode. In general, all devices should be interrogated in patients who have received electrocautery. This should occur before discharge or transfer from the cardiac telemetry environment in cases where monopolar electrocautery is used, and within 1 month on an outpatient basis otherwise. It is important to keep patients in a monitored setting with appropriate defibrillation equipment available until device features are reactivated.

Do electromagnetic fields affect the pacemaker?
The risk of device malfunction related to an electromagnetic field is quite low, especially since modern devices use bipolar pacing and sensing configurations.[26,27] Pacemaker manufacturers do not recommend any special precautions when using common household appliances.[28] Portable media players are generally safe; however, research suggests that devices kept within 5 cm (2 inches) of the pacemaker generator frequently cause programmer interference.[29] Cellular phones are unlikely to cause clinically significant interference with pacemakers,[30,31] but they should not be kept in the breast pocket over the device. A study of early cellular phone technology demonstrated interference in 1.5% of pacemakers, although these results were not reproducible in recent studies using newer cellular phone technology.[32,33] Electromagnetic security systems such as antishoplifting gates and metal detectors may cause device abnormalities with continued exposure to the electromagnetic field.[34] 

Patients who are working with welding machines, electric motors, and degaussing coils may have their pacemakers oversense an external electrical field. This may result in lack of pacing or inadvertent ICD therapy. Assessment of potential electromagnetic sources in the workplace should be performed after pacemaker implantation to minimize the risk of device interference. Most manufacturers provide toll-free telephone numbers for obtaining advice about specific appliances and device models.

What does a beeping device mean?
Many devices are programmed to emit an audible tone if a periodic self-check uncovers an internal error. Possible causes include lead dysfunction, software failure, and battery depletion. Patients should contact their pacemaker clinic or cardiologist immediately or go to the emergency department if they notice this beeping.

When can a patient drive or fly after pacemaker insertion?
According to the driver medical fitness information for medical professionals from RoadSafetyBC[35] and the 2010 BC Guide in Determining Fitness to Drive,[36] patients with recent permanent pacemaker insertion can drive, provided it has been at least 1 week since insertion. Commercial drivers must wait 1 month, and they must not have experienced any episodes of impaired consciousness since the implantation. In addition, patients must demonstrate normal sensing and capture on a postimplant ECG. Patients can continue to drive as long as they have their device checked regularly at a pacemaker clinic and such checks confirm proper pacemaker function. 

The recommendations for flying after pacemaker insertion are that patients must wait 1 day without pneumothorax and ensure that the device functions normally and is programmed appropriately.[37]

Information for licensed pilots wishing to return to flying after pacemaker implantation can be found at Transport Canada’s website: www.tc.gc.ca/eng/civilaviation/publications/tp13312-2-cardiovascular-menu-2356.htm [18].[38] Pilots must wait at least 3 months after successful implantation before a return to flying can be considered. Each case is then approached on an individual basis. 

Can patients with a permanent pacemaker undergo magnetic resonance imaging?
MRI scanning can affect permanent pacemakers. Possible movement of the device, programming changes, inhibition of pacing, asynchronous pacing, and heating and or cardiac stimulation from induced currents in lead wires are all possible complications. A few studies have reported on the relative safety of scanning patients with devices,[39] yet guidelines still consider the presence of a pacemaker to be a contraindication for MRI evaluation.[40] However, if the benefits outweigh the risks, MRI scanning may be possible in a centre with expertise in MRI and cardiac electrophysiology. Multiple pacemaker systems have now been tested in specific MRI environments and deemed MRI conditional. These devices are currently being implanted in British Columbia. If an MRI evaluation is required, it is best to have a discussion with the radiologist to ascertain whether the benefits of the scan will outweigh the risks. The device should also be interrogated by a cardiologist before and after the MRI evaluation.

Summary
Many patients have benefited from the contribution John Hopps made to the development of cardiac pacemakers. Pacemakers and implantable cardiac defibrillators are now used to address a range of heart rhythm problems. Permanent pacemaker insertion may lead to complications, but proper postoperative care can prevent infection, and routine antibiotic prophylaxis is not required. Patients can usually drive a car 1 week after implantation and take a flight 1 day after. Patients should be made aware of the possible effects of electrocautery and electromagnetic fields on pacemaker function, and informed that MRI scanning may be possible if the benefits outweigh the risks. 

Competing interests
Dr Bennett has received fees for speaking and consultancy services provided to device manufacturers Medtronic, St. Jude Medical, and Boston Scientific. The other authors of this article have not received fees from these manufacturers and have no additional competing interests to declare.

This article has been peer reviewed.

Dr Bains is a cardiologist at the Abbotsford Regional Hospital. Dr Chatur is a PGY-3 resident in internal medicine at the University of British Columbia. Dr Ignaszewski is a PGY-3 resident in internal medicine at SUNY Upstate Medical University in Syracuse, New York. Ms Ladhar is a BSc candidate at the University of British Columbia. Dr Bennett is a cardiac electrophysiologist and lead of the arrhythmia program at Vancouver General Hospital.