28 Ağustos 2009 Cuma

Heart Block Disease

Heart block is when electrical signals from the atrium do not reach the ventricle.
The sinus node is the heart's natural pacemaker. A heartbeat begins when the sinus node starts electrical signals in the upper right chamber of the heart (right atrium). Electrical signals from the sinus node travel through a group of cells called the atrioventricular node (AV node) before moving to the ventricle.

Heartblock is when the AV node does not let all electrical signals reach the ventricles. This causes a slow or unsteady heartbeat and does not allow enough blood to circulate through the body. Heart block can cause an abnormally low heart rate (bradycardia) with symptoms such as dizziness, extreme fatigue, shortness of breath, or fainting spells. A pacemaker compensates for the impaired AV node by restoring the heart rate to a level that meets the demands of everyday living.

27 Ağustos 2009 Perşembe

Single Chamber Pacemakers - pacemaker types

A single-chamber pacemaker uses one lead, placed either in the right atrium or the right ventricle of your heart. (Most single-chamber pacemakers have a lead attached to the right ventricle.)

When Attached in the Atrium- Leads attached in the right atrium are designed to correct abnormalities in the heart's sinoatrial (SA) node (a condition known as "sick sinus syndrome" ). This kind of atrial pacing corrects the slow or irregular heart rates that are common with this condition. A pacemaker lead attached in the atrium will ensure that your heart's atrium will contract at an exact millisecond so blood will be pumped into the ventricle.

When Attached in the Ventricle - Leads attached in the right ventricle correct a slow or unsteady heartbeat that results from a condition called "heart block," in which the heart's necessary electrical currents are blocked from reaching the atrioventricular (AV) node. A pacemaker lead attached in the ventricle will ensure that your heart's ventricles contract rhythmically and fully, to increase the amount of blood that your heart can pump into your lungs and body.

24 Ağustos 2009 Pazartesi

Can Patients with Implantable Cardioverter-Defibrillators Use Cellular Phones?

Although several studies have examined the safety of cellular phone use in patients with pacemakers, the impact of digital cellular telephones on implantable cardioverter-defibrillators (ICDs) has been less studied. Electromagnetic fields may interfere with an ICD, causing inappropriate sensing or temporary suspension of arrhythmia detection. This investigation evaluated the effect of digital cellular telephone use on ICD function in patients and in vitro.

A group of 41 patients with ICDs (manufactured by Medtronic, Inc.) performed a series of tests using a digital cellular telephone (AT&T model 6650 with NADC/TDMA-50 technology). Patients were connected to an electrocardiogram monitor and continuously observed while they received and transmitted calls at both the right and left ears; moving the entire route of the lead from electrode in the heart to its connector end; and on top of the implantation site (to simulate carrying the telephone in the upper shirt pocket or at the belt). The effect of increasing the electromagnetic field intensity was analyzed in vitro by suspending an ICD in a saline bath and observing the field required for the ICD to sense electromagnetic interference.

For the tests conducted on patients, no ventricular tachycardia or fibrillation was activated by the electromagnetic interference in any patient. There was no evidence of pacing inhibition or changes to the programmed pacing intervals during any test. The in vitro tests indicated no interaction between the digital phone and ICD function during normal operation. However, the static magnetic field generated by the cellular phone placed over the ICD at a distance of 0.5 cm or less can activate the internal reed switch, which would result in temporary suspension of ventricular tachycardia and fibrillation detection.

The investigators concluded that the TDMA-50 cellular telephones did not interfere with the types of ICDs examined in this study. However, based on the results of the in vitro tests, they recommended the following:

1. maintaining a minimal separation of 15 cm (6 inches) between a 0.6W cellular phone and antenna to the implanted device, and 30 cm (12 inches) for telephones with 3W or more of power;
2. holding the telephone on the ear opposite the side of the implanted device;
3. not holding the telephone near the chest while dialing or conversing, nor carrying the telephone in a breast pocket or on a belt within 15 cm of the implanted device (whether or not it is in use); and
4. storing the telephone in a location opposite the side of the implanted device.

Digital Cellular Telephone Interaction With Implantable Cardioverter-Defibrillators
Authors: Fetter, JG, et al
Source: Journal of the American College of Cardiology

20 Ağustos 2009 Perşembe

Future expectations in pacing systems

Something currently being done in a clinical trial is placement of a transvenous lead into a coronary sinus branch vein in order to pace the left ventricle. "A completely transvenous lead system of course simplifies the procedure."

She also noted that current studies – such as MADIT II (Multicenter Automatic Defibrillator Implantation Trial II) and SCD HFT (Sudden Cardiac Death in Heart Failure Trial) – are examining whether CHF patients should prophylactically receive defibrillators. "Because these patients remain at risk for sudden cardiac death [SCD], this therapy is being looked at in CHF patients who have not even had sustained ventricular tachycardia [VT] or ventricular fibrillation [VF].

"Consequently, another development I foresee is a combined biventricular pacemaker and defibrillator. This makes sense in theory because many heart failure patients who have survived VT or VF receive defibrillator therapy, and eventually they succumb to pump failure. It’s a complex issue, because sudden deaths often occur in the setting of worsening heart failure. Implanting today’s defibrillators can reduce SCD mortality, but it can’t lower the mortality risk from progressive CHF. A defibrillator that offers biventricular pacing, however, might potentially treat both problems by reducing SCD and stabilizing pump function. To test this hypothesis, the VENTAK¨ CHF study is now under way."

Because of the sheer number of patients with a history of CHF and arrhythmias, Dr. Saxon said she believes this area could develop its own medical specialty. "This is a burgeoning area of interest now. And with the expanding knowledge base we expect in the next several years, I wouldn’t be surprised if a new cardiac specialty was eventually established with its own academic track."

According to Dr. Saxon, it will be some time before researchers know whether new pacing modalities, such as biventricular pacing, can affect mortality. "In both the VIGOR CHF and the VENTAK CHF studies, researchers are measuring the effects on only cardiac performance and quality of life. If we find positive results, it would of course be ideal if investigators went on to show prolonged survival, too.

"The use of pacing to treat CHF is a new frontier for us as investigators. There is room for much good work to be done in this area, and we are excited at the prospect of helping these patients whose choices are currently so limited." (guidant.com)

19 Ağustos 2009 Çarşamba

pacing research

Other pacing research : Some researchers are exploring different options for biventricular pacing. For example, one of the inclusion criteria for the VIGOR CHF trial is that patients have BBB. Dr. Saxon mentioned, however, that there is no firm consensus as to whether BBB is a necessary criterion for biventricular pacing. She and her colleagues are conducting other acute studies to determine if patients with no overt BBB can improve with biventricular pacing.

"There are also many questions about how biventricular pacing should be applied," she pointed out. "For instance, no one knows the precise location of the ideal LV pacing site. It could be the LV apex, the far lateral wall or closer to the base of the heart. Researchers are also wondering which is more important in reducing CHF symptoms: finding the best LV pacing site or pacing both ventricles. And other investigators are focusing solely on the timing of ventricular activation – whether it’s better to pace both ventricles simultaneously or to delay pacing one ventricle by several milliseconds."

Dr. Saxon explained that while biventricular pacing is the area of most intense interest right now, researchers are continuing to explore other types of pacing to treat CHF. "Whereas a standard dual-chamber pacemaker paces the right atrium, some experimental systems are using left atrial dual-chamber pacing via the coronary sinus. No data have yet been published on this approach, though." (guidant.com)

18 Ağustos 2009 Salı

biventricular pacing studies

Current biventricular pacing studies : Dr. Saxon pointed out that biventricular pacing was first considered as a potential therapy because CHF patients have marked dyssynchrony in ventricular contraction, due to tissue damage from a previous infarct or simply from muscle deterioration. This damage or scarring promotes delays in left ventricular (LV) activation and reduces contractility. "The theory behind biventricular pacing is to resynchronize ventricular function by activating both ventricles at the same time. This, in turn, might improve cardiac contraction and eliminate patient symptoms."

She added that researchers have evaluated this type of pacing primarily in small groups of end-stage patients who were not transplant candidates. Bakker et al. conducted a study of 12 such patients and reported improvements in both hemodynamics and functional capacity. The investigators found that mean LV ejection fraction (LVEF) increased by 8 ± 2%, mean New York Heart Association Class improved from 4 to 2.5 (p = 0.03) and mean peak VO2 increased by 4.4 ml/min/kg (95% CI: 2.2-6.6).5, 6 Dr. Saxon has also published data on several patients whose cardiac function improved with biventricular pacing.

"Consequently the VIGOR® CHF study was developed, using a pacemaker still under investigation that paces both ventricles simultaneously," she explained. The VIGOR CHF trial is expected to enroll over 100 patients at 25 centers worldwide. All patients must have advanced CHF and, despite maximal medical therapy, must remain symptomatic.

"Patients must also have left or right bundle branch block [BBB], since in concept it seems that patients with this type of conduction system delay might benefit the most from restored synchrony."

Dr. Saxon went on to explain that patients in the VIGOR CHF study receive a dual-chamber pacemaker by standard implant techniques, with a right atrial lead to promote AV synchrony and a ventricular lead implanted in the right ventricle. Patients will be paced in the VDD mode.

"When designing this study, the investigators looked at ways to protect these very sick patients, who are susceptible to adverse effects from invasive studies. We are using co-investigators – an electrophysiologist, a heart failure specialist, an experienced cardiovascular surgeon and an echocardiographer. It takes a lot of effort to coordinate these teams at each center, but this unique approach seemed necessary to help ensure patient safety."

The endpoints of the VIGOR CHF study will assess changes in LVEF, peak exercise ability and quality of life issues, as well as medical cost. "We hope not only to resynchronize ventricular contractions, but also to reduce paradoxical septal wall motion," she said. The study is expected to take approximately three years. (guidant.com)

research with pacing therapy

Prior research with pacing therapy : Around 1990 there were early published reports about the benefits of dual-chamber pacing with a shortened atrioventricular (AV) delay.2-4 "The studies found that CHF patients improved significantly with a 'superphysiologic’ AV delay of about 100 ms," said Dr. Saxon. "This sparked a lot of enthusiasm. However, subsequent studies have not been able to replicate the early results, except in one subgroup – patients who have a marked delay in their AV nodal conduction, and thus have long baseline PR intervals. In these patients, the ventricular contraction is delayed, leading to inadequate filling and mitral valve regurgitation. A pacemaker with a shorter AV delay can help solve this problem. A consensus is now emerging that while reducing the AV delay can help patients in this one small niche group, it’s not a therapy that can be applied broadly. However, these studies were among the first to show that pacing could be used to treat a segment of CHF patients who had no traditional bradycardia indications."

She added that decreasing the AV delay has the potential to help more CHF patients, but the AV delay must be tailored to the patient. "If a physician is willing to spend the time and order sophisticated tests to help pinpoint a patient’s optimal AV delay, there will usually be some benefit – sometimes incremental, sometimes dramatic. But this strategy is certainly not widely applicable to CHF patients." (guidant.com)

Pacing to Treat Congestive Heart Failure

The use of pacing therapy to treat congestive heart failure (CHF) is under investigation. Because CHF is not an approved indication for pacing, Guidant does not recommend the use of pacemakers to treat CHF patients.

Treatment for congestive heart failure (CHF) currently is a subject of intense interest because CHF is such a widespread problem, according to Leslie A. Saxon, M.D. CHF, affecting more than 3 million people in the United States, "is the single most frequent cause of hospitalization in patients over age 65," she said. "Each year 400,000 new cases are diagnosed and 40,000 people die from this disease. These numbers continue to rise as patients are living longer, because we are better able to treat their hypertension and myocardial infarction."

Dr. Saxon noted that medical therapy for CHF has advanced significantly in the past 10 years from offering palliation to prolonging survival. The medications most frequently used are angiotensin-converting enzyme (ACE) inhibitors, diuretics, digoxin and nitrates. "Most recently, in a subset of patients with CHF, beta blockers appear to prolong survival.1 However, even with all the advances in drug therapy, mortality remains very significant, at about 10% to 20% annually. And it’s important to mention that even patients who receive maximal medical treatment – and whose survival is prolonged – continue to be symptomatic.

"Once a patient’s function is severely compromised, left ventricular assist devices [LVADs] can of course be of some help. Transplantation is another option, but only for a small minority, since patients on the waiting list outnumber donor hearts by about 20 to 1."

Dr. Saxon explained that because LVADs and transplantation are reserved for – but can help only a minority of – the most debilitated patients, and because drug therapy cannot alleviate all the symptoms of CHF, researchers continue to look for better answers. "We need to improve both cardiac performance and quality of life for all CHF patients. This is why many of us are turning our attention to pacing – to see whether novel pacing modalities will benefit patients who are already on optimal drug therapy.'' Leslie A. Saxon, M.D.,

Identifying a Junctional Rhythm by Utilizing Electrograms

A 75-year-old man was admitted in March 1998 with respiratory and congestive heart failure. The patient’s past history was positive for sick sinus syndrome, mitral and aortic insufficiency, marked left ventricular systolic dysfunction, as well as coronary artery disease and chronic obstructive pulmonary disease. At the time of presentation, the patient’s intrinsic heart rate was 85 bpm.

A month earlier the patient had been implanted with a VIGOR® DR Model 1230 pacemaker. The pacemaker was initially programmed bipolar, to the DDD mode, with a lower rate limit of 55 ppm, an upper rate limit of 110 ppm and a maximum sensor rate of 120 ppm. The atrial amplitude was set at 2.5 V at 0.6 ms pulse width, with an atrial sensitivity of 0.5 mV. The ventricular amplitude was set at 2.5 V at 0.3 ms pulse width, with a ventricular sensitivity of 1.5 mV. The dynamic atrioventricular (AV) delay was programmed on, with the maximum AV delay at 220 ms and the minimum AV delay at 100 ms. Atrial tachy response mode switching was also enabled.

Upon evaluating his pacemaker function, I noted that the electrogram (EGM) tracing revealed closely paired atrial and ventricular activity. However, there was an unusual presentation to the event markers, since atrial and ventricular activity did not always appear to be appropriately notated. When the ventricular activity occurred prior to atrial activity, the event markers noted the ventricular event as a premature ventricular contraction (PVC); there was no marker for the atrial activity. But in a few instances when the atrial activity preceded the ventricular activity, both atrial and ventricular sensing were appropriately noted.

When the pacing rate was increased above the intrinsic rate, both atrial and ventricular capture were normal. Magnet testing also demonstrated appropriate AV pacing. Pacing thresholds were within normal limits, demonstrating that the leads were intact and capturing appropriately.

I concluded that the patient’s underlying rhythm was an accelerated junctional rhythm. Because the electrical impulses were originating in the AV node, both atrial and ventricular activation were occurring in rapid succession. Often ventricular activation was detected prior to atrial activation, and in these cases – because there was no preceding atrial activity – the ventricular events were classified as PVCs. The atrial activity that immediately followed was not sensed because a ventricular sensed event sets up an 80-ms atrial blanking window. Any atrial activity during that 80-ms interval is not sensed by the pacing system.

On occasion, when atrial activity occurred prior to ventricular activity, both the atrial and the ventricular events were sensed by the system and noted by the event markers (Figure 2: As, Vs). (Following an atrial sensed event, there is no blanking interval precluding ventricular sensing.)

The EGMs in this device helped confirm that the pacemaker was functioning appropriately, given this patient’s accelerated junctional rhythm. The patient is not symptomatic, and he continues to do well.

Henry D. Storch, M.D., is a cardiologist with the Olean Medical Group in Olean, N.Y.

16 Ağustos 2009 Pazar

pacemaker surgery - implantation

Where a Pacemaker is Implanted

The location of where a pacemaker is placed (or implanted) depends upon the patient's medical condition, age, and lifestyle. Pacemakers can be implanted on the left or right side of the chest, or in the abdominal area. The pacemaker is generally implanted after the leads have been implanted. The type of anesthesia and length of hospital stay depend on the patient's medical condition.

pacemaker surgery

Many pacemaker patients will tell you not to worry about pacemaker surgery. The implant procedure has become routine and common today. In many cases, less than an hour of pacemaker surgery is required.

Many pacemaker implants can be done as an outpatient. Most patients receive a local anesthetic and remain awake during the pacemaker surgery procedure.

Some kinds of pacemaker implants may require general anesthesia and a brief hospital stay. If hospitalization is required, you will likely be home in just a few days. Ask your physician for specific details.

This section has suggestions about what a patient generally needs to do before surgery, information on where pacemakers and pacing leads are implanted in the body, what happens during the procedure, and what to expect afterwards.

This information is general. Your medical condition, age, and other factors determine the type of pacemaker and lead to be implanted. Refer to your physician to review the factors used to determine the appropriate lead and pacemaker and for specific instructions before and after pacemaker surgery.

pacemaker precautions - travelling

Most people with pacemakers can travel with ease, by car, bus, train, or airline. You should, however, take the following precautions before walking through security systems.

It is unlikely that your pacemaker will set off -- or be harmed by -- home, retail, or library security systems. Just walk normally through store theft detectors and do not linger near the theft detector.

Always carry your pacemaker ID card, should your pacemaker set off a metal detector or security system.

pacemaker precautions - workplace

Office equipment. Most office equipment is unlikely to interfere with your pacemaker. This includes such items as desktop and laptop computers, larger, mainframe-type computers, fax machines, desktop computer back-up devices, modems, copy machines, laser printers, dot-matrix printers, electric typewriters, and other similar equipment.

Industrial magnets. Do not carry or hold large magnets or magnetic materials near your pacemaker.

Heavy industrial equipment. Heavy electrical or industrial equipment often produces high electromagnetic interference and can interfere with the proper functioning of your pacemaker

pacemaker precautions - activities

With your doctor's approval, you should feel free to travel, drive your car, bathe, shower, swim, resume sexual activities, return to work, walk, hike, garden, bowl, golf, fish, or other similar activities.

Consult your doctor before engaging in more strenuous sports such as racquetball or tennis.

Returning to your daily activities should make you feel better, not worse. If you feel worse, notify your physician

pacemaker precautions - home

Home power tools. It's safe to use electric hedge clippers, leaf blowers, lawn mowers, and snow blowers. If you're using gas-powered tools, turn the engines "off" before making any adjustments. (pacemaker precautions - home) Most home power tools are safe to use, according to the following guidelines:

Keep all equipment in good condition to avoid electrical shock.

It is best not to operate power tools alone.

Be certain that the tool is properly grounded. If you use power machinery frequently, a ground-fault-interrupt system would be a wise investment. This inexpensive device is a good safety measure because it prevents a sustained electrical shock.

Avoid using any power tool locked in the "on" position, should you need to quickly turn off the equipment.

Avoid using a chain saw because your hands and body come into close contact with the electric spark-generating components. It is the spark generating components that could interact with your pacemaker.(pacemaker precautions - home)

pacemaker precautions - electrical appliances

General household electrical appliances . Your Medtronic pacemaker has built-in features that protect it from electromagnetic fields created by common household appliances and light office equipment such as:

Microwave ovens

Televisions, FM and AM radios, video cassette recorders (VCRs), video games, compact disc (CD) players, stereos, desktop and laptop computers

Electric blankets and heating pads

Tabletop appliances such as toasters, blenders, electric can openers, and food processors

Hand-held items such as home (and salon) hair dryers, shavers, or electric knives

Large appliances including washers, dryers, and electric stoves

Vacuum cleaners, electric brooms

pacemaker precautions: home use of heart pacemakers

People with pacemakers can participate in most activities of daily life. The following section offers guidelines about basic home tools, equipment, and electrical appliances.

If you suspect interference with your pacemaker, simply move away from or turn off the electrical device. Your pacemaker will not be permanently affected and will resume normal operation.(pacemaker precautions)

Cellular and mobile phones. Cellular phones are unlikely to interfere with your pacemaker if proper precautions are followed:

Maintain a distance of at least 6 inches between the cellular phone and your pacemaker. For phones transmitting above 3 watts (such as some portable and mobile cellular phones), maintain a distance of at least 12 inches between the base of the antenna and the pacemaker and follow the above precautions as well.

Hold the phone to the ear opposite the side where your pacemaker is implanted. For example, if your pacemaker is implanted in your right chest area, hold your cellular phone against your left ear.

Do not carry a cellular phone in a pocket or on a belt within 6 inches (15 centimeters) of your pacemaker.

Cordless phones. Ordinary cordless telephones and standard desk and wall telephones that are commonly used in the home are safe for pacemaker patients to use.(pacemaker precautions)

Large stereo speakers. Large stereo speakers can pose some risk of interfering with your pacemaker, due to the large magnets that they often contain. Do not lift large stereo speakers close to your implant site, as this would possibly position the magnets too close to your pacemaker.(pacemaker precautions)

15 Ağustos 2009 Cumartesi

pacemaker precautions - medical procedures

Medical procedures that may be done using precautionary measures.

The following medical procedures will generally not interfere with your pacemaker. However, it's always best to check with your physician before participating in any new or unusual medical treatments or procedures.

Diagnostic X-rays, including chest X-rays, and mammograms. If you have an upper chest implant, it may be necessary to adjust the x-ray equipment to make you more comfortable and lessen the pressure on your pacemaker.

Therapeutic ultrasound and electrolysis. With proper precautions, and providing the equipment is not used directly over the implant site, this procedure can be performed for people with pacemakers.

Dental procedures, including dental drills, ultrasonic probes to clean teeth or x-rays. These procedures can be performed. It is always a good idea to inform your dentist before beginning any dental procedure that you have a pacemaker.

pacemaker precautions - medical treatments

This section provides recommendations and discussions of medical procedures of which pacemaker patients should be aware. Notify doctors and dentists about your pacemaker implant as well as where the pacemaker has been implanted in your body. If you have a rate-responsive pacemaker, remind your medical care givers that your pacemaker is designed to increase and decrease its rate as part of its normal operation.

Be cautious about certain medical procedures.

MRI (Magnetic Resonance Imaging) is not recommended for pacemaker patients at this time. MRI produces high levels of electromagnetic interference (EMI), and poses a substantial risk of interfering with your pacemaker. If medical conditions dictate a need for MRI, discuss your pacemaker needs with your treating physician and cardiologist.

A consultation with your treating physician and cardiologist will help to weigh the risks and benefits of the following medical treatments:

Diathermy
Electrosurgery
Electrocautery
External defibrillation
Lithotripsy
Radiation therapy

pacemaker precautions

Tools and equipment that use electricity and magnets have electromagnetic fields around them. These fields are usually weak and will generally not affect your pacemaker.

However, strong electromagnetic fields have the potential to alter the proper functioning of your pacing system because these fields generate EMI (electromagnetic interference). A strong electromagnetic field can "blind" the pacemaker to your heart's rhythm and keep the pacemaker from treating you. EMI can also cause your pacemaker to send pacing beats when your heart does not need them.

If you move away from the source of EMI, your Medtronic pacemaker will return to normal functioning.

There are several safeguards built into your Medtronic pacemaker to shield it from electromagnetic interference. Such safeguards include electronic filters that differentiate between natural heartbeat signals and EMI signals, as well as the metal housing that surrounds and shields the pacemaker's battery and circuitry.