CDU Senior

A multicenter study presented during last month's North American Society for Pacing and Electrophysiology (NASPE; Natick, Massachusetts) meeting showed that, most of the time, ICDs could correct a person's dangerous, abnormal heart rhythms through pacing rather than a sometimes painful shock.

The study appears to put to rest a debate regarding whether pacing should be attempted before shock: Not only does pacing correct the most common dangerous arrhythmia nearly 80% of the time, even when it does not work the short delay before a shock is attempted does not decrease the survival rate. "Trying pacing first takes a total of 15 to 30 seconds," said Hugh Calkins, MD, director of electrophysiology and professor of medicine at Johns Hopkins Medical Center (Baltimore, Maryland). "There appears to be no downside to trying pacing first, yet there are two major upsides – no pain for the patient and less drain on the ICD battery when pacing alone is used."

People who are known to be at risk for sudden cardiac arrest due to an arrhythmia – typically from damage sustained from a heart attack or due to genetic disease – often are given implantable cardioverter defibrillators (ICDs). Sudden cardiac arrest kills at least 400,000 people in the U.S. every year, according to the Centers for Disease Control and Prevention (Atlanta, Georgia).

Calkins said electrophysiologists have been divided regarding programming preference: about half of ICDs in this country are set by physicians to pace first before delivering a shock, and the rest are set to immediately shock a heart out of the arrhythmia. ICDs can be quickly and easily reprogrammed noninvasively in the physician's office with a remote device.

"Our multicenter study confirms what other studies have found," Calkins said. "ICDs should routinely be set to pace before they shock."

The study was part of the Low Energy Safety Study and included 636 patients from 32 investigational centers, who were followed an average of more than two years at 32 U.S. centers. Of those patients, 113 experienced 632 spontaneous episodes of an arrhythmia called ventricular tachycardia, with a heart rate of less than 200 beats per minute. Seventy-nine of the patients had their ICDs programmed to pace first before shocking and the remaining 34 for shock first. Pacing was attempted first in 548 episodes of ventricular tachycardia and successfully corrected the arrhythmia 429 times (78%). If pacing did not work, the ICD delivered a shock; after pacing and one shock, the arrhythmia was corrected in 91% of cases. Shock was used immediately in 84 episodes of ventricular tachycardia, and one shock was successful 74 times (88%). Continued shocks corrected the arrhythmia in the remaining patients and no subjects died during the study.

Although some people aren't even aware they have received a shock – especially if it occurs while they are sleeping – others have described it as feeling as though they were kicked in the back."Certainly that's preferable to death, but if you can avoid the shock, why not?" Calkins asked.

In other news from the NASPE scientific sessions and exhibit floor:

A further case was made for dual-chamber (atrial) pacing by Mark Carlson, MD, of the University Hospitals (Cleveland, Ohio). He said that dual-chamber pacing could decrease the risk for atrial fibrillation (AF) in patients who require pacing for sick sinus syndrome (SSS). In addition, he said an algorithm that increases atrial pacing to slightly above intrinsic heart rates and yet provides for normal physiologic variations in heart rate may further decrease the risk of AF.

Several previous studies have attempted to elucidate further on the benefits of pacing to prevent AF, including a retrospective study in which 507 patients underwent permanent pacemaker implantation for sick sinus syndrome and were followed for a mean of 59 months. The results showed that patients who underwent ventricular pacing alone had more AF than those patients who had dual chamber pacemakers.

Of particular note, Carlson said, is the Canadian Trial of Physiologic Pacing, in which researchers showed that AF was less likely to occur in patients who had dual chamber pacemakers than in patients who had ventricular pacing. In that study, physiologic pacing reduced the development of chronic AF by 27.1%, from 3.84% per year to 2.8% per year.

In ADOPT (Atrial Dynamic Overdrive Pacing Trial), presented at last year's NASPE meeting, Carlson and his colleagues tested an algorithm that would provide physiologic changes in heart rate, but still pace above or slightly above the patient's intrinsic heart rate.

This algorithm was then used prospectively in patients with SSS, and found to decrease symptomatic AF burden by roughly 25% in patients with the algorithm programmed "on" compared with those who had the algorithm "off." Data from ADOPT also confirmed that dual chamber pacing alone may also decrease the risk for AF, according to Carlson. "Therefore, the algorithm adds benefit above that achieved with dual chamber pacing alone."

Questions that still remain to be answered are whether such an algorithm would be beneficial in patients who would not otherwise require a pacemaker, and whether it is possible that pacing could suppress AF in patients who do not have evidence of bradycardia. Carlson said that he and his fellow researchers are designing a study to address these and other questions.

Living and reliving the horror of the Sept. 11 terrorist attacks was not only tough on the psyche, it also likely affected the body and may have been particularly harmful to diseased hearts, suggested Columbia University (New York) and Yale University (New Haven, Connecticut) research presented at the NASPE meeting.

The studies also suggest that if not for ICDs, the death toll in the wake of the disaster would probably have been even higher.

According to the Columbia study, life-threatening arrhythmias were more than twice as likely to occur in the month after Sept. 11 as the month before. That study was on 200 people with ICDs in the New York/New Jersey area. A Yale study of generally healthy people suggested that stress was affecting their bodies and hearts in the week after the attacks.

"It could be that with the extensive media coverage, the catastrophe had no geographic boundary," said Jonathan Steinberg, MD, chief of the division of cardiology and director of arrhythmia service at St. Luke's-Roosevelt Hospital Center and professor of medicine at Columbia University College of Physicians and Surgeons (both New York) and subspecialty director of the electrophysiology laboratory at Valley Hospital (Ridgewood, New Jersey). "Although our study didn't address the national picture, it is not unreasonable to assume the event likely affected people with vulnerable hearts throughout the country, not necessarily all of whom were protected by ICDs."

People saved from cardiac arrest and death by police and paramedics with portable defibrillators go on to live normal lives for many years, according to Mayo Clinic (Rochester, Minnesota) research. The study focused on the first 10 years of an early defibrillation program set up in Olmsted County, Minnesota, in 1990. All police officers and paramedics in the county are equipped with portable automatic external defibrillators (AEDs) to shock hearts that are experiencing life-threatening abnormal rhythms, which can lead to sudden cardiac arrest and death within five minutes if not corrected.

This well-organized early defibrillation program is credited with a 39% survival rate of cardiac arrest victims in the county. It is well above the national average which ranges between 3% and 34%. During the study, 44% of patients received ICDs.

"Our study illustrates the importance of a well-organized, effective early defibrillation program," said Douglas Packer, MD, an electrophysiologist at the Mayo Clinic.

In the 10-year study period, 200 people (average age of 62) suffered ventricular tachycardia or ventricular fibrillation. Of those patients, 145 (72%) were defibrillated and survived to be admitted to the hospital, and 79 (39%) were eventually discharged from the hospital. After nearly 4-1/2 years, 76% of those people were still alive.

Biophan Technologies (Rochester, New York), developers of the first MRI-safe, wearable pacemaker, demonstrated a functional design concept of an MRI-safe lead for a defibrillator. The defibrillator can deliver a 800-volt, 40-joule charge to a patient whose heart is determined to be in fibrillation, where the muscle contractions are random and irregular so that the heart does not effectively pump blood. The electrical discharge stops the contractions (defibrillates the heart) and allows the heart to re-establish a regular heart rhythm. Biophan's fiber optic solution for making pacemakers safe in an MRI machine cannot be extended to the defibrillation function because of the voltage and energy required. Biophan is working to bring MRI compatibility to the pacemaker, implantable cardioverter-defibrillator and biomedical device industries.

CardioDynamics (San Diego, California) reported results of a clinical study that demonstrated improvements when using its ICG technology in optimizing pacemaker settings in congestive heart failure patients. The study examined the potential benefit of acute pacemaker optimization during temporary heart chamber pacing and demonstrated ICG technology to be a highly effective, efficient, non-invasive tool for this unmet need. According to the study, 88% of the pacemaker patients demonstrated benefits of improved blood flow, with a mean increase in ICG-determined cardiac output of 54%. Study results confirmed excellent ICG correlation to echocardiographic optimization settings.

Cardiome Pharma (Vancouver, British Columbia) said that a preclinical study showed its lead antiarrhythmic drug, RSD1235, demonstrated a rapid and selective termination of atrial fibrillation. RSD1235 is a new chemical entity designed to treat AF. Its mechanism of action involves blockade of multiple ion channels important in managing AF. RSD1235 has a wide safety range in preclinical studies. In Phase I testing, no significant adverse events were observed including no signs of cardiac depression, torsades or central nervous system liability, even at dosing levels up to five-fold above the expected effective dose. Phase II efficacy studies are under way with completion expected the second half of 2002. Its primary endpoint is conversion of AF within 30 minutes of infusion. RSD1235 is currently formulated for IV use for acute termination in hospital. The 60-patient, placebo-controlled, double-blinded study is being conducted at 20 sites throughout North America.

GE Medical Systems Information Technologies (GEMSIT; Milwaukee, Wisconsin) said during NASPE that its CardioLink network is the first and only tool that connects electrophysiology labs, providing what it referred to as "unprecedented access" to case data without optical media. It said the system provides clinicians with "near real-time access" to EP patient data from anywhere on the company's CardioLab EP monitoring system, even while other clinicians are viewing the same data. GEMSIT said CardioLink simplifies data entry and storage and makes case data easily and simultaneously available to clinicians, which enhances clinical productivity and accuracy. Mike Genau, vice president of cardiology systems for GEMSIT, said CardioLink "connects what once were islands of information into one system that physicians, nurses and technicians can use before, during and after a case is in progress." Historically, EP lab personnel have charted cases on paper and then transferred the data to an end report. The company said that with CardioLink, all case data are sent to one electronic patient file that can be accessed from any workstation on the hospital network for review and analysis. Genau said the system is deployed at nearly 60 U.S. sites.

Spectranetics (Colorado Springs, Colorado) released its SLS II lead removal laser sheath. Available in the 16 Fr size, it features a slick inner coating to facilitate passage of the laser sheath over the lead. The sheath was designed with a more flexible distal segment and 15 degree bevel on the tip to ease advancement over acute angles, and it has an additional 10 cm of SLS body length for tall patients. Its greater body strength enables it to migrate tortuous anatomy more easily. In addition, the company has added a suture cleat to its Lead Locking Device, a complementary mechanical device that facilitates lead removal by providing traction. Spectranetics said the enhancements are based on feedback from physicians.