CD&D National Editor and Staff Reports

An infrequently used surgical procedure that bypasses a narrowed aortic valve can restore blood flow from the heart to the rest of the body and can give high-risk patients an alternative to conventional valve surgery. That is the finding of a study conducted at the University of Maryland Medical Center (Baltimore), the data appearing in the Sept. 30 edition of Circulation.

The researchers conclude that the procedure, called aortic valve bypass, is an important treatment option for high-risk elderly patients with a narrowed aortic valve, a condition called aortic stenosis. The procedure can be performed in a minimally invasive way without stopping the heart. Many of the patients in the study had previously been considered too frail to benefit from surgery.

James Gammie, MD, associate professor of surgery at the University of Maryland School of Medicine and cardiac surgeon at the University of Maryland Medical Center, said that because of the risks for elderly patients for aortic valve replacement, "almost 60% of patients with symptoms related to aortic stenosis are never referred to surgery."

The study's principal investigator, Gammie said that survival for these patients without surgery is poor. Only 20% are alive three years after diagnosis. "But our research and five years of experience with the bypass procedure suggests there is a group of patients, typically considered inoperable because they are at the upper level of the risk spectrum, who could benefit from aortic valve bypass," he said.

The aortic valve controls the flow of blood from the heart's main pumping chamber. In aortic stenosis, calcium deposits narrow the valve, impairing the heart's ability to pump. Aortic stenosis is the most common heart valve disease of the elderly in the U.S., with more than 50,000 requiring surgery for the problem each year.

During conventional valve replacement, the surgeon opens the chest, stops the heart for about 90 minutes, opens the aorta just above the aortic valve, cuts out the old valve and sews in a new one. While valve replacement has benefited millions of patients with good outcomes, in elderly patients, particularly those with other health conditions, the death rate can exceed 10%.

Using the alternative bypass strategy, surgeons at the University of Maryland Medical Center refined a procedure originally called an apicoaortic conduit, developed in the 1970s and initially used for children. In this procedure, most of the blood flow from the heart is diverted through a tube containing a standard replacement valve, placed near the apex of the left ventricle, the pointed tip at the bottom of the heart, to the aorta.

The surgeons work through an incision between two ribs on the left side of the chest. During the first cases, a large incision was needed, but the procedure was then modified so that only a small, three-inch opening between the ribs is required.

"We are excited because for the first time we can surgically treat a narrowed aortic valve through a minimally-invasive approach with the heart beating, compared to the traditional breastbone-splitting approach," said Gammie.

Between 2003 and 2007, the surgeons treated 31 high-risk aortic stenosis patients with the bypass strategy. Many of the patients also had other conditions ranging from chronic obstructive pulmonary disease to heart attack or diabetes. The average age was 81, and nearly half had been refused conventional surgery. Early in the series, four of the 31 patients did not survive but there were no deaths among the most recent 16 consecutive patients.

The procedure was as effective as conventional aortic valve replacement surgery at relieving the obstruction of blood leaving the heart, according to the study. Stroke and kidney problems were uncommon. Because the impaired aortic valve was left in place, some blood flow continued through that valve. But postsurgical blood flow measurements indicated that in most patients, approximately 70% of cardiac output flowed through the new bypass.

Cardiac arrest outcomes vary widely

Some 166,000 to 310,000 Americans every year experience an out-of-hospital cardiac arrest (OHCA), and resuscitation is not attempted in many of these cases. "Accurate estimation of the burden of OHCA is essential to evaluate progress toward improving public health by reducing cardiovascular disease," according to authors of a recent study appearing in the Journal of the American Medical Association (2008;300[12]:1423-1431).

Graham Nichol, MD, of the University of Washington (Seattle), and colleagues conducted a study to determine whether cardiac arrest incidence and outcome differed across geographic regions. The finding was wide variation.

Among 10 sites, with a total population of 21.4 million for the areas studied, there were 20,520 cardiac arrests assessed by emergency service personnel. Resuscitation was attempted in 11,898 cases (58% of total); 2,729 (22.9% treated) had initial rhythm of ventricular fibrillation or ventricular tachycardia or rhythms that were shockable by an automated external defibrillator; and 954 (4.6%) were discharged alive.

The incidence of EMS-treated cardiac arrest per 100,000 individuals ranged from 40.3 to 86.7; for ventricular fibrillation, the incidence per 100,000 ranged from 9.3 to 19. The EMS-treated cardiac arrest survival across sites ranged from 3% to 16.3%; ventricular fibrillation survival ranged from 7.7% to 39.9%, with significant differences across sites for incidence and survival.

The study included data on all out-of-hospital cardiac arrests in 10 North American sites (eight U.S., two Canadian) from May 2006 to April 30, 2007, followed up to hospital discharge and including data available as of June 28, 2008.

Cases were assessed by organized emergency medical services (EMS) personnel. The 10 sites were participants in the Resuscitation Outcomes Consortium, and were located in Alabama; Dallas; Iowa; Milwaukee; Ottawa, Ontario; Pittsburgh; Portland, Oregon; Seattle; Toronto; and Vancouver, British Columbia.

"These findings have implications for pre-hospital emergency care. The five-fold variation in survival after EMS-treated cardiac arrest and five-fold variation in survival after ventricular fibrillation demonstrate that cardiac arrest is a treatable condition," the authors wrote.

MRI-based assessment of left atrium damage

Researchers at the University of Utah (Salt Lake City) have reported the development of an MRI-based method for detecting and quantifying injury to the wall of the heart's left atrium (LA) in patients who have undergone a procedure to treat atrial fibrillation (AF). The results appear in the Oct. 7 issue of the Journal of the American College of Cardiology.

One effective method of treating AF is radiofrequency (RF) ablation in which mild, painless radiofrequency energy is used to destroy carefully selected heart muscle cells to stop them from conducting extra electrical impulses. Previous research suggested scar formation within the left atrium (LA) after RF ablation helps to predict the success of the procedure in preventing the recurrence of AF.

Nassir Marrouche, MD, assistant professor of internal medicine in the University of Utah School of Medicine and director of the Atrial-Fibrillation Program, and colleagues developed a technique called delayed-enhancement cardiovascular MRI (DE-CMRI) to create 3-D images of the LA, both before and after RF ablation in patients with AF. They processed and analyzed these images using custom software tools and then used computer algorithms to calculate the extent of LA wall injury.

"Until now, there has not been an accurate, non-invasive way to assess LA scar formation," said Marrouche. He said that the DE-CMRI method for detecting and measuring the extent of LA wall scarring could "potentially predict the success of RF ablation" in patients with AF.

The researchers found that all patients who underwent RF ablation showed evidence of LA wall injury on MRI three months after the procedure. The pattern of tissue injury correlated with the areas where the RF energy was applied during RF ablation, and thus, was presumed to reflect tissue scarring. They also found that the patients with a higher percentage of LA wall injury were more likely to be free of arrhythmia than patients with lower percentages, suggesting the degree of scarring is linked to the likelihood of success in the RF ablation procedure.

"DE-CMRI is an established method for evaluating the tissues of the heart after a heart attack," said Marrouche. "But performing DE-CMRI to detect left atrium wall injury is challenging because the wall of the left atrium is so thin."

The technique used by Marrouche and his colleagues achieves a much greater imaging resolution than the 2-D technique typically used to evaluate the extent of tissue damage after a heart attack or in other cardiac disease processes. Marrouche and his colleagues also developed methods of processing the MRI images in order to visualize the entire volume of LA wall injury in 3-D.

BiVADs life-saving for 8 youngsters

A recent study in the Cardiovascular Surgery Supplement of Circulation, the journal of the American Heart Association (Dallas), reported nine pediatric patients with severe heart failure kept alive for an average of 35 days with miniaturized heart assist pumps.

The data emphasize the importance of continued development and refinement of mechanical ventricular assist devices in the pediatric population, researchers said.

"It is not unusual for a child at the top of the transplant candidate list to wait several months before an organ becomes available," said Sanjiv Gandhi, MD, lead author of the study, cardiothoracic surgeon and surgical director of the heart failure program at Saint Louis Children's Hospital (St. Louis).

Researchers implanted biventricular assist devices (BiVADs) in seven girls and two boys ranging in age from 12 days to 17 years, all with severe heart failure due to cardiomyopathy or complex congenital heart defects and weighed less than 88 pounds. One child died from kidney failure before receiving a heart transplant. After 19 months of follow-up, the other eight were alive with new hearts.

Children who need heart transplants and are very ill can be placed on external circulatory support machines, but their long-term use is associated with significant risks, according to the report. Additionally, these patients must be immobilized, which impairs physical rehabilitation efforts.

In this study, complications such as postoperative bleeding and blood clots blocking a blood vessel occurred infrequently, but there was a high incidence of blood clotting in the pumps.

Small heart-pump devices have been available in Europe for several years, but they are not yet approved for use in North America. However, the miniaturized Berlin Heart Excor ventricular-assist device from Berlin Heart (Berlin, Germany) recently became available in North America on a compassionate-use basis, meaning patients can be approved for the pumps if they have no other treatment options.

Viral infection/arrhythmia link found

Virus infections have been thought to cause cardiac arrhythmia, but there has been no definitive explanation of why this is so.

A group of researchers – Ulrike Lisewski, Dr. Yu Shi, Michael Radke and Professor Michael Gotthardt of the Max Delbr ck Center for Molecular Medicine (MDC; Berlin-Buch, Germany) – has reported discovery of the molecular mechanism explaining this. The researchers demonstrated that the receptor which the virus uses to infect heart cells is normally necessary for regular heart beat in mice. And when the receptor is absent or non-functioning, arrhythmia occurs.

They assume that both the virus infection and the autoimmune disease can block the receptor which, in turn, disrupts the heart's normal rhythm. The study is published online in the Journal of Experimental Medicine.

In order to beat correctly and to pump blood through the body, specialized heart fibers generate electric signals that control the heart beat. Cardiac arrhythmia occurs when these signals are not correctly generated or forwarded. There, a receptor called Coxsackievirus-Adenovirus-Receptor (CAR) is embedded in specific cell-cell contacts (tight junctions) of the specialized heart fibers. CAR was discovered as the critical protein responsible for virus entry during infection with Coxsackie and Adenoviruses. Its role in the adult heart was previously unknown.

To investigate CAR's task in a healthy organism, the MDC scientists switched off the CAR-gene in adult mice, and they could no longer produce the receptors and developed cardiac arrhythmia. "That is an interesting observation because these special cell-cell-contacts, the tight junctions, have not been connected to arrhythmia so far," Gotthardt said.

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