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The US Cardiovascular Disease Arena-In Brief A Round-up of Trends, Statistics, and Clinical Research

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One-third of Patients Not Receiving Defibrillation in Time

Patients are not receiving defibrillation soon enough after initial cardiac arrest, according to a study published in the New England Journal of Medicine. Delay in defibrillation—defined as coming after more than two minutes—is associated with a lower survival rate and lower likelihood of return to spontaneous circulation following hospital discharge.

Drawing on data from the National Registry of Cardiopulmonary Resuscitation, 30.1% of patients were found to have received defibrillation after two minutes. Multiple factors contributing to delay—including occurrence of cardiac arrest after normal hours of hospital operation and in patients occupying unmonitored beds—were all examined.

“Although several studies have shown an association between defibrillation time and survival, these were relatively small studies that typically included patients whose arrest rhythms would not have benefited from defibrillation,” said Paul S Chan, MD, a cardiologist at Saint Luke’s Mid-America Heart Institute, Kansas City. “We found that delayed fibrillation was common and that rapid defibrillation was associated with sizable survival gains in these high-risk patients.”

Americans in the Dark About High Blood Pressure Risks

Only 42% of American adults associate high blood pressure with increased risk for stroke and heart attack, according to the American Heart Association (AHA). Based on telephone interviews with over one thousand American adults, ‘A Survey of Americans and Their Knowledge Regarding High Blood Pressure’ was carried out by the National Association of Chronic Disease Directors (NACDD). Weighting figures for age, sex, ethnicity, and region to ensure accurate extrapolation for the wider US adult population, the study found that although 72% of the sample population were aware of typical factors contributing to high blood pressure—such as obesity, lack of exercise, and high salt intake—only 42% associate high blood pressure with increased risk for stroke and heart attack. Seventy-six percent of those surveyed were not concerned about getting high blood pressure, a figure rising to 80% in those over 55 years of age. Only 10% of those with high blood pressure were taking measures to improve diet and exercise regimes, with 4% confessing to making no changes.

With one-third of the US population suffering from high blood pressure, such widespread apathy—due in part to the fact that high blood pressure exhibits few symptoms—is a source of considerable concern.

Slowdown in Fight Against Coronary Disease

After 50 years of progress in the fight against coronary disease in the US, we have slowed to a halt, according to an autopsy study published in the Archives of Internal Medicine. Researchers at the Mayo Clinic in Minnesota and the University of British Columbia in Vancouver acknowledged that after a significant reduction in the prevalence of heart disease and coronary artery death from the 1960s, the rate of decline slowed after 1995, and since 2000 has arguably reversed.

The conclusions were based on an analysis of death certificates and pathology reports of nonelderly residents in Olmsted County, Minnesota. Coronary disease was classified into five grades representing percentage of reduction in left anterior descending (LAD), left circumflex (LCx), right coronary artery (RCA), and left main artery (LMA). Over the full period (1981–2004), 8.2% of the 425 individuals had high-grade disease. Age- and sex-adjusted regression analyses revealed temporal declines over the full period (1981–2004) for high-grade disease, any disease, and grade of coronary disease. Declines in the grade of coronary disease ended after 1995 (p=0.01 for every artery) and possibly reversed after 2000 (p=0.06 for LCx). “Our findings show that temporal declines in the grade of coronary artery disease at autopsy have ended, together with suggestive evidence that declines have recently reversed,” concluded the authors.

Cardiac Resynchronization Therapy Does Not Reduce Arrhythmia Frequency

Increased ejection fraction following cardiac resynchronization therapy (CRT) could be due to improved hemodynamic status from ventricular reverse remodeling and not reductions in frequency of ventricular rhythm, according to a study published in Heart.

Used in conduction disturbances and ventricular dyssynchrony, CRT is associated with improved cardiac survival rates, but Peter Brady and researchers at the Mayo Clinic found no direct causal link between arrhythmia frequency and CRT. All patients studied in a 52-patient follow-up had suffered heart failure and upgraded from an implantable cardioverter– defibrillator (ICD) to a CRT defibrillator. Ejection fraction increased from 22 to 27% after CRT, but the frequencies of sustained ventricular arrhythmias and ventricular fibrillation did not significantly change.

“These data do not support the use of CRT alone as an effective therapy for frequent ventricular arrhythmias and appropriate ICD shocks in patients with worsening heart failure to risk of sudden cardiac death,” the authors concluded.

The Sustainable Pacemaker

Researchers at Stanford University have developed a heart-powered pacemaker charged by the heart’s own movement. The generator works when the contraction of the heart muscle causes relative motion between a magnet and a conductor, inducing an electric current in a wire running into the implanted pacemaker via electromagnetic induction of the piezoelectric effect. The pacemaker would receive up to 160 microwatts more power from the pulsating of the myocardium or pericardium than it requires to function—surplus energy that could be stored to power the pacemaker should the heart fail.

Researcher David Tran, MD, and his team hope that the invention could double the lifetime of today’s pacemakers, meaning less invasive operations to replace standard pacemaker batteries, which expire after an average of four or five years. The breakthrough could also reduce the size of commercial pacemakers from 16mm to between 1 and 8mm. Dr Tran also suggests that similar systems, generating power from alternative sources such as heat differentials, physiological pressures, and blood flow, could be used to power defibrillators, ventricular assist devices, muscle stimulators, neurological stimulators, cochlear implants, monitoring devices, and drug pumps.

Ultrasound Can Detect Fetal Cardiac Problems

Diameter pulse waveforms (DPWs) used in ultrasound technology can be helpful in evaluating cardiac function in unborn babies, claim researchers at Tokai University School of Medicine, Ishara City.

By non-invasive scanning via paired phase-locked echo tracking, the researchers observed in utero DPWs of wave parameters A, X, V, and Y from the IVC of 90 healthy fetuses at 20–40 weeks. Recordings were also made of 21 fetuses with arrhythmias or cardiac structure abnormalities.

The results, which were published in the October 2007 issue of the American Heart Journal, showed that fetuses with cardiac dysfunction presented a shallow DPW with low X amplitude pattern and the X nadir underdeveloped, a result that “is consistent with impaired contractility and reduced ventricular output,” according to the researchers. They added that “measurement of the X nadir could be useful in detecting fetuses with altered cardiac function.”

The interval from V peak to A peak was higher than from A to V in fetuses with cardiac structure abnormalities, and all four fetuses with a relatively shortened systolic duration as a percentage of the cardiac cycle did not survive. The researchers concluded that “assessment of fetal cardiac function using the DPW may be applicable to a variety of conditions, including cardiac abnormalities.”