The Cardioverter-Defibrillator Conundrum: Sometimes You Turn the Pacemaker Off
Turning the pacemaker feature off or programming in the longest possible escape interval is probably the prudent course in patients with implanted cardioverter-defibrillators who have had pacemaker-induced tachycardia and have no symptoms indicating the need for a pacemaker, said German researchers in a report on a small, single-center study in this week’s issue of Circulation, the journal of the American Heart Association (Circulation. 2003;108:192–197.)
Scientists from the Medical Clinic at University Hospital in Mainz, Germany, enrolled 13 patients who had previously experienced pacemaker-induced tachycardia in 1 of 2 study arms. The patients in arm 1 had augmentation of the baseline frequency of the pacemaker to 60 beats per minute, and those in arm 2 had their pacemakers turned off. The patients were monitored for a year and then crossed over to the other arm of the study. Researchers were attempting to assess what led to the recurrence of the pacemaker-induced tachycardia.
During the period of the study, no pacemaker-induced tachycardia occurred in patients whose pacemaker function was turned off. However, in the group with pacemakers programmed to 60 beats per minute, pacemaker-induced tachycardia recurred in 5 of 6 patients. At the end of the study, 8 of the patients were monitored for a prolonged period of time with their pacemaker function off. Spontaneous episodes of ventricular tachycardia or fibrillation were observed in 5 patients, but no pacemaker-induced tachycardia was seen.
The authors noted: “The pathophysiology of PIT [pacemaker-induced tachycardia] is still unclear, and it will not be clarified through this study. However, it appears obvious that a pause followed by a ventricular stimulus is to be held responsible,” although they hasten to add that it is not the sole cause of pacemaker-induced tachycardia.
“In patients with implantable pacemakers, the rate of sudden cardiac death is 23% of all deaths, which is much higher than that in comparable cohorts without pacemakers. Several pacemaker recipients have structural heart disease, and PITs may occur that lead to lethal tachyarrhythmias in these patients. . . .we recommend that for patients with paroxysmal bradycardia and structural heart disease with depressed left ventricular function, the indication for the implantation of an ICD [implanted cardioverter-defibrillator] instead of a pacemaker should be discussed.”
C-Reactive Protein Increases Stroke Risk
An elevated C-reactive protein (CRP) level increases the risk of ischemic stroke, independent of the degree of atherosclerosis, said researchers for the federally funded Cardiovascular Health Study in a report in this week’s issue of Circulation (Circulation. 2003;108:166–170).
The researchers evaluated 5417 study participants 65 years of age or older who had no history of stroke or chronic atrial fibrillation. During a 10.2-year follow-up period, there were 469 strokes in the population. The association of CRP levels with intima-media thickness (IMT) was significantly different depending on the degree of narrowing of the intima. For example, there was no association of CRP level and stroke in those who had the least amount of narrowing in the carotid artery, and the level of association increased as the degree of narrowing increased.
The researchers concluded: “We conclude that elevated CRP is a risk factor for ischemic stroke, independent of atherosclerosis severity as measured by carotid IMT. The association of CRP with stroke is more apparent in the presence of a higher carotid IMT. CRP and carotid IMT may each be independent integrals in determining the risk of ischemic stroke.”
Lenfant Announces Retirement
Claude Lenfant, MD, the longest-serving director of the National Heart, Lung and Blood Institute (NHLBI), announced his retirement effective August 30, 2003.
Dr Lenfant assumed his post as head of the NHLBI in July 1982. Under his leadership, the institute funded and oversaw the completion of major clinical trials that had direct effects on the way heart disease is treated and/or prevented. For example, his institute was responsible for the first studies that attempted to interrupt the damaged done by heart attacks and life-threatening cardiac arrhythmias. On his watch at the NHLBI, the institute proved the value of reducing blood pressure and serum cholesterol levels by lifestyle and pharmacological means.
He also oversaw the establishment of Programs of Excellence in Molecular Biology, Programs of Genomic Applications, and the Proteomics Initiative. These basic science research plans will eventually uncover the causes of diseases of the heart, lungs, and blood and lead to definitive methods of preventing these major killers.
Dr Lenfant also promoted programs that educated professionals and the public in areas such as cholesterol-lowering, asthma treatment and prevention, and the need for prompt attention to the symptoms of a heart attack.
Dr Lenfant has received the American Medical Association’s Dr Nathan Davis Award, the American Heart Association’s Gold Heart Award, the Association of Black Cardiologists’ Legend of Cardiology Award, the American Society of Hematology’s Outstanding Service Award, and the National Sleep Foundation’s Person of the Year recognition.
In a released statement, National Institutes of Health Director Elias A. Zerhouni, MD, said, “Claude Lenfant is a talented and capable administrator and a first-class scientist. Under his leadership and guidance, NHLBI supported and conducted research that has benefited millions of people. His departure will be a significant loss.”
US Hypertensive Rate Stands at One Third of Adults—and Growing
An estimated 58 million US adults—nearly one third of the population—are hypertensive—a statistic that has alarming implications for national health, according to a report in the July 9, 2003, issue of The Journal of the American Medical Association (JAMA. 2003;290:199–206).
Using a blood pressure of 140/90 mm Hg as the standard of normal, Ihab Hajjar, MD, MS, of the University of South Carolina, Columbia, and Theodore A. Kotchen, MD, of the Medical College of Wisconsin, Milwaukee, analyzed the most recent National Health and Nutrition Examination Survey (NHANES) conducted for the National Center for Health Statistics from 1999 to 2000 and found that 28.7% had hypertension, an increase of 3.7% over the NHANES study conducted from 1988 to 1991. Non-Hispanic blacks had the highest rate at 33.5%. Blood pressure was highest in women and people aged 60 years or more. Approximately 30% of those with hypertension did not know they had it. A startling 42% of those with high blood pressure were not receiving treatment, and blood pressure was not adequately controlled in an even more startling 69%.
The problem is one of control, the authors noted. Although rates of control have improved, they remain unacceptably low. Unclear is what the rate of hypertension would be if the authors had adhered to the recommendations of the Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation and Treatment of High Blood Pressure, which suggested adding a classification of “prehypertensive” to the lexicon. That report would call people prehypertensive if they had a systolic blood pressure of 120 to 139 mm Hg or a diastolic blood pressure 80 to 89 mm Hg. That recommendation, along with others found at http://www.nhlbi.nih.gov/guidelines/hypertension/jncintro.htm, prompted much comment in the professional communities because it expanded greatly the population that should at least be monitored along with increasing the numbers of drugs recommended for use in the hypertensive population itself.