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| TITLE |
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Analysis of cause-specific mortality in the Atrial Fibrillation Follow-up Investigation of Rhythm Management (AFFIRM) study.
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| AUTHORS |
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Jonathan S Steinberg, Ara Sadaniantz, Jack Kron, Andrew D Krahn, D Marty Denny, J C Daubert, W Barton Campbell, Edward Havranek, Katherine Murray, Brian Olshansky, Gearoid O'Neill, Magdi Sami, Stanley Schmidt, Randle Storm, Miguel Zabalgoitia, John Miller, Mary Chandler, Elaine M Nasco, H L Greene
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| PUBLICATION INFORMATION |
Journal Name: Circulation
Volume: 109(16)
Pages: 1973-80
Date Published: 04/27/2004
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| ABSTRACT/REVIEW |
What were the researchers trying to learn in this study?
The researchers analyzed the specific causes of death among the two treatment groups in the AFFIRM trial.
The AFFIRM trial compared two strategies for treating this condition in patients at high risk of stroke. The rhythm control strategy uses various anti-arrhythmic drugs alone or in combination with other procedures (cardioversion) to improve the heartbeat rhythm. The rate-control strategy allows the atrial fibrillation to continue but uses medications to slow the heartbeat. The result of that trial showed that rate-control was at least as effective as rhythm control and that it was an acceptable strategy for treating these patients. An unexpected result of the trial showed that the rhythm-control group had a slightly higher rate of deaths than the rate-control group.
What did they find?
During an average follow-up of 3.5 years, there were 356 deaths in the rhythm-control patients and 310 deaths in the rate-control patients. Of the deaths attributed to heart diseases (cardiac causes) there were 129 patients (9%) in the rhythm-control group and 130 patients (10%) in the rate-control group. Both groups had similar rates of arrhythmic and nonarrhythmic cardiac deaths.
The numbers of deaths attributed to blood vessel disease (vascular deaths) were similar in the 2 groups: 35 (3%) in the rhythm-control group and 37 (3%) in the rate-control group. There were no differences in the rates of stroke due to lack of blood flow to the brain (ischemic stroke) and strokes due to bleeding in the brain (central nervous system hemorrhage).
In the rhythm-control group, there were 169 noncardiovascular deaths (47.5% of the total number of deaths), whereas in the rate-control arm, there were 113 noncardiovascular deaths (36.5% of the total number of deaths). Differences in noncardiovascular death rates were due to lung-related (pulmonary) and cancer-related deaths.
Who was studied?
In AFFIRM, 2,033 patients were randomly assigned to a rhythm-control strategy and 2,027 patients to a rate-control strategy. All patients had been diagnosed with atrial fibrillation and were either over 65 years old or if under 65, had at least one high-risk factor for stroke.
How was the study done?
A committee of doctors reviewed all deaths of patients enrolled in AFFIRM without knowing to which treatment group the patient belonged to determine the specific cause of death based on records submitted to the committee. The cause of death was defined as that which initiated the terminal event and was not necessarily the event that immediately preceded the death. Emphasis was placed on identifying the primary cause of death, especially when other intermediate events preceded the actual cessation of respiration and circulation. The committee then categorized the deaths as being due to cardiac, vascular, noncardiovascular, and uncertain mechanisms.
What did researchers know before starting this study?
Atrial fibrillation is an undisputed risk factor for stroke and is the most common cardiac cause of stroke. The incremental risk of stroke attributed to atrial fibrillation varies depending on the patient population studied but most studies have concluded that people with AFIB have a 5-fold increased risk of stroke. Chronic anticoagulation with warfarin markedly reduces this risk, and was required in all AFFIRM patients at study entry.
Why did they do it?
The main objective of the AFFIRM trial was to determine if one treatment strategy provided better survival compared to the other strategy. Consequently, determining the specific cause of death was essential to answering the primary question of the study. Also, due to the unexpected result of the trial showing that the rhythm-control group had a slightly higher rate of deaths than the rate-control group, the researchers wanted to understand why that was so.
What did the researchers say their study results mean?
The researchers concluded that drug-based management of atrial fibrillation with a rhythm-control strategy offered no advantage over a rate-control strategy in cardiac or vascular deaths and may be associated with an increased noncardiovascular death rate.
If normal (sinus) rhythm were to be achieved permanently, these negative physiological effects may disappear. Antiarrhythmic drug therapy, however, rarely abolishes atrial fibrillation and thus, a risk may remain. Furthermore, atrial fibrillation itself may not be the direct cause of increased deaths. The reason for the failure of a rhythm-control strategy to improve cardiac fatality rates is uncertain. Sinus rhythm was achieved moderately well in this arm in the AFFIRM study, with 62.6% of patients in the rhythm-control arm still had sinus rhythm at the 5-year visit (compared with 34.6% in the rate-control arm). However, many patients continued to have atrial fibrillation, and probably many more had atrial fibrillation that was episodic and unrecorded at the time of the follow-up clinic exam.
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