doi: 10.1161/01.RES.0000124606.14903.6F
© 2004 American Heart Association, Inc.
Editorials |
Understanding Cardiac Alternans
The Answer Lies in the Ca2+ Store
From the Laboratory of Experimental Cardiology, University of Leuven, Leuven, Belgium.
Correspondence to Karin R. Sipido, MD, PhD, Laboratory of Experimental Cardiology, KUL, Campus Gasthuisberg O/N 7th Floor, Herestraat 49, B-3000 Leuven, Belgium. E-mail Karin.Sipido@med.kuleuven.ac.be
Key Words: cardiac alternans • [Ca2+]i transients • sarcoplasmic reticulum
An extract of the first 250 words of the full text is provided, because this article has no abstract. |
Pulsus alternans is a condition wherein the heartbeat cyclically varies between weak and strong despite a constant heart rate. It was first described many years ago in experimental conditions, but it can be observed clinically, in particular, in patients with heart failure, where the presence of alternans portends a bad outcome (reviewed in1). Typically, alternans occurs at high heart rates, but the threshold frequency can be lowered by various conditions such as ionic disturbances or ischemia.
The alternation of the strength of the pulse, or mechanical alternans, is accompanied by alternation of the electrical activity, the so-called "electrical alternans." This is particularly evident on the repolarization phase: action potential recordings in vitro show alternation of the duration of the action potential (AP), either concordant with the mechanical alternans (long AP with a strong beat) or discordant (short AP with strong beat) (reviewed in1). Electrical alternans can be observed at the ECG level as alternation of the ST-segment and T-wave amplitude and form; T-wave alternans is commonly referred to as TWA.
Clinical Relevance of T-Wave Alternans and Link to Cellular Studies
TWA directly reflects the presence of an arrhythmogenic substrate, ie, instability of repolarization resulting in temporal dispersion but also spatial dispersion. The cellular processes and (disturbed) coupling then create a substrate for microreentry. TWA has indeed been associated with an increased incidence of arrhythmias in a variety of conditions (reviewed in1,2). Recently there has been an increased interest in the phenomenon as a prognostic parameter, particularly within the heart failure population and in patients at increased risk
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