T-Wave Alternans and the Susceptibility to Ventricular Arrhythmias
Sanjiv M. Narayan, MB, MD, FACC*, ,*
* University of California, San Diego
Veterans Affairs Medical Center, La Jolla, California.
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Figure 1 T-wave alternans (TWA) of increasing subtlety detected through the years. (A) Gross alternans of elevated ST/T-segments in a patient with angina pectoris preceding ventricular tachycardia (VT); (B) Visible alternans of T-wave polarity in a woman without angina, heralding polymorphic VT; (C)Subtle but visible TWA after tachycardia termination, without arterial pressure alternans (bottom); (D)Visually inapparent microvolt-level TWA, uncovered by digital signal processing (8,23). *The more positive T-wave of each alternating pair. Panel A was reprinted with permission from reference 11. Panel B was reprinted with permission from reference 22, Copyright ©2006 Massachusetts Medical Society. Panel C was reprinted with permission from reference 21.
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Figure 2 "Orderly transition" from stable rhythm, via T-wave alternans (TWA), to ventricular fibrillation (VF). Electrocardiograms (ECGs) of canine hearts after the onset of ischemia (times in min:s) show period doubling to TWA, i.e., two clusters in the Poincarré plot (T-wave amplitude of each beat against its successor). Further multupling causes higher-order oscillations, complex forms, and then VF. Reprinted with permission from reference 28.
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Figure 3 Mechanisms underlying T-wave alternans (TWA). (Left) spatial dispersion of repolarization. Compared to region 2, region 1 has longer action potential duration (APD) and depolarizes every other cycle (beats 1 and 3). (Right) Temporal dispersion of repolarization. Action potential duration alternates between cycles, either from alternans of cytosolic calcium (not shown) or steep APD restitution. Action potential duration restitution (inset) is the relationship of APD to diastolic interval (DI), the interval separating the current action potential from the prior one. If restitution is steep (slope >1), DI shortening abruptly shortens APD, which abruptly lengthens the next DI and APD, leading to APD alternans.
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Figure 5 Evidence-based flow chart for primary prevention of sudden cardiac arrest (SCA) including T-wave alternans (TWA). Scenarios where TWA has been validated are referenced, and labels I to III are keys to these sections of the text. *High-risk subgroup of (12) with left ventricular ejection fraction (LVEF) slightly higher than 35%, at 39 ± 18%. See Tables 1 and 2.
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T). In the final spectrum (summated for all time points), 
1.9 µV in two precordial or one vector lead (here Valt
4 to 6 µV in V3 to V6) with (ii) k-score