T-Wave Alternans, Restitution of Human Action Potential Duration, and Outcome
Sanjiv M. Narayan, MD, FRCP, FACC*,*,
Michael R. Franz, MD, PhD ,
Gautam Lalani, MD*,
Jason Kim, BS* and
Ashwani Sastry, MD*,
* University of California and Veterans Affairs Medical Center, San Diego, California
Veterans Affairs Medical Center, Washington, DC
Cornell University Medical Center, New York, New York.
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Figure 1 MAPs During Single Ventricular Extrastimuli
Study subjects with coronary disease and left ventricular (LV) ejection fractions 26% (A) and 38% (B). (C) Control subject. (D) Diastolic interval (DI) span from monophasic action potential duration at 90% repolarization (MAPD90) of the preceding beat to the computed maximum rate of change of voltage of the present beat. MAP = monophasic action potential; RV = right ventricular.
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Figure 2 Simultaneous Dual-Site MAP Recordings
(A) Study subject at the right ventricular (RV) apex and left ventricular (LV) apex. Maximum action potential duration (APD) restitution slopes were RV 1.58 and LV 1.19. (B) Study subject at the apex (RVA) and outflow tract (RVOT). Maximum APD restitution slopes were RVA 1.42 and RVOT 1.32. MAP = monophasic action potential.
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Figure 3 Discordance of TWA (Positive) and APD Restitution (Maximum Slope <1) for Study Subject B in Figure 1
Despite positive T-wave alternans (TWA) at 109 beats/min (BPM) (cycle length 550 ms) and action potential duration (APD) alternans (shown in beat plot), the APD restitution was flat (maximum slope 0.73 from sequential linear plots). Importantly, note that diastolic intervals during alternans lie on the flat portion of the APD restitution curve at this rate. HR = heart rate; LV = left ventricular; Neg = negative; Resp = respiratory alternans; RR Alt = heart rate alternans; VM = voltage of alternation; other abbreviations as in Figure 1.
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Figure 4 Discordance of TWA (Negative) and APD Restitution (Maximum Slope >1) for Control Subject B in Figure 1
T-wave alternans is negative, corresponding to the absence of APD alternans. However, APD restitution is steep (maximum slope 1.82). Note that diastolic intervals at this rate (109 beats/min) interact with the flat portion of the APD restitution curve, even though the left-hand portion is steep. Alt = alternans; other abbreviations as in Figures 1 and 3.
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Figure 5 Kaplan-Meier Survival Curves Using TWA as the Primary End Point (Study Subjects)
Abnormal T-wave alternans (TWA) separates patients who meet versus those who do not meet the primary end point (p = 0.024). ICD = implantable cardioverter-defibrillator; Rx = treatment; VT/VF = ventricular tachycardia/ventricular fibrillation.
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Figure 6 Kaplan-Meier Survival Curves Using Maximum APD Restitution Slope >1 as the Primary End Point
Slope >1 did not separate study patients who did and did not meet the primary end point (p = 0.85). APD = action potential duration; other abbreviations as in Figure 5.
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