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Exploiting rate-related hysteresis in repolarization alternans to improve risk stratification for ventricular tachycardia

^a Division of Cardiology/Electrophysiology, Washington University School of Medicine, St. Louis, Missouri, USA

View larger version (22K): [in a new window]   Figure 1 Spectral computation of RPA. Left panel, The first two QRS-aligned and baseline-corrected beats from a series of 64 beats at 120 beats/min (500 ms CL pacing). JT alternation is computed from interbeat power spectra at successive time points within 1) the entire JT interval (R); and windows of half of this duration in 2) early (RE); 3) middle (RM); and 4) late (RL) repolarization. Right panel, Summation of spectra at each time point reveals RPA as the magnitude at 0.5 cycles/beat, T. T is related to noise (0.33 to 0.48 cycles/beat) as TWAR, where TWAR 3 is significant (TWAR = 67.6 here for R). The mean voltage of JT alternation was Valt = 7.67 µV.

View larger version (19K): [in a new window]   Figure 2 The Valt changes asymmetrically with heart rate acceleration then deceleration, showing hysteresis on either side of the heart rate symmetry line (400 ms CL pacing). A, Inducible patients showed significant increases in Valt as the pacing rate increased from 100 beats/min (600 ms CL) to 120 beats/min (500 ms CL) to 150 beats/min (400 ms CL) for all regions of repolarization. Valt was significantly greater during deceleration than acceleration at 120 beats/min (R; p = 0.015), with redistribution from RL toward RE and RM (RM > RL; p = 0.045). Valt resumed baseline at 100 beats/min. B, Noninducible patients showed different hysteresis without an acceleration-related increase in Valt, but then an increase on deceleration to 120 beats/min (p = 0.004) and to 100 beats/min (p = 0.049) with earlier redistribution of RPA (RM > RL, p = 0.048; RM > RE, p = 0.041).

View larger version (47K): [in a new window]   Figure 3 The RPA decays rapidly after heart rate acceleration, in this case from CL 600 to 500 ms CL (120 beats/min), with TWAR for overlapping analyses commencing with beats 0, 5, 10 and 15 (epoch 1; immediate) being significantly larger than that for epoch 2 (early; p < 0.02) or epoch 3 (middle; p < 0.01). Solid bars = inducible patients; hatched bars = noninducible patients.

View larger version (18K): [in a new window]   Figure 4 Receiver-operating characteristics of Valt and TWAR (discriminant levels indicated on curves) for VT at 120 beats/min, showing markedly superior specificity of (A) acceleration over (B) deceleration. Improved specificity and specificity (curves upward and to the right) follow the use of Valt over TWAR, late over whole JT segment analysis and acceleration over deceleration sequences at 500 ms CL pacing. Similar trends were evident at other CLs.