Sensitivity and specificity of concealed entrainment for the identification of a critical isthmus in the atrium: relationship to rate, anatomic location and antidromic penetration
Joseph B. Morton, MBBSa,
Prashanthan Sanders, MBBSa,
Vincent Deen, MBBSa,
Jithendra K. Vohra, MD, FACCa and
Jonathan M. Kalman, MBBS, PhD, FACC*,a
a Department of Cardiology, The Royal Melbourne Hospital and University of Melbourne, Melbourne, Australia
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Figure 1 Percentage of entrainment episodes diagnosed as concealed entrainment according to the site and rate of pacing. DCS = distal coronary sinus; PCS = proximal CS; HSRA/HLRA/LLRA = high septal/high lateral and low lateral right atrium; ISTH ENT = isthmus entrance; ISTH EXIT = isthmus exit.
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Figure 2 Entrainment from the high lateral right atrium (HLRA). (A)Electrocardiogram (ECG) recorded during entrainment from the HLRA at flutter cycle length (FCL)-10 and FCL–40 compared to the non-paced flutter wave. At FCL–10 the paced flutter wave appears identical to the non-paced flutter wave in the limb leads, with minor differences in amplitude and morphology observed in the anterior leads (V1 to V6). Three blinded observers recorded this as concealed entrainment. At FCL–40 the paced flutter wave is clearly different and was recorded as manifest entrainment by all three observers. (B)Intracardiac electrogram recording during entrainment at FCL–10 ms from the HLRA (TA 13/14). The post-pacing interval (PPI) minus FCL is 15 ms, confirming that the HLRA is within the circuit. The upward arrows indicate the orthodromic activation times from TA 19/20 to 17/18 (10 ms) and TA 17/18 to 15/16 (10 ms) are unchanged during entrainment consistent with orthodromic capture of TA 17/18 and 15/16. However, the entrained TA 15/16 electrogram is different in morphology from the non-entrained electrogram, suggesting fusion between the antidromic (downward arrows) and orthodromic(upward arrows) wave fronts at this point. Also shown: surface ECG leads II and III, and distal and proximal coronary sinus (DCS/PCS) recordings. (C) Entrainment at FCL–40 ms from the HLRA. The PPI minus FCL is 20 ms, confirming that the HLRA is within the circuit. TA 15/16 and 17/18 are now captured by the antidromic wave front (solid downward arrow), with associated electrogram morphology change and activation timing ahead of TA 19/20, which is still orthodromically activated with activation timing and morphology not significantly different from spontaneous flutter (dashed downward line from TA 1/2 to TA 19/20). The phenomenon described by Cosio et al. (17) of orthodromic overlap is also evident with orthodromic activation of TA11/12 and 9/10 (by the n wave front) occurring simultaneously with orthodromic activation (by the previous n–1 wave front) of TA 19/20. Surface ECG fusion may be a "fusion" of these two processes (antidromic penetration and orthodromic overlap), though in the present analysis the observation of manifest entrainment was statistically related to the extent of antidromic penetration.
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Figure 3 Entrainment from the isthmus entrance. (A) Electrocardiogram recorded during entrainment from the isthmus entrance at FCL–10 and FCL–40 ms compared to the non-paced flutter wave. At FCL–10 the paced flutter wave appears identical to the non-paced flutter wave and was recorded as concealed by three blinded observers. At FCL–40 the paced flutter wave is different from the non-paced flutter wave (note aVL and V1 in particular) and was recorded as manifest entrainment by three observers. (B) Intracardiac electrogram recording during entrainment at FCL–10 ms from the isthmus entrance (TA 1/2). Consistent capture could not be achieved from TA 5/6 on this occasion and the catheter was repositioned so that TA1/2 was now at the isthmus entrance. The PPI minus FCL is 10 ms confirming that this site is within the circuit. The upward arrows indicate the orthodromic activation times from TA 19/20 to TA 7/8 (110 ms), TA 5/6 (120 ms) and TA 3/4 (130 ms). During entrainment there is fusion between the antidromic (downward arrows) and orthodromic wavefronts at TA 3/4, which is now activated slightly earlier (125 ms).
(C) Entrainment at FCL–40 ms from the isthmus entrance. The PPI minus FCL is 20 ms, confirming the site is within the circuit. TA 3/4 and 5/6 are now captured by the antidromic wave front (downward arrows) with associated electrogram morphology change and activation ahead of TA 7/8, which is still orthodromically activated (TA 19/20 to 7/8 activation time 110 ms), though with a slight electrogram morphology change suggesting possible fusion between the orthodromic and antidromic wave fronts at this site. Abbreviations as in Figure 2.
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Figure 4 Entrainment from the isthmus exit. (A) Electrocardiogram recorded during entrainment from the isthmus exit at 10 ms and 40 ms below the flutter cycle length (FCL–10 and FCL–40) compared to the non-paced flutter wave. At both FCL–10 and FCL–40 the paced flutter wave appears identical to the non-paced flutter wave and was recorded as concealed by three blinded observers on both occasions. (B) Intracardiac electrogram recording during entrainment at FCL–40 ms from the isthmus exit (TA 1/2). The PPI minus FCL is 5 ms, confirming that this site is within the circuit. The upward arrows indicate the orthodromic activation time from TA 19/20 to TA 3/4 (80 ms), which is unchanged during entrainment consistent with orthodromic capture of TA 3/4. Allowing for the pacing spike artifact, there is no electrogram morphology change in TA 3/4 either.
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Figure 5 Mean antidromic penetration (AP) plotted against entrainment rate. When compared to other sites within the atrial flutter circuit, there was significant blunting (p = 0.003) in the extent of AP measured from the isthmus exit at entrainment rates of FCL–30 (8 ± 3 mm) and FCL–40 (9 ± 3 mm). FCL = flutter cycle length; HSRA/HLRA/LLRA = high septal, high lateral and low lateral right atrium.
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