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A New Method for Estimating Preexcitation Index Without Extrastimulus Technique and Its Usefulness in Determining the Mechanism of Supraventricular Tachycardia Takeshi Yamashita, MD, Hiroshi Inoue, MD, Akira Nozaki, MD, Tsong-Teh Kuo, MD, Masahiro Usui, MD, Shinichiro Saihara, MD, and Tsuneaki Sugimoto, MD

The preexcitation index has been shown to be useful in determining the mechanism of paroxysmal supraventricular tachycardia (SW) and the site of the accessory pathway in atrioventricular (AV) reentrant tachycardia. To test whether a preexcitation index could be computed analytically instead of by scanning the whole SVT cycle with extrastimuli, 19 patients with SVT were studied. The new index was computed using the following formula: (AV conduction time during SVT) + (ventriculoatrial conduction time during ventricular pacing at the SVT cycle length) (SVT cycle length). There was a strong correlation between the preexcitation index determined by the extrastimulus technique and the new index in 15 patients in whom the preexcitation index could be determined (r = 0.99, p 90 ms only in patients with dual AV nodal pathways. In the 4 patients in whom the preexcitation index could not be determined by the extrastimulus technique, the new index could differentiate AV reentrant tachycardia (index for 2 patients, 60 and 60 ms, respectively) from AV nodal reentrant tachycardia (index for 2 patients, 100 and 105 ms, respectively). In conclusion, the new index provided help in determining the mechanism of SVT, even when retrograde atrial preexcitation by a ventricular extrastimulus did not occur. (Am J Cardiol 1991;67:830-834)

From the Second Department of Internal Medicine, Tokyo University Hospital, Tokyo, Japan. Manuscript received September 24, 1990; revised manuscript received and accepted December 7, 1990. Address for reprints: Takeshi Yamashita, MD, the Second Department of Internal Medicine, Tokyo University Hospital, 7-3- 1, Hongo, Bunkyc-ku, Tokyo 113, Japan.

830

THE AMERICAN JOURNAL OF CARDIOLOGY VOLUME 67

premature ventricular stimulus introduced at an appropriate moment during paroxysmal supraventricular tachycardia (SVT) may preexcite the subsequent atria1 cycle. Retrograde atria1 preexcitation has been used to verify the participation of an accessorypathway in the SVT circuit.tm3Recently, a preexcitation index was proposedas an aid in distinguishing atrioventricular (AV) reentrant tachycardia from AV nodal reentrant tachycardia and determining the site of the accessory pathway in AV reentrant tachycardia.4 To determine the preexcitation index, the whole SVT cycle needs to be scanned by ventricular extrastimuli. This procedure is time-consuming and, in certain cases,inappropriate, particularly in patients with left-sided free wall accessorypathways or dual AV nodal pathways.2,495 The preexcitation index is affected mainly by the SVT cycle length, the distance between the pacing site and the reentrant circuit, and the refractory period of the pacing site.4m6 We hypothesizedfrom this that the preexcitation index could be calculated analytically, using the ventriculoatrial conduction time during ventricular pacing and the AV conduction time during the SVT. The purpose of this study was to test this hypothesis.

A

METHODS Study patients: The study group comprised 19 patients, 14 men and 5 women aged 12 to 68 years (mean f standard deviation 42 ?C15) with SVT who underwent electrophysiologic study in the drug-free state. Fourteen of 19 patients had orthodromic AV reentrant tachycardia’ (8 with manifest and 6 with concealed Wolff-Parkinson-White syndrome). The remaining 5 patients had AV nodal reentrant tachycardia.7 Patients were divided into 2 groups according to whether the preexcitation index could be determined by the extrastimulus technique (group A, 15 patients) or not (group B, 4 patients).

Electrophysiologic study: Multipolar electrodecatheters (United States Catheters and Instruments, 6Fr) were introduced percutaneously and positioned in the high right atrium, right ventricular apex, His bundle region and, if possible, the coronary sinus, If an electrode catheter could not be introduced into the coronary sinus, a left atria1 electrogram was recorded through an esophageallead.8 The distal pair of electrodes were used for electrical stimulation, and the proximal pair for recording. Stimulation was performed with 2-ms rectangular pulses at twice the late diastolic threshold using a digital programmable stimulator (Fukuda Denshi, BC02). Intracardiac electrogramsfiltered at 30 to 500 Hz and electrocardiographic leads I, aVF, and Vi were recorded simultaneously at paper speedsof 50 to 100 mm/s on an ink-jet recorder (Nihon Kohden, RIJ2108) and on an FM tape using a cassettetape recorder (TEAC MR-40) for later analysis. Pacing protocol: In each patient, SVT with narrow QRS was induced by ventricular extrastimulation. A single extrastimulus was introduced during the SVT from the right ventricular apex. The coupling interval was shortened in 5-ms stepsuntil either the ventricular effective refractory period was reachedor the SVT was terminated. Atria1 preexcitation by a ventricular extrastimulus during SVT was consideredpresent (group A, 15 patients) when the atria1 cycle length encompassing the ventricular premature complex decreasedsuddenly by 210 ms.4 In the remaining 4 patients (group B),

retrograde atria1 preexcitation did not occur with a single ventricular extrastimulus. The preexcitation index was defined as the difference between the SVT cycle length and the longest coupling interval of the ventricular extrastimulus that prcexcited the atria.4 During SVT, the anterograde conduction time (Tl) from the earliest atria1 activation among the recording sites to the right ventricular apex was determined. The retrograde conduction time (T2) from the right ventricular apex to the earliest atria1 activation was determined during right ventricular pacing at SVT cycle length. Analytical prediction of preexcitation index: Our new index was computed by the following formula: Tl + T2 - CL, where CL is the SVT cycle length (Figure 1). Figure 1 shows the fundamentals for constructing the formula. The right ventricular electrogram is recorded at EGl, and the earliest atria1 activation at EG2. The exit and entry of the reentrant circuit are supposedto be located at the samesite, i.e., point P. Tl is the anterograde conduction time from EG2 to EGl during SVT, which is equal to the SVT cycle length minus Z plus Y (Figure 1A). T2 is the retrograde conduction time from EGl to EG2 during ventricular pacing at the SVT cycle length, which is equal to X plus Z (Figure 1B). For the wave front produced by an extrastimulus from EGl to collide with the spontaneousorthodromic wave front at point P, the spontaneouswave front should be located at point Q, which lies by time X short of point P (Figure 1C). It is time X plus Y before

*+EGI

TI=antegrade during

1

Cm

conduction

the

0I

time

*-EGI

(EGMEGI)

TZ=retrograde during

tachycardia

Atrium

D.

conduction ventricular

pacing

time

(EGI

at the

+EGZ) CL

PI=x+Y TI+TZ=(CL-Z+Y)+(X+Z) =x+Y+cL :.

PI=TI

+T2-CL

Ventricle

FIGURE 1. Schema for estimating the preexcitation index (PI) in patients with atrioventricular reentrant tachycardia. In this figure, the entry site is the same as the exit site (Point P). The right ventticular electrogram is recorded at EGl, and the earliest atrial activation site at EG2. A, 11 is the anterograde conduction time from EG2 to EGl during atrioventricular reentrant tachycardia, which is equal to the tachycardia cycle length (CL.) minus Z (conduction time from Point P to EG2) Plus Y (conduction time from Point P to EGl). B, T2 is the rettrograde conduction time from EGl to EG2 during vent&&r Pacing at CL, which is equal to X (conduction time from EGl to Point P) Plus Z. C, for the wave front pro&ced by an extrastimuius delivered from EC1 to collide with the spontaneous orthodromic wave front at Point P, the extrastimulus should be deli&red when the spontaneous orthodromic wave front is located at Point Q, which lies by time X short of Point P. This indicates that the preexcitation index equals tbne X plus Y. lime X and Y can be computed mathematically, as shown in D. See text for details. AP = accessory pathway; AVN = atrioventricular node. Star indicates the pacing site.

THE AMERICAN JOURNAL OF CARDIOLOGY APRIL 15, 1991

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TABLE Pt. No.

I Electrophysiologic

Data

Typeof PSvr

PI (ms)

Tl (ms)

T2 (ms)

CL (ms)

Our Index (ms)

GroupA 1 25F 2 27M 3 30M 4 36M 5 39M 6 47M 7 49M 8 49M 9 52F 10 53M 11 62M 12 68M 13 39M 14 53M 15 6OF

CWPW WPW CWPW CWPW WPW CWPW WPW WPW WPW CWPW CWPW WPW AVNRT AVN RT AVNRT

40 70 60 60 40 50 60 10 80 110 70 60 110 100 190

200 160 160 290 200 250 170 190 220 230 300 200 240 230 440

130 160 220 160 140 130 180 130 150 210 180 150 180 160 180

300 270 320 400 310 340 300 310 310 350 420 300 320 300 450

30 50 60 50 30 40 50 10 60 90 60 50 100 90 170

Group 1 2 3 4

WPW WPW AVNRT AVNRT

-

220 190 370 260

110 130 120 110

270 260 390 265

60 60 100 105

Age (Y 0 &Sex

B 12M 19M 29F 45F

AVNRT = atrwentr~cular nodal reentrant tachycardia; c = concealed, CL = cycle length of paroxysmal supraventrlcular tachycardla: PI = preexatatlon Index; PSVT = paroxysmal supraventricular tachycardla; Tl = atrloventricular conductjon time during paroxysmal supraventncular tachycardla; T2 = ventnculoatrlal conduction time during right ventricular pacing at the cycle length; WPW = Wolff~Parkinson-White syndrome. Our Index IS computed as Tl + 72 -cycle length

the orthodromic wave front is expected to reach EGl, when the orthodromic wave front lies at point Q. This indicates that the preexcitation index equals time X plus Y. Time X plus Y cannot be determined by conventional electrophysiologic study, but can be calculated mathematically, as shown in Figure 1D. Our index calculated by this formula was compared with the preexcitation index determined by the extrastimulus technique in group A patients. Additionally, we tested whether our index could differentiate AV reentrant tachycardia from AV nodal reentrant tachycardia in group B patients, in whom retrograde atria1 preexcitation did not occur with the extrastimulus technique. Statistical analysis: Data are expressedas means f standard deviation. The relation between the preexcitation index and our index was evaluated by linear regression analysis. Statistical significance was set at p 75 ms occurred only with a left-sided free wall accessorypathway or dual AV nodal pathways, and a preexcitation index

A new method for estimating preexcitation index without extrastimulus technique and its usefulness in determining the mechanism of supraventricular tachycardia.

The preexcitation index has been shown to be useful in determining the mechanism of paroxysmal supraventricular tachycardia (SVT) and the site of the ...
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