Journal of Electrocardiology Vol. 31 No. 4 1998,

Inf luence of Right Ventricular Site of St imulat ion and Infarct Location on the

Inducibi l i ty of Ventricular Tachycardia in Pat ients With Coronary Artery Disease

Mark Harvey, MD, Rajiva Goyal, MD, Bradley P. Knight, MD, K. Ching Man, DO, S. Adam Strickberger, MD, and Fred Morady, MD

Abstract: No prior studies have evaluated the relationship between the site of right ventricular stimulation, the site of prior infarction, and the inducibility of ventricular tachycardia (VT). This study was performed to determine if the location of pathologic Q waves influences the inducibility of VT at various right ventricular sites in patients with coronary artery disease (CAD) and a history of myocardial infarction (MI). In 30 patients with a history of sustained, monomorphic VT, CAD, prior MI, and pathologic Q waves, programmed ventricular stimulation was performed at the right ventricular apex, septum, and outflow tract, in random order. There was electrocardiographic evidence of an MI that was inferior in 11 patients, anterior in 10 patients, and both inferior and anterior in 9 patients. Sustained, monomorphic VT was induced in 27 of 30 patients (90%). There were no significant differences among the three sites in the rate of inducibility of VT. The rate of inducible VT at each of the three right ventricular sites was not affected by the location of prior infarction. In conclusion, among patients with sustained, monomorphic VT, CAD, and a history of MI, the incidence of inducible sustained, monomorphic VT is not influenced by the location of prior infarction, regardless of whether pro- grammed ventricular stimulation is performed at the right ventricular apex, septum, or outflow tract. Key words: ventricular tachycardia, myocardial infarction, programmed ventricular stimulation.

In some patients wi th co ronary ar tery disease (CAD), the inducibili ty of ventr icular tachycardia (VT) by p r o g r a m m e d ventr icular s t imulat ion m a y

From the Department of Internal Medicine, Division of Cardiology, University of Michigan Medical Center, Ann Arbor, Michigan.

Reprint requests: Fred Morady, MD, University of Michigan Medical Center, 1500 East Medical Center Dr., BI-F245, Ann Arbor, MI 48109-0022.

Copyright © 1998 by Churchill Livingstone ® 0022-0736/98/3104-000255.00/0

depend on the site of st imulation, and it has been suggested that this may be due to the relat ionship of the s t imulat ion site to areas of myocard ia l scar (1-3). However , no prior studies have evaluated the relat ionship be tween the site of right ventric- ular st imulation, the site of prior infarction, and the inducibili ty of VT. This s tudy was pe r fo rmed to de termine w h e t h e r the locat ion of pathologic Q waves influences the inducibili ty of VT at various right ventr icular sites in patients wi th CAD and a his tory of myocard ia l infarct ion (MI).

278

Ventricular Tachycardia

Table 1. Results of Programmed Ventricular Stimulation at Three Right Ventricular Sites in 30 Patients

Apex Septum Outflow Tract

Inducibility rate (%) 90 87 90 Morphology of induced VT: 33/67 46/54 41/59

LBBB/RBBB (%) Cycle length of induced VT (ms) 340 -+ 48* 334 _+ 56 344 _+ 52

There were no significant differences between the three right ventricular sites. * Mean --_ standard deviation; LBBB, left bundle branch block; RBBB, right

bundle branch block; VT, ventricular tachycardia.

• Harveyet al. 279

Materials and Methods

Patient Characteristics

The subjects of this prospect ive study were 30 patients wi th a history ot sustained, m o n o m o r p h i c VT, CAD, prior MI, and pathologic Q waves w h o u n d e r w e n t an electrophysiology test. Patients w h o were deemed unsuitable for repeated inductions of VT requiring cardioversion were excluded. There were 26 m e n and 4 w o m e n (mean age, 64 + 11 years). The electrocardiogram (ECG) demons t ra ted Q-wave evidence of an old MI that was inferior in 11 patients, anter ior in 10 patients, and bo th infe- rior and anter ior in 9 patients. Coronary angiogra- phy demons t ra ted triple-vessel disease in 22, dou- ble-vessel disease in 3, and single-vessel disease in 5 patients. The m e a n left ventr icular ejection fraction was 0.34 +_ 0.12. Seven patients were being t reated wi th amiodarone at the t ime of the electrophysiol- ogy test; the remain ing patients were not being t reated wi th an an t ia r rhy thmic drug.

W h e n compared with a convent ional s t imulat ion protocol in patients wi th CAD, this accelerated protocol has been demons t ra ted to improve the specificity and efficiency of p r o g r a m m e d ventr icu- lar s t imulat ion wi thou t altering the yield of sus- tained, m o n o m o r p h i c VT (4). The endpoint of the s t imulat ion protocol at each of the three right ventr icular sites was the induct ion of sustained, m o n o m o r p h i c VT or comple t ion of the protocol. Sustained VT was defined as lasting 30 seconds or longer or requir ing te rmina t ion because of h e m o - dynamic compromise . W h e n e v e r possible, a 12- lead ECG was recorded during VT.

Analysis of Data

Values are expressed as m e a n _+ l s tandard deviation. Cont inuous variables were compared by analysis of variance, and discrete variables were compared by cont ingency table analysis. P values < .05 were considered significant.

Programmed Ventricular Stimulation Protocol

After in formed consent was obtained, pro- g r a m m e d ventr icular s t imulat ion was pe r fo rmed wi th a quadripolar electrode catheter posi t ioned sequential ly at three right ventr icular sites. In every patient, p r o g r a m m e d ventr icular s t imulat ion was pe r fo rmed at the right ventr icular apex, septum, and out f low tract, wi th the sequence de te rmined in r a n d o m fashion. The posit ion of the catheter was verified by f luoroscopy and by the QRS axis during pacing.

Pacing was pe r fo rmed at twice the diastolic threshold and wi th a pulse width of 2 ms, using a p rog rammab le s t imulator (Bloom Associates, Read- ing, PA). P rog rammed ventr icular s t imulat ion was pe r fo rmed wi th an accelerated protocol using three basic drive cycle lengths and four extrast imuli (4).

Results

Sustained, m o n o m o r p h i c VT was induced in 27 of 30 patients (90%). The inducibility rates of VT and the characteristics of the induced tachycardias at each of the three right ventr icular sites are shown in Table 1. There were no significant differences a m o n g the three sites in the rate of inducibility of VT, in the relative proport ions of left and right bundle b ranch block morpho logy of the induced VTs, or in the m e a n cycle length of the induced VTs.

The inducibility of VT at each of the three right ventr icular sites was not affected by the location of prior infarction (Table 2).

VT was uni formly inducible or un i formly not inducible at all three right ventr icular sites in 27 of 30 patients (90%). In two patients, VT was induc- ible at two of the three right ventr icular sites, and in

280 Journal of Electrocardiology Vol. 31 No. 4 October 1998

Table 2. Inducibility Rates of Sustained, Monomorphic Ventricular Tachycardia at Three Right Ventricular Sites According to Location of Pathologic Q Waves

Anterior Q Waves Inferior Q Waves Anterior & Inferior Q Waves Stimulation Site (10 Patients) (11 Patients) (9 Patients)

Apex (%) 100 91 78 Septum (%) 90 73 100 Outflow Tract (%) 100 82 89

There were no significant differences between any of the inducibility rates.

one patient only at one of the three right ventric- ular sites.

Discussion

Main Findings

The results of this study indicate that among patients with sustained, monomorph ic VT, CAD, and a history of MI, the inducibility of sustained, monomorph ic VT is not influenced by the location of prior transmural infaction, regardless of whether p rogrammed ventricular stimulation is performed at the right ventricular apex, septum, or outf low tract.

Infarct Location and Inducibility of VT

In an experimental study, the site of stimulation relative to the location of MI has been demon- strated to be important for the induction of VT (5). Factors such as the distance between the site of stimulation and the site of origin of VT, as well as the conduction properties and refractoriness ot the intervening myocardium, may influence the ability of p rogrammed stimulation in the right ventricle to induce VT.

The present study demonstrates no relationship between the site of right ventricular stimulation, the location of prior infarction, and the inducibility of monomorph ic VT. This finding is consistent with the results of a prior study that demonstrated that the distance from the right ventricular apex to the site of origin of VT, as determined by endocardial mapping, was not a major determinant of the inducibility of VT in patients with CAD (6). In the same study, there also was no correlation between the site of MI and the method of induction of VT (6). Therefore, in contrast to the findings in an

experimental model of infarction, there is no evi- dence that the location of an MI influences the inducibility of VT at various stimulation sites in patients with CAD.

Clinical Implications

Programmed ventricular stimulation to induce VT conventionally has been performed first at the right ventricular apex, then at a second or third right ventricular site if necessary. The results of this study demonstrate that in patients with CAD, there is no advantage to first performing stimulation at the right ventricular apex as opposed to the outf low tract or septum. The overall yield of monomorph ic VT does not differ among the three right ventricular sites and is not affected by the site of prior MI.

References

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2. Wellens H J J, Duren DR, Lie KI: Observations on mechanisms of ventricular tachycardia in man. Circu- lation 54:237, 1976

3. Josephson ME, Horowitz LN, Farshidi A, Kastor JA: Recurrent sustained ventricular tachycardia. I. Mech- anisms. Circulation 57:431, 1978

4. Hummel JD, Stickberger SA, Daoud E et al: Results and efficiency of programmed ventricular stimulation with four extrastimuli compared with one, two, and three extrastimuli. Circulation 90:2827, 1994

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