CLINICAL STUDIES
Clinical, Electrocardiographic and Electrophysiologic Observations in Patients With Paroxysmal Supraventricular Tachycardia
DELON WU, MD, FACC PABLO DENES, MD, FACC FERNANDO AFATlY.-LEON, MD, FACC RAMESH DHINGRA, MD, FACC CHRISTOPHER R.C. WYNDHAM, MD ROBERT BAUERNFEIND, tvlD PERVAIZE LATIF, MD KENNETH M. ROSEN, MD, FACC Chicago, Illinois
From the Section of Cardiology, Department of Medicine, Abraham Lincoln School of Medicine, Universlty of Illinois Cullege of wicine, Chicago, Illinois. This study w&supported In part by Traininc (fant PHS 0587946 tiom the U.S. Public Health-Service, Bethesda, karyland and Grant 08794-02 from the I(letiohal Institut@ of Health, Bethesda, Maryland. hQnuscript received September 6. 1977; revised manriscript received October 25,1977, :ccepted October 26. 1977. Address for reprints: hIon Wu, MD, Section of cardiology, University dflilinpis HOS~W,PO BOX 6998, Chicago, Illinois 60080.
Seventy-nine patients without velitricuiar preexcitation but with documented paroxysmal supraventricuiar tachycardia were analyzed. Eiectrophysioiogic studies swsted atrioventricuiar (A-V) nodal reentrance in 50 patients, reeflrance utilizing a concealed extranodal pathway in 9, sinus or atriai reentran$e in i and ectopic automatic tachycardia in 3. A definite mechaniv of tachycardia could not be defined in 10 patients (including 7 wh?+ !achycardia was not inducible). The three largest groups with indycible tachycardias were compared in regard to age, presence ‘M org@c Fart dikease, rate of tachycardia, functional bundle branch block dt$ng tachycardia and relation of the P wave and QRS cornpiex during tachycardia. A-V nodal reentrance was characterized by a narrow QFt$ con?piex and a P wave occurring sinluitaneousiy with the QRS complex during tachycardia. Reentrance utilizing a concealed extranodal pathway was characterized by young age, absence of organic he&t disease, fast heart rate, presence of bundle branch block during tachycardia and a P wave foilowing the QRS compiex durtng tachycardia. Sinoatriai reentraqce was characterized by frequent organic heart disease, a narrow QRS’compiex and a P wave in front of the QRS complex during tachy&rd/a. in conciuston, i mechanism of parqtysmai supraventricular tachycardia could be defined in’most patients. Observations of clinical and eiectrocardipgraphic fe’atures in these patients should allow prediction of the mechanism 61 the tachy;cardia.
In the early 1970’s it was demonstrated that most patients with paroxysmal supraventricular tachycardia responded to atria1 coupled stimulation with induction of atria1 echoes and reproduction of tachycardia.1-3 It was noted that induction of echoes was related to achievement of a critical atrioventricular (A-V) nodal conduction time, suggesting A-V nodal reentrance. It tias implied that most or all paroxysmal supraventricular tachycardia occurring in patients without ventricular preexcitation reflected sustained A-V nodal reentrance. Subsequent studies demonstrated additional electrophysiologic mechanisms responsible for the occurrence of tachycardia, such as A-V reentrance utilizing concealed extranodal pathways,@ sinus reentrance,sJe atria1 reentrancelo and atria1 ectopic firing.lrJ2 Until the present study, there have been no investigations of a large series of patients with paroxysmal supraventricular tachycardia (without manifest preexcitation) in whom reproducibility and the electrophysiologic mechanism responsible for the arrhythmia’were systematically studied. In addition, the clinical and electrocardiographic features associated with specific mechanisms of paroxysmal tachycardia have not been delineated. In this study, we report clinical electrocardiographic
May 22, 1978
The American Journal of CARDIOLOGY
Volume 41
1045
PAROXYSMAL
SUPRAVENTRICULAR TACHYCARDIA-WU
ET AL
observations in a large consecutively studied series of patients with paroxysmal supraventricular tachycardia and relate these findings to result8 of electrophysiologic study. Methods Patient selection: Criteria for inclusion in the study included (1) a history of electrocardiographically documented recurrent paroxysmal supraventricular tachycardia13; (2) absence of evidence of preexcitation in all available electrocardiograms (most patients had four or more electrocardiograms for review); and (3) performance of extensive electrophysiologic studies using programmed atria1 and ventricular stimulation and endocardial mapping during induced tachycardia. Seventy-nine patients studied between July 1972 and January 1977 fulfilled these criteria. The group consisted of 45 male and 34 female subjects aged 12 to 81 years (mean f standard deviation 52 f 16). Electrophysiologic studies: These studies were performed during the postabsorptive, nonsedated state. Informed written consent was obtained from all patients. Cardiac drugs were discontinued at least 48 hours before the study. A tripolar electrode catheter was percutaneously passed through a femoral vein and placed across the tricuspid valve for His bundle recording.l* A second hexapolar catheter was placed at the right ventricular apex through an antecubital vein. The distal two electrodes (tip) were utilized for ventricular pacing, the middle two electrodes (10 cm from the tip) for recording of right atria1 electrograms, and the proximal two electrodes (13.5 cm from the tip) for right atria1 pacing. A third bipolar catheter with an interelectrode distance of 1 cm was positioned in the coronary sinus for mapping of retrograde atria1 activation sequence during induced tachycardia. Multiple surface electrocardiographic leads as well as intracardiac electrograms were recorded simultaneously on a multichannel oscilloscopic photographic recorder (Electronics for Medicine DR-16) at paper speeds of 100 and 200 mm/set. Stimuli were provided by a programmable digital stimulator (manufactured by M. Bloom, Narbeth, Pennsylvania) with a strength of approximately twice diastolic threshold and a duration of 2 msec. Electrophysiologic studies included the following15-18: (1) Incremental atria1 pacing, (2) atria1 extrastimulus testing at two or more cycle lengths, (3) incremental ventricular pacing, (4) ventricular extrastimulus testing at one or more cycle lengths, (5) mapping of retrograde atria1 activation sequence during paroxysmal supraventricular tachycardia from multiple sites including low septal right atrium, coronary sinus (proximal, middle and distal), low lateral right atrium and high right atrium, and (6) atria1 or ventricular extrastimulus testing, or both, during tachycardia. Retrograde stimulation studies were not performed in patients studied before 1973. Statistical analysis: Clinical and electrocardiographic data among groups as a whole were analyzed statistically utilizing one way classification analysis of variance or multiple contingency tables. Individual groups were then compared with Student’s t test or the chi square test. Results In ‘72 of the 79 patients, paroxysmal supraventricular tachycardia was reproduced in the cardiac catheterization laboratory, allowing delineation of the mechanism of the arrhythmia as described later. In seven pa-
tients, arrhythmia could not be reproduced, so that determination of a mechanism was impossible.
1046
May22,
1978
The American
Journal
of CARDIOLOGY
Electrophysiologic Characteristics
A-V nodal reentrant tachycardia: Fifty of the 72 patients (69 percent) had A-V nodal reentrant paroxysmal tachycardia diagnosed utilizing combinations of the following diagnostic criteria: (1) induction of tachycardia related to achievement of a critical A-H (atrio-His bundle) delay, with both incremental atria1 pacing and atria1 extrastimulus testing (48 patients) 3J5J7Jg-21; (2) demonstration of discontinuous Al-A2 and HI-H2 curves, suggesting dual A-V nodal pathways, with induction of tachycardia relating to anterograde block in the fast pathway (34 patients)15Jg-27; (3) induction of tachycardia related to achievement of a critical V-A (ventriculoatrial) delay, during incremental ventricular pacing and with ventricular extrastimulus testing (seven patients)15J7>28; and (4) demonstration of discontinuous VI-V2, Al-A2 curves, suggesting retrograde dual A-V nodal pathways, with induction of tachycardia relating to retrograde block in the A-V nodal fast pathway (two patients).28 Because criteria (1) and (2) could be fulfilled in patients with concealed extranodal pathways, one or more of the following additional criteria were required for the diagnosis of A-V nodal reentry: (5) demonstration of atria1 activation before or simultaneous with onset of ventricular activation during tachycardia, suggesting that the ventricles were not a distal common pathway for reentrance (32 patients)17; (6) normal retrograde atria1 activation sequence during tachycardia with the low septal right atrium being activated earlier than all other atria1 recording sites (50 patients) 18y2g;(7) increase of V-A interval with incremental ventricular pacing with type I V-A block at a critical rate, suggesting retrograde A-V nodal conduction (16 patients)15J7; and (8) demonstration of His bundle activation (Hz) preceding the atria1 activation (AZ) with ventricular extrastimulus testing during ventricular pacing or paroxysmal supraventricular tachycardia, or both, suggesting retrograde A-V nodal conduction (21 patients).17 Reentrance tachycardia utilizing a concealed extranodal pathway: Nine of the 72 patients (13 percent) had A-V reentrance utilizing a concealed extranodal pathway conducting in retrograde manner on the basis of combinations of the following criteria: (1) induction of tachycardia related to achievement of a critical A-V conduction time (nine patients),4-8 (2) capture of the atria with a ventricular extrastimulus delivered during tachycardia when the His bundle was refractory (five patients),@ (3) increase in V-A interval during tachycardia with functional bundle branch block ispsilateral to a concealed extranodal pathway (five patients),b-8 (4) fixed V-A interval during incremental ventricular pacing (nine patients),8J7>30 and (5) abnormal retrograde atria1 activation sequence during tachycardia with the left atrium being activated before the low septal right atrium (nine patients).%16 With these criteria, all nine patients had evidence of a concealed left-sided extranodal pathway that participated in the supraventricular tachycardia. None of the nine
Volume
41
PAROXYSMAL
patients had discontinuous Al-As or Hi-Hz curves. One of the nine patients manifested anterograde preexcitation only when the mid or distal coronary sinus was stimulated. Sinus or atria1 reentrance tachycardia: Seven of the 72 patients (10 percent) had sinus or atria1 reentrance diagnosed utilizing combinations of the following diagnostic criteria: (1) Induction of tachycardia was related to achievement of critical atrial rates and critical Al-As coupling intervals.gJOB1 (2) Induction of tachycardia was not related to achievement of critical A-H, A-V or V-A conduction time (seven patients).10,31 (3) Induction of tachycardia occurred with ventricular stimulation (extrastimulus technique or incremental pacing) upon achievement of critical atria1 coupling intervals (three patients). With this type of induction, the sequence of induction was Vs - Az - As (first beat of tachycardia). This was in contrast to induction of tachycardia from the ventricles with A-V nodal reentrance or A-V reentrance utilizing an anomalous pathway conducting in retrograde manner, where the sequence was V2 - A2 - Vs (first beat of tachycardia).1°r3i (4) Induction of tachycardia occurred with initiating atrial stimuli that were blocked proximal to the His bundle recording site (five patients).1°T31 (5) Tachycardia was sustained despite A-V block proximal to the His bundle recording site (three patients).lOal (6) V-A conduction was absent, excluding concealed extranodal pathways and A-V nodal reentrance.10*31~32 A diagnosis of sinus nodal reentrance was made when atria1 activation sequence and P wave contour resembled those of sinus P waves (two patients). l”y31A diagnosis of atria1 reentrance was made when atria1 activation sequence and P wave contour were different from those of sinus P waves (five patients).i0v31 Automatic ectopic tachycardia: Three of the 72 patients (4 percent) had a diagnosis of automatic ectopic tachycardia (atrial focus in 1 and His bundle in 2). The criteria for diagnosis of automatic ectopic tachycardia included the following: (1) spontaneous onset of tachycardia not related to any initiating event, either critical rates or coupling intervals (three patients),10J2p31 (2) spontaneous tachycardia during study with the initiating beat being identical to subsequent beats of tachycardia (three patients),11J2131 (3) inability to initiate and terminate the tachycardia with atrial and ventricular stimulations,‘lJ2B1 (4) demonstration of ectopic focus recovery time after cessation of overdrive pacing (three patients),12y33 and (5) absence of dual A-V nodal pathways or concealed extranodal pathways (three patients). Undefined mechanism of tachycardia: In 3 of the 72 patients (4 percent), differentiation between A-V nodal reentrance and reentrance utilizing a concealed extranodal pathway could not be made. In these three patients, induction of tachycardia was related to achievement of a critical A-H interval (not independent of a critical A-V interval). Because all had atria1 activation occurring after ventricular activation during tachycardia and none had retrograde stimulation
SUPRAVENTRICULAR
TACHYCARDIA-WU
ET AL
studies, the presence or absence of a concealed extranodal pathway could not be determined. Selected Clinical Characteristics Selected clinical characteristics were analyzed and compared in the three largest groups: those with A-V nodal reentrance, those with A-V reentrance utilizing concealed extranodal pathways, and those with sinoatria1 reentrance. Age and sex: The mean age (f standard error of the mean) was 55 f 2 years (range 24 to 81) among patients with A-V nodal reentrance, 40 f 6 years (range 12 to 69) among patients with concealed extranodal pathways and 49 f 7 years (range 13 to 63) among patients with sinus or atria1 reentrance. Patients with concealed extranodal pathways were significantly younger than those with A-V nodal reentrance (P
Clinical, Electrocardiographic and Electrophysiologic Observations in Patients With Paroxysmal Supraventricular Tachycardia
DELON WU, MD, FACC PABLO DENES, MD, FACC FERNANDO AFATlY.-LEON, MD, FACC RAMESH DHINGRA, MD, FACC CHRISTOPHER R.C. WYNDHAM, MD ROBERT BAUERNFEIND, tvlD PERVAIZE LATIF, MD KENNETH M. ROSEN, MD, FACC Chicago, Illinois
From the Section of Cardiology, Department of Medicine, Abraham Lincoln School of Medicine, Universlty of Illinois Cullege of wicine, Chicago, Illinois. This study w&supported In part by Traininc (fant PHS 0587946 tiom the U.S. Public Health-Service, Bethesda, karyland and Grant 08794-02 from the I(letiohal Institut@ of Health, Bethesda, Maryland. hQnuscript received September 6. 1977; revised manriscript received October 25,1977, :ccepted October 26. 1977. Address for reprints: hIon Wu, MD, Section of cardiology, University dflilinpis HOS~W,PO BOX 6998, Chicago, Illinois 60080.
Seventy-nine patients without velitricuiar preexcitation but with documented paroxysmal supraventricuiar tachycardia were analyzed. Eiectrophysioiogic studies swsted atrioventricuiar (A-V) nodal reentrance in 50 patients, reeflrance utilizing a concealed extranodal pathway in 9, sinus or atriai reentran$e in i and ectopic automatic tachycardia in 3. A definite mechaniv of tachycardia could not be defined in 10 patients (including 7 wh?+ !achycardia was not inducible). The three largest groups with indycible tachycardias were compared in regard to age, presence ‘M org@c Fart dikease, rate of tachycardia, functional bundle branch block dt$ng tachycardia and relation of the P wave and QRS cornpiex during tachycardia. A-V nodal reentrance was characterized by a narrow QFt$ con?piex and a P wave occurring sinluitaneousiy with the QRS complex during tachycardia. Reentrance utilizing a concealed extranodal pathway was characterized by young age, absence of organic he&t disease, fast heart rate, presence of bundle branch block during tachycardia and a P wave foilowing the QRS compiex durtng tachycardia. Sinoatriai reentraqce was characterized by frequent organic heart disease, a narrow QRS’compiex and a P wave in front of the QRS complex during tachy&rd/a. in conciuston, i mechanism of parqtysmai supraventricular tachycardia could be defined in’most patients. Observations of clinical and eiectrocardipgraphic fe’atures in these patients should allow prediction of the mechanism 61 the tachy;cardia.
In the early 1970’s it was demonstrated that most patients with paroxysmal supraventricular tachycardia responded to atria1 coupled stimulation with induction of atria1 echoes and reproduction of tachycardia.1-3 It was noted that induction of echoes was related to achievement of a critical atrioventricular (A-V) nodal conduction time, suggesting A-V nodal reentrance. It tias implied that most or all paroxysmal supraventricular tachycardia occurring in patients without ventricular preexcitation reflected sustained A-V nodal reentrance. Subsequent studies demonstrated additional electrophysiologic mechanisms responsible for the occurrence of tachycardia, such as A-V reentrance utilizing concealed extranodal pathways,@ sinus reentrance,sJe atria1 reentrancelo and atria1 ectopic firing.lrJ2 Until the present study, there have been no investigations of a large series of patients with paroxysmal supraventricular tachycardia (without manifest preexcitation) in whom reproducibility and the electrophysiologic mechanism responsible for the arrhythmia’were systematically studied. In addition, the clinical and electrocardiographic features associated with specific mechanisms of paroxysmal tachycardia have not been delineated. In this study, we report clinical electrocardiographic
May 22, 1978
The American Journal of CARDIOLOGY
Volume 41
1045
PAROXYSMAL
SUPRAVENTRICULAR TACHYCARDIA-WU
ET AL
observations in a large consecutively studied series of patients with paroxysmal supraventricular tachycardia and relate these findings to result8 of electrophysiologic study. Methods Patient selection: Criteria for inclusion in the study included (1) a history of electrocardiographically documented recurrent paroxysmal supraventricular tachycardia13; (2) absence of evidence of preexcitation in all available electrocardiograms (most patients had four or more electrocardiograms for review); and (3) performance of extensive electrophysiologic studies using programmed atria1 and ventricular stimulation and endocardial mapping during induced tachycardia. Seventy-nine patients studied between July 1972 and January 1977 fulfilled these criteria. The group consisted of 45 male and 34 female subjects aged 12 to 81 years (mean f standard deviation 52 f 16). Electrophysiologic studies: These studies were performed during the postabsorptive, nonsedated state. Informed written consent was obtained from all patients. Cardiac drugs were discontinued at least 48 hours before the study. A tripolar electrode catheter was percutaneously passed through a femoral vein and placed across the tricuspid valve for His bundle recording.l* A second hexapolar catheter was placed at the right ventricular apex through an antecubital vein. The distal two electrodes (tip) were utilized for ventricular pacing, the middle two electrodes (10 cm from the tip) for recording of right atria1 electrograms, and the proximal two electrodes (13.5 cm from the tip) for right atria1 pacing. A third bipolar catheter with an interelectrode distance of 1 cm was positioned in the coronary sinus for mapping of retrograde atria1 activation sequence during induced tachycardia. Multiple surface electrocardiographic leads as well as intracardiac electrograms were recorded simultaneously on a multichannel oscilloscopic photographic recorder (Electronics for Medicine DR-16) at paper speeds of 100 and 200 mm/set. Stimuli were provided by a programmable digital stimulator (manufactured by M. Bloom, Narbeth, Pennsylvania) with a strength of approximately twice diastolic threshold and a duration of 2 msec. Electrophysiologic studies included the following15-18: (1) Incremental atria1 pacing, (2) atria1 extrastimulus testing at two or more cycle lengths, (3) incremental ventricular pacing, (4) ventricular extrastimulus testing at one or more cycle lengths, (5) mapping of retrograde atria1 activation sequence during paroxysmal supraventricular tachycardia from multiple sites including low septal right atrium, coronary sinus (proximal, middle and distal), low lateral right atrium and high right atrium, and (6) atria1 or ventricular extrastimulus testing, or both, during tachycardia. Retrograde stimulation studies were not performed in patients studied before 1973. Statistical analysis: Clinical and electrocardiographic data among groups as a whole were analyzed statistically utilizing one way classification analysis of variance or multiple contingency tables. Individual groups were then compared with Student’s t test or the chi square test. Results In ‘72 of the 79 patients, paroxysmal supraventricular tachycardia was reproduced in the cardiac catheterization laboratory, allowing delineation of the mechanism of the arrhythmia as described later. In seven pa-
tients, arrhythmia could not be reproduced, so that determination of a mechanism was impossible.
1046
May22,
1978
The American
Journal
of CARDIOLOGY
Electrophysiologic Characteristics
A-V nodal reentrant tachycardia: Fifty of the 72 patients (69 percent) had A-V nodal reentrant paroxysmal tachycardia diagnosed utilizing combinations of the following diagnostic criteria: (1) induction of tachycardia related to achievement of a critical A-H (atrio-His bundle) delay, with both incremental atria1 pacing and atria1 extrastimulus testing (48 patients) 3J5J7Jg-21; (2) demonstration of discontinuous Al-A2 and HI-H2 curves, suggesting dual A-V nodal pathways, with induction of tachycardia relating to anterograde block in the fast pathway (34 patients)15Jg-27; (3) induction of tachycardia related to achievement of a critical V-A (ventriculoatrial) delay, during incremental ventricular pacing and with ventricular extrastimulus testing (seven patients)15J7>28; and (4) demonstration of discontinuous VI-V2, Al-A2 curves, suggesting retrograde dual A-V nodal pathways, with induction of tachycardia relating to retrograde block in the A-V nodal fast pathway (two patients).28 Because criteria (1) and (2) could be fulfilled in patients with concealed extranodal pathways, one or more of the following additional criteria were required for the diagnosis of A-V nodal reentry: (5) demonstration of atria1 activation before or simultaneous with onset of ventricular activation during tachycardia, suggesting that the ventricles were not a distal common pathway for reentrance (32 patients)17; (6) normal retrograde atria1 activation sequence during tachycardia with the low septal right atrium being activated earlier than all other atria1 recording sites (50 patients) 18y2g;(7) increase of V-A interval with incremental ventricular pacing with type I V-A block at a critical rate, suggesting retrograde A-V nodal conduction (16 patients)15J7; and (8) demonstration of His bundle activation (Hz) preceding the atria1 activation (AZ) with ventricular extrastimulus testing during ventricular pacing or paroxysmal supraventricular tachycardia, or both, suggesting retrograde A-V nodal conduction (21 patients).17 Reentrance tachycardia utilizing a concealed extranodal pathway: Nine of the 72 patients (13 percent) had A-V reentrance utilizing a concealed extranodal pathway conducting in retrograde manner on the basis of combinations of the following criteria: (1) induction of tachycardia related to achievement of a critical A-V conduction time (nine patients),4-8 (2) capture of the atria with a ventricular extrastimulus delivered during tachycardia when the His bundle was refractory (five patients),@ (3) increase in V-A interval during tachycardia with functional bundle branch block ispsilateral to a concealed extranodal pathway (five patients),b-8 (4) fixed V-A interval during incremental ventricular pacing (nine patients),8J7>30 and (5) abnormal retrograde atria1 activation sequence during tachycardia with the left atrium being activated before the low septal right atrium (nine patients).%16 With these criteria, all nine patients had evidence of a concealed left-sided extranodal pathway that participated in the supraventricular tachycardia. None of the nine
Volume
41
PAROXYSMAL
patients had discontinuous Al-As or Hi-Hz curves. One of the nine patients manifested anterograde preexcitation only when the mid or distal coronary sinus was stimulated. Sinus or atria1 reentrance tachycardia: Seven of the 72 patients (10 percent) had sinus or atria1 reentrance diagnosed utilizing combinations of the following diagnostic criteria: (1) Induction of tachycardia was related to achievement of critical atrial rates and critical Al-As coupling intervals.gJOB1 (2) Induction of tachycardia was not related to achievement of critical A-H, A-V or V-A conduction time (seven patients).10,31 (3) Induction of tachycardia occurred with ventricular stimulation (extrastimulus technique or incremental pacing) upon achievement of critical atria1 coupling intervals (three patients). With this type of induction, the sequence of induction was Vs - Az - As (first beat of tachycardia). This was in contrast to induction of tachycardia from the ventricles with A-V nodal reentrance or A-V reentrance utilizing an anomalous pathway conducting in retrograde manner, where the sequence was V2 - A2 - Vs (first beat of tachycardia).1°r3i (4) Induction of tachycardia occurred with initiating atrial stimuli that were blocked proximal to the His bundle recording site (five patients).1°T31 (5) Tachycardia was sustained despite A-V block proximal to the His bundle recording site (three patients).lOal (6) V-A conduction was absent, excluding concealed extranodal pathways and A-V nodal reentrance.10*31~32 A diagnosis of sinus nodal reentrance was made when atria1 activation sequence and P wave contour resembled those of sinus P waves (two patients). l”y31A diagnosis of atria1 reentrance was made when atria1 activation sequence and P wave contour were different from those of sinus P waves (five patients).i0v31 Automatic ectopic tachycardia: Three of the 72 patients (4 percent) had a diagnosis of automatic ectopic tachycardia (atrial focus in 1 and His bundle in 2). The criteria for diagnosis of automatic ectopic tachycardia included the following: (1) spontaneous onset of tachycardia not related to any initiating event, either critical rates or coupling intervals (three patients),10J2p31 (2) spontaneous tachycardia during study with the initiating beat being identical to subsequent beats of tachycardia (three patients),11J2131 (3) inability to initiate and terminate the tachycardia with atrial and ventricular stimulations,‘lJ2B1 (4) demonstration of ectopic focus recovery time after cessation of overdrive pacing (three patients),12y33 and (5) absence of dual A-V nodal pathways or concealed extranodal pathways (three patients). Undefined mechanism of tachycardia: In 3 of the 72 patients (4 percent), differentiation between A-V nodal reentrance and reentrance utilizing a concealed extranodal pathway could not be made. In these three patients, induction of tachycardia was related to achievement of a critical A-H interval (not independent of a critical A-V interval). Because all had atria1 activation occurring after ventricular activation during tachycardia and none had retrograde stimulation
SUPRAVENTRICULAR
TACHYCARDIA-WU
ET AL
studies, the presence or absence of a concealed extranodal pathway could not be determined. Selected Clinical Characteristics Selected clinical characteristics were analyzed and compared in the three largest groups: those with A-V nodal reentrance, those with A-V reentrance utilizing concealed extranodal pathways, and those with sinoatria1 reentrance. Age and sex: The mean age (f standard error of the mean) was 55 f 2 years (range 24 to 81) among patients with A-V nodal reentrance, 40 f 6 years (range 12 to 69) among patients with concealed extranodal pathways and 49 f 7 years (range 13 to 63) among patients with sinus or atria1 reentrance. Patients with concealed extranodal pathways were significantly younger than those with A-V nodal reentrance (P
