(Circulation. 1997;95:2668-2676.)
© 1997 American Heart Association, Inc.
Articles |
Body-Surface QRST Integral Mapping
Arrhythmogenic Right Ventricular Dysplasia Versus Idiopathic Right Ventricular Tachycardia
the Department of Cardiology, Heart-Lung Institute, University Hospital Utrecht, Netherlands (H.A.P.P., B.A.S., E.F.D.W., R.N.W.H., E.O.R. de M.); the Section of Cardiac Electrophysiology, Department of Medicine, and the Cardiovascular Research Institute, University of California, San Francisco (A.S.); and the Department of Medical Physics, Academic Medical Center, Amsterdam, Netherlands (C.A.G.).
Correspondence to Heidi A.P. Peeters, MD, Department of Cardiology, Heart-Lung Institute, University Hospital Utrecht, Heidelberglaan 100, 3584 CX Utrecht, The Netherlands. E-mail j.a.vangestel{at}hli.azu.nl
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Abstract |
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Background Ventricular tachycardia originating in the right ventricle may arise in the presence or absence of structural heart disease. The two main causes of right ventricular tachycardia are arrhythmogenic right ventricular dysplasia (ARVD) and idiopathic right ventricular tachycardia (IRVT) originating from the outflow tract. This study was carried out to determine whether body-surface QRST integral mapping can differentiate patients with ARVD from patients with IRVT.
Methods and Results Body-surface QRST integral maps were obtained during sinus rhythm in 8 patients with ARVD, 8 patients with IRVT, and 27 healthy control subjects. QRST integral maps were analyzed both visually and mathematically. All control subjects had a normal dipolar QRST integral map. In all patients with ARVD, a specific dipolar QRST integral map with an abnormally large negative area covering the entire inferior and right anterior thorax was recorded. In 6 of 8 patients with IRVT, a normal map pattern was found, whereas the remaining 2 patients showed an abnormally large negative area on the right anterior thorax.
Conclusions Patients with ARVD display a specific abnormal QRST integral map that may be related to delayed repolarization in the structurally abnormal right ventricle. The majority of patients with IRVT demonstrate a normal QRST integral map. A slightly abnormal QRST integral map was noted in 2 of 8 patients with IRVT, which may be related to minor structural abnormalities, undetectable by the present routine diagnostic techniques. These preliminary results indicate that body-surface QRST integral mapping may become an important diagnostic tool to differentiate patients with ARVD from those with IRVT.
Key Words: cardiomyopathy • electrocardiography • electrophysiology • mapping • arrhythmia
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Introduction |
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Ventricular tachycardia originating in the right ventricle may arise in the presence or absence of demonstrable structural heart disease. The two main patient groups in which right-sided VT occurs are patients with ARVD and patients with IRVT originating in the RVOT. The clinical characteristics are often very similar, and therefore, a distinction between these two groups may be difficult. It is important, however, to make the correct diagnosis because of significant differences in treatment and long-term prognosis and because of the possible genetic causes of ARVD.1
ARVD is characterized by replacement of ventricular myocardial fibers by fibrous and fatty tissue combined with the occurrence of ventricular arrhythmias.2 3 4 Diagnosis relies on the clinical demonstration of structural, functional, and electrophysiological abnormalities.5 6 Abnormal depolarization may cause 
waves or localized prolongation of the QRS complex on the standard 12-lead ECG2 3 or late potentials on the signal-averaged ECG7 during sinus rhythm. Although the 12-lead ECG most commonly demonstrates right precordial T-wave inversion,3 to date little is known about the abnormal repolarization process in patients with ARVD. In IRVT originating from the RVOT, VT occurs in the absence of apparent structural heart disease.8 The underlying mechanism of this arrhythmia is thought to be cAMP-mediated triggered activity.9 No specific ECG abnormality can be demonstrated.8
Body-surface QRST integral mapping has been shown to be a useful noninvasive method to assess the spatial distribution of primary ventricular recovery properties.10 11 Several studies have demonstrated that body-surface QRST integral mapping is superior to the standard 12-lead ECG in the detection of abnormal ventricular repolarization in patients at risk for developing life-threatening ventricular arrhythmias.12 13 14 15
The aim of the present study was to assess spatial ventricular repolarization properties in patients with ARVD and IRVT and to examine whether body-surface QRST integral mapping may be a useful additional diagnostic tool to differentiate these two patient groups. In addition, QRST integral map findings were compared with ECG parameters determined on the 12-lead ECG to assess whether abnormal map patterns could be related to specific abnormalities on the 12-lead ECG.
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Methods |
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Study Population
A group of 8 patients with ARVD, a group of 8 patients with IRVT, and a control group of 27 healthy volunteers were studied. Informed consent was obtained from all patients and control subjects. Evaluation in all patients with ARVD or IRVT included history, physical examination, laboratory tests, chest radiograph, 12-lead ECG recording, 24-hour Holter monitoring, exercise stress testing, two-dimensional and color Doppler echocardiography, and an electrophysiological study including catheter mapping in all but 1 patient with ARVD. Patients with ARVD, in addition, underwent right and left ventricular cineangiography in the right and left anterior oblique views and coronary angiography. In a subset of patients with IRVT, biplane right and left ventricular cineangiography (2 patients), coronary angiography (2 patients), and endomyocardial biopsy (1 patient) were also performed. All control subjects underwent physical examination, 12-lead ECG recording, and echocardiography. In this study, sustained VT was defined as lasting at least 30 seconds or if lasting <30 seconds, leading to loss of consciousness. Otherwise, a VT was defined as nonsustained.
Patients with ARVD. There were 7 men and 1 woman with ARVD (mean age, 38±9 years; range, 22 to 52 years). All patients had symptomatic ventricular arrhythmias. The diagnosis of ARVD was based on echocardiographic and angiographic demonstration of characteristic localized or global structural and functional abnormalities of the right ventricle. Left ventricular echocardiograms and cineangiograms were normal in all patients. All patients fulfilled the criteria for diagnosis of ARVD.6 Familial involvement could be demonstrated only in patient 4, whose brother had died suddenly at the age of 17 years and in whom ARVD was diagnosed at autopsy. Six of 8 patients had previously developed recurrent spontaneous monomorphic sustained VT that deteriorated into ventricular fibrillation in 1 patient. In these 6 patients, 11 different spontaneous monomorphic VT configurations (clinical arrhythmias) were documented while the patients were off antiarrhythmic drugs. The remaining 2 patients had cardiac arrest due to ventricular fibrillation as the first manifestation of the disease. All spontaneously occurring arrhythmias were inducible by programmed electrical stimulation. Characteristics of the patients with ARVD are shown in Table 1
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Patients with IRVT. This group consisted of 3 men and 5 women (mean age, 40±11 years; range, 26 to 59 years) suffering from spontaneous monomorphic IRVT with a left bundle-branch block morphology. Catheter mapping showed that all VTs arose from the RVOT. Diagnostic procedures showed normal findings in all patients. In each patient, only one spontaneous VT could be recorded. The VT occurred repetitively in nonsustained salvos in 4 patients and was sustained during exercise in the other 4 patients. The clinical VT was inducible by programmed electrical stimulation in only 1 patient.
Control subjects. The control group consisted of 27 healthy volunteers, 17 men and 10 women (mean age, 33±14 years; range, 17 to 62 years). Diagnostic tests were normal in all subjects.
ECG Data Acquisition and Processing
Body-surface mapping and 12-lead ECG recording were performed during sinus rhythm with a portable computerized mapping system and a 62-lead electrode set. In each patient, antiarrhythmic medication was discontinued for at least 5 drug half-lives. The control subjects did not use any medication. Unipolar lead recordings from 62 torso sites (Fig 1A) and a standard 12-lead ECG were obtained simultaneously, with Wilson's central terminal used as reference. The electrode set was connected to a front end containing 64 miniature ECG preamplifiers and a 14-bit analog-to-digital converter with a sampling rate of 1000 Hz. Digitized data were optically transmitted to a 486 microcomputer for data acquisition and storage. This computer was connected to a Commodore Amiga 1200 microcomputer that was used for processing, analysis, and graphic display of the data. Baseline correction was performed with an interpolation algorithm by manual selection of an isoelectric time instant preceding the P wave and after the end of the T wave. A mean of 2.3±1.6 leads per patient with unsatisfactory signal quality were rejected and substituted by values computed from neighboring leads. QRS onset was determined as the time instant at which one of the extremes exceeded ±0.05 mV. T-wave offset was defined as the time instant at which one of the extreme values declined below ±0.05 mV. Finally, QRST integral maps were computed by use of the sum of all potentials from QRS onset to T-wave offset in each lead (Fig 1B).
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Data Analysis
Body-surface mapping. Values are given as the mean±SD. Individual QRST integral maps of patients with ARVD and IRVT were visually compared with each other and with the computed mean QRST integral map of the control group. A mean QRST integral map was also computed for each of the two patient groups. The mean QRST integral map was calculated by dividing the sum of the values obtained at each lead point in the group by the number of subjects in that group. Visual analysis was focused on the location and mutual distance of the extremes and the morphology of the zero line. Two quantitative techniques were used to assess pattern differences in patients with ARVD or IRVT compared with the mean map obtained in the control group. First, to obtain a global overview of the group differences, the mean QRST integral maps of the three groups were mathematically compared by calculating a correlation coefficient between a pair of maps (normalized inner product) according to a previously described method.16 Second, to assess whether the QRST integral map in a given patient was statistically different from the mean map obtained in the control group, the mean QRST integral map ±2 SD of the control group was subtracted from the QRST integral map of each individual patient with ARVD or IRVT. The resulting departure map contains a departure area that represents the torso region in which a statistically significant deviation from the normal QRST value occurs.17 Thus, this quantitative technique allows highlighting of the regional differences in QRST integral pattern of individual patients with ARVD and IRVT.
12-lead ECG. Data are given as the mean±SD. Standard 12-lead ECGs of patients with ARVD or IRVT and the control subjects were randomly analyzed by two electrophysiologists who were blinded to all patient information. In case of conflicting analysis, discussion led to mutual consent. The 12-lead ECGs of the control group were all within normal limits. The QT interval was determined manually in both patient groups and in the control subjects. In 0.6±0.7 leads per individual, the QT interval was not measurable because the end of the T wave could not be clearly determined. QT dispersion on the 12-lead ECG was calculated for each individual by subtracting the shortest QT interval from the longest QT interval. QT dispersion of more than the mean value in the control group plus 2 SD was considered abnormal. The mean QT dispersion in the control group was 32±12 ms. Therefore, abnormal QT dispersion was defined at 
56 ms.
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Results |
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Qualitative Analysis of Body-Surface QRST Integral Maps
Control subjects. In all control subjects, a normal dipolar QRST integral map pattern was found, featuring a negative extreme in the right upper sternal area and a positive extreme in the left mammary region.18 This typical normal repolarization pattern is characterized by an inferior and leftward direction of the electromotive force (Fig 1
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Patients with ARVD. All patients with ARVD demonstrated an abnormal dipolar QRST integral map pattern consisting of a large area with negative potentials covering the right anterior and entire inferior thorax. In addition, the minimum was located at a lower than normal position in the middle anterior region, whereas the maximum had the same position as in the control group but was contained in a much smaller area, with positive potentials on the left axillary region and upper back. As a consequence, the electromotive force during repolarization was oriented in a leftward and horizontal or superior direction. A typical example of this QRST integral map pattern, which was observed in 7 of 8 patients, is shown in Fig 2A. In the remaining patient (patient 2), a variant map pattern was observed in which the area with positive potentials was more extensive and reached the inferior border of the map (Fig 2B).
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Patients with IRVT. Six of the 8 patients with IRVT showed a QRST integral map pattern similar to that found in the control group (Fig 3A). In two patients (patients 1 and 8), there was a larger area with negative isointegrals covering the right anterior and posterior sides of the thorax (Fig 3B), although much less extensive than the negative area observed in the ARVD group. A rather broad positive area reached the inferior border of the map. The negative extreme also displayed a lower position on the middle anterior chest, resulting in a horizontal and leftward direction of the electromotive repolarization force.
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Comparison of mean QRST integral maps. The mean QRST integral maps of the control group, the ARVD group, and the IRVT group are depicted in Fig 4 to demonstrate the overall group differences. The most prominent difference is the extensive distribution of the negative area in the mean map of the ARVD group (Fig 4B) compared with the mean maps of the normal group (Fig 4A) and the IRVT group (Fig 4C). The mean QRST integral map of the IRVT group features an area with negative isointegrals on the right anterior torso that extends more inferiorly compared with the negative isointegral distribution in the mean QRST integral map of the control group. In contrast to previous findings in several other patient groups with ventricular arrhythmias,12 13 14 15 none of the patients with ARVD or IRVT demonstrated a nondipolar QRST integral map pattern.
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Quantitative Analysis of Body-Surface QRST Integral Maps
Correlation of mean QRST integral maps. Visual evaluation of the mean QRST integral maps of the three groups was substantiated by computing correlation coefficients between pairs of these maps. Only the mean maps obtained in the IRVT group and the control group correlated well (r=.92). The mean map in the ARVD group showed a low correlation with the mean control map (r=-.18) and mean IRVT map (r=.19).
Departure maps of patients with ARVD. All eight patients with ARVD had departure areas on the departure maps (Fig 5). The areas on these departure maps showed a consistent torso distribution. In all patients, extensive negative departure areas were located on the anterior and inferior region of the thorax. A very small positive departure area was present on the upper part of the back in five patients (patients 1 through 5) and on the right anterosuperior side of the chest in patient 7.
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Departure maps of patients with IRVT. A distinct negative departure area on the right side of the thorax was observed in the departure maps of patients 1 and 8 (Fig 6). This abnormal departure area is clearly caused by the abnormal negative integral distribution on the right half of the torso that was observed in the individual QRST integral maps of patients 1 and 8 (Fig 3B). In addition, a negative departure area was present on the left side of the torso of patient 4 and a positive departure area on the right superior part of the back of patient 2. However, visual inspection of the QRST integral maps of the latter two patients did not demonstrate any abnormal low or high voltages in these particular regions.
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12-Lead ECG
Patients with ARVD. The 12-lead ECG abnormalities that were observed in patients with ARVD are shown in Table 2 and included left axis deviation in 3 patients, widened QRS complex (110 ms) in 2, right bundle-branch block in 1, waves in 2, fractionation of the QRS complex in 5, and precordial T-wave inversion in 7. Increased QT dispersion was seen in only 1 patient.
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Patients with IRVT. Six of 8 patients with IRVT showed a 12-lead ECG that was within normal limits. In the remaining 2 patients, the 12-lead ECG was borderline abnormal, showing low-amplitude R waves in V2 and V3 in patient 1 and inverted T waves in precordial leads V1 and V2 in patient 8. There was no increased QT dispersion in any of the patients with IRVT.
12-Lead ECG Compared With QRST Integral Map
Patients with ARVD. Qualitative comparison showed no relation between 12-lead ECG repolarization abnormalities and distinct QRST integral map characteristics in patients with ARVD. One might assume that the abnormal negative QRST integral area on the inferior and right anterior side of the thorax found in all patients with ARVD may be associated with precordial T-wave inversion on the 12-lead ECG. However, patient 6 with ARVD displayed the specific abnormal QRST integral map pattern in the absence of precordial T-wave inversion on the standard 12-lead ECG (Fig 7).
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Patients with IRVT. In the patients with IRVT who showed an abnormal right anterior negativity on the QRST integral map, the 12-lead ECG showed low-voltage R waves in leads V2 and V3 (patient 1) and inverted T waves in V1 and V2 (patient 8). However, these minor findings were considered only borderline abnormal.
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Discussion |
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Detection of Primary Repolarization Properties Using Body-Surface QRST Integral Mapping
Wilson et al10 introduced the concept that the QRST integral is largely independent of the ventricular activation sequence and reflects primary ventricular repolarization properties. Experimental evidence supporting this concept was attained by Abildskov et al.11 They demonstrated that the QRST integral of an epicardial electrogram obtained at a given site is specifically related to the local refractory period at that same site.11 They suggested that QRST integrals in multiple surface ECG leads may be used to identify inhomogeneity in local refractoriness and thus susceptibility to ventricular arrhythmias. These findings have led to the clinical introduction of body-surface QRST integral mapping to assess vulnerability to ventricular arrhythmias in various cardiac disorders.12 13 14 15 In these studies, the occurrence of ventricular arrhythmias appeared to be associated with a nondipolar QRST integral map in a considerable subset of patients. De Ambroggi et al14 performed QRST integral mapping in patients with idiopathic long-QT syndrome and found nondipolar maps in 6 of 25 patients and a specific abnormal dipolar map pattern in 13 of 25 patients. This abnormal dipolar map pattern consisted of a large area with negative potentials covering the right anterior thorax. These authors postulated that QRST integrals recorded from torso areas facing myocardial regions with longer refractory periods are characterized by a negative voltage. They suggested that the prominent anterior negativity in the QRST integral map of some patients with the idiopathic long-QT syndrome resulted from delayed repolarization of the underlying anterior wall of the right ventricle or the interventricular septum. They suggested that the regionally delayed repolarization resulted from decreased right sympathetic activity in the idiopathic long-QT syndrome.
Patients With ARVD
In patients with ARVD, ventricular arrhythmias can often be provoked by exercise stress testing or induced by programmed electrical stimulation.5 The relatively easy inducibility in conjunction with the frequently noted presence of late potentials,7 the finding of areas of slow conduction during endocardial mapping of the right ventricle,3 5 and the replacement of right ventricular myocardium by fatty and fibrous tissue5 suggest an underlying substrate that leads to reentrant ventricular arrhythmias. Although all of these findings relate to abnormal and delayed depolarization, our study demonstrates that abnormal repolarization is also present in patients with ARVD. It is not unlikely to assume that these repolarization abnormalities may also play a role in creating conditions that facilitate the occurrence of ventricular arrhythmias. To date, however, little is known about the effect of ARVD on ventricular repolarization and the arrhythmogenic potential of ARVD-related repolarization abnormalities.
We observed increased QT dispersion on the 12-lead ECG in only 1 of 8 patients. However, Corrado et al19 also measured QT dispersion on the 12-lead ECG in patients with ARVD and found significantly higher QT dispersion than in control subjects. The discrepancy with our findings may be caused by factors such as antiarrhythmic agents or the presence of a subtype of ARVD in that part of Europe.
In the present study, we used body-surface QRST integral mapping to examine primary ventricular recovery properties in patients with ARVD. Our patients with ARVD consistently showed a characteristic abnormal dipolar QRST integral map with one variant. These maps were characterized by a large negative area over the right anterior and inferior chest regardless of the presence or absence of precordial T-wave inversion on the standard 12-lead ECG (Figs 2 and 7). The pattern of the QRST integral map was not related to the location of the focal structural abnormalities or to the site of origin of the VT (Table 1). De Ambroggi et al20 also performed a preliminary study using body-surface mapping in 6 patients with ARVD and found an abnormal negative area on the QRST integral map in only 1 patient. The discrepancy with our results may be caused by the fact that all their patients had a "mild" form of ARVD, although the authors do not provide an exact description of the disease state in terms of structural, functional, or electrophysiological abnormalities.
The present findings suggest that a dipolar but abnormally configured QRST integral map, like a nondipolar QRST integral map, may also be indicative of arrhythmogenic vulnerability. In accordance with the findings of De Ambroggi14 in patients with the long-QT syndrome, we feel that the abnormal negativity covering the entire right anterior and inferior part of the torso in patients with ARVD may reflect regionally delayed repolarization of the underlying structurally altered myocardium. Thus, the negative QRST integrals in patients with ARVD may be caused by delayed repolarization in the right ventricular anterior wall, the posterior and inferior parts of the right ventricle, and possibly also in the interventricular septum. These areas of delayed repolarization in the right ventricle may be at least partially responsible for the occurrence of ventricular arrhythmias in these patients.
There are two possible underlying mechanisms that may explain altered primary repolarization in ARVD: (1) the regional occurrence of abnormal action potentials in the right ventricle and (2) regional denervation of the right ventricular myocardium.
Abnormal action potential hypothesis. In the normal heart, markedly different electrophysiological characteristics exist among myocardial cells in the ventricular wall.21 Transmembrane action potentials tend to be shorter in duration at the epicardium and basal regions and longer in duration at the endocardium and apex.22 It is possible that the structural abnormalities in the dysplastic right ventricle affect myocardial cells in such a way that their action potential duration becomes abnormally prolonged. Since the disease process in ARVD proceeds from the epicardium to the endocardium,4 cells at the epicardium, which normally have the shortest action potential duration, may be affected first. In addition, a regional prolongation of action potentials occurring predominantly in the dysplastic segments of the right ventricular myocardium may also cause altered electrotonic interactions, which in turn may influence primary repolarization properties.23 We hypothesize that these phenomena lead to locally unstable electrophysiological conditions that may be responsible for the increased vulnerability to ventricular arrhythmias.3 7 Thus, in addition to the factors that cause abnormal depolarization in ARVD, the above-mentioned repolarization phenomena may also be of importance for the occurrence of ventricular arrhythmias.
Denervation hypothesis. Several experimental studies have shown that abnormal and inhomogeneous electrophysiological properties with respect to refractoriness develop in regionally denervated myocardium and lead to increased vulnerability to ventricular arrhythmias.24 25 In addition, an imbalance of sympathetic tone has been reported to increase the propensity for developing ventricular arrhythmias.26 Previous studies in patients with ARVD have also demonstrated that ventricular arrhythmias are often induced by exercise, stress, or catecholamine exposure.27 Moreover, Wichter et al28 recently demonstrated by [123I]MIBG scintigraphy that regional abnormalities of sympathetic innervation frequently occur in patients with ARVD. The reduced uptake of [123I]MIBG indicates that regional sympathetic denervation may at least partly account for dispersion of refractoriness due to local lengthening of the refractory period in affected areas, in contrast to shorter refractory periods in the surrounding still normal myocardium, particularly during increased adrenergic drive. Furthermore, since sympathetic nerve trunks are located in the subepicardium and fibrofatty infiltration in ARVD progresses from the epicardium toward the endocardium,4 sympathetic denervation may occur rather early in the disease process. This may explain the profound arrhythmogenic potential early in the course of the disease.
Patients With IRVT
Idiopathic VT originating in the RVOT can be sustained and exercise-induced or nonsustained and repetitive.9 During electrophysiological study, these arrhythmias are often not inducible by the extrastimulus technique but rather occur during increased adrenergic drive by rapid atrial or ventricular pacing or isoproterenol infusion. The underlying mechanism is probably a cAMP-mediated triggered activity.9
In this study, two patients with IRVT (patients 1 and 8) demonstrated an abnormal dipolar QRST integral map pattern with prominent negativity on the right anterior and posterior thorax. This map pattern was comparable to the abnormal dipolar map pattern described by De Ambroggi et al14 in patients with the idiopathic long-QT syndrome. Therefore, one may assume that the map pattern in these two patients with IRVT is also related to delayed repolarization in the anterior right ventricular wall or septum, albeit most probably due to an underlying mechanism different from that in patients with the long-QT syndrome. In two other patients with IRVT (patients 2 and 4), the QRST integral maps revealed a normal pattern, whereas the departure maps featured a positive and a negative departure area, respectively. Twelve-lead ECG findings in the patients with IRVT were within normal limits in 6 patients and borderline abnormal in 2 patients. It should be stressed that 1 of the latter 2 patients demonstrated inverted T waves in leads V1 and V2. This particular patient also had an abnormal QRST integral map. It is possible that the patients with an abnormal QRST integral map or departure map will develop demonstrable structural heart disease in the future. However, at the time of investigation, other clinical findings could not distinguish these patients from the rest of the group with IRVT.
Carlson et al29 demonstrated that focal structural abnormalities can occur in patients with IRVT. They performed cine MRI in 22 patients with IRVT originating from the RVOT and demonstrated focal wall motion abnormalities of the RVOT in 95% of their patient group. However, in 3 of 5 patients in whom right ventricular angiography was performed, several abnormalities characteristic for ARVD were observed. Thus, the study by Carlson et al29 most probably did not solely contain patients with IRVT but also included at least some typical cases of ARVD. Right ventricular angiograms were not routinely performed in our patients with IRVT. Two of our patients with IRVT (patients 1 and 8) demonstrated a map pattern that was comparable although not identical to the pattern observed in patient 2 with ARVD (compare Figs 2B and 3B). Therefore, we cannot exclude that these 2 patients may represent borderline cases in whom ARVD may become apparent during follow-up. Nevertheless, it should be realized that most patients with IRVT do not develop any structural cardiac disease during long-term follow-up.8
Study Limitations
A major limitation of this study is the relatively limited patient sample. This is because ARVD is uncommon in the Netherlands. However, the consistency in the map patterns obtained in these 8 patients suggests that these results should also be applicable in a larger group of patients.
Although QRST integral maps are largely independent of the activation sequence, studies have shown that altered activation sequences can cause local electrotonic interactions that may lead to subtle changes in QRST integral maps.30 Therefore, we cannot exclude the possibility that abnormal conduction in our patients with ARVD did have a minor influence on the QRST integral map pattern. This seems unlikely, however, because the presence or absence of a widened QRS complex or right bundle-branch block did not result in any significant differences of the QRST integral maps.
In 4 patients with ARVD, the disease had already been diagnosed many years earlier (mean, 14±8 years). Therefore, one might presume that body-surface mapping reveals the characteristic abnormal QRST integral pattern predominantly late in the course of the disease. However, the fact that 4 of our patients were symptomatic for only 6 months to 2 years may indicate that the abnormal map pattern can be obtained at a relatively early stage, when the disease has just become clinically apparent by the occurrence of ventricular arrhythmias.
Because MRI was not routinely applied in our patients, we cannot exclude the possibility that early-stage cardiomyopathy was present in the 2 patients with IRVT expressing an abnormal QRST integral map. Follow-up of these 2 patients and further study of larger patient groups are warranted to find the cause of the abnormal map pattern in some patients with IRVT.
Clinical Implications
This is the first study to demonstrate a specific abnormal dipolar QRST integral map pattern in patients with ARVD. The present results suggest that body-surface QRST integral mapping may be used clinically as a noninvasive diagnostic tool to differentiate patients with ARVD from those with IRVT. The body-surface QRST integral mapping technique may prove particularly valuable in discriminating ARVD from IRVT at a relatively early stage in the diagnostic evaluation process when a patient presents with VT originating from the RVOT. In addition, this technique may also prove useful in identification of ARVD in asymptomatic family members or when results of other diagnostic techniques are inconclusive. However, the sensitivity, specificity, and predictive value of body-surface QRST integral mapping in the evaluation of patients with ARVD will have to be confirmed by larger prospective studies.
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Selected Abbreviations and Acronyms |
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Acknowledgments |
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This study was supported by grant 93.080 from the Netherlands Heart Foundation. We are indebted to Auke Latour, MSc, for his support in data analysis and preparation of the illustrations.
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Footnotes |
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Presented in part at the 68th Scientific Sessions of the American Heart Association, Anaheim, Calif, November 13-16, 1995, and at the 17th Scientific Sessions of the North American Society for Pacing and Electrophysiology, Seattle, Wash, May 15-18, 1996, and published in abstract form (Circulation. 1995;92[suppl I]:I-408).
Received August 15, 1996; revision received February 13, 1997; accepted February 20, 1997.
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