Do repolarization abnormalities in hypertrophic cardiomyopathy represent impaired fatty acid utilization?: An observation with QRST isointegral maps

Journal of Electrocardiology Vol. 30 No. 1 1997

Do Repolarization Abnormalities in Hypertrophic Cardiomyopathy Represent

Impaired Fatty Acid Utilization?

An Observation With QRST Isointegral Maps

Y o s h i h i d e K a w a k a m i , M D , * S a t o s h i S h i m a d a , M D , *

Yasu lh iko Saka i , M D , * M i c h i h i r o S u w a , M D , * H i k a r u N a g a o , M D , *

Y u z o H i r o t a , M D , * K e i s h i r o K a w a m u r a , M D , * I t a r u A d a c h i , M D , t a n d

I s a m u N a r a b a y a s h i , M D t

Abstract: To identify the clinical significance of the isointegral body surface map of the QRST interval (QRST map) and the occurrence of repolarization abnormalities in patients with hypertrophic cardiomyopathy (HCM), the QRST map and signal-averaged electrocardiogram were evaluated in 50 patients with HCM, in 33 of whom the results were compared with nuclear images both for radioiodine-labeled fatty acid metabolism and for radiothallium perfusion. The QRST departure map was used to determine two parameters of difference between patient and control recordings: the subnormal area (the number of lead points at which the departure index values were negative and lay more than 2 SDs from the mean of the normal control group) and the subnormal minimum (the absolute value of the minimum in the departure map). Late potentials were detected in 6 (12%) of the 50 patients; they were observed in 3 of the 5 patients with dilated-phase HCM but in only 3 (7%) of the other 45 patients. The subnormal area and minimum values were lower in nonobstructive HCM than in dilated-phase HCM. Of the 33 patients examined by myocardial imaging, 28 (33%) had a filling defect or decreased uptake, as shown on fatty acid metabolic images, and 10 of the 28 also showed abnormal myocardial perfusion images, while the 18 others showed normal perfusion images. These 28 patients showed significantly larger values of the subnormal area and minimum than patients with normal results in both image tests, regardless of whether or not myocardial perfusion imaging abnormalities were present. The localization of filling defects or of decreased uptake presented in fatty acid metabolic images corresponded to the position of the minimum on the QRST departure map. These results suggest that the QRST map is useful for detection of repolarization abnormalities in HCM and that these abnormalities are highly related to impaired fatty acid utilization of the myocardium. Key words: QRST isointegral map, hypertrophic cardiomyopathy, radioiodine-labeled fatty acid metabolic imaging, late potentials.

From the *Third Division, Department of Internal Medicine and ~-Department of Radiology, Osaka Medical College, Osaka, Japan Reprint requests: Yoshihide Kawakami, MD, Third Division, Department of Internal Medicine, Osaka Medical College, 2-7 Daigaku-

cho, Takatsuki, Osaka 569, Japan.

21

22 Journal of Electrocardiology Vol. 30 No. 1 January 1997

The ventricular gradient reflecting the isointegral value of the QRST interval, reported by Wil- son et al. (1), is theoretically independent of the ventricular activation sequence and useful in identifying whether the T wave change is primary or secondary to QRS deflection. On the basis of this concept, Abildskov et al. (2,3) introduced a method of clinically applying the isointegral body surface map of the QRST interval (QRST map) by using the body surface mapping technique. The QRST map has been employed for the evaluation of the localization and size of lesions of myocardial ischemia and infarction (4-6) repolarization abnormalities of essential hypertension and/or left ventricular hypertrophy (7,8), the presence of right ventricular overload (9,10), and susceptibility to malignant arrhythmia in patients with long QT syndrome (11). It is well known that repolarization abnormalities, presenting as ST-segment depression and T wave inversion on the standard 12-lead electrocardiogram (ECG), are almost always present in hypertrophic cardiomyopathy (HCM) (12). Using the QRST map technique, Hirai et al. (8) found that repolarization abnormalities were present in patients with HCM even when left ventricular hypertrophy was assessed as mild by echocardiography.

Recently, nuclear imaging with iodine-i23-beta- methyl-iodophenyl-pentadecanoic acid has been introduced to investigate myocardial fatty acid utilization. Although the main energy source of the normal myocardium is free fatty acids, impaired fatty acid uptake has been frequently observed in patients with HCM while the myocardial perfusion imaging with thallium-201 remains normal (13,14). We hypothesized that primary repolarization abnormalities detected by the QRST map might be related not only to impaired myocardial perfusion but also to impaired free fatty acid utilization.

The signal-averaged electrocardiogram (SAECG) has been used for identification of late potentials, which stratify the risk of sudden death and sus- tained ventricular arrhythmias (15). Although the incidence of late potentials in HCM is low (16), their presence indicates a slow conduction area of malignant reentrant tachyarrhythmias, and it is interpreted as the result of extensive tissue damage. This may also be related to the impairment of myocardial fatty acid utilization.

The purposes of this study in patients with HCM were to compare the findings of the SAECG, the QRST map, and fatty acid metabolic and myocardial perfusion images and to evaluate the possible association between repolarization abnormalities

and late potentials, impaired fatty acid utilization, and impaired myocardial perfusion.

Materials and Methods

The study population consisted of 38 men and 12 women with HCM of (mean age, 54.5 years; range, 20-74 years) whose diagnosis had been con- firmed by two-dimensional and Doppler echocardiography, cardiac catheterization, and endomy- ocardial biopsy. Patients who also had concomitant preexcitation syndrome, complete bundle branch block, or prominent intraventricular conduction delay were excluded.

The 50 subjects were divided into the following four groups according to localization of hypertrophy and physiologic status: apical hypertrophy (apical HCM, n=20); hypertrophic obstructive cardiomyopathy (obstructive HCM, n=12); hypertrophic nonobstructive cardiomyopathy (nonobstructive HCM, n= 13); and dilated-phase hypertrophic cardiomyopathy (dilated phase HCM, n=5). Apical localization of hypertrophy on the echocardiogram, giant negative T wave on the ECG, and a characteristic "spade-like" appearance on the left ventriculogram (17) were present in all patients with apical HCM. In patients with dilated-phase HCM, the diagnosis of HCM had been established previously, and these patients were followed until they developed heart failure with hypokinetic and dilated left ventricles (18).

The control subjects were 40 normal individu- als (20 men and 20 women; mean age, 31.6 years; range, i8-43 years) without a history of cardiac disorder or systemic hypertension, whose ECGs, chest radiographs, and physical examinations were normal.

Body surface maps were recorded to construct the QRST map with use of the VCM-3000 system (Fukuda Denshi Co., Tokyo, Japan). This involved placing 87 unipolar electrodes on the chest surface according to the method described by Yamada (19) (59 leads on the anterior chest and 28 leads on the back) with reference to Wilson's central terminal. A standard 12-lead ECG and a Frank (X,Y,Z), lead ECG were recorded simultaneously. These ECG data were scanned by multiplexers, digitized by A/D converters at a rate of 1,000 samples per second throughout the QRST waves, and stored on floppy disks. After two-point baseline adjustment at the flat portion of the TP-segment before the P and after the T deflection of the selected PQRST complex, the QRST map was constructed. The QRST time integrals represent the sums of all potentials from the QRS onset to the T offset for

each lead. All time integral values were calculated by multiplying millivolts by milliseconds and expressed as mV • ms. The isointegral lines were displayed ,on the QRST map by means of the VCM- 3000 system. The isointegral departure index body surface map of the QRST interval (QRST departure map) was also constructed by the deviation of the patient's data from the normal QRST isointegral values at each lead, calculated as the mean of the recordings from the 40 normal subjects.

The deviation was; expressed as departure index, defined as (QRST isointegral value - mean QRST isointegral value)/SD (5). When a departure index value was negative and lay more than 2SD from the mean on the QRST departure map, the reduction was considered statistically significant, and the reduction area was ,designated as a -2SD area. The following parameters were then derived: the number of lead points within each -2SD area (subnormal area, reflecting the extent of statistically abnormal negative area) and the absolute value of departure index at the minimum (subnormal minimum, reflecting the magnitude of deviation from normal) in each QRST departure map.

We simultaneously recorded the SAECGs from a modified X (standard lead I), Y (lead aVF), and Z (precordial lead V2) lead system using the Multi- cardiner VCM-3000 and VL 303 according to Sire- son's method (15). Ectopic and grossly noisy beats were rejected by a template algorithm, and 200 beats were averaged. Each lead was filtered with a bidirectional, high-.pass digital filter, which was designed to eliminate filter ringing (20). The signal from each lead was recorded at a bandwidth of 40-300 Hz and was then converted from ana- log to digital data with 12-bit accuracy at a sam- pling rate of 1 kHz. The filtered signals from the three leads were combined into a vector magnitude, ~X2+Y2+Z 2 (21). The end of the filtered vector magnitude QRS complex (filtered QRS) was designated as the point at which the amplitude of the filtered QRS became less than three times the noise level. Late potentials, shown as low-amplitude, high-frequency signals at the end of the filtered QRS, were defined as being present when any two of the following three criteria were met: the root mean square voltage in the last 40 ms of the filtered QRS was less than 15 gV; the filtered QRS duration was greater than 130 ms; and the filtered QRS duration after the voltage decreased to less than 40 gV was more than 40 ms (22).

Nuclear imagings for both radioiodine-labeled fatty acid metabolism and radiothallium perfusion were performed within 1 month of the body surface mapping and SAECG studies in 33 of the 50

QRST Isointegral Map in HCM • Kawakami et al. 23

patients. In fatty acid metabolic imaging, the patient was kept in the fasting condition until the end of the procedure. Each patient at rest received 111 MBq of iodine-123-beta-methyl-iodophenyl- pentadecanoic acid (Nippon Medi-Physics Co., Chiba, Japan) intravenously, and 30 minutes after the injection images were obtained with a gamma camera (Toshiba GCA-9300A/HG) equipped with a low-energy, high-resolution collimator centered on the 160-keV photopeak with 24% window (13, 23). In myocardial perfusion imaging, which was performed on another day, 74 MBq of thallium- 201 was injected intravenously, and images were obtained 15 minutes after the injection with a gamma camera (Siemens ZLC-7500) equipped with a low-energy, high-resolution collimator centered on the 70-keV photopeak with a 20% window. In both imagings, single-photon emission computed tomographic images at slices in the ver- tical long-axis, short-axis, and horizontal long-axis planes were reconstructed by using a Shepp-Logan filtered back projection algorithm. The uptake was classified into normal, increased, decreased, and defect categories by visual analysis, and we evaluated impaired regional fatty acid metabolism and impaired myocardial perfusion.

The subnormal area and minimum in the four I-ICM groups are expressed as mean ±SD, and in the three groups classified according to the scintigraphic findings, the data are expressed as the median, range, and mean _+SD because of the abnormality of the distribution. The Tukey-Kramer method was used for the pairwise comparisons and P values < .05 (two-sided) were considered to be statistically significant for differences between two groups of subjects.

Results

Late Potential

Late potentials were detected by the SAECG in 6 (12%) of the 50 patients with EICM, and they were most frequently observed in the dilated- phase HCM group (3 of the 5 patients). Late potentials were present in only 3 (7%) of the other 45 patients. Both fatty acid metabolic and myocardial perfusion images showed defect or decreased uptake in all patients with late potentials. Figure 1 demonstrates a representative SAECG of a 47-year-old man with dilated-phase HCM. Of note, the terminal portion of the filtered QRS shows fragmented signals of low amplitude and long duration.

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• $ Fig. 1. A representative signal-averaged ECG (magnitude lead) in a patient with dilated-phase hypertrophic cardiomyopathy. Arrowhead indicates late potentials (root-mean-square voltage in the last 40 ms [RMS 40]; 3.3 g V; filtered QRS duration, 131 ms). S, start point for measurement of RMS 40; E, endpoint of filtered QRS.

ORST Map

As shown in Figure 2, the m e a n QRST map obtained f rom the data for the 40 normal individu- als demons t ra ted smooth bipolar surface distribution, wi th a m a x i m u m at the site of G4 (V4 of the

ECG) and a m i n i m u m at the site of D7 (right upper quadran t of the chest).

The extent (subnormal area) and intensi ty (subnormal m i n i m u m ) of repolarization abnormali t ies in the four groups of HCM patients are shown in Table 1. The subnormal area value was lower (P < .01) in the nonobst ruct ive HCM group than in the dilated-phase HCM group, and as compared with each of the other three groups of HCM patients, the nonobst ruct ive HCM group showed the small- est subnormal m i n i m u m value (P < .01 or .05). Conversely, the subnormal area and m i n i m u m values were larger in the dilated-phase HCM group than in the nonobst ruct ive HCM group. The inten- sity of repolarization abnormali t ies was least severe in the nonobst ruct ive HCM group, and the extent and intensi ty of repolarizat ion abnormali t ies were more severe in the di lated-phase HCM group than in the nonobst ruct ive HCM group.

Scintigraphic Findings

Among the 33 patients w h o unde rwen t fatty acid metabol ic and myocardia l perfusion imagings, no rmal or increased uptake was detected on bo th imaging studies in only five patients (group 1, 15 %). In 18 patients (group 2), the fatty acid metabolic images showed defect or decreased uptake, while the myocardia l perfusion images were nor- real or showed increased uptake. The remaining 10 patients (group 3) showed defect or decreased uptake on bo th images. Table 2 demonst ra tes the compar ison of the subnormal area and m i n i m u m values on the QRST depar ture map in the groups wi th the three different pat terns of up take on fatty acid metabol ic and myocardia l perfusion images. The subnormal area and m i n i m u m values were clearly larger in groups 2 and 3, but no difference was observed be tween these two groups. Thus, the extent and intensi ty of repolarizat ion abnormali t ies

Fig. 2. Normal mean QRST isointegral map. Isointegral contours are separated by 40 mV • ms, and shading indicates negative areas. Maxi- mum and minimum are indicated by plus and minus signs. Open circles (O) show the six precordial lead points of the ECG.

A B C D E F G H I J K L MA


Table 1. Subnormal Area and Minimum in the Four Hypertrophic Cardiomyopathy Groups

Group S u b n o r m a l Area* S u b n o r m a l M i n i m u m *

Apical EICM (n = 20) 18.6 + 8.1 4.8 + 2.0 Obstructive HCM (n = 12) 1 9 . 1 + 9 . 4 4.4_+ 1.2 t ~ ] t Nonobst ruct ive HCM (n = 13) 10.9 + 8.9 I t 2.6 ± 1.2 Dilated-phase HCM (n = 5) 27.4 + 7.7 5.1 + 1.6

*Data are expressed as m e a n ± SD. -{P < .01; SP < .05. There are no significant differences be t ween two groups whe re none are indicated. Subnormal area, n u m - ber of lead points whe re the depar ture index values are negat ive and lie more t h a n 2SD on the QRST depar ture map; subno rma l m i n i m u m , absolute value of depar ture index at the m i n i m u m on the QRST depar ture map; EICM, hyper t rophic cardiomyopathy.

were more severe in the patients with abnormalities in fatty acid metabolic images than in the patients with normal scintigraphic findings, regardless of the presence or absence of myocardial perfusion imaging abnormalities.

Correlation of the Localization of Abnormalities between Scintigraphy and the QRST Departure Maps

Figure 3 shows the fatty acid metabolic images and QRST departure map of a 47-year-old man with dilated-phase HCM. Scintigraphic defect and decreased uptake were detected in the inferior and apical segments, associated with a dilated left ventricle and disproportionately thickened septal and lateral segments. The QRST departure map showed an extensive -2SD area on the lower part of the left anterior chest and back (subnormal area 39 points and subnormal minimum 4.7 SD), which indicated the regional repolarization abnormalities in the inferior and apical segments and corresponded with the findings of fatty acid metabolic images.

Figure 4 shows the myocardial perfusion and fatty acid metabolic images, QRST departure map,

and ECG of a 64-year-old man with apical HCM. While myocardial perfusion was increased in the apical segment, fatty acid uptake was decreased in the same segment. Extensive repolarization abnormalities were evident on the QRST departure map (subnormal area 29 points and subnormal minimum 5.8 SD), as well as on the ECG (giant negative T waves, mainly in the left precordial leads). These electrical abnormalities corresponded not with the findings of myocardial perfusion images but rather with the findings of fatty acid metabolic images.

Twenty-eight patients who showed defect or decreased uptake in fatty acid metabolic images were classified into three groups according to the affected segments, namely, the anteroseptal, apical, and inferior regions. The correlation of the localization of the minimum on the QRST departure map with the filling defect in the fatty acid metabolic images was displayed on the body surface map (Fig. 5). The positions of the minima (mean ±SD) for the anteroseptal, apical, and inferior defect groups were distributed on the left upper parasternal (F-G 4-5), high left lateral (G-H 4-5), and left lower parasternal (F-G 2-4) areas, respectively. Thus, each group showed different distribu-

Table 2. Subnormal Area and Minimum in Three Different Patterns of Uptake of Fatty Acid Metabolic and Myocardial Perfusion Images

S u b n o r m a l Area S u b n o r m a l M i n i m u m

Group* M e d i a n R a n g e M e a n + SD M e d i a n R a n g e M e a n +_ SD

1 ( n = 5) 0 0-12 3.8 + 5.51f ~ 1.5 1.2-3.0 1.9 + 0.71+. 2 ( n = 18) 21 0-30 20.4 + 6.9 J |J- 4.7 1.7-6.8 4.7 + 1.5~-[J - 3 ( n = 10) 24 8-39 2 4 . 4 + 8 . 4 J 4.5 3.1-11.1 5 . 2 + 2 . 4 J

*Group 1 is' comprised of pat ients w i thou t filling defect or decreased uptake on bo th fatty acid metabolic and myocardia l per fus ion images, group 2 of those wi th defect or decreased uptake only on fatty acid metabolic images and no t on myocardia l per fus ion images, and group 3 of those wi th defect or decreased uptake on bo th types of images, t P < .01; there are no significant differences be tween two groups whe re n o n e are indicated.

26 Journal of Eiectrocardiology Vol. 30 No. 1 January 1997

A Fatty Acid Metabolic Images

Short Axis Horizontal Long Axis

B

4- " ~ 3 - .2.0

2-

1 , I I I I I I I I I I I

A B C D E F G FI I J K L M A

Fig. 3. (A) Fatty acid metabolic images at short axis (left) and horizontal long axis (right) and (B) QRST isointegral departure map of a 47-year-old man with dilated phase hypertrophic cardiomyopathy. Shading indicates -2SD area.

t ion of the m i n i m u m on the QRST depar ture map, which might indicate the correspondence be tween the localization of fatty acid metabol ic abnormal i - ties and the posit ion of the m i n i m u m on the QRST depar ture map.

.

4- o

3-

2-

1

Fig. 5. The distribution of the minima is displayed on the body surface map according to the fatty acid metabolic imaging abnormalities. In patients with filling defects localized in the anteroseptal (O), apical (A), and inferior (11) areas by fatty acid metabolic imaging, the positions of the minima are at F-G 4--5, G-H 4-5, and F- G 2-4 areas, respectively. Open circles (O) show the six precordial lead points of the ECG.

Discussion

It has been emphasized that the QRST map, which is independen t of activation sequence and dependen t on repolarizat ion properties, is a useful and convenient m e t h o d of data reduction. The usefulness of the QRST m a p as a noninvas ive indi- cator has been conf i rmed in its application to detect abnormal repolarizat ion propert ies (4-11) and to assess the vulnerabil i ty to ventr icular a r rhy thmia (24,25) of patients wi th various hear t diseases. However, the clinical usefulness of the

Myocard ia l Fa t ty Acid /-~ A Per fus ion Image Metabolic Image

B r 6 -

5- 4-

Hor izon ta l Long Axis

2- 0,0

1 ! ' "~'~ . . . . , , , - " , , Ai bE .l J K L M A

Fig. 4. (A) Myocardial perfusion (left) and fatty acid metabolic (right) images at horizontal long axis; (B) QRST isointegral departure map; and (C) ECG of a 64-year-old man with apical hypertrophy. Shading indicates -2SD area.


QRST map in patients with HCM has not been well studied. In this study, we compared the findings of the QRST map, the SAECG, and fatty acid metabolic and myocardial perfusion images.

For the assessnctent of the electrophysiologic instability and the extent of repolarization abnormalities in HCM, tile presence of late potentials in the SAECG and the subnormal area and minimum calculated from the QRST departure map were examined in four groups with different types of HCM. Late potentials were detected in 6 (12%) of the 50 patients, being most frequently observed in patients with dilated-phase HCM, who were known to have impaired systolic function as the end stage of HCM (26). Excluding the patients with dilated-phase HCM, late potentials were found in only 3 (7%) of the other 45 patients. The incidence of late potentials in HCM has been reported to range from 12.5% to 20% (16,27). This low incidence in the time.-domain method SAECG might be due to the concealment of fragmented ventricular activation by high-amplitude QRS deflection in HCM. In addition, the high incidence in the dilated-phase HCM group (three of five patients) suggests the presence of delayed electrical activation with myocardial injury such as myocardial fibrosis. All patients with late potentials had a defect or decreased uptake on both the fatty acid metabolic and the myocardial perfusion images. This finding suggests that HCM patients with late potentials have more extensive myocardial damage than patients without them.

In the nonobstructive HCM group, the subnormal minimum value was small. This finding suggests that the repolarization abnormalities in this group are not severe, which may be due both to diffuse left ventricular hypertrophy, which cancels regional repolarization abnormalities, and to inclu- sion of early-stage HCM patients in this group. Con- versely, the subnormal area and minimum values in the dilated-phase HCM group were larger than in the nonobstructiw, • HCM group. Hayashi et al. (4), and Tonooka et al. (5) have reported the accuracy of the QRST map in estimating the localization and size of myocardial[ infarction. They demonstrated, moreover, a close ,correlation between the extent of the -2SD area and the myocardial perfusion defect score in patients with myocardial infarction. In our study, the subnormal area and minimum values were significantly greater in the dilated-phase HCM group than in the nonobstructive HCM group. However, there were only five patients in the dilated-phase HCM group. Therefore, we should extend our investigation to a larger study population to determine whether the subnormal area and

minimum values are useful for evaluating the severity of pathologic changes in HCM as well as those in myocardial infarction (4, 5).

The myocardium uses mainly free fatty acids for its energy source, but alternatively uses glucose when it is exposed to hypoxic conditions. Yone- kura et al. (28) have demonstrated that in the hypertrophied left ventricle while the epicardial half of the myocardium uses free fatty acid, the endocardial half uses glucose predominantly. Con- genital defects of free fatty acid uptake at the myocardial cell membrane in patients with ICCM were recently demonstrated by Tanaka and Kawa- mura (29) and Tanaka et al. (30). They also showed that inhibition of free fatty acid uptake to the myocardium would cause myocardial hypertrophy (31). Nuclear imaging of radioiodine- labeled fatty acid metabolism was recently introduced to evaluate this impaired fatty acid utilization. Myocardial perfusion imaging is a reli- able method of evaluating the impairment of the myocardium. The region of perfusion defect depicted by this imaging technique is considered to be the ischemic or fibrotic area in patients with myocardial infarction and dilated cardiomyopathy (32,33). We previously reported that the distribution of the minima and the -2SD areas on the QRST departure map reflected the injured area in patients with dilated cardiomyopathy as assessed by comparison with myocardial perfusion images (34). Fatty acid metabolic imaging, however, is independent of myocardial perfusion imaging. A filling defect or decreased uptake is frequently seen in HCM even in the absence of abnormalities on myocardial perfusion images (35). Furthermore, it has been reported that fatty acid metabolic imaging may play an important role in the diagnosis of early-stage HCM when myocardial perfusion or function is still normal ( 13,36).

In this investigation, the group with a filling defect or decreased uptake apparent in fatty acid metabolic images (groups 2 and 3) had significantly larger subnormal area and minimum values as compared with the normal uptake group (group 1), but there was no significant difference for subnormal area or for subnormal minimum between the groups with (group 3) and without (group 2) defects visualized in myocardial perfusion images. These results suggest that both subnormal area and subnormal minimum are closely associated with the findings of fatty acid metabolic images regardless of the findings of myocardial perfusion images. If so, the repolarization abnormalities assessed by using the QRST map are related to the impaired fatty acid utilization. In addition, this investigation

28 Journal of Electrocardiology Vol. 30 No. 1 January 1997

reveals that the localization of the defect or decreased uptake in fatty acid metabol ic images corresponds to the posit ion of the m i n i m u m on the QRST depar ture map. Overall, it is suggested that the repolarization abnormali t ies in HCM are highly related to impaired fatty acid utilization.

Study Limitations

Our investigation has several limitations. First, we could not assess fatty acid metabol ic images by quanti tat ive analysis employing such paramete rs as up take index in each segment . A correlation coeffi- cient of ei ther subnormal area or subnormal mini- m u m with a decreased uptake index should be obtained to evaluate whe t he r the QRST depar ture map index correlates wi th the severity depicted on the images and wh e t he r it reveals the extent of the injured area. Second, the localization of filling defect or decreased uptake shown on tat ty acid metabol ic images was classified into only three regions. Strict compar ison be tween the posit ion of the m i n i m u m on the QRST depar ture map and abnormal area in fatty acid metabol ic images was impossible because there were several patients wi th two or more decreased uptake segments, especially in the dilated-phase I-ICM group. Finally, the distribution of the m i n i m a on the QRST departure map over lapped with each other. Accordingly, fur ther study with larger pat ient populat ions is needed to confirm the precise localization of the injured area as derived f rom the QRST depar ture map findings.

Conclusion

This investigation demonst ra tes the practical usefulness and clinical significance of the QRST map in identifying the extent and localization of repolarization abnormali t ies in patients wi th HCM. The QRST m a p m a y also provide valuable informa- tion in the evaluat ion of HCM. This investigation also suggests that the occurrence of repolarizat ion abnormali t ies in HCM might be due to impaired myocardia l free fatty acid metabol ism. These results require fur ther validation by prospect ively applying the QRST map to a large n u m b e r of patients wi th HCM.

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Documents

Do repolarization abnormalities in hypertrophic cardiomyopathy represent impaired fatty acid utilization?: An observation with QRST isointegral maps