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Enzymes and Protein Markers |
1
Clinical Biochemistry Department and
2
Arrhythmia Unit, Ramón y Cajal Hospital, Department of Medicine, Alcalá University, 28034 Madrid, Spain.
a Address correspondence to this author at: Arrhythmia Unit, Ramón y Cajal Hospital, Ctra. Colmenar Viejo, km 9,100, 28034 Madrid, Spain. Fax 91-3368183; e-mail concepcion.moro{at}hrc.es.
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Abstract |
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 Top Abstract IntroductionMaterials and MethodsResultsDiscussionReferences |
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Introduction |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Cardiac troponin I (cTnI) is a newly available biochemical marker of myocardial lesions (7). The troponins, present as a group of three subunits in the troponin complex on the thin filament of muscle myofibrils, are involved in the regulation of muscle contraction. Troponin T is the tropomyosin-binding subunit, troponin I is the actomyosin ATPase-inhibiting subunit, and troponin C is the calcium-binding subunit (8)(9)(10)(11)(12). Only troponins T and I have cardiospecific isoforms. Troponin T was introduced first; however, most studies indicate that cTnI is as specific as or more cardiospecific than troponin T (13)(14) and that it is not detectable in sera of healthy volunteers. Therefore, its appearance in blood would be a clear signal of cardiac myocite damage.
We designed this study to determine the frequency of increased serum concentrations of several cardiac biochemical markers in patients that underwent RF catheter ablation and to establish the sensitivity and specificity of cTnI for quantifying the presence of minor cardiac damage after ablation.
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Materials and Methods |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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We analyzed the data of 51 consecutive patients who underwent catheter ablation. A control group of 16 patients, who underwent electrophysiological study without ablation, was also included and analyzed consecutively and prospectively. This control group was introduced to prove that the increases of serum cTnI and other biochemical markers were attributable either to the RF application or to the positioning of the intracardiac catheters, through mechanical lesions of the myocardium. We tried to isolate the effect of the RF lesion from the mechanical effect of the manipulating catheter.
The electrophysiological study was performed with the patient in a nonsedated and fasting state, with conventional techniques of intracardiac recording and pacing. Depending on the substrate for ablation, we introduced percutaneously two to four multipolar electrode catheters from the femoral artery or vein and, sometimes, from the internal jugular vein. The catheters were positioned in the high right atrium, the His bundle, the right ventricular apex, or left ventricle. Positioning of the diagnostic catheters was performed under biplane fluoroscopy, using standard projections.
Left accessory pathways were approached using the retrograde aortic technique, except in two patients, using a transeptal technique. Mapping and ablation were performed with a 7 Fr deflectable catheter with a 4-mm tip electrode (Ablatr or Marinr, Medtronic). The RF source was the Atakr from Medtronic, under temperature monitoring. We analyzed the following data in every ablation procedure: target, atrium or ventricle aspect, number of RF applications, total time of RF application, and mean temperature achieved. We included all the RF pulses used, both successful and failed or prematurely interrupted.
There were 23 female and 28 male patients in the ablation group, with a mean age of 42 ± 19 years. The control group was composed of 16 patients, 4 female and 12 male, with a mean age higher than that of the ablation group, 55 ± 20 years. The ablation group included 14 with left accessory pathways, 7 with right accessory pathways, 12 with atrio-ventricular nodal reentry tachycardia, 13 with atrial flutter or fibrillation, and 5 with ventricular tachycardia. In the patients of the control group, the electrophysiological study was indicated to study the AV node and sinus function in 2 patients, atrial flutter in 3 patients, and programmed electrical stimulation in 11 patients. The selection of patients to be included in the control or ablation group could not be randomized (although it was consecutive and prospective). Because of the different indications for these techniques, the control group has a slightly higher mean age and a different cardiac pathology. However, this should not influence the results of the study.
We determined and contrasted the serum concentrations of CK-MB mass, cTnI, myoglobin, and CK activity. We also registered any change in clinical status, modifications of the ST segment, and new arrhythmias after the procedure.
We collected peripheral blood samples for serum analysis (5 or 10 mL of blood, collected in dry vessels), according to a fixed schedule. The first sample (10 mL) was taken just after peripheral vein access ("initial" sample). The second blood sample of 5 mL ("basal") was obtained after the catheters were positioned in the heart. The other blood samples (5 mL) were taken as follows: 20 min after the last RF application or after the procedure was completed, and at 2, 4, 8, 24, and 48 h afterwards. The samples were centrifuged just after collection, aliquoted, and frozen to -20 °C until processing. The mean time before processing was 25 ± 5 days.
We used 5 mL from the initial sample of blood to perform a routine biochemical study including: glucose, creatinine, urea, sodium, potassium, and calcium concentrations, and aspartate aminotransferase and lactate dehydrogenase activity, using standard techniques, with an analyzer Hitachi 747 (Boehringer Mannheim). The cardiac markers cTnI, myoglobin, and CK-MB mass were determined using the "sandwich" technique, with double monoclonal antibodies, by an automatic enzymofluoroimmunoassay (radial bipartition) Stratus II (Baxter Dade). The CK activity was determined using an analyzer Integra (Roche). The reference ranges at our laboratory for the cardiac markers were as follows: CK, 35–200 U/L; CK-MB mass, 0.5–5 µg/L; myoglobin, 20–80 µg/L; and cTnI, 0.0–0.8 µg/L.
For obvious reasons, in our study there was no anatomic demonstration of injury to the myocardium in addition to the biochemical markers. Thus, a "gold standard" for the definition of sensitivity and diagnostic accuracy for each marker was difficult to find. However, we know that when we ablate an arrhythmogenic focus in the human myocardium, we see the direct electrophysiological effect of this lesion (i.e., the disappearance of an arrhythmia or a delta wave in a Wolff-Parkinson-White syndrome), which implies that a small tissue lesion has occurred. Moreover, when we applied a radio frequency in close contact to the myocardium to produce necrosis, we observed a rise of the temperature (monitored by a thermistor in the tip of the catheter). In all patients in the ablation group, we saw these electrophysiological effects of the lesion produced by the radio frequency, thus confirming the injury to the myocardium.
After the ablation or the electrophysiological study, the patients were evaluated twice each day. A physical examination was routinely performed once each day, as well as a 12-lead electrocardiogram, to observe modifications of the repolarization.
statistics
Continuous variables were expressed as means and SDs when the
distributions were documented to be gaussian after analyzing the
frequency distributions by the Kolmogorov–Smirnov statistical test.
The nonparametric Wilcoxon test was used when the variables lacked a
gaussian distribution, and the data were expressed as median and
interquartile range. To determine statistical differences between
continuous variables, we used the Student t-test and ANOVA.
To compare discrete variables, we used the 
test. A
P value <0.05 was considered significant. The correlations
between variables were assessed by linear regression (Pearson). To
compare the performance of the biochemical markers, the ROC curves were
estimated and the areas under these curves were calculated for every
biochemical marker. The Z statistic, corrected with the
method introduced by Hanley and McNeil (15), was used for
comparison of the ROC curves. A Z value >1.86 was
considered significant.
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Results |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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We performed a study of sensitivity and specificity (in the control and ablation groups) to evaluate what would be the optimal cutoff concentration for cTnI. We selected four cutoff values (0.7, 0.8, 0.9, and 1.0 µg/L) with good values for sensitivity (93%, 93%, 87%, and 86%, respectively) and specificity (75%, 75%, 81%, and 88%, respectively). The mean of the baseline values of the 67 patients included in this study plus 2 SD, was 0.78 µg/L. Consequently, we decided to use the cutoff of 0.8 µg/L to discriminate between patients with or without cardiac damage.
control group
Serum cTnI was increased in four patients (mean concentration of
1.22 ± 0.4 µg/L). Three of these patients presented peak values
between 0.9 and 1.1 µg/L, lower than those found in patients after RF
ablation. In the other patient, the highest release of cTnI was 1.9
µg/L (perhaps attributable to a difficult positioning of the
catheters into the heart). In the same patient, CK activity (258 U/L)
and CK-MB mass (6.4 µg/L) were increased. Three patients presented a
mild increase of myoglobin (84, 91, and 103 µg/L).
The mean duration of the procedure was 93 ± 30 min, and the mean number of catheters used was 2.3 ± 1.0. In these four patients, we performed the electrophysiological study to induce ventricular tachycardia, which was finally induced in three of them. Eleven patients were studied for ventricular tachycardia, three were studied for atrial flutter, and two were studied for conduction and sinus node function study. We cannot conclude if the differences between these groups were significant. The number of catheters used did not differ because we routinely used two catheters for these studies.
ablation group
No patient presented modifications of the ST segment after RF
ablation, excluding those after Wolff-Parkinson-White syndrome ablation
who presented the "electrical cardiac memory" (seven patients). No
patient presented chest pain or symptoms suggestive of ischemic heart
disease.
The concentrations of CK-MB mass, myoglobin, and cTnI were
significantly higher in the ablation group than in the control group
(P <0.01). cTnI was the biochemical marker that showed
abnormal values in 47 out of 51 (92%) patients who underwent RF
ablation. In the other 4 patients, we observed small increases of cTnI,
which did not achieve the cutoff concentration. CK-MB mass was
increased in 63% of patients, almost two-thirds of cTnI. The CK
activity increased to pathological values in 30% of the patients, and
the myoglobin reached abnormal concentrations in 67%. In studies such
as the present one, where the concentrations in samples collected
serially are evaluated, it is also appropriate to know the peak value
of every biochemical marker in the ablation group; therefore, we saw
that CK activity and myoglobin would reach values triple their initial
values after ablation in some patients. However, both cTnI and CK-MB
mass have values even 30-fold higher than those of the initial samples
(Table 1
).
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For the estimation of the diagnostic accuracy of cTnI and the other
biochemical markers of myocardial lesions, we used the analysis of the
ROC curves. The area under the ROC curve for cTnI was 0.9375 (SE,
0.0319). The area was 0.86 (0.0486) for CK-MB, 0.76 (0.0689) for
myoglobin, and 0.75 (0.0745) for CK. Moreover, when the areas were
compared using the Z statistic, cTnI was the only marker
that presented statistically significant differences compared with the
other markers (P <0.05). CK-MB mass, CK activity, and
myoglobin did not have statistically significant differences among them
(Fig. 1
).
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After demonstrating the superior diagnostic accuracy of cTnI in
comparison with the other biochemical markers, we analyzed the
correlation between the peak cTnI and the following data obtained from
the RF generator: number of applications, mean temperature, and total
time of application. The best linear correlation was found between the
peak concentration of cTnI and the number of RF applications, with a
linear correlation coefficient of 0.688 (P <0.0001). We
also found good correlation between the peak concentration of cTnI and
the total RF application time (r = 0.672,
P <0.0001). However, there apparently is no correlation
between the peak concentration of cTnI and the mean temperature
achieved (r = 0.083; Table 2
). We did the same analysis for the CK-MB mass. In spite of the
good correlation between the peak concentrations of CK-MB mass and cTnI
(r = 0.741, P <0.0001) in the ablation
group, the correlations between CK-MB and the mean temperature, number
of applications, and total time were clearly lower to those found for
cTnI (Table 2
).
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To determine if the release of cTnI, and thus the size of the
myocardial lesion, was different for each arrhythmia targeted, we
separated different groups. The mean peak cTnI released varied between
the lowest for AV nodal reentry (1.5 ± 0.8 µg/L) and the
highest for patients with atrial flutter (6.0 ± 5.7 µg/L; Table 3
). It is important to observe that the correlation was
different for every substrate targeted, being the worst for the AV
node reentry tachycardia (r =0.25, P = 0.43)
and the best for the ablation of ventricular tachycardia
(r = 0.99, P <0.0001; Table 3
). With ANOVA
among these groups, a significant difference (P = 0.11)
was not found. We found significant differences only between the groups
of AV node reentry and atrial flutter/fibrillation (P =
0.039).
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To determine if there were differences in the release of cTnI according to age and gender, we used ANOVA; we did not find statistically significant differences, with P = 0.57 and 0.7 for age and gender, respectively.
kinetics
In the ablation group, the peak mean value of cTnI occurred 8
h after ablation. However, in some patients, we detected abnormal
values as early as 20 min after RF ablation. At 48 h after
ablation, only cTnI was markedly increased, whereas the other
biochemical markers were within health-related reference limits, except
for a mild increase of the concentrations of CK. Similarly, the peak
cTnI and the peaks values for myoglobin, CK, and CK-MB were always
found before the expected time, in comparison with ischemic cardiac
disease. Out of 51 patients, only 2 presented a double pattern of
release of cTnI; both patients did not achieve abnormal concentrations
for cTnI (both <0.8 µg/L). In the control group, we found normal
release kinetics, without achieving abnormal concentrations. Although a
doubling appeared (below the cutoff concentration), for the CK-MB and
cTnI curves, it was because of the release of cardiac markers found in
only some patients of the control group. Fig. 2
shows the mean kinetics for all the biochemical markers for
both the control and the ablation group.
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Discussion |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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cTnI is thus the best marker to detect minor cardiac damage in both control and ablation groups. With the analysis of diagnostic accuracy performed using the ROC curves, the superiority of cTnI in comparison with the other biochemical markers clearly appears.
We also found in our study a moderate linear correlation, statistically significant, between the peak concentration of cTnI and the number of RF ablation applications (r = 0.688) and the total time of RF application (r = 0.671). However, it seems that no correlation exists between the release of cTnI and the mean temperature achieved during the ablation (r = 0.083). This could be attributable to the temperatures used during this procedure, which usually are similar or have slight differences (in our study, the mean was 57 ± 5 °C); however, the number of applications (9.8 ± 11.6 applications) and the total time (7.6 ± 10.9 min) varied considerably among the patients. Thus, in view of the above data, because the temperature is a constant (we always performed the ablation under temperature monitoring), it seems clear that the myocardial lesions produced by the radio frequency are larger and release more cTnI with a higher number of applications and a longer total time of application.
The correlation was different for every arrhythmia targeted. This could be attributable to both the different technique used for every arrhythmia and the aspect of the endocardium treated (atrial or ventricular). The contact and pressure of the catheter on the endocardium could be different for every case (17)(18). The lowest release of cTnI was found in the AV node reentrant tachycardia, and the highest in the atrial flutter/fibrillation. These arrhythmias also required the lowest and the highest number of RF applications. In spite of the fact that, in our study, the group of patients treated for atrial arrhythmias released the highest amount of cTnI, when the release/number of applications ratio was evaluated, the highest relationship was obtained with the ventricular tachycardia ablation (with a lower number of applications, the patients had a considerable release of cTnI). The peak concentration of cTnI was higher for the left accessory pathway ablation than for the right accessory pathway ablation. The ablation of the left accessory pathways required fewer RF pulses than the right pathways. The ablation site for the right accessory pathways was usually found in the atrial endocardium (just above the tricuspid annulus), and there was probably lower pressure from the catheter.
In the ablation group, the biochemical markers reached peak values earlier than those usually found in the setting of ischemic heart disease (19). However, these values cannot be directly compared with the results of this study because different assays, standardized differently, were used. The ablation creates an immediate myocardial necrosis (which is usually slower, even for hours, in ischemic events). The release begins earlier, after the alterations of the cell membrane. The myoglobin peak, the earlier marker of myocardial infarction (2–3 h), was also found earlier in our study (20 min after ablation). The peak CK-MB and CK were also observed at 4 and 8 h after the procedure, respectively. However, after a myocardial infarction, they are usually seen at 12 and 24 h, respectively. cTnI reaches peak concentration after a myocardial infarction at 12–16 h (7)(19)(20)(21); in our study it reached the peak concentration at 8 h. However, the possibility that the peak was actually reached between 8 and 24 h exists, because we have no samples between these hours.
There are no published data about the release and kinetics of cTnI after RF catheter ablation; therefore, we cannot establish any comparison. We do have the data of the release of several cardiac biochemical markers, including cTnI, after a myocardial infarction. In one of these studies, in patients with myocardial infarction, the peak concentrations of cTnI ranged between 18.5 and 477 µg/L (19).
In our study, the cTnI peak was between 0.4 and 21.4 µg/L, with a mean of 3.9 µg/L. The typical peak value found in our study was, in most of the patients, low (ranging between 3 and 4 µg/L), well below of those found in the literature for myocardial infarction (19). No patient experienced peroperative myocardial infarction, according to the standard criteria for the diagnosis. This could be useful information to know in patients who might have the potential for other ischemic events or who may have clinical presentations that suggest this possibility. Although we demonstrate a relationship between peak values of cTnI and the size of the myocardial lesions, we need to be careful because the relationship of cTnI and its kinetics to the size of myocardial lesions is not well established. Further studies are needed to better evaluate this point.
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Footnotes |
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References |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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The following articles in journals at HighWire Press have cited this article:
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  E. Sbarouni, P. Georgiadou, D. Panagiotakos, E. G. Livanis, G. N. Theodorakis, and D. Th. Kremastinos Ischaemia modified albumin in radiofrequency catheter ablation Europace, February 1, 2007; 9(2): 127 - 129. [Abstract] [Full Text] [PDF]
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 D J Grainger and H W L Bethell High titres of serum antinuclear antibodies, mostly directed against nucleolar antigens, are associated with the presence of coronary atherosclerosis Ann Rheum Dis, February 1, 2002; 61(2): 110 - 114. [Abstract] [Full Text] [PDF]
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| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
), which however, returned to within
the cutoff (– – – –) after 8 h. The peak concentration of cTnI
(
) was reached later than that of myoglobin but remained abnormally
increased a long time (>2 days). (
), CK-MB; (
), CK.