Author + information
- Received August 17, 1998
- Revision received March 6, 1999
- Accepted April 14, 1999
- Published online August 1, 1999.
- Lluı́s Mont, MDa,* (, )
- Mariana Valentino, MDa,
- Antonia Sambola, MDa,
- Mariona Matas, RNa,
- Luis Aguinaga, MDa and
- Josep Brugada, MDa
- ↵*Reprint requests and correspondence: Dr. Lluı́s Mont, Arrhythmia Unit, Cardiovascular Institute, Hospital Clinic, University of Barcelona, Villarroel 170, 08036 Barcelona, Spain
The purpose of this study was to analyze the type of arrhythmia recurrence, based on stored electrograms, in patients with a healed myocardial infarction (MI) who received an implantable defibrillator.
Previous studies suggest that patients presenting with cardiac arrest (CA) tend to recur as ventricular fibrillation (VF), whereas those suffering sustained monomorphic ventricular tachycardia (SMVT) tend to recur as SMVT. However, these data have not been confirmed in a homogeneous population of patients with MI.
A total of 88 patients was divided into three groups according to their clinical presentation: SMVT (n = 57), CA (n = 16) or syncope (n = 15).
There were no significant differences in clinical characteristics among groups. In the electrophysiologic study SMVT was induced in 93%, 94% and 80% of patients, respectively (p = NS). During the follow-up period, 52% of patients presented a total of 671 episodes of ventricular arrhythmia treated by the defibrillator. All recurrences were as SMVT except for one VF. There were 610 episodes of SMVT treated with antitachycardia pacing, with an effectiveness of 96%. A total of 61 episodes was treated initially with cardioversion. No differences in the probability of recurrence were observed among groups, although the statistical power was low (50%).
In patients with an old infarction and malignant ventricular arrhythmias, the majority of recurrences are due to SMVT independently of the clinical presentation (SMVT, CA or syncope) or the induced arrhythmia at the electrophysiologic study. The programming of an antitachycardia zone seems to be appropriate also for patients who present with CA or syncope.
There are some conflicting data about the influence of clinical presentation in the type and frequency of recurrences in patients suffering sustained ventricular arrhythmias (1–5). Some studies that analyzed an episode of cardiac arrest (CA) in patients carrying a Holter recording showed that the initial arrhythmia leading to CA was sustained monomorphic ventricular tachycardia (SMVT), which degenerates into ventricular fibrillation (VF) (3–5). However, more recent studies, analyzing arrhythmia recurrences in patients carrying implantable cardiac defibrillators (ICDs), suggest that patients presenting with CA or syncope had fewer recurrences than those with SMVT, and that survivors of CA tend to recur as VF as opposed to patients with SMVT, who recur as ventricular tachycardia (VT) (1,2). The study by Raitt et al. (1)was done in patients carrying ICDs without electrogram recording capabilities, raising some doubts in the interpretation of the arrhythmia recurrences. Furthermore, several pathologic substrates of the arrhythmia were included, which may have led to misleading information. Knowledge of the type of recurrences should be a determinant in programming the antitachycardia pacing or in choosing a device with antitachycardia pacing capability.
The aim of our study was to analyze the influence of initial arrhythmia in the recurrence of ventricular arrhythmias in patients with a healed myocardial infarction (MI) who received an ICD with electrogram storage.
Between January 1992 and February 1997, 166 automatic implantable defibrillators were implanted at our institution. Of them, 88 had a healed MI and received an ICD with electrogram storage. Patients were divided into three groups according to their clinical presentation: patients with SMVT (VT group, n = 57), patients recovered from CA (CA group, n = 16) and patients with syncope of unknown origin and VT/VF induced during the electrophysiologic study (EPS) (syncope group, n = 15). None of the patients had acute MI at the moment of the ventricular arrhythmia, and a reversible cause that could have precipitated the arrhythmia was excluded.
A patient was included in the SMVT group when there was electrocardiographic (ECG) documentation of the arrhythmia. Patients were included in the CA group when the patient presented with CA that required cardiac resuscitation including defibrillation and there was no ECG documentation of SMVT. Patients were included in the syncope group when there was a history of syncope of unknown origin and inducible ventricular arrhythmias at the EPS.
Analysis of recurrences
Recurrence as SMVT was defined as a regular tachycardia with uniform electrogram different from sinus rhythm (Fig. 1). Recurrence as “fast” SMVT was defined as SMVT with a cycle length between 220 and 300 ms (Fig. 2). Ventricular fibrillation was defined as polymorphic ventricular arrhythmia with a cycle length of <220 ms treated with cardiac shock (Fig. 3).
All patients underwent an EPS previous to the ICD implantation. The procedure was done using local anesthesia with a light sedation. All antiarrhythmic drugs were discontinued for at least 5 drug half-lives except in those who had been taking amiodarone. The programmed ventricular stimulation was done at the apex of the right ventricle at three drive train cycle lengths and during sinus rhythm up to three extrastimuli according to a previously described protocol (6). Patients were considered “inducible” when a sustained VT or VF was provoked. The induction of nonsustained VT (less than 30 s without collapse) was not considered as inducible arrhythmia.
Implantable cardioverter defibrillator
All patients who recovered from CA were considered candidates for ICD implantation after reversible causes were independently discarded from the EPS results. Patients from the SMVT group were treated with an ICD when the initial VT was syncopal, poorly tolerated due to a presyncope, angina or systolic arterial tension of <90 mm Hg or when VT was refractory to antiarrhythmic medication, including amiodarone. Patients who presented with a syncope received an ICD when during the EPS a sustained ventricular arrhythmia was induced and no other causes for syncope were identified using other tests (e.g., echocardiogram, Holter recording, tilt test, exercise testing or coronary angiogram). All the devices had the capability of electrogram storage. Devices were systematically programmed in two zones independently from the clinical presentation or from the arrhythmia induced during the EPS. The first zone was for the detection of VT with a heart rate cutoff between 180 and 200 beats/min or 10 beats/min below the rate of the clinical or the induced tachycardia when available. In this zone the criteria for the detection of “sudden onset” (9%) and stability (40 ms) were programmed if the device had the capability. As a safety feature, the sustained rate duration criteria were activated when available. The efficacy of this programming has been previously reported (7). In the VT zone an empiric antitachycardia pacing algorithm was programmed. The algorithm was not tested with EPS (8). The therapy in this zone was programmed with two schemes of antitachycardia pacing (ATP). The first (ATP1) used a maximum of eight bursts, consisting of sequences of ventricular impulses initiated by four in the first burst to a maximum of eight (with a step increment of one impulse each burst), starting at 81% of the tachycardia cycle length, and with a decrement of 4 ms in the coupling interval from burst to burst (minimal interval of 200 ms). The second scheme (ATP2) was delivered if tachycardia was not terminated by ATP1. It consisted of a maximum of eight ramps with the same number of ventricular impulses (from four to eight) and the same decrement in coupling interval (4 ms) as in ATP 1, but with a decrement of 4 ms between the impulses within the ramp and a decrement of 6 ms in the initial cycle length from one ramp to the next. The ATP attempts were delivered until tachycardia was reverted, or up to a maximum of 60 to 120 s. If ATP was unsuccessful, a low energy cardioversion was delivered. A second zone was established for VF or fast VT with a cutoff rate of 200 beats/min with only shock therapy.
Patients were discharged on the third day after implant if no complications occurred. Device interrogation was performed one month after discharge, at three months and thereafter every six months, unless the patient had arrhythmic symptoms or device shocks. The arrhythmic episodes were documented through patient interrogation and from the electrograms. If the electrograms were not available the episode was excluded from the analysis. The episodes were analyzed by two experienced observers to determine the type of arrhythmia.
Statistical calculations were performed using the SPSS package (9). The Fisher exact test or the chi-square test was used for categorical variables. One-way analysis of variance or the Kruskal–Wallis test were used for comparisons of continuous variables among the three groups. Survival curves were plotted using the Kaplan–Meier method and analyzed by the log-rank test. A value of p less than 0.05 was considered statistically significant.
The analysis of clinical variables in the three groups of patients is shown in Table 1. No differences were observed with regard to age, gender, three-vessel disease, localization of the infarction, ejection fraction, functional class, previous revascularization surgery and antiarrhythmic treatment.
All patients were inducible at the electrophysiologic testing to a SMVT or VF except one. In this patient the ICD was implanted because he presented with a fast, syncopal VT. There were no differences in the number of extrastimuli required for induction or in the type of arrhythmia induced in the three groups (Table 2).
The induced SMVT was “slower” in the VT group (310-ms cycle vs. 247 ms and 266 ms in CA and syncope groups, respectively) (p < 0.01).
The implanted devices were the following: Guidant-CPI (St. Paul, Minnesota) model Ventak PRXII and III (31 patients), Mini and Mini II (48 patients), Medtronic (Minneapolis, Minnesota) model Microjewell (4 patients) and Ventritex Contour (St. Jude Medical Ventritex, Sylmar, California) (5 patients). The implant was abdominal in 32 and thoracic in 56 patients. All individuals received a single lead. None of them required subcutaneous patch. There were six complications related to implant (9%): one pneumothorax, two hematomas in patients who received anticoagulation, a cardiogenic shock solved with medical therapy, a generator extrusion of an abdominal device that required surgical reimplantation and a late infection of the pocket with explantation and replacement of the whole system.
The mean follow-up period was the same for the three groups (20 ± 11, 23 ± 15 and 16 ± 9 months for the VT, CA and syncope groups, respectively, p = NS). Five patients died due to a cardiac cause (one of MI and four of cardiogenic shock). No CAs were observed. A total of 53 patients (60%) required antiarrhythmic therapy during follow-up to diminish the number of recurrences (Table 3). The proportion of patients receiving antiarrhythmics was similar in the three groups. Thirty-six patients (68%) received amiodarone, 6 (11%) were treated with sotalol and 11 (21%) were treated with atenolol.
During the follow-up period 46 patients (52%) presented at least one episode of sustained ventricular arrhythmia detected and treated by the device. A total of 137 episodes of recurrences that occurred in four patients with electrical storm were excluded from the analysis because the electrograms of the episodes were not available due to memory saturation. Nevertheless, the episodes analyzed in these four patients corresponded to SMVT. A total of 671 were analyzed. All recurrences were SMVT with the exception of one patient who presented VF (Fig. 3). The induction of VF during the EPS was not predictive of the recurrence as VF, because none of the patients induced to VF suffered VF during the follow-up period (Table 3). However, the induction of SMVT at the EPS was highly predictive of recurrence as SMVT, because all the episodes of recurrence were as SMVT except one.
When analyzing the probability of recurrence and the number of episodes per patient, the syncope group showed a lower percentage, although these differences were not statistically significant (Fig. 4, Table 3). The statistical power to detect differences in the probability of recurrence between the syncope group and the SMVT group was low (51% for an observed difference among groups of 33%). The power to detect differences in the number of episodes between the syncope and the SMVT group was also limited (68% for a mean number of episodes of 5.5 ± 5 vs. 15.8 ± 30, respectively). This was due to the small number of patients and recurrences in the syncope group. The cycle length of detected VT was not different among the three groups during the follow-up period (Table 4).
Five VT patients (15.2%), one patient (13%) of the CA group and one patient (15%) of the syncope group suffered only “fast” VT episodes treated with direct shock because of the high rate of the tachycardia that was directly counted in the VF zone of the device (Table 3). The remaining patients had “fast” and “slow” or only “slow” tachycardias. Tachycardias detected in the VT zone of the device were treated with antitachycardia pacing with an effectiveness of 98%, 91% and 88% for the VT, CA and syncope groups, respectively (p = NS). The efficacy of the ATP was not significantly different in patients receiving antiarrhythmic therapy as compared with those who were not on antiarrhythmics.
The introduction of ICDs with the capability to store electrograms has allowed establishment of the type of recurrences observed in patients with ventricular arrhythmias. The aim of our study was to analyze the influence of the clinical presentation on the observed recurrences in a group of patients with a healed infarction. Contrary to what has been suggested in a previous study (1), we observed that patients with ventricular arrhythmias, whose clinical presentation was VT, CA or syncope, did not significantly differ in the type of recurrence, which was usually SMVT independently from its form of presentation and from the induced arrhythmia at the EPS.
There were no differences among the three groups in their basal clinical characteristics. Previous studies have found differences according to clinical presentation (10), but they have considered several etiologies, which may have distorted the results. Our data are in agreement with the findings reported by Stevenson et al. (11)in patients with healed MI. They only found a higher percentage of multiple areas of MI in survivors of CA as compared with those with VT.
Characteristics of the EPS
The three groups presented a high inducibility to SMVT; this fact is in agreement with previous studies that observed that a healed infarction was a powerful predictor of inducibility of SMVT at the EPS (1,6).
The inducibility to any sustained arrhythmia was 100% in the syncope group, because this was a requirement in these patients to receive a defibrillator. However, there was a 100% inducibility at the CA group, which is higher than that reported in patients recovered from CA. Even in the study by Brugada et al. (6), in which the same stimulation protocol was applied to patients with healed infarction recovered from CA, the inducibility observed was lower (77%). This may be due to an unwanted bias toward implantation of the device in inducible patients. On the other hand, we observed that the induced VT was faster in the CA and syncope groups as compared with the SMVT group. This had already been observed by Brugada et al. (6). However, we did not observe differences in the cycle length of the recurrences among the three groups. Only two of the seven patients in whom the induced arrhythmia was VF recurred during the follow-up, and both presented episodes of SMVT. Therefore, the induction of VF during the EPS was not predictive of the type of recurrence, at variance with what has been reported by Mitra et al. (12). However, the later report also included patients with diverse underlying cardiopathies, and this may explain the observed differences.
Type and frequency of recurrences
Classical studies that analyzed the Holter recording in patients who died suddenly while wearing the recorder showed that death due to tachyarrhythmia was often the consequence of a tachycardia that degenerated into VF (3–5). These data are coincident with our observations. However, a recent study by Raitt et al. suggests that survivors of CA tend to have recurrences as VF, whereas those suffering SMVT tend to recur as VT (1). Several facts may explain this apparent discordance. First of all, this study included patients with several cardiopathies (from normal hearts to dilated cardiomyopathies). It is well known that patients with a healed infarction have a different underlying mechanism of the arrhythmia than patients with normal heart or other cardiopathies, and that they tend to have arrhythmias based on stable reentry circuits within the infarcted zone (13). Our data support the concept that in patients with healed infarction without acute reinfarction, the recurrent arrhythmias are initially SMVT. A second difference from the study by Raitt et al. (1)is that the latter was performed with devices without electrogram storage, which may have led to misclassification of some cases of fast VT as VF.
In our study we have not observed significant differences in the probability of recurrence or in the number of episodes per patient between the three groups. Menz et al. (2), in a similar analysis, found a higher probability of recurrence in patients presenting with SMVT. However, his series included several etiologies that may greatly influence the results, as we have already pointed out.
The majority of episodes of SMVT were treated with antitachycardia pacing with high effectiveness in the three groups. The percentage of episodes of “fast” VT not amenable to antitachycardia pacing was similar among the three groups. According to these observations, the use of the empirical antitachycardia algorithm is recommendable in the three groups, and there is no need to perform a predischarge EPS to test the efficacy of the algorithm.
Observations in patients with syncope of unknown etiology and healed infarction
Patients with syncope as the presenting symptom showed similar clinical characteristics and results at the EPS. There were no differences with the other groups in the type and probability of recurrence. However, there seems to be a tendency toward a lower number of recurrences, although not significant, due presumably to the small number of patients in this group. Link et al. (14)have observed a significant percentage (22%) of appropriate therapies of the ICD in patients with syncope and inducible arrhythmias after a short follow-up. We have recently published data showing that all patients who completed one year of follow-up received appropriate therapy (15). All of these data strongly support the use of defibrillator with antitachycardia pacing in these patients, despite the lack of ECG recording of the index episode.
Clinical implications for the use of ICDs
Several variables are well known as predictive of therapy by the ICD, among them the depressed ejection fraction, the inducibility to SMVT and the number of extrastimuli required for induction (16,17). However, the importance of the underlying cardiopathy in determining the type of recurrence has not been emphasized. The fact that patients with healed MI tend to recur as SMVT independently of the clinical presentation or the induced arrhythmia has important consequences in choosing the kind of device and the subsequent programming. According to our findings, patients with malignant ventricular arrhythmias and healed infarction should receive an ICD with antitachycardia pacing programming even if the clinical presentation was VF, or VT was not induced at the EPS.
The small number of patients in the CA and syncope groups may be the reason that no significant differences in the probability of recurrence between groups were observed; in fact, the statistical power to detect meaningful differences in the probability of recurrences and in the number of recurrences was 51% and 68%, respectively. However, this would not affect the main finding in the study that in patients with healed infarction and malignant ventricular arrhythmias, recurrences occur as SMVT independently of the clinical presentation.
- antitachycardia pacing
- cardiac arrest
- electrophysiologic study
- implantable cardiac defibrillator
- myocardial infarction
- sustained monomorphic ventricular tachycardia
- ventricular fibrillation
- ventricular tachycardia
- Received August 17, 1998.
- Revision received March 6, 1999.
- Accepted April 14, 1999.
- American College of Cardiology
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