Download Arrhythmic risk stratification of post–myocardial infarction patients

Arrhythmic risk stratification of post–myocardial
infarction patients
Franco Naccarella, MD, FACC,* Giovannina Lepera, MD,* and Angelo Rolli, MD†
Post–myocardial infarction risk stratification, especially arrhythmic risk stratification, is an issue that has still not been wholly
addressed in modern clinical cardiology. In the past 10 years,
arrhythmic risk stratification has been approached mainly by
evaluating frequency and complexity of premature ventricular
contractions, detected on Holter monitoring, often in association with determination of percent ejection fraction. This
methodology has been proven to be limited and fallacious
according to the Cardiac Arrhythmia Suppression Trial I and II
(CAST I,II) results, in which suppression of premature ventricular contractions or premature ventricular beats throughout by
antiarrhythmic drugs resulted in an increase in both cardiac and
arrhythmic mortality. Only amiodarone as an antiarrhythmic
drug, as proven in the recent European Myocardial Infarct
Amiodarone Trial (EMIAT) and Canadian Amiodarone
Myocardial Infarction Trial (CAMIAT), was effective in reducing
arrhythmic mortality without affecting cardiac mortality, in
patients selected mainly because of a reduced ejection fraction, with and without premature ventricular contractions.
Conversely, it is well known that β-blockers are effective in
preventing sudden death in post–acute myocardial infarction
(AMI) patients, thus reducing cardiac and arrhythmic mortality.
Conversely, in other institutions, risk stratification in post-AMI
patients has been performed by electrophysiologic study
obtained, without any previous noninvasive arrhythmic risk stratification, in all post-AMI patients. In recent years, many other
noninvasive electrocardiology parameters, such as late potentials (signal-averaged electrocardiography), heart rate variability,
baroreflex sensitivity, and, more recently, T-wave alternance,
have been shown to be useful, but they are associated with a
low specificity in the noninvasive identification of patients at
high risk for arrhythmic mortality. Conversely, in the Multicenter
Automatic Defibrillation Implantation Trial (MADIT), electrophysiology confirmed that inducibility of ventricular tachycardia
shows high specificity and a high predictive value for arrhythmic
events. Nevertheless, the MADIT study population is not
comparable to a cohort of consecutive patients who have
recently had a myocardial infarction. In this setting, the highest
risk of arrhythmic events can be observed in patients with
depressed percent ejection fraction (< 35%) and in the first 6
months after AMI. Today, the most convincing approach seems
to be the one combining both noninvasive risk stratification
parameters (eg, premature ventricular beats > 10/h or reduced
heart rate variability < 70 ms or a positive signal-averaged electrocardiogram) followed by a further arrhythmic risk stratification, obtained through electrophysiologic study. Several
published and ongoing trials that utilize various arrhythmic risk
stratification techniques as part of their protocol are reviewed.
*Dipartimento di Cardiologia, Azienda Sanitaria della Citta’ di Bologna, Bologna,
Italy; †Divisione di Cardiologia Azienda Ospedaliera di Parma, Parma, Italy
Correspondence to Franco Naccarella, MD, FACC, Cardiologia Bologna, Via
Mascarella 77/5, 40126 Bologna, Italy; e-mail: [email protected]
Current Opinion in Cardiology 2000, 15:1–6
Abbreviations
AMI
ARS
BEST ICD
EF%
EPS
ICD
GISSI
HRV
MADIT
NIRS
NSVT
PVB
acute myocardial infarction
arrhythmic risk stratification
Best Strategy Plus ICD Study
percent ejection fraction
electrophysiologic study
implantable cardioverter defibrillator
Gruppo Italiano per lo Studio della Sopravvivenza nell’infarto-1
Study
heart rate variability
Multicenter Automatic Defibrillation Implantation Trial
noninvasive risk stratification
nonsustained ventricular tachycardia
premature ventricular beat
ISSN 0268–4705 © 2000 Lippincott Williams & Wilkins, Inc.
Arrhythmic risk stratification (ARS) of post–acute
myocardial infarction (AMI) patients is intended to identify subgroups of patients with different risks of sudden
death, using clinical parameters and data derived from
noninvasive risk stratification (NIRS) or invasive procedures. Furthermore, ARS is obtained to identify the best
therapeutic strategy for these patients.
In fact, recent clinical studies have demonstrated that
antiarrhythmic drugs, such as amiodarone, did not change
total cardiac mortality, although they did decrease
arrhythmic and sudden death mortality. Conversely, in
the Cardiac Arrhythmia Suppression Trial, class IC and
IA antiarrhythmic drugs showed an increase in both
cardiac and arrhythmic mortality (CAST I,II).
In the Multicenter Automatic Defibrillation Implantation Trial (MADIT) II and Antiarrhythmics Versus
Implantable Defibrillators Trial studies, implantable
cardioverter defibrillator (ICD) therapy was the most
effective treatment for both primary and secondary
prevention of sudden death, in comparison with conventional antiarrhythmic drugs. Today the most important
problem is to identify patients best suited for the treatment that will be more effective in the primary prevention of sudden death. Furthermore, physicians should
be able to identify patients, both at very high risk of
future arrhythmic events or sudden death who are, at
the same time, at low risk of nonarrhythmic mortality.
Curr Opin Cardiol 2000, 15:1–6 © 2000 Lippincott Williams & Wilkins, Inc.
1
2 Arrhythmias
Ventricular function
Left ventricular function, measured as percent ejection
fraction (EF%) is still, even in the postfibrinolytic
therapy era, the most useful indicator in predicting
cardiac mortality, which it predicts better than arrhythmic mortality (Table 1) [1–22].
Ventricular arrhythmias
Frequent premature ventricular beats (PVB) still represent an independent prognostic factor for cardiac and
arrhythmic mortality [1–22]. Premature ventricular beats
are more frequently documented in patients with
reduced EF% (31.8% of patients with EF < 35%). A
two- to threefold increase in the mortality rate is
observed in this subgroup of patients 6 months after
AMI (data from the Gruppo Italiano per lo Studio della
Sopravvivenza nell’Infarto-1 Study [GISSI] study)
(Tables 1 and 2) [1,3•,5–22].
Nonsustained ventricular tachycardia (NSVT) is
observed in 11% to 15% of post-AMI patients. The presence of NSVT is associated with a 21% mortality (34%
mortality in patients with reduced EF%) in comparison
with 8% mortality among patients without NSVT. The
risk, independent of EF%, was more evident in the first
6 months after an AMI, but persisted over a 3-year
follow-up period. In the GISSI study, NSVT was documented in 7% of patients (12.3% in those with reduced
EF%). It did not affect total mortality, but only arrhythmic mortality, which was verified to be as low as 1%, in
the first 6 months. Thus, the frequency and complexity
of ventricular arrhythmias should still be assessed in the
immediate posthospital phase of MI, only in patients
with a reduced EF% (< 35%). These parameters identify patients at high risk of sudden death, who should be
further stratified by electrophysiologic study (EPS), as
proposed in the Best Strategy Plus ICD (BEST ICD)
Study, to identify those at higher risk of sudden death
(Tables 1 and 2).
With this purpose, EPS has previously been used, as a
single and basic method, for ARS of post-AMI patients.
Conversely, some other groups have used the so-called
noninvasive approach. This approach focuses mainly on
Table 1. Relationship between percent ejection fraction and
premature ventricular beats in the Multicenter Investigation for
Limitation of Infarct Size study (MILIS)
Patients
PVB < 10
PVB > 10
PVB < 10
PVB > 10
EF > 40%
EF < 40%
EF > 40%
EF < 40%
Global
mortality, %
Sudden
death
mortality, %
Relative risk
5
19
20
40
2
10
8
18
1
6
5
11
EF, ejection fraction; PVB, premature ventricular beats.
defining the frequency and complexity of ventricular
arrhythmias by electrocardiographic recording techniques (Tables 1, 2, 3, and 4). Today, a more comprehensive approach includes EPS after the risk stratification has been completed by using EF% and ambient
ventricular arrhythmia identification or other NIRS
parameters. Using this approach, two studies (MADIT
II and BEST AICD) have been recently proposed (Figs.
1 and 2).
The MADIT II study will verify whether the implantation of an ICD, in moderately high risk patients, will
result in a significant reduction in overall mortality,
when compared with no ICD treatment. Furthermore, a
secondary objective will be to determine whether
ventricular tachyarrhythmias and ventricular fibrillation,
induced during implantation, are associated with more
appropriate ICD discharge, during the follow-up, than is
seen in noninducible ICD patients. This will also prove
the utility of EPS in risk stratification of these patients.
The trial is also supposed to prove, as a secondary objective, whether Holter monitoring, signal-averaged electrocardiography, heart rate variability (HRV), QT
dispersion, or T-wave alternance, obtained after
randomization, can identify patients with higher mortality in the conventional treatment arm. Moreover, information will be collected to determine whether NIRSidentified high-risk patients have more appropriate ICD
discharges [13–18,23–27,28•,29•].
Even the BEST ICD study will try to prove the utility
of a combined sequential noninvasive ARS followed by
EPS (Fig. 1). The main differences between MADIT II
and BEST ICD, in this respect, are as follows. In the
BEST ICD study, noninvasive ARS will be limited to
PVB frequency on Holter monitoring or reduced HRV
(< 70 ms) or positive signal-averaged electrocardiogram,
whereas, in the MADIT II study, all the noninvasive
electrocardiology methods for ARS will be assessed. In
the BEST ICD study, EPS will be obtained after a 2:3
randomization of patients who have been previously
selected by NIRS, whereas in the MADIT II study,
only patients randomly assigned to receive ICD will be
tested by EPS. Successively, all patients, randomly allocated between ICD and no-ICD, will be tested by
NIRS.
Conversely, another study using the ICD, in both postAMI patients with coronary artery disease or patients with
dilated nonischemic cardiomyopathy with heart failure
and EF% less than 35%, will not use any noninvasive
ARS at all (Fig. 3). In other words, clinicians think that
the NIRS methods could be more valuable in ARS of
post-AMI patients without congestive heart failure, in
comparison with patients with congestive heart failure,
Arrhythmic risk stratification of post–myocardial infarction patients Naccarella et al. 3
Table 2. Sensitivity and specificity of ventricular arrhythmias in the Betablocker Heart Attack Trial (BHAT) in predicting
total mortality and sudden cardiac mortality
Total mortality, %
Premature ventricular beats
features
Sudden death mortality, %
Sensitivity
Specificity
Sensitivity
Specificity
26
33
44
14
88
82
76
94
25
34
43
16
87
80
75
94
10/h
Repetitive
10/h or repetitive (either)
10/h and repetitive (both)
due mainly to dilated nonischemic cardiomyopathy or
minor or chronic coronary artery disease. At least, the clinical value of the NIRS methods, in association with or
followed by EPS, should be more easily assessed in postAMI patients, about whom we do have more information
on the usefulness of NIRS alone or primary EPS for ARS.
Signal-averaged electrocardiography
Late potentials have been documented in 25% to 50% of
patients 1 to 4 weeks after AMI. They are predictive of
spontaneous or inducible ventricular arrhythmias or
sudden death (even with a low specificity in this respect),
even though they have been more frequently documented
in patients with reduced EF% and their prognostic significance is independent of the EF% itself [8,19,26,28•].
A very high number of false-positive results have been
observed with this method. Thus, late potentials show
great limitations when used alone in this clinical setting.
There is substantial agreement among cardiologists to
use late potentials together with other parameters or
NIRS methods or in association with EPS [26,28•].
Neurovegetative tone measurements
Increasingly widespread attention has been paid to the
use of neurovegetative tone measurements, specifically
HRV and baroreflex sensitivity in the NIRS of postAMI patients [9,10•,19–22].
HRV and total post-AMI mortality. The observed
mortality was independent of other prognostic factors,
and a fivefold increase in mortality has been observed
in patients exhibiting an HRV of less than 50 ms. The
change in HRV can be observed soon after an AMI
and can be almost completely reversed 6 to 12 weeks
after the episode, with some exceptions due to age
and sex. The prognostic value of reduced HRV is
more evident in the subgroup of patients with an EF%
of less than 30% [10•].
Concurrent with this normalization, a reduction in
mortality has been observed in the Cardiac Arrhythmia
Pilot Study (CAPS). The new predictive value is
preserved even if the evaluation is performed after 1
year and also after fibrinolytic therapy. Even HRV
measurements, performed in the frequency domain, do
not improve the positive predictive value of those
indices, which have the same limitations as other NIRS
parameters or methods.
Numerous technical limitations and variability of these
parameters according to sex, age, and drug interferences,
EF%, AMI location, and concomitant diseases have been
observed. Furthermore, HRV evaluation cannot be
performed in patients with atrial fibrillation or frequent
arrhythmias as premature atrial or ventricular beats.
Baroreflex sensitivity
In the Multicenter Postinfarction Study (MPS), a
strong correlation has been found between reduced
A linear relation has been proved between an increase in
blood pressure and changes in the RR interval. This
Table 3. Prognostic significance of inducible ventricular arrhythmias in post–acute myocardial infarction patients
Study
Bhandari
Roy
Santarelli
Richards
Marchlinski
Breithardt
Hamer
Denniss
Bhandari
Waspe
Naccarella
All patients:
Observations
75
150
50
165
46
132
70
403
53
50
120
1314
EPS
VT VF, %
Arrhythmic events, %
44
23
46
23
22
46
17
34
33
17
19
Mean value: 30.5
VF, ventricular fibrillation; VT, ventricular tachycardia; EPS, electrophysiologic study.
15
5
0
33
17
16
42
12
37
42
30
69.4
EPS negative, %
56
77
54
77
78
54
83
66
66
83
43
69.4
Arrhythmic events, %
5
1
0
3
9
4
9
4
6
9
5
5
4 Arrhythmias
Table 4. Results of programmed electrical stimulation in post–acute myocardial infarction patients with nonsustained
ventricular tachycardia
No structural
heart
Observations disease, %
Study
Gomes
Sulpizi
Veltri
Buxton
Khasha
Zheutlin
Winters
Klein
Kowey
Wilber
Manolis
Turitto
73
61
33
62
40
88
53
40
205
100
52
105
10
23
12
0
NSVT
27
15
42
45
20
37
25
55
64
43
40
24
0
0
912
Induced ventricular
arrhythmias, %
10
46
21
24
25
7.5
VT, %
VF, %
11
15
21
39
7
0
0
6
22
14
21
5
Arrhythmic
events rate,
%
31
11
14
25
0
12
0
40
19
0
9
14
36
Noninducible
ventricular
Arrhythmic
arrhythmias, events rate,
%
%
73
39
58
31
10
6
23
12
0
0
0
0
36
63
65
7
3
6
52
6
versus
versus
NSVT, nonsustained ventricular tachycardia; VF, ventricular fibrillation; VT, ventricular tachycardia.
relation can be changed and decreased after an AMI: its
decrease correlates with an increase in the number of
arrhythmic events and makes ventricular tachycardia
episodes more easily inducible at EPS [10•].
Figure 1. Patient enrollment cascade of Best Strategy Plus ICD
Study (BEST-ICD)
EF < 35%
Noninvasive testing:
Holter and SAECG
NSVT or VT
MADIT
screening
The recent Autonomic Tone and Reflexes After
Myocardial Infarction Study (1284 post-AMI patients,
with a mean follow-up of 21 months and a total of 49
cardiac deaths) showed that reduced baroreflex sensitivity represents a prognostic parameter independent of
EF% and the presence of ventricular arrhythmias with a
prognostic value in addition to that of a reduced HRV.
Commentary on this study confirms that a reduced
baroreflex sensitivity associated with a reduced EF% (<
35%) in patients less than 65 years of age increases the
relative risk of arrhythmic events to the point where no
other ARS procedures would be necessary. The clinical
and prognostic value of combining HRV and baroreflex
PVBs ≥ 10/h
or HRV (SDNN < 70 ms)
or SAECG+
Metoprolol
(if not initiated before)
Contraindicated,
not tolerated, or
other exclusion
criteria
Figure 2. Study design of Multicenter Automatic Defibrillation
Implantation Trial (MADIT) II
Out
Randomization 2:3
(BB + conv.
therapy)
Conventional
strategy
CAD, ≥ MI > 1 mo after AMI
LV-EF ≤ 30%; age > 21 y
EPS
–
+
BB + conv. ICD + BB +
therapy conv. therapy
EP-guided
strategy
© 2000 Lippincott Williams & Wilkins
BB, β-blockers; EF, ejection fraction; EP, electrophysiologic; EPS, electrophysiologic study; HRV, heart rate variability; ICD, implantable cardioverter defibrillator;
MADIT, Multicenter Automatic Defibrillation Implantation Trial; NSVT, nonsustained ventricular tachycardia; PVB, premature ventricular beats; SAECG, signalaveraged electrocardiogram; SDNN, standard deviation of normal RR interval
variability on electrocardiograms; VT, ventricular tachycardia.
R
NIRS
ICD
+ EPS
Follow-up
No-ICD
BB, ACE-I
No AAD
© 2000 Lippincott Williams & Wilkins
PE: total mortality
AAD, antiarrhythmic drugs; ACE-I, angiotensin-converting enzyme inhibitors;
AMI, acute myocardial infarction; BB, β-blockers; CAD, coronary artery disease;
EPS, electrophysiologic study; ICD, implantable cardioverter defibrillator; LV-EF,
left ventricular ejection fraction; MI, myocardial infarction; NIRS, noninvasive risk
stratification.
Arrhythmic risk stratification of post–myocardial infarction patients Naccarella et al. 5
Figure 3. Study design of the Sudden Cardiac Death–Heart
Failure Trial (SCD-HeFT)
I
Conventional Rx
+
Placebo
Double
blind
CAD + DCM
CHF – NYHA II + III
LV-EF ≤ 35%
R
II
III
Conventional Rx
+
Amiodarone
Conventional Rx
+
ICD
© 2000 Lippincott Williams & Wilkins
(single lead,
pectoral,
outpatient
implantation
CAD, coronary artery disease; CHF, congestive heart failure; DCM, dilated nonischemic cardiomyopathy; ICD, implantable cardioverter defibrillator; LV-EF, left
ventricular ejection fraction; NYHA, New York Heart Association classification.
sensitivity in ARS of post-AMI patients will be strongly
enhanced by the demonstration that both indices are
more predictive of the occurrence or nonoccurrence of
arrhythmic events, as supported by previous clinical and
experimental studies.
Electrophysiologic study
Previous studies have demonstrated that the induction
of sustained ventricular tachyarrhythmias during EPS
performed after a recent AMI represents the strongest
predictive factor for the occurrence of future arrhythmic
events. The differences in the positive predictive value
of EPS, observed in the medical literature, are mainly
due to differences in the patient population, in the stimulation protocols, and particularly in the time intervals
between EPS and AMI [12,23–27,28•,29•].
Furthermore, EPS is an invasive procedure that can only
be performed in specially equipped hospitals and by fully
trained personnel, can be associated with complications
and risks, and is costly. Therefore, EPS should not be
proposed as the main procedure for post-AMI ARS.
Table 3 gives the results of studies using EPS in a nonselected post-AMI patient population. In Table 4, similar
results of EPS, obtained in patients with NSVT, are
shown. Today, it is well accepted that the most appropriate use of EPS should be in patients already selected for
having positive results on NIRS.
In previous studies, Pedretti et al. [22,26] showed that
patients having one of certain parameters—EF% less than
40%, late potentials, frequent PVB (Lown class 4A and
B)—represent 20% to 25% of all post-AMI patients. In
our experience this frequency is about 10% to 15% [10•].
Furthermore, these patients showed a 30% incidence of
ventricular arrhythmias in a 15-month follow-up period. In
these patients, the inducibility of ventricular tachyarrhythmias during EPS has been shown to be the most effective
independent variable predictive of arrhythmic events
(specificity of 97% and positive predictive value of 65% of
EPS vs 88% and 30%, respectively, of NIRS methods).
Acknowledgments: We thank Donatella and Roberto Orlando for typing and
preparing the final manuscript, tables, and figures and Alejandro Nunez for
correcting the English version of the text.
References and recommended reading
Papers of particular interest, published within the annual period of review,
have been highlighted as:
•
••
Of special interest
Of outstanding interest
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••
Raviele A, Bongiorni MG, Brignole M, Cappato R, Capucci A, Gaita F, et
al.: Which strategy is “best” after myocardial infarction? The Beta-Blocker
Strategy Plus Implantable Cardioverter Defibrillator Trial: rationale and
study design. Am J Cardiol 1999, 83:104D-111D.
This article represents a prospective ongoing protocol that will assess the
usefulness of ICD in medium-high-risk post-AMI patients (different subgroups)
selected on the basis of an increased risk of sudden death (the BEST ICD
study).
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Klein H, Auricchio A, Reek S, Geller C: New primary prevention trials of
sudden cardiac death in patients with left ventricular dysfunction: SCDHEFT and MADIT-II. Am J Cardiol 1999, 83:91D–97D.
This article refers to two studies assessing the usefulness of ICD in post-AMI
patients with reduced EF% (MADIT II) and in patients with congestive heart
failure, New York Heart Association II and III (SCD-HeFT).