macrowave t alternans or macroscopic alternation in a

Transcription

MACROWAVE T ALTERNANS OR MACROSCOPIC
ALTERNATION IN A PATIENT WITH
ACQUIRED LONG QT INTERVAL
Case of Dr. Raimundo Barbosa de Barros MD, from Ceará, Brazil
Commentaries and presentation: Dr. Andrés Ricardo Pérez Riera MD
English
Dearest friend Professor. Andrés This feminine patient of 79 years old, was interned in another
hospital in treatment with azitromicina consequence of respiratory infection.
In the fifth day she presented several syncope’s episodes having been transferred to our
institution (Hospital of Messejana).
The ECG carried through in the emergency disclosed prolonged QT Interval with macro Twave alternans (TWA) beat-to-beat (See below II long). Probably this sick person presented
episodes of torsades of pointes (not registered).
After 5 days, with drugs interruption, partial reduction of the QT interval prolongation was
observed. Unhappily the patient does not possess previous ECGs for comparison.
What you find?
Raimundo Barbosa de Barros. MD Ceará, Brazil
Portuguese
Prezado amigo Prof. Andrés
Esta paciente de 79 anos anos ,fem,estava internada em outro hospital em tratamento para
infecção respiratória com azitromicina.No quinto dia apresenou episódios sincopais sendo
transferida para nossa instituição(Hospital de Messejana).ECG realizado na emergência revela
QTL com alternância de onda T (vide traçado longo).Provavelmente esta doente apresentou
episódios de torsades de pointes(não documentados).Concorda? Após 5 dias observa-se
redução parcial do QT.Infelizmente a paciente não possui ECGs prévios para comparação.O
que voce acha?
Dr. Raimundo Barbosa de Barros Ceará Brasil
LONG II LEAD
MACRO T-WAVE ALTERNANS (TWA) BEAT-TO-BEAT
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T WAVE ALTERNANS: MACRO AND MICROVOLT
AI
AI
A) MACROSCOPIC OR MACROVOLT
T WAVE WITH POLARITY MACROVOLT ALTERNANS
LONG QT INTERVAL
AII) T WAVE WITH AMPLITUDE MACROVOLT ALTERNANS
AII
B
B
T wave alternans. 1:1
sequence type, with A-B,
A-B pattern. In the upper
part (AI) we see polarity
macrovolt
alternans,
visible
in
the
conventional
ECG
tracing.
Similar
to
present case.
In the central part (AII),
we see the so-called
amplitude
macrovolt
alternans, also called
macroscopic.
B) MICROSCOPIC OR MICROVOLT
In the lower part (B) we
see microvolt T wave
alternans
(mATW
or
MTWA). This pattern is
not detectable by visual
inspection of surface
ECG.
MICROVOLT T WAVE ALTERNANS (MTWA) AS
NONINVASIVE MARKER FOR ARRHYTHMOGENIC
SUDDEN CARDIAC DEATH RISK
From English: TWA: T “wave alternans”, mTWA microvolt T-wave alternans or
Microvolt T wave alternans (MTWA).
The alternation may be defined as a beat-to-beat variation of morphology, amplitude
and/or polarity of P waves, QRS complex, T or U waves, isolated or in combination,
considering they originate in a pacemaker.
The alternation may be defined as a beat-to-beat variation of morphology, amplitude
and/or polarity of P waves, QRS complex, T or U waves in isolation or combined,
considering they originate in a pacemaker.
The most frequent type of alternation is the one that affects only the QRS complex.
When it includes the three main waves (P, QRS and T), it is called total alternation, which
is observed in cases of cardiac tamponade. This type of alternation is in fact, just a
pseudo or apparent electrical alternans, because it results from a sequential rotational
change of the heart suspended within the pericardial bag1. In it there is no intrinsic
electrophysiological alternation; therefore, there will be no increased risk of
tachyarrhythmic events.
1) Armoundas AA, et al.Card Electrophysiol Rev. 1997;1:390-394.
T or U wave alternans in association to long QTU interval and appearance of ventricular
tachycardia (VT) of the Torsade de Pointes (TdP) type, is a rare fact, and it may be due
to 2:1 propagation of early depolarization or alteration in repolarization kinetics. The
constant probability of early depolarizations occurring, related to phase 0 and alteration
during phase 2, suggests ionic mechanism synchronized with depolarization.
Both clinically and experimentally, the long QTU interval with TU alternans, depends on
tachycardia; i.e. the increase in HR enhances the electrical instability in such cases1.
1) Habbab MA, et al. Pacing Clin Electrophysiol. 1992; 15:916-931.
Alternation of T wave only may manifest as different alternated polarities (AI) or lower
and greater voltage of the alternating wave (AII) with a 1:1 type sequence in a pattern
called A-B, A-B. This sequence could be 2:1 or more rarely, 3:1.
When T wave alternans can be detected by visual inspection of surface ECG, it is called
macrovolt T wave alternans or macroscopic alternation, which has two varieties: of
polarity and of amplitude.
In the first one, a wave of positive polarity with another one of negative polarity,
alternate sequentially. This variety was described for the first time by Schwartz and
Malliani, in patients carriers of congenital long QT syndrome. These authors showed
that changes in T wave polarity may be reproduced experimentally, by stimulation of the
left stellate ganglion1.
T wave alternans consists of polarity or voltage modifications in the main wave, which
represents ventricular repolarization (T wave) along with the ST segment preceding it
and the U wave after it. The phenomena correspond to ST segment (phase 2), T wave
(phase 3) and U wave (phase 4) of action potential (AP).
1) Schwartz PJ, et al. Am Heart J 1975; 89: 45-50.
Isolated T wave alternans (phase 3 of AP) in absence of QRS complex changes (phase 0
of AP) or of P wave, was described for the first time by Hering in 1908 and 19091;2 and by
Lewis in 19103. In 1913 Mines described it as the consequence of electrolytic alterations4
and Taussig in the papillary muscle of cats in 19285.
Microvolt T wave alternans is more frequent during tachycardia, either spontaneous or
induced by exercise in treadmill or bicycle, pharmacologically, by artificial atrial or
simultaneous atrioventricular pacing, or during sudden changes in cardiac cycle extension.
Isolated T wave alternans, not related to tachycardia, may be observed macroscopically,
and it usually indicates advanced or severe heart disease, electrolytic alteration, or
congenital long QT syndrome: “macroscopic T-wave alternans” 6
1) Hering HE. Munchen Med Wochenshr 1908;4:1417-1421.
2) Hering HE. Z Exp Pathol Ther 1909;7:363
3) Lewis T, et al. J Med 1910; 4:141-144.
4) Mines GR. J Physiol 1913:46:188-235.
5) Taussig HB. Bull Johns Hopkins Hosp.1928; 43:81.
6) GrabowskiM, Circulation 2004;110:e459-60.
MAIN CAUSES OF MTWA
1)
2)
3)
4)
5)
6)
1)
2)
3)
4)
5)
Tachycardia, either spontaneous or induced by exercise, drugs or pacemaker;
Sudden changes in cycle length or heart rate1;
Electrolytic disorders: E.g.: severe hyperpotasemia in uremia, in
hypomagnesemia2 and experimentally in hypocalcemia in dogs3;
Hypothermia.
Idiopathic dilated cardiomyopathy: a prospective observational study suggests
that the presence of MTWA during stress test in this group of patients, is a
strong independent predictor of VTs4. In spite of this, the study included
patients that had a cardioverter defibrillator implant, which is considered a bias
in the sample selection.
In hypertrophic cardiomyopathy (HCM): Momiyama et al5 studied 14 patients
carriers of HCM and 7 controls, and observed a positive result in 71% of
patients carriers of HCM and 0% in the 4 controls.
Fisch C, et al. Am Heart J 1971; 81:817.
Habbab MA, et al. Pacing Clin Electrophysiol. 1992;15:916-931.
Navarro-Lopez F, et al. J Electrocardiol. 1978; 11: 103-108.
Hohnloser SH, et al. J Am Coll Cardiol. 2003;41:2220-2224.
Momiyama Y, et al. Jpn Circ J. 1997;61:650-656.
MAIN CAUSES OF MTWA
7)
8)
9)
1)
2)
3)
Arrhythmogenic RV dysplasia: from 7 patients carriers of ARVD, 86% presented
positive MTWA, and just 8% of the patients idiopathic MVT originating the RV
outflow tract1.
Post-acute myocardial infarction (after 4 to 6 weeks of the event) 2 Cardiac
Arrhythmias and Risk Stratification after Myocardial infarction (CARISMA)
investigators: patients with MTWA presented less ejection fraction and greater
QT interval dispersion, in comparison to those with inconsistent results;
In acute myocardial ischemia, especially Prinzmetal’s variant angina3;
Kinoshita O, et al. Cardiology. 2003;100:86-92.
Raatikainen MJ, et al. Pacing Clin Electrophysiol. 2005; 28:193-197.
Murda'h MA, et al. Pacing Clin Electrophysiol. 1997; 20:2641-2657.
MAIN CAUSES OF MTWA
10)
In post-resuscitation period;
11)
In acute pulmonary embolism;
12)
Rarely after use of amiodarone1;
13)
In heredo-familial long QT syndromes, of the Romano-Ward or Jervell-LangeNielsen types2; 3; 4 ;
14)
In Brugada syndrome: T wave alternans has been observed spontaneously, or
as a response to endovenous administration of certain class I antiarrhythmic
agents, during glycose tolerance test and atrial pacing5; 6 .
1) Bardaji A, et al. J Electrocardiol. 1993;26:155-157.
2) Hiejima K, et al. Br Heart J. 1976; 38:767-70.
3) Schwartz PJ, et al. Am Heart J 1975; 89:45-50.
4) Zareba W, et al. J Am Coll Cardiol 1994; 23:1541-6
5) Nishizaki M, et al. J Cardiovasc Electrophysiol. 2005;16:217-220.
6) Tada H, et al. PACE 2000;23:413-415.
MEASUREMENT OF MTWA
The measurement of T wave alternans, whether in microvolts or microvolt alternans is
too small to be seen in the ECG. It may be documented by a special method, during
high heart rates of 110 bpm, by submaximal stress test, artificial atrial or atrioventricular
pacing, or drugs.
When it is present, it may be highly predictive of VT/VF and sudden cardiac death, and
superior to other noninvasive markers for risk of fatal arrhythmias.
Microvolt T wave alternans
mATW
MTWA
Rangede
Faixa
ofalternância
alternation em
in !!VV
da
of Tamplitude
wave amplitude
da onda T
Batimento
beat to beata batimento
Appropriate alignment
Alinhamento
apropriado
dos
of
QRS
complexos
complexes
QRS
T wave alternans is expressed in !V. The measurement of microvolt T wave alternans is
made through a computerized system, with specific processing of the signal, and it
requires using special electrodes with multicontact sensors.
RISK MARKERS FOR SUDDEN CARDIAC DEATH
BY SEVERE VENTRICULAR ARRHYTHMIA:
SVT/VF
NONINVASIVE
1)
Presence of late potentials in high resolution ECG (HRECG): it assesses the
presence of late potentials at the end of depolarization, and therefore, it is limited
in the presence of dromotropic disorders (branch blocks). This method in general,
has shown to have less correlation as predictor of sudden cardiac death (SCD) by
ventricular arrhythmia, in comparison to microvolt T wave alternans1. The method
has been approved by the FDA for clinical use in the identification of patients with
risk of sudden cardiac death;
1) Gold MR, et al. J Am Coll Cardiol 1999; 33 (suppl):145A.)
SVT/VF
NONINVASIVE
2)
Heart rate variability (HRV). Decreased variability of RR interval;
3)
Increased QT interval dispersion;
4)
Long QT interval;
5)
Presence of NS-VT or premature ventricular contractions in long duration
ECG or 24 hs Holter;
6)
Estimation of ejection fraction by echocardiogram or other noninvasive
methods: values <40% constitute a risk marker;
7)
Heart rate turbulence (HRT)
8)
V Index: new method that quantifies vagal tone. It identifies post-AMI patients
in low risk.
SVT/VF
NONINVASIVE
9)
Microvolt T wave alternans (MWTA): it analyzes ventricular repolarization. In
patients carriers of CHF by ischemic and nonischemic heart disease, the
positive predictive value for arrhythmic events was 19.3% in a 21-month follow
up (95% confidence interval 17.7% to 21.0%), the negative predictive value was
97.2 (95% CI 96.5% to 97.9%) and the univariate relative risk of events was
3.77 (95% CI 2.39 to 5.95). There were no differences in the predictive value
between patients with CHF by ischemic and nonischemic heart disease. The
positive predictive value varied depending on the population studied (p <
0.0001)1. The method has been approved by the FDA for clinical use in the
identification of patients with risk of sudden cardiac death.
1) Gehi AK,et al. J Am Coll Cardiol. 2005; 46:75-82.
SVT/VF
INVASIVE
Electrophysiologic study: regrettably, this method besides being invasive and imperfect,
is costly1. According to the opinion by Pedretti et al2 the electrophysiologic study should
not be performed and cardioverter defibrillators should not be implanted in postinfarction patients with moderate ventricular dysfunction (EF between 30% and 40%)
with preserved autonomic balance, negative MTWA test and without nonsustained VT.
1)
2)
Buxton AE, et al. N Engl J Med 1999; 341:1882-1890.
Pedretti RF, et al. Ital Heart J. 2005; 6:180-189.
HOW TO EXPLAIN T WAVE ALTERNANS
ELECTROPHYSIOLOGICALLY?
According to Lepeschkin, T wave alternans results from alternation in monophasic action
potential (AP) duration, associated to changes in the diastolic interval, which is longer after a
shorter AP.
Alternating action potentials.
Ventricular repolarization (return to the polarized or rest state), should have the same
depolarization sequence; i.e. it should start in the middle 1/3 of the left septal surface,
after activating the rest of the septum, free walls of the two ventricles from the
endocardium to the epicardium, and from the apex to the basal (superior) regions.
Due to temperature and pressure reasons, the process is inverted; i.e. repolarization
onset is delayed in the endocardial region of the left septum, and thus, it begins in the
epicardium and from the base of the apex1.
1) Cowan JC, et al. Br Heart J. 1988;60:424-433.
These sequential changes are due to the fact that repolarization occurs during
mechanical systole, which makes the pressure exerted on the endocardium to be
greater than on the epicardium. Thus, the endocardial vessels are compressed, with
relative physiological ischemia in comparison to the epicardium. The phenomenon
results in repolarization delay in the endocardial region, which explains repolarization
originating in the epicardium.
In patients with aortic stenosis and inverted T wave, repolarization sequence is
processed following the path of depolarization.
As the repolarization process (T vector) is electrically reverse to depolarization (QRS),
the vector representing it is heading from epicardium to the endocardium, pointing its
positive end (+) to the epicardium, gaining positive charges in the direction of the
endocardium, where the origin (-) of the vector is located. In adults, T vector of
repolarization is relatively parallel to the QRS vector of depolarization.
Experimental studies have shown that the alternation is due to located AP variation,
promoting longer and heterogeneous recovery in some area of the ventricular
myocardium. This heterogeneity in the ventricular wall thickness constitutes the substrate
for reentry in phase 2.
For instance in Brugada syndrome, phase 2 shortening, plateau or dome is observed
(between 40% and 70%) in the epicardium, but not in the endocardium, in the RV outflow
tract, causing marked transmural dispersion of repolarization in this area, being
responsible for ST segment elevation from V1 to V2 or V3, thus fostering the appearance
of arrhythmias by phase 2 reentry.
In the RV outflow tract epicardium, the Ito channel of phase 1 is the most prominent one
(greater outward K+), resulting in significant transmural dispersion of repolarization
between the epicardium and the endocardium, an ideal substrate for triggering
arrhythmias by reentry. Other factors such as muscarinic parasympathetic autonomic
stimulus, neurogenic triggers, class IA (ajmaline, procainamide) and IC (flecainide,
pilsicainide) antiarrhythmic drugs, fever, antidepressants, antimalarial agents, and other
external influences may trigger reentrant tachyarrhythmic effects.
The drugs and clinical settings that may exacerbate this electrophysiological substrate
are:
1)
2)
3)
4)
5)
Potassium channel openers such as pinacidil1;
Some sodium rapid channel blockers of class IA (ajmaline and procainamide) and IC
(flecainide2);
Increase in inward Ca2+ 3.
Metabolic inhibition4.
Simulation of ischemia5.
Ito channel block by 4-aminopyridine restores homogeneity and prevents reentry in all
cases.
1)
2)
3)
4)
5)
Di Diego JM, et al. Circulation 1993; 88 1177-1189.
Krishnan SC, et al. Circulation 1993; 87:562-573.
Di Diego JM, et al. Circulation 1994; 89:1839-1850.
Antezelevitch C, et. al.: Clinical implications of electrical heterogeneity in the heart: The electrophysiology and
pharmacology of epicardial, M and endocardial cells. In Podrid PJ, Kowey PR, eds; Cardiac Arrhytmia:
Mecahnism, Diagnosis and Management Baltimore, William and Wilkins, 1995,pp 88-107.
Lukas A, et al. Cardiovasc Res 1996; 32:593-603.
CLINICAL SETTINGS WHERE MTWA TECHNOLOGY
MAY BE USEFUL AS A PREDICTOR OF POTENTIALLY
LETHAL VENTRICULAR ARRHYTHMIAS
1)
In professional athletes: the MTWA technology has shown to be a noninvasive tool in
evaluating risk in professional competitive athletes. In this population, the method has
shown a high negative predictive value when used along with the electrophysiologic
study. The positive predictive value was present in a limited number of cases;
however, in subjects with high risk of SCD1;
2)
Symptoms of heart failure;
3)
Nonischemic
dilated
cardiomyopathy:
patients
carriers
of
nonischemic
cardiomyopathy, in whom VT events are observed, are carriers of more extended
disease, reflecting a greater myocardial damage. In these cases, MTWA positivity is
more prevalent. Such cases display a greater propensity to arrhythmic SCD2;
1)
2)
4)
Hypertrophic cardiomyopathy;
5)
Arrhythmogenic RV dysplasia;
6)
Ischemic heart disease;
7)
Post-myocardial infarction (after 30 days);
Furlanello F, et al. Ann Noninvasive Electrocardiol. 2004; 9: 201-206.
1) Klingenheben T, et al. J Cardiovasc Electrophysiol. 2005;16:620-624.
CLINICAL SETTINGS WHERE MTWA TECHNOLOGY
MAY BE USEFUL AS A PREDICTOR OF POTENTIALLY
LETHAL VENTRICULAR ARRHYTHMIAS
1)
2)
8)
Long QT syndromes: they may cause even macrovolt T wave alternans1;
9)
Hypertensive heart disease: value of MTWA: the risk of arrhythmia in patients
carriers of high blood pressure, is very increased in the cases in which the MTWA is
present. MTWA prevalence is greater in hypertensive patients with left ventricular
hypertrophy. The sensitivity to identify the patients in risk is approximately 70%2.
Grabowski M, Circulation 2004;110:e459-60.
Hennersdorf MG, et al. Hypertension. 2001;37:199
MEASUREMENT OF MICROVOLT T WAVE
ALTERNANS
A technology is used that has:
1)
Special multisegmented high resolution
electrodes that reduce the noise with
multicontact
sensors,
developed
by
Cambridge Heart Bedfford MA Inc;
(multisegment
Hi-Res
electrodes,
Cambridge Heart, Bedford, MA),
Special multisegmented high resolution
electrodes
ALTERNANS
2)
Special conducting gel;
3)
Electrical signal processing system, based on the spectral analysis method
(“Fast Fourier Transform” method: FFT) with a patented system for reduction of
noise;
4)
Generally, 128 beats that are captured at multiple T wave moments and
amplitudes, and are subjected to spectral analysis by the FFT method to
generate a spectrum of power.
ALTERNANS
5)
The MTWA must be sustained for more than 1 minute1.
6)
Since the MTWA is detectable only with a high HR, the study with atrial or
atrioventricular pacemaker increasing HR up to approximately 100 bpm, is very
appropriate2. The MTWA is not present in rest, so it must be performed during
exercise in the treadmill or bicycle, with submaximal test, drug challenge, or
atrial or atrioventricular pacemaker to increase heart rate.
1)
2)
Cohen RJ: In Zipes DJ, Jalife J (eds.): CardiacElectrophysiology: from cell to bedside. 3rd edition. Philadelphia,
WB Saunders, 2000
Albrecht P,et al. J Electrocardiol. 1996; 29:46-51.
CRITERIA OF MICROVOLT T WAVE ALTERNANS
POSITIVITY
1)
Sustained T wave alternans with recorded onset in a heart rate below 110
bpm. The patients in whom microvolt is recorded in rates below 110 bpm, are
those in greater risk. If MTWA occurs only in ranges above 140 bpm, there is
no risk of fatal arrhythmias1;
1)
2)
Magnitude above 1.9 µV;
3)
Rate of alternation above 3.
Hohnloser SH, et al. J Cardiovasc Electrophysiol 1997; 8:987-93.
CRITERIA OF MICROVOLT T WAVE ALTERNANS
POSITIVITY
Positive result: the test is considered positive if we record sustained MTWA that
initiates with heart rate !110 bpm or sustained alternations are recorded in rest when
heart rate is greater than 110 bpm1.
Indeterminate result: the test is considered to be indeterminate, when it is not possible
in a definite way, to classify it as positive or negative. Positive microvolt T wave
alternans indicates the need of electrophysiologic study, from which approximately 50%
will have indication of automatic cardioverter defibrillation implantation and the rest,
management with drugs and follow up2.
Negative result: if the test does not meet the positivity criteria or a HR of 105 bpm for at
least one minute, with noise ! 1.8 microvolts, the percentage of nonaccountable beats !
10% of significant alternation ("1.9 microvolts) is not present.
1)
2)
Haghjoo M , et al. Int J Cardiol. 2006;109:293-306.
MTG Newsletter. Special Report: T-Wave Alternants Test, October 1999/Vol.6, N.10.
INDICATIONS TO CONDUCT THE MICROVOLT T
WAVE ALTERNANS (MTWA) TEST
1)
Patients with syncope, presyncope or palpitations, with suspicion of being
caused by VT, but in whom clinical data indicating electrophysiologic study are
not yet documented.
2)
Patients with positive family history of SCD in first-degree relatives, younger
than 45 years old;
3)
Patients carriers of ischemic heart disease with EF ! 40%;
4)
Post-acute infarction patients, after 30 days and before 24 months. The method
has a greater value when correlated to the electrophysiologic study, in
comparison to other noninvasive, SCD-risk-marker methods, such as HRECG,
RR variability and QT interval dispersion1;2;
1) Rosenbaum DS, et al. N Eng J Med 1994; 330:235-241.
2) Hohnloser SH, et al. J Cardiovasc Electrophys 1998; 9:1258-1268.
INDICATIONS TO CONDUCT THE MICROVOLT T
WAVE ALTERNANS (MTWA) TEST
5)
Patients carriers of nonischemic idiopathic dilated cardiomyopathy, who
developed congestive heart failure1;
6)
Patients carriers of arrhythmogenic RV dysplasia;
7)
Patients carriers of hypertrophic cardiomyopathy2;
8)
Patients carriers of congenital long QT syndrome;
9)
Possible candidate to implantation of automatic cardioverter defibrillator
that may reinforce such indication.
10)
In the presence of negative electrophysiologic study and high clinical
suspicion of VT. It helps in choosing a more or less aggressive
management.
11)
Patients with recorded VT/VF, associated to possibly reversible cause.
1) Klingenheben T, et al. J Cardiovasc Electrophysiol. 2005;16:620-624.
2) Kuroda N, et al. Jpn Circ J. 2001;65:974-978.
CONTRAINDICATIONS TO PERFORM THE MTWA
TEST
1)
Acute phase of MI (before 30 days).
2)
Recent acute ischemia.
3)
Severe arrhythmia in effect.
4)
Endocarditis.
5)
Aortic stenosis.
6)
Pulmonary embolism.
7)
Neuromuscular or disabling osteomuscular disease.
8)
Severe ventricular dysfunction.
LIMITATIONS OF MICROVOLT T WAVE
ALTERNANS
Recording the MTWA is limited by the following settings:
1)
2)
3)
4)
Use of beta blockers or bradycardizing drugs: the autonomous sympathetic
system influences on MTWA appearance. Administering beta blockers causes
significant decrease of TWA, especially in the group of patients with VT, which
would partially explain why VT is inhibited by beta blockers1.
It is not possible to perform the method in carriers of atrial flutter.
It is not possible to conduct it in the presence of chronic atrial fibrillation;
Presence of frequent premature contractions, both atrial and ventricular (>10% of
tracings);
Indeterminate results are described in 25% of the cases.
1) Komiya N, et al. Pacing Clin Electrophysiol. 2005;28:680-684.
Measurement of microvolt T wave alternans
Special multisegmented Hi-Res
electrodes
Reduction of noise
Consecutive beats where T wave beats are measured, arranged exactly at the
time they occur.
128 beats
Average
Power spectrum
Frequency of breathing
Pedaling
Alternation
Frequency (beat cycle)
Frequency (beat cycle)
Measurement of microvolt T wave alternans (MTWA). Special electrodes along with
particular technologies of signal processing, enable measuring MTWA with a minimized
interference of artifacts associated to the movements of exercise. FFT: Fast Fourier
Transform Methods.
ALTERNANS
In the power spectrum, the time of the series is computed by using the method of rapid
Fourier transformation (FFR). During the exercise of pedaling in bicycle, the maximums
correspond to the rates of breathing, pedaling and alternation.
Measuring MTWA (microvolt T wave alternans) is based on the spectral breakdown of a
beat-to-beat series of T wave voltage, estimated by Fourier analysis. The square
magnitude of the amplitude of spectral harmonics (or power spectrum), is extracted from
the beat-to-beat series of T wave voltage. To quantify it, the abovementioned criteria are
used.

macrowave t alternans or macroscopic alternation in a

Transcription

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