Improved robust T-wave alternans detectors

New statistical and spectral detectors, the modified matched pairs t test, the extended spectral method and the modified spectral method, were proposed for T-wave alternans (TWA) detection gaining robustness according to trend and single-frequency interferences. They were compared to classic detectors such as matched pairs t test, unpaired t test, spectral method, generalized likelihood ratio test and estimated TWA amplitude within a simulation framework and applied to real data. The optimal detection threshold was selected by using a full Monte-Carlo simulation where signals, with and without alternans episodes, were corrupted by Gaussian noise with different power and single-frequency interferences with different tones. All the combinations of noise and frequency were selected and repeated 500 times in order to compute probability of detection ([Formula: see text]) and the false alarm probability ([Formula: see text]), providing ROC curves. The study group consisted of 50 patients with implantable cardioverter-defibrillator (age: [Formula: see text]; LVEF: [Formula: see text]), who were paced (ventricular pacing) at 100 bpm. Two-minute recordings were analyzed. The XYZ orthogonal lead system was used. The best performance was reached by using the modified matched pairs t test (in comparison with the spectral method and other reference methods).

Influence of mobile phones on accuracy of ECG interpretation algorithm in automated external defibrillator

BACKGROUND

Automated External Defibrillators (AED) are a recommended tool for out-of-hospital emergency medical services. Mobile phones (GSM) are a potential source of electromagnetic interference which may cause failure of ECG interpretation and subsequent inappropriate action of AED's.

METHODS

We evaluated the influence of 900 MHz GSM phones on the accuracy of automatic ECG interpretation with a GSM Mobile Station Tester with adjustable power and mode of transmission (Hewlett-Packard HP5515A), GSM phones (Alcatel, Ericsson, Nokia, Panasonic), ECG simulator (Metron) and four AEDs (Fore Runner-Hewlett-Packard, Heartstart 3000-Laerdal, Cardio-Aid 100-Artema, Heartstream XLT-Agilent). The protocol included 18 different ECG patterns, different ECG voltages, and different power and mode of transmission.

RESULTS

The first stage of the protocol included minimal power of signal transmitted from GSM Mobile Station Tester and maximum power of GSM phone's signal--hence maximal potential interference to AED. The protocol was based on close direct contact between the GSM phone and the AED device. Regardless of the ECG pattern, with both 0.5 and 1.0 mV ECG voltage, and the GSM phone placed on various parts of AED device or at the patient cable, no failure of AED algorithm occurred. No detectable noise was seen at AED's ECG display.

CONCLUSION

AEDs seems to be well protected against clinically significant failure caused by noise from 900 MHz GSM phones.

QT interval dispersion in ventricular beats: a noninvasive marker of susceptibility to sustained ventricular arrhythmias

Increased QT dispersion (QTd) calculated from sinus beats has been shown to identify patients prone to sustained VT. However, predictive accuracy of this parameter is limited. Electrophysiological properties of the myocardium may be altered by a premature ventricular beats, which is a well-established trigger for sustained VT. Therefore, the author hypothesised that QTd in spontaneous or paced ventricular beats may improve identification of patients with inducible sustained VT. In 28 consecutive patients (men, mean age 61 +/- 13 years) who underwent programmed ventricular stimulation, the values of QTd calculated in sinus and ventricular beats were compared between inducible and noninducible patients. The mean QTd values obtained using three different methods differed significantly, QTd in paced ventricular beats being the highest, QTd in spontaneous ventricular beats was intermediate, and QTd in sinus beats was the lowest (83.9 +/- 30 vs 63.0 +/- 29 ms vs 53.9 +/- 27 ms, P < 0.0001 and P < 0.004, respectively). In 13 (46%) patients sustained VT was induced. QTd values were significantly higher in inducible than noninducible patients (QTd sinus beats: 67.5 +/- 31 vs 42.1 +/- 11 ms, P = 0.02; QTd spontaneous ventricular beats: 79.3 +/- 35 vs 46.7 +/- 13 ms, P = 0.008, and QTd-paced ventricular beats: 104.8 +/- 32 vs 65.9 +/- 9 ms, P = 0.0009). The receiver operator characteristic curves showed that at a sensitivity level of 100%, the highest specificity for identification of inducible patients had QTd measured in paced ventricular beats (87%) followed by QTd in spontaneous ventricular beats (45%), and QTd in sinus beats (40%). In conclusion, (1) QTd in ventricular beats is greater than in sinus beats, and (2) QTd calculated from paced ventricular beats identifies patients with inducible sustained VT better than QTd measured during sinus rhythm.

Passive-fixation J-shaped versus straight leads in atrial position: comparison of efficacy and safety

To compare the efficacy and safety of straight and J-shaped passive-fixation atrial leads we retrospectively analyzed the results of 100 consecutive implantations of atrial leads at one institution. There were seven cases of upgrades of VVIR to DDDR systems and in one case an active-fixation lead was chosen as a primary approach. These eight patients were excluded from the analysis. The final study group consisted of 92 cases (69 DDDR, 23 AAIR), 69 were J and 23 straight leads. The stimulation threshold, slew rate, impedance, P wave amplitude, and procedural time did not differ significantly between the two types of leads used. During the long-term follow-up of 6-53 months (30 +/- 11.9 months), replacements using active-fixation leads were required in two patients with straight leads and three patients with J leads (P = NS). In addition, one J lead showed signs of damage (impedance > 3,000 Ohm). Long-term follow-up values of the stimulation thresholds and P wave amplitudes did not differ between the groups (P = NS). Transesophageal echocardiography performed in 13 patients revealed a trend toward more distal placement of straight leads within the right atrial appendage. In conclusion, J-shaped leads do not seem to be superior to the straight leads for atrial implantations.

Effects of intravenous amiodarone on ventricular refractoriness, intraventricular conduction, and ventricular tachycardia induction

AIMS

Intravenous amiodarone has recently emerged as an important drug for the acute treatment of ventricular tachyarrhythmias. However, electrophysiological actions and the efficacy of the drug in the suppression of ventricular tachycardia inducibility have not yet been fully established. The present study was designed to address these issues.

METHODS AND RESULTS

The study group consisted of 18 patients (all males, mean age 75 +/- 14 years), who underwent electrophysiological study due to a history of sustained ventricular tachyarrhythmia or syncope with non-sustained ventricular tachycardia detected on ambulatory ECG monitoring. The effects of 5 mg.kg(-1) or 10 mg.kg(-1) of intravenous amiodarone on (1) ventricular refractoriness (QTc interval, right ventricular effective refractory period and monophasic action potential duration), (2) intraventricular conduction (paced-QRS and signal-averaged QRS duration), and (3) ventricular tachycardia inducibility, were examined. The drug had no significant effect on ventricular refractoriness. However, a relatively small but significant slowing of intraventricular conduction was seen (paced-QRS duration: 182 +/- 27 ms vs 191 +/- 28 ms, P<0.0007; 183 +/- 32 ms vs 195 +/- 33 ms, P<0.0007; and 177 +/- 21 ms vs 192 +/- 24 ms, P<0.003, at the cycle lengths of 600, 500 and 400 ms, respectively). This effect was more evident during extrasystolic beats than during stable pacing (for example, at the cycle length of 600 ms, the magnitude of amiodarone-induced lengthening of QRS duration was 23.9 +/- 17.6 ms vs 9.7 +/- 7.2 ms, P<0.009, respectively). Intravenous amiodarone did not prevent induction of sustained ventricular tachycardia in any of five patients inducible at baseline. Of six patients with non-sustained ventricular tachycardia, five had sustained ventricular tachycardia or fibrillation induced after amiodarone infusion.

CONCLUSION

Intravenous amiodarone does not prolong ventricular refractoriness, slows intraventricular conduction and may facilitate inducibility of sustained ventricular arrhythmias.

Effects of captopril on ventricular arrhythmias in the early and late phase of suspected acute myocardial infarction. Randomized, placebo-controlled substudy of ISIS-4

The antiarrhythmic effect of oral captopril was studied during the early (day 3) and late (day 14) phase of acute myocardial infarction among 304 patients in a randomized placebo-controlled substudy of ISIS-4. Ventricular arrhythmias (ventricular ectopic beats per hour) occurred significantly less frequently among captopril-allocated patients than among those allocated placebo at day 3 (logarithmic scale: 0.48 +/- 0.8 captopril vs 0.84 +/- 1.3 placebo; P < 0.003) and at day 14 (0.51 +/- 1.0 vs 0.77 +/- 1.3; P < 0.05). The number of patients with frequent ventricular arrhythmias (more than 10 ventricular ectopic beats per hour) was also significantly lower among those allocated captopril at day 3 (7.3% vs 14.4%; P < 0.05) and at day 14 (7.3% vs 14.8%; P < 0.05). These results support the hypothesis that the activation of the renin-angiotensin-aldosterone and sympathetic system may underlie heart rhythm disturbances in acute myocardial infarction, and that early use of converting enzyme inhibitor therapy may ameliorate these disturbances.

The incidence of asymptomatic paroxysmal atrial fibrillation in patients treated with propranolol or propafenone

Anti-arrhythmic therapy for paroxysmal atrial fibrillation leads to complete symptomatic relief in a number of patients. The elimination of symptoms may be associated either with a complete elimination of arrhythmia or with a conversion of symptomatic atrial fibrillation into asymptomatic episodes of arrhythmia. The aim of the study was to evaluate the occurrence of asymptomatic paroxysmal atrial fibrillation in 52 patients treated with propafenone (35 drug trials) or propranolol (34 drug trials) by means of ambulatory ECG Holter monitoring. Propafenone was clinically effective (complete relief of symptoms) in 26 (74%) patients. However, in 7 cases (27%) asymptomatic episodes of arrhythmia were still recorded when awake. In patients treated with propranolol clinical symptoms were absent in 18 (53%). However, in 4 (22%) patients attacks of paroxysmal atrial fibrillation were present. The mechanism of drug-induced conversion of symptomatic episodes of atrial fibrillation into asymptomatic spells of arrhythmia was a marked shortening in duration of episodes in 7 patients (from 2215 +/- 3843 s to 16 +/- 10 s, N.S.) or by a significant slowing of ventricular response during atrial fibrillation in 4 patients (from 125 +/- 27 to 84 +/- 8 beats/min, P = 0.05). In conclusion, in a significant proportion of patients with symptomatic paroxysmal atrial fibrillation asymptomatic episodes of arrhythmia may occur while on anti-arrhythmic drug therapy. Some of these patients, particularly those with other risk factors for stroke such as advanced age or the presence of organic heart disease, may require anti-coagulant therapy or change in anti-arrhythmic treatment, and can be selected on the basis of ambulatory ECG monitoring.

[Extent of left-ventricular damage after myocardial infarction and the occurrence of mural thrombi]

The aim of the study was to estimate a detailed relationship between the extent of left ventricular damage after myocardial infarction (MI) and occurrence of mural thrombi examined with two dimensional echocardiography (2Decho). The examinations were undertaken in 47 patients (pts) (age 40-86 years) after transmural anterior MI. 2Decho was performed in all pts according to American Society of Echocardiography from the is day to the 4th month after MI. Heger index was used for the estimation of LV wall motion disturbances. The criterion of mural thrombus was the presence of an additional echo by LV wall visible in at least two echocardiographic views. It was determined that the incidence of mural thrombi is correlated with statistically significant larger LV damage expressed with higher Heger index and higher number of hypo-, a-, and dyskinetic LV segments. The study revealed the relationship between the extent of LV damage after MI, the presence of LV dyskinesia, LV enlargement, ST segment elevation in ecg and the incidence of mural thrombi.