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Decrease in the High Frequency QRS Components Depending on the Local Conduction Delay Jpn Circ J 1998; 62: 844–848 Decrease in the High Frequency QRS Components Depending on the Local Conduction Delay Tetsu Watanabe, MD; Michiyasu Yamaki, MD; Hidetada Tachibana, MD; Isao Kubota, MD; Hitonobu Tomoike, MD The high frequency components contained in the QRS complex (HF-QRS) are a powerful indicator for the risk of sudden cardiac death. However, it is controversial whether conduction delay increases or decreases the HF- QRS. In 21 anesthetized, open-chest dogs, the right atrium was constantly paced. A cannula was inserted into the left anterior descending artery and flecainide, lidocaine or disopyramide was infused to slow the local conduc- tion. Sixty unipolar electrograms were recorded from the entire ventricular surface and were signal-averaged. Data were filtered (30–250Hz) by using fast-Fourier transform. The HF-QRS was calculated by integrating the filtered QRS signal. Activation time (AT; dV/dt minimum) was delayed and the HF-QRS was reduced in the area perfused by flecainide, lidocaine or disopyramide. The percent increase in AT closely correlated the percentage decrease in the HF-QRS; the correlation coefficients were 0.75, 0.83 and 0.76 for flecainide, lido- caine and disopyramide infusion, respectively, (p<0.001). Decrease in the HF-QRS linearly correlated with the local conduction delay. This study proved that conduction delay decreases the HF-QRS, and that the HF-QRS is a potent indicator of disturbed local conduction. (Jpn Circ J 1998; 62: 844–848) Key Words: Disopyramide; Fast-Fourier transform; Flecainide; Lidocaine; Signal averaging ate potentials, or high-frequency low-amplitude anesthetized with sodium pentobarbital (30mg/kg, iv) and signals in the terminal portion of the QRS received supplemental doses as needed. Dogs were venti- L complex, are considered to be a powerful indicator lated by a respirator with room air supplemented with for the risk of ventricular arrhythmia and sudden cardiac oxygen (3–5 L/min). The thorax was opened at the fifth death in patients with ischemic heart disease. Studies on intercostal space, then the pericardium was opened and a experimental chronic ischemia led researchers to believe pericardial cradle was made to support the heart in the that this originated in the slowed conduction.1–3 Recently, appropriate position. The sinus node was crushed, and the frequency-domain analysis has been used as a reliable and right atrium was paced at a cycle length of 400msec using quantitative tool for detecting high-frequency low-ampli- a model SEN-7203 stimulator (Nihon Koden, Tokyo, tude signals on ECG. Several reports have shown that Japan). After an intravenous bolus administration of acute4–7 or chronic myocardial ischemia8–10 does not heparin (10,000 IU), a 24-gauge plastic cannula was increase, but there is a decrease in the high frequency inserted into the left anterior descending artery (LAD) at components in the QRS complex (HF-QRS). the distal site of the second diagonal branch. The cannula However, when examining the causality of the HF-QRS, was kept open by continuous infusion of saline at 1ml/min. myocardial ischemia may be not an ideal tool, because A globe-shaped electrode array was placed on a ventricular myocardial ischemia includes complicated electrical surface for simultaneous monitoring of electrograms from changes such as the altered potential for potassium ion, and 60 epicardial sites. Each unipolar electrode consisted of anaerobic metabolism, which leads to intracellular acidifi- fine silver wire (0.2-mm diameter) sutured to the sock. The cation and an increase in cellular osmolarity.11–13 In the electrode array was 6 rows (1–6) and 10 columns (A–J). present study, we evoked a conduction delay by using All recording electrodes were referenced to the Wilson’s sodium channel blockers and examined the direct relation- central terminal, and multichannel electrograms were digi- ship between the HF-QRS and the conduction delay. The tized every millisecond using a multiplexed data process- purpose of this study was to define whether the conduction ing system (CD-G015, Chunichi Denshi, Nagoya, Japan) as delay increases or decreases the HF-QRS. described in a previous study.14 The thoracic cavity was covered with plastic wrap to prevent cooling and dehumid- ifying. Body temperature was maintained at 37–38°C. An Methods arterial line was inserted into the right femoral artery to Instrumentation continuously monitor the mean arterial pressure. The elec- Twenty-one adult mongrel dogs (weight, 12–33kg) were trocardiogram lead II and blood pressure were recorded simultaneously throughout the study on a model 2G66 (Received May 11, 1998; revised manuscript received July 21, 1998; recorder (NEC San-ei, Tokyo, Japan). accepted August 5, 1998) First Department of Internal Medicine, Yamagata University School Experimental Protocol of Medicine, Yamagata, Japan Flecainide (low dose: 10μg/kg per min; high dose: Mailing address: Tetsu Watanabe, MD, First Department of Internal Medicine, Yamagata University School of Medicine, 2-2-2 Iida-Nishi, 100μg/kg per min, n=7), lidocaine (low dose: 0.12mg/kg Yamagata 990-9585, Japan. E-mail: [email protected] per min; high dose: 0.6mg/kg per min, n=7) or disopyra- u.ac.jp mide (low dose: 20μg/kg per min; high dose: 200μg/kg per Japanese Circulation Journal Vol.62, November 1998 Conduction Delay and High Frequency QRS Components 845 Fig1. Representative maps of activation times at control, and during low-dose and high-dose infusion of flecainide. (*)The site of ‘the earliest activation’. Arrows indicate the epicardial electrograms at the center of perfused region: lead ‘D2’ and non-perfused region: lead ‘H2’. Fig2. The HF-QRS area maps at control, and during low-dose and high-dose infusion of flecainide in the same each experiment as indicated in Fig1. Arrows indicate filtered QRS complexes at the center of the perfused region: lead ‘D2’ and non-perfused region: lead ‘H2’. Japanese Circulation Journal Vol.62, November 1998 846 WATANABE T et al. Fig3. Changes in ATs (A) and the HF-QRS (B) for each sodium channel blocker at the center of the perfused region. ATs were signifi- cantly delayed by a high-dose infu- sion of each sodium channel blocker. Low-dose disopyramide infusion significantly delayed ATs. The HF-QRS was reduced by infu- sion of each sodium channel blocker. Low-dose lidocaine and each high-dose sodium channel blocker significantly reduced the HF-QRS. AT, activation time; HF- QRS, high frequency QRS compo- nent; *p<0.05 vs control, †p<0.05 vs low dose. min, n=7) was intracoronarily infused by an infusion pump components was calculated by integrating the electrogram (model SP-100, JMS, Hiroshima, Japan). The lower dose during the QRS interval,16 which we called ‘HF-QRS’. of flecainide, disopyramide or lidocaine was 1% of the Epicardial activation of each electrogram was defined as intravenous dose in experimental study and the higher dose the minimum derivative of the QRS signal.18 The earliest was 5–10%.15 After baseline measurements, the low-dose activation measured on the cardiac surface was assigned to protocol was performed during the first 10 min, and the time zero and the activation time (AT) was determined high one was continued for the next 10 min. Epicardial from time zero to each activation, and an isochronal map electrograms were recorded 10 min after beginning the was constructed.14 Changes in AT and the HF-QRS for each low-dose infusion. When wide QRS complexes, which sodium channel blocker were measured at the center of the were produced by each sodium channel blockade, or spon- perfused region. taneous ventricular tachyarrhythmias were recognized, electrograms were immediately recorded. Statistical Analysis Quantitative data are reported as mean±SE. Statistical Analysis of Multichannel Epicardial Electrograms analysis was performed with the Wilcoxon signed-ranks Electrograms were averaged to cancel random noise by test. A confidence level of 95% was considered statistically means of a SUN 4/2 microcomputer (SUN Microsystems, significant. Mountain View, CA, USA) as previously reported.14 The cross-correlation function was used to reject ectopic beats and artifacts (cross-correlation coefficients below a thresh- Results old value: 0.95).16 The number of beats averaged was from Effects of Sodium Channel Blockers on AT and the HF- 50 to 56 (mean, 54). The signal-averaged ECG data were QRS Area stored on a magneto-optical disk for later analysis. A root The 21 dogs were divided into 3 groups: 7 were given mean square (RMS) voltage based on all 60 leads was flecainide, 7 lidocaine, 7 disopyramide. Fig1 illustrates the plotted to determine both the onset and offset of QRS. The cardiac surface distribution of the ATs before (control) and flat portion of the PR segment was defined as the zero after flecainide infusion (low and high dose of flecainide) level. The RMS values were computed from the averaged in a representative experiment with an asterisk indicating (but not filtered) ECG wave forms. the site of ‘the earliest activation’. The delay in ATs was For analysis with the fast-Fourier transform algorithm not apparent on the maps at control or during low-dose (FFT), ECG data were padded with zeros for a total 1024 infusion of flecainide. However, a marked delay in ATs points. A time series f(t) representing the ECG complex was seen in the perfused area during high-dose infusion. was subjected to a 1,024-point FFT analysis to produce a The configuration of the electrogram showed a widened frequency series F(w). A product of F(w) with a transfer QRS complex and an increased R wave in the perfused function, H(w), was computed to produce a filtered wave area. G(w) in a frequency domain.
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