Late potentials in a porcine model of anterior wall myocardial infarction and their relation to inducible ventricular tachycardia

Spectrotemporal mapping of high-resolution ECGs in experimental myocardial infarction: comparison with time-domain analysis and epicardial electrograms

The study was undertaken to evaluate the relationship of signal-averaged ECG (SA-ECG) readings in the frequency domain (STM) and epicardial electrograms (EE) recorded before and after acute myocardial infarction (AMI) in pigs and to compare the changes with findings in time-domain analysis (TDA). In 20 pigs the left anterior descending artery (LAD) was ligated. Prior to ligation, a SA-ECG was recorded (method of Simson) and bipolar electrodes were used to register EE in the areas supplied by the LAD and the circumflex artery (CIRC). Five minutes after LAD ligation, all measurements were repeated. Time-domain parameters were QRS duration (QRS D) and the duration of the signal below 30 microV (LAS 30). Beginning at a point of 20 ms before the QRS end, the frequency spectra (0-200 Hz) of 25 segments of 80-ms duration at the QRS end were analyzed. The volumes below the 25 curves were analyzed separately for 0-50 Hz, 51-100 Hz, 101-150 Hz, and 151-200 Hz. After AMI, five pigs died within 7 minutes. In 15 pigs, QRS D as well as LAS 30 lengthened significantly (P<0.05; P<0.001). Spectrotemporal mapping (STM) showed a significant decrease of the frequencies above 50 Hz (51-200 Hz) in the entire group and in the animals with late potentials (P<0.05). EE of the LAD area were significantly prolonged (P<0.01); this did not correlate with the changes in STM parameters. In pigs acute myocardial infarction causes a shift towards lower frequencies in the STM which most likely reflects the slowed depolarisation in the ischemic area.

Electrophysiological, rate dependent, and autonomic effects of the class III antiarrhythmic almokalant after myocardial infarction in the pig

Ventricular arrhythmias remain a major problem, in particular in patients with left ventricular dysfunction or heart failure. In this group of patients, Class I drugs were shown to be ineffective, and they even increased mortality during chronic treatment. New antiarrhythmic agents should preferably not only have pure antiarrhythmic effects, but should also be free from adverse autonomic properties. In the present study, the electrophysiological, rate dependent and autonomic effects of intravenously administered almokalant, a new Class III antiarrhythmic drug, were investigated in nine pigs surviving a myocardial infarction. The ventricular effective refractory period (VERP) increased after almokalant (loading dose: 0.05 mumol.kg-1.min-1, continuous infusion: 0.0025 mumol.kg-1.min-1) from 292 +/- 25 to 308 +/- 13 ms (pacing cycle length [PCL] 500 ms + 1 extrasystole [ES]), from 249 +/- 19 to 261 +/- 16 ms (PCL 400 ms +1ES), and from 209 +/- 18 to 219 +/- 18 ms (PCL 300 ms +1ES). The VERPs increased most after three ES at PCL 400 ms: from 167 +/- 27 to 186 +/- 29 ms (P < 0.05) and at PCL 300 ms: from 150 +/- 29 to 174 +/- 27 ms (P < 0.05). The ventricular monophasic action potential durations (MAPD) were similarly prolonged and the ratio VERP/MAPD did not change. Prolongation of MAPD after almokalant remained present at short pacing cycle lengths. Before almokalant infusion, sustained monomorphic ventricular tachycardia (VT) was inducible in two pigs, and nonsustained VT in a third animal. After almokalant, only one pig remained inducible. Two weeks after myocardial infarction, heart rate variability and baroreflex sensitivity were reduced. Furthermore, subsequent electrophysiological testing transiently reduced these parameters of autonomic activity. During almokalant however, no changes in autonomic functions were observed after programmed stimulation. Heart rate variability decreased after myocardial infarction from 6.3 +/- 2.5 ms to 5.4 +/- 4.2 ms (P = NS). After programmed stimulation, it further decreased to 2.8 +/- 2.0 ms (P = 0.028). Almokalant infusion prevented autonomic deterioration: 3.3 +/- 2.2 ms before stimulation and 3.3 +/- 1.3 after stimulation (P = NS). In postinfarct pigs, almokalant prolongs VERP and MAPD at shorter pacing cycle lengths. The results indicate absence of reverse rate dependence and of adverse autonomic changes.

Rate-dependent effects of the class III antiarrhythmic drug almokalant on refractoriness in the pig

The electrophysiologic effects of intravenously administered almokalant, a new class III antiarrhythmic drug, in 7 isoflurane-anesthetized pigs after low and high dose were investigated. Low-dose almokalant included bolus infusion of 0.05 mumol/kg/min for 5 min followed by a continuous infusion of 0.0025 mumol/kg/min for 40 min. Thereafter, a high dose of 0.2 mumol/kg/min for 5 min and 0.01 mumol/kg/min for 40 min was given. PR, QRS, AH, and HV intervals did not change during almokalant administration. The QT interval increased dose dependently from 337 +/- 17 to 442 +/- 20 ms at high dose (p < 0.05). Atrial refractory periods (AERP) were prolonged dose dependently at a 500-ms pacing cycle length from 178 +/- 15 at baseline to 227 +/- 27 and 253 +/- 23 ms during low- and high-dose almokalant infusion, respectively. For pacing cycle lengths of 400 and 300 ms, these values were 180 +/- 11, 207 +/- 25, and 259 +/- 34 and 157 +/- 12, 193 +/- 21, and 234 +/- 28 ms, respectively. At a pacing cycle length of 500 ms, mean ventricular effective refractory period (VERP) was 270 +/- 25 ms as compared with 306 +/- 24 and 337 +/- 17 during low and high dose, respectively. A similar pattern of VERP changes during both low- and high-dose infusion was noted at the shorter pacing cycle lengths, with an increase from 240 +/- 23 to 274 +/- 22 and 279 +/- 24 ms during a 400-ms cycle length and from 210 +/- 17 to 235 +/- 19 and 234 +/- 21 ms during a 300-ms cycle length. The ratio of the VERP and ventricular monophasic action potential duration (VAPD) did not change significantly. The Wenckebach cycle length increased by 36 +/- 36 and 83 +/- 37 ms with low- and high-dose almokalant infusion, respectively. The percent increase of AERP at pacing cycle lengths of 500, 400, and 300 ms during high-dose almokalant was 42, 44, and 49%, respectively; these increases for VERP were 25, 16, and 11%, respectively. In conclusion, prolongation of refractoriness by almokalant was more pronounced at the atrial than the ventricular level. Prolongation of refractoriness was maintained at short pacing cycle lengths especially in the atrium, indicating absence of reverse-use dependence of almokalant in the porcine heart. The marked atrial effects, paralleled by atrioventricular conduction slowing, and the absence of reverse use-dependence all contribute to the feasibility of use of almokalant, in particular in the treatment of supraventricular tachyarrhythmias.