Clinical value of monophasic action potentials

The method of monophasic action potential (MAP) recording has experienced a significant surge in interest since the introduction of the contact electrode, which in contrast to the suction electrode, allows the safe and simple use of this technique in the clinical electrophysiology laboratory. MAP recording not only provide for a more precise determination of local activation, but most importantly, permit direct measurement of myocardial repolarization and action potential duration (APD), respectively. This had led to new insights into the cycle-length-dependence of the human APD, both in response to single extrastimuli and to steady-state heart rate changes. An advancement of the contact electrode catheter design now permits simultaneous pacing and MAP recording, and thereby, simultaneous determinations of APD and effective refractory periods (EPP) at the same endocardial site in the human heart. MAP recordings have demonstrated significant usefulness in the direct monitoring of antiarrhythmic drug effects, both in terms of dosage control and in the direct measurement of antiarrhythmic drug effects on the relationship between ERP and APD (ERP/ARD-ratio). Because MAP recordings reflect the local cellular electrophysiology, they also provide a more sensitive and precise index of myocardial ischemia than conventional ECG recordings. This can be utilized to assess the success of revascularizing procedures directly during or after the intervention. Recently, MAP recordings helped to discover early after-depolarizations in patients with "torsade de pointes", providing a possible explanation for the mechanism of polymorphous ventricular tachycardia in man.     

Effect of sotalol, aprindine and the combination aprindine-sotalol on monophasic action potential duration

The effects of sotalol, aprindine and the combination aprindine-sotalol in the intact dog heart were evaluated during constant atrial pacing with the use of monophasic action potential (MAP) recording. A first group of five dogs was given 1.5 mg kg-1 body weight of sotalol, followed by a second infusion of 1.5 mg kg-1 30 min later. Both doses of sotalol produced a statistically significant increase in right atrial MAP duration at 50% of repolarization (RAMAP50) and right ventricular MAP duration at 90% of repolarization (RVMAP90). To a second group of six dogs aprindine 1 mg kg-1 and aprindine 2 mg kg-1 were administered intravenously. The infusion of aprindine did not alter right atrial and right ventricular MAP duration. The addition of 1.5 mg kg-1 of sotalol to the dogs pretreated with aprindine 2 mg kg-1 resulted in a 25% increase in RAMAP50 and a 21% prolongation of RVMAP90. In summary, sotalol lengthens atrial and ventricular monophasic action potential duration and still prolongs repolarization of monophasic action potentials after previous administration of aprindine. A combination of sotalol, a beta-adrenergic blocker possessing class III efficacy, with a class I antiarrhythmic agent may be useful with respect to their electro-physiological action.     

Acute effects of aldosterone on intracardiac monophasic action potentials

BACKGROUND: Elevated plasma aldosterone levels represent an independent risk factor for increased mortality in congestive heart failure. Sudden cardiac deaths contribute substantially to the excessive mortality in congestive heart failure and so does atrial fibrillation as one of the major causes of stroke in elderly persons. So far, the electrophysiological properties of aldosterone have not been thoroughly characterized. In the present study, the effects of aldosterone on intracardiac monophasic action potentials were investigated in humans. METHODS AND RESULTS: Monophasic action potentials were recorded in six patients with supraventricular arrhythmias. Eleven ml of 0.9% NaCl (placebo) were injected intravenously, and monophasic action potentials recorded for 10 min. Thereafter, aldosterone (0.5 mg in 0.9% NaCl) was injected and recording of monophasic action potentials continued as previously. The mean action potential duration at 90% repolarization was calculated for the entire 10-min period of each treatment. All patients were in sinus rhythm and had normal electrolyte status. In the placebo period, mean MAPd90 was 287+/-22 ms (mean+/-S.D.), and 299+/-25 ms following aldosterone (P<0.02). After adjustment for heart rate, the difference remained statistically significant (P<0.01). The maximal effect of aldosterone was seen 4-6 min after injection. CONCLUSION: Aldosterone increases monophasic action potential duration within minutes after intravenous application. Therefore, this effect is likely to be mediated nongenomically. It may be hypothesized that aldosterone exerts its unfavorable effects partly via altering myocardial repolarization.     

Long-term recording of monophasic action potentials from human endocardium

In 36 patients undergoing routine cardiac catheterization, a new “contact electrode” catheter technique was used to record monophasic action potentials (MAPs) from right atrial and right and left ventricular endocardial sites without the application of suction. Although of smaller amplitude, typically ranging from 15 to 40 mV, and of different reversal ratio (33 ± 3%), MAP recordings closely resembled transmembrane action potentials in configuration and duration. Continuous MAP recordings of stable amplitude and, during regular pacing, of constant duration (± 1% at 90% repolarization) could be made from the same endocardial site for test periods of 1 hour (n = 4), permitting direct evaluation of the effect of cycle length alterations on local myocardial repolarization. A linear relation was found between MAP duration and basic cycle length varying from 350 to 700 ms. These rate-dependent changes in MAP duration were caused by a change in the slow phase of repolarization (phase 2), whereas the slope of rapid repolarization (phase 3) was unaltered. Single premature MAPs or MAPs after a pause showed changes in both phases. No MAPs could be recorded in areas of infarcted, aneurysmal myocardium, indicating that local viable myocardium is a prerequisite for the generation of the monophasic signal. Thus, in human subjects this catheter permits safe, long-term recording of MAPs which, although of smaller amplitude than transmembrane action potentials, bear appropriate and predictable phase relations. Such recordings may be useful in evaluating changes in local myocardial electrical activity induced by pacing or resulting from myocardial disease, or both.     

Changes in transmembrane action potentials and monophasic action potentials of phase 3 intraventricular block in rabbits]

The model of phase 3 intraventricular block was produced in 10 rabbits by giving 2.5% solution of potassium chloride intravenously under natural breathing and sinus rhythm. Transmembrane action potentials and monophasic action potentials were recorded respectively. The results showed that RP, APA, Vmax, MAPA and MVmax all decreased and both APD and MAPD shortened at the time of ventricular conduction block, when ventricular conduction was improved by vagal stimulation, RP, APA, Vmax, MAPA and MVmax all increased and both APD and MAPD lengthened. In addition, APD and MAPD measured at the same site in normal conduction, conduction block and conduction improved by vagal stimulation were in consensus.     

Recording monophasic action potentials using a platinum-electrode ablation catheter.

AIMS: The monophasic action potential (MAP) is conventionally recorded using Ag-AgCl electrodes which are not suitable for delivering radiofrequency currents. To be able to use the sharp MAP upstroke for identifying the local activation, as a step towards the development of a MAP-guided catheter ablation technique, the possibility of recording MAP via platinum electrodes of an ordinary ablation catheter was explored. METHODS AND RESULTS: One hundred and forty-two MAP recordings from the endocardium were obtained via an ablation catheter in 40 patients undergoing electrophysiological study/catheter ablation. During sinus rhythm and pacing, 90% of the ventricular and 100% of the atrial MAPs had stable baselines. The amplitudes were 13 +/- 4.2 mV for ventricular and 2.4 +/- 0.8 mV for atrial MAPs. During mapping and ablation, MAPs and uni- and bipolar electrograms were recorded simultaneously using the same tip electrode in eight patients. The MAPs provided more distinct local activation than the electrograms. During 17 MAP recordings, additional MAPs were recorded simultaneously using an Ag-AgCl electrode catheter in the immediate vicinity of the ablation catheter. The MAPs taken with the ablation catheter had characteristics consistent with those taken with the Ag-AgCl catheter. CONCLUSIONS: (1) Platinum electrodes can be used for timely recording of MAPs in patients. (2) It is feasible to record MAPs and deliver radiofrequency currents via the same platinum-tip electrode. These findings suggest that MAP-guided catheter ablation is technically possible.     

Localization of regional myocardial ischemia by recording of monophasic action potentials

Identification of regional myocardial ischemia by TQ-ST segment mapping, while commonly used, is relatively imprecise and nonspecific. In 41 open-chest dogs we examined whether monophasic action potentials (MAPs) recorded from the myocardial surface by means of a new contact-electrode technique could be used to more precisely and specifically index regional myocardial ischemia. After ligation of the left anterior descending coronary artery (LAD), epicardial and endocardial MAPs from the ischemic region demonstrated shortening of plateau duration followed by a progressive loss in amplitude to 48 +/- 8% and in maximum upstroke velocity (dV/dtmax) to 9 +/- 2% of control (n = 7). Regional hyperkalemia produced by intracoronary injection of potassium chloride also resulted in regional decreases in duration, amplitude, and dV/dtmax of the MAP. Similar to previously reported effects on transmembrane action potentials, ischemia- or hyperkalemia-induced loss in MAP amplitude was due to decreases in both diastolic (negative) and systolic (positive) potential and paralleled TQ segment depression and "true" ST segment elevation in unipolar direct current-coupled electrograms recorded from an adjacent site. In eight canine hearts we compared the abilities of MAP recordings and TQ-ST segment measurements in defining a region of myocardial ischemia. Transmural ischemia with a sharp flow border was produced by LAD ligation and distal embolization with dental rubber. One hour later simultaneous MAP and TQ-ST mapping was performed in each dog at 45 to 65 epicardial sites inside and outside the ischemic region. TQ-ST voltage was significantly increased 10 to 20 mm outside the visible cyanotic border, reaching a maximum just inside the border and decreasing progressively toward the center of the ischemic region to values not significantly different from those from sites 10 mm outside the ischemic border. In contrast, MAP amplitude and dV/dtmax were normal up to 5 to 10 mm outside the cyanotic border, decreased sharply across a lateral transition zone of only 8 mm to 8.7 +/- 2.3% and 4.3 +/- 0.9% of control, respectively, at sites 4 to 6 mm inside the border, and were uniformly abnormal across the entire ischemic region. Recordings made 3 hr after LAD ligation revealed an overall decline in the magnitude of TQ-ST, making definition of the ischemic border by TQ-ST even less precise, whereas the differences between MAPs from normal and ischemic myocardium had become even more pronounced than after 1 hr. Thus, unlike TQ-ST segment measurements, MAP recordings uniquely define ischemic and nonischemic sites and more precisely localize the border of an ischemic region.(ABSTRACT TRUNCATED AT 400 WORDS)     

使用铂电极记录单相动作电位的可行性研究

目的探讨使用用于射频消融的普通铂电极记录心内膜单相动作电位(MAP)的可行性。方法 20例阵发性室上性心动过速行导管消融的患者分两组,分别使用铂电极和银-氯化银(Ag-AgCl)电极在右室心尖部及右室流出道进行MAP标测,测量各标测点MAP的振幅(AMP)、动作电位复极达90%的时程(APD90)、激动时间(AT)和复极时间(RT),比较两组间各指标的差异。结果在右室心尖部和右室流出道Ag-AgCl电极组和铂电极组分别测得48和46个标测点,其中铂电极组仅有3个标测点基线干扰较大,并且该组振幅大于10 mV的标测点共有33个,基本满足稳定的MAP信号的要求。与Ag-AgCl电极组相比,铂电极组测得的MAP的AMP、APD90、AT、RT值均没有显著差异(P均0.05)。结论在临床研究中使用铂电极代替Ag-AgCl接触电极作为同时记录MAP和射频消融的两用电极具有可行性。     

Study of monophasic action potentials of the myocardium by endocavitary approach. Methodology

The suction electrode makes it possible to record the monophasic action potentials (MAP) of the heart in situ. The technical characteristics of the tripolar electrode which we use are described. The O phase of the MAP is more prolonged than that of the intracellular action potential, but makes it possible to demonstrate the time of arrival of the activation wave in front of the exploring electrode. The phase 1-2 and the phase 3 have their characteristic contour in the right atrium and ventricle. The duration of repolarization makes it possible to assess the refractory period of different parts of the atrial and ventricular myocardium. The relatively simple and harmless method of recording of the monophasic action potentials by the endocardial route, both in the animal and in man, widens our investigation field of electrophysiology applied to the study of arrhythmias, of the repolarization disturbances and of the drug influences on the cell activity.     

Right ventricular monophasic action potentials in patients with long QT syndrome.

In 3 patients with the long QT syndrome, one caused by quinidine and 2 of congenital origin, right ventricular monophasic action potentials were excessively prolonged and of varying shapes in different recording sites. In addition, effective refractory periods of the ventricular muscle were abnormally long.     

Effect of mexiletine on monophasic action potentials recorded from the right ventricle in man.

The effect of mexiletine, a new antiarrhythmic agent, on ventricular refractoriness and monophasic action potentials recorded from the right ventricle was studied in nine subjects. The effective refractory period of the right ventricle was determined by the extra stimulus technique using a pacing electrode situated at the right ventricular apex. Following this determination the right ventricular apex was paced at a constant cycle length and premature stimuli were introduced starting at a coupling interval of 2 ms greater than the ventricular refractory period and then at progressively increasing coupling intervals of 5 ms increments. Simultaneous recordings of monophasic action potentials of both the regular paced beats and the induced premature beats were made using a specially designed suction electrode catheter. The monophasic action potential durations were measured at 50% and 90% repolarisation. All these control measurements were repeated after an intravenous dose of 2 mg.kg-1 body wt. of mexiletine. The results showed that mexiletine did not significantly change the effective ventricular refractory period nor did it alter the monophasic action potential duration of the regular paced beat. The drug did, however, significantly prolong the monophasic action potential duration of the early induced premature beats and it is possible that this property of the drug may be related to its antiarrhythmic activity.     

Right atrium monophasic action potentials during atrial flutter and fibrillation in man.

Monophasic action potentials recorded in two patients with atrial flutter and one patient with atrial fibrillation showed a nonuniform depolarization of the right atrial wall. In each of the two patients with atrial flutter, there was a site where two separate action potential deflections were recorded for each flutter wave. It was supposed that this was the site of re-entry for a cycling wavelet subsidiary to the main flutter wave. In the patient with atrial fibrillation, three types of electric atrial activity were found: regular activity at 180 per minute similar to that found in flutter, small irregular activity at a rate of 400 per minute, and a mixed type of the former two. The significance of these findings for the mechanism of atrial flutter and fibrillation is discussed.     

Electrocardiographic and electrophysiologic studies in patients with torsades de pointe--role of monophasic action potentials

The study group consisted of 26 patients with a history of documented Torsade de Pointes (TdP) who were divides into 3 groups according to the causes of TdP. Group I consisted of 5 patients with congenital long QT syndrome. Group II consisted of 15 patients with TdP caused by antiarrhythmic drugs. Group III consisted of 6 patients with TdP caused by bradycardia resulting from third degree atrioventricular block. The QT interval was determined from a 12-lead electrocardiogram. Monophasic Action Potential (MAP) was recorded by a 6 F USCI electrode catheter. Isoproterenol infusion resulted in TU abnormality in all patients in Group I and induced a hump at phase 3 slope of MAP in all 3 patients tested. The QT interval change before and after IA administration was significantly larger in Group II patients compared to those without TdP (0.132 +/- 0.062 vs 0.029 +/- 0.31 sec, less than 0.005). Injection of 100 mg. of disopyramide in 2 patients in Group II resulted a hump at phase 3 slope of the MAP in both of them. The QT prolongation associated with decreasing the pacing rate from 70 to 50/min was significantly larger in patients with Group III compared to patients with bradycardia but without TdP (0.02 +/- 0.04 vs 0.07 +/- 0.05 sec, p less than 0.005). The results suggests: 1) different approaches are necessary for evaluation of TU abnormalities in patients with TdP according to the causes of TdP, 2) MAP might be a useful method for evaluating TU abnormality in patients with TdP.     

In vitro validation of a new cardiac catheter technique for recording monophasic action potentials

Monophasic action potential (MAP) recording with non-suction, 'contact' electrode catheters has been shown possible and safe during clinical catheterization, but direct validation of this new technique is lacking. We therefore recorded these contact electrode MAPs simultaneously with transmembrane action potentials (TAPs) from closely adjacent sites in perfused and superfused rabbit septum preparations and performed a quantitative comparison between the two signals for duration and area at 30, 60 and 90% repolarization. To obtain a variety of action potential durations and configurations for the comparison, the rate and rhythm of stimulation and the extracellular calcium or potassium ion concentration were changed. With action potential duration at 90% repolarization made to vary from 150 to 513 ms, the mean absolute difference +/- SD between the simultaneous intra- and extracellular recordings was 5.4 +/- 11.3 ms and the linear correlation coefficient was r = 0.96 +/- 0.03. Similar agreement between the two types of recordings was found for measurements for area and at 60 and 30% repolarization levels. These data confirm that MAPs recorded with this clinically safe contact electrode technique can be used to measure accurately the repolarization time course of transmembrane action potentials.