Persistent T-wave changes after alteration of the ventricular activation sequence. New insights into cellular mechanisms of 'cardiac memory'

Evaluation of T-wave memory after accessory pathway ablation in pediatric patients with Wolff-Parkinson-White syndrome

BACKGROUND

T-wave memory (TWM) is a rare cause of T-wave inversion (TWI). Alterations in ventricular activation due to abnormal depolarization may cause repolarization abnormalities on the ECG, even if myocardial conduction returns to normal. These repolarization changes are defined as TWM. In our study, we aimed to determine the frequency of TWM development and the predictors affecting it in the pediatric population who underwent accessory pathway (AP) ablation due to Wolff-Parkinson-White (WPW) syndrome.

METHODS

The data of patients with manifest AP who underwent electrophysiological studies and ablation between 2015 and 2021 were retrospectively analyzed. The study included 180 patients who were under 21 years of age and had at least one year of follow-up after ablation. Patients with structural heart disease, intermittent WPWs, recurrent ablation, other arrhythmia substrates, and those with less than one-year follow-up were excluded from the study. The ECG data of the patients before the procedure, in the first 24 h after the procedure, three months, and in the first year were recorded. The standard ablation technique was used in all patients.

RESULTS

Postprocedure TWM was observed in 116 (64.4%) patients. Ninety-three patients (51.7%) had a right-sided AP, and 87 patients (48.3%) had a left-sided AP. The presence of posteroseptal AP was found to be significantly higher in the group that developed TWM. Of these patients, 107 (93.1%) patients showed improvement at the end of the first year. Preprocedural absolute QRS-T angle, postprocedural PR interval, and right posteroseptal pathway location were identified as predictors of TWM.

CONCLUSION

The development of TWM is particularly associated with the right-sided pathway location, especially the right posteroseptal pathway location. The predictors of TWM are the preprocedural QRS-T angle, the postprocedural PR interval, and the presence of the right posteroseptal AP.

Arrhythmogenic Effects of Cardiac Memory

Cardiac memory is the term used to describe an interesting electrocardiographic phenomenon. Whenever a QRS complex is wide and abnormal, such as during ventricular pacing, the T waves will also be abnormal and will point to the opposite direction of the wide QRS. If the QRS then normalizes, such as after cessation of ventricular pacing, the T waves will normalize as well, but at a later stage. The period of cardiac memory is the phase between the sudden normalization of the QRS and the eventual and gradual return of the T waves to their baseline morphology. Cardiac memory is assumed to be an innocent electrocardiographic curiosity. However, during cardiac memory, reduction of repolarizing potassium currents increases left ventricular repolarization gradients. Therefore, when cardiac memory occurs in patients who already have a prolonged QT interval (for whatever reason), it can lead to a frank long QT syndrome with QT-related ventricular arrhythmias (torsades de pointes). These arrhythmogenic effects of cardiac memory are not generally appreciated and are reviewed here for the first time.

Pediatric T-wave memory after accessory pathway ablation in Wolff-Parkinson-White syndrome

BACKGROUND

Altered ventricular depolarization due to manifest accessory pathway conduction (ie, Wolff-Parkinson-White syndrome) leads to repolarization abnormalities that persist after pathway ablation. The term T-wave memory (TWM) has been applied to these changes, as the postablation T-wave vector "remembers" the pre-excited QRS vector. In adults, these abnormalities can be misinterpreted as ischemia leading to unnecessary interventions. To date, no comprehensive studies have evaluated this phenomenon in the pediatric population.

OBJECTIVE

The purpose of this study was to define TWM in the pediatric population, identify preablation risk factors, and delineate the timeline of recovery.

METHODS

Pre- and postablation electrocardiograms (ECGs) in patients ≤25 years were analyzed over a 5-year period. Frontal plane QTc interval, T-wave axis, QRST angle, and T-wave inversions were used to identify patients with TWM. Univariate analysis was performed to determine the association of preablation ECG features with the outcome of TWM.

RESULTS

TWM was present in 42% of pediatric patients, with resolution occurring within 3 months of ablation. Preablation QRS axis <0° was a strong predictor of TWM (odds ratio [OR] 15.2; 95% confidence interval [CI] 5.7-40), followed by posteroseptal pathway location (right posteroseptal-OR 8.9; 95% CI 4.2-18.8; left posteroseptal-OR 6.1; 95% CI 1.7-22.3). The degree of pre-excitation had a modest association with the development of TWM. No adverse events were observed.

CONCLUSION

TWM is less common in children compared to adults, and normalization occurred within 3 months postablation. The most predictive features for the development of TWM include a leftward pre-excited QRS axis and posteroseptal pathway location.

Surface ECG criteria can discriminate post-septal pacing cardiac memory from ischemic T wave inversions

Cardiac memory (CM) refers to transient T wave changes that appear after cessation of a period of abnormal ventricular activation, such as right ventricular (RV) pacing. ECG criteria for differentiating post-pacing CM from ischemia-induced T wave changes were previously published only for apical, but not for septal RV pacing.

AIM

To find ECG criteria for discriminating post-septal pacing CM from ischemic T wave inversions.

METHODS

ECGs were analyzed in 2 groups: CM (n = 23) and ischemia (n = 26). CM was induced by 2 weeks of DDD pacing with a short AV delay. Ischemic patients were grouped by culprit vessel: left anterior descending (LAD), circumflex (Cx), right coronary artery (RCA).

RESULTS

CM was visible on the ECG after 1 week of ventricular pacing, started to disappear in <1 week after pacing cessation and was completely reversible within 4 weeks of pacing cessation. T wave axis differed between CM (75.8 ± 18.5°) and Cx (-25.2 ± 25.5°, p < 0.01) and RCA (-18.3 ± 18.9°, p < 0.01) groups, but not compared to LAD group (96.4 ± 65.0°, p = 0.17). The combination of (1) positive T wave in aVF; and (2) (i) T wave amplitude in aVF ≥ the absolute value of the most negative precordial T wave, or (ii) positive T wave in V5 and positive or isoelectric T wave in lead I identified CM from all ischemia with a sensitivity of 91% and a specificity of 92%.

CONCLUSION

ECG criteria can discriminate post-septal RV pacing CM from ischemic changes with high sensitivity and specificity.

Short-Long Heart Rate Variation Increases Dispersion of Action Potential Duration in Long QT Type 2 Transgenic Rabbit Model

The initiation of polymorphic ventricular tachycardia in long QT syndrome type 2 (LQT2) has been associated with a characteristic ECG pattern of short-long RR intervals. We hypothesize that this characteristic pattern increases APD dispersion in LQT2, thereby promoting arrhythmia. We investigated APD dispersion and its dependence on two previous cycle lengths (CLs) in transgenic rabbit models of LQT2, LQT1, and their littermate controls (LMC) using random stimulation protocols. The results show that the short-long RR pattern was associated with a larger APD dispersion in LQT2 but not in LQT1 rabbits. The multivariate analyses of APD as a function of two previous CLs (APD_n = C + α₁CL_n−1 + α₂CL_n−2) showed that α₁ (APD restitution slope) is largest and heterogeneous in LQT2 but uniform in LQT1, enhancing APD dispersion under long CL_n−1 in LQT2. The α₂ (short-term memory) was negative in LQT2 while positive in LQT1, and the spatial pattern of α₁ was inversely correlated to α₂ in LQT2, which explains why a short-long combination causes a larger APD dispersion in LQT2 but not in LQT1 rabbits. In conclusion, short-long RR pattern increased APD dispersion only in LQT2 rabbits through heterogeneous APD restitution and the short-term memory, underscoring the genotype-specific triggering of arrhythmias in LQT syndrome.

Factors underlying elevated troponin I levels following pacemaker primo-implantation

BACKGROUND

Cardiac troponins are routinely used as markers of myocardial damage. Originally, they were only intended for use in diagnosing acute coronary syndromes; however, we now know that raised serum troponin levels are not always caused by ischemia. There are many other clinical conditions that cause damage to cardiomyocytes, leading to raised levels of troponin. However, the specificity of cardiac troponins towards the myocardium is absolute. Our work focuses on mechanical damage to the myocardium and on monitoring the factors that raise the levels of cardiospecific markers after primo-implantation of a pacemaker with an actively fixed electrode.

AIMS

(i) To determine whether the use of a primo-implanted pacemaker with an electrode system with active fixation will raise troponin levels over baseline. (ii) To assess whether troponin I elevation is dependent on procedure complexity.

METHODS

We enrolled 219 consecutive patients indicated for pacemaker primo-implantation; cardiospecific marker values (troponin I, CKMB, myoglobin) were determined before the implantation procedure and again at 6- and 18-h intervals after the procedure. We monitored duration of cardiac skiascopy, number of attempts to place the electrode (active penetration into the tissue) and intervention range (single-chamber versus dual-chamber pacing), and we assessed the clinical data.

RESULTS

The average age of the enrolled patients was 78.2 ± 8.0 years (median age, 80 years); women constituted 45% of the group. We implanted 128 dual-chamber and 91 single-chamber devices with an average skiascopic time of 38.6 ± 22.0 s (median, 33.5 s). Troponin I serum levels increased from an initial 0.03 ± 0.07 μg/L (median, 0.01) to 0.18 ± 0.17 μg/L (median, 0.13) and 0.09 ± 0.18 μg/L (median, 0.04) at 6 and 18 h, respectively. The differences were statistically significant (P < 0.001 or P < 0.001). We confirmed a correlation between troponin increase and duration of skiascopy (P < 0.001). We also demonstrated a correlation between increased troponin I and number of attempts to place a pacemaker electrode (penetration into the tissue) at 6 h (P < 0.001) post-implantation.

CONCLUSION

We detected slightly elevated troponin I levels in patients with primo-implanted pacemakers using electrodes with active fixation. We demonstrated a direct correlation between myocardial damage (number of electrode penetrations into the myocardium) and troponin I elevation, as well as between complexity (severity) of the implantation procedure (indicated by prolonged skiascopy) and raised troponin I. The described phenomenon demonstrates the loss of the diagnostic role of troponin I early after pacemaker primo-implantation in patients with concomitant chest pain.

Intermittent left bundle branch block: an overlooked cause of electrocardiographic changes that mimic high-grade stenosis of the left anterior descending coronary artery

CONTEXT

The electrocardiographic (ECG) pattern of high-grade stenosis of the left anterior descending coronary artery (LAD) is important clinically because of the high risk of myocardial infarction and cardiac death if the pattern is not recognized. Although the recognition of this pattern is currently widespread, false-positive ECG changes that mimic this pattern are infrequently reported.

OBJECTIVE

To demonstrate that ECG changes from intermittent left bundle branch block (LBBB) and cardiac memory can mimic anterior ischemia.

METHODS

Medical record review of cardiology patients in whom ECG tracings showed intermittent LBBB and anterior T-wave changes during normal QRS conduction. Patients were included if ECG changes suggestive of high-grade LAD stenosis in leads V2 and V3 met the following criteria: (1) the QRS conduction was essentially normal during periods of absent LBBB; (2) the ST segment took off from an isoelectric point or only slightly elevated from baseline; and (3) the ST segment sloped up gradually with an abrupt and sharp down stroke leading to terminal T-wave inversion. Additional criteria were little or no ST segment elevation, no loss of precordial R waves, and ECG changes suggestive of high-grade LAD stenosis demonstrated in precordial leads V2 and V3. All patients demonstrated intermittent LBBB, and patients were excluded if a ventricular pacemaker was present. The case series began in 2003 and continued until 2011.

RESULTS

Sixteen patients (3 male) with intermittent LBBB were identified with ST- and T-wave changes during normal ventricular conduction that matched the pattern described by Hein J.J. Wellens, MD. Of these patients, none had evidence of clinically substantial coronary artery disease. Eleven patients had stress testing with myocardial perfusion imaging, and 5 patients underwent cardiac catheterization. In 1 patient whose ECG pattern showed high-grade LAD stenosis but normal coronary arteries at catheterization, a stress test was later performed, which provoked LBBB. All other patients had spontaneous, intermittent periods of LBBB and normal conduction.

CONCLUSION

The ECG pattern of high-grade LAD stenosis has proven to be an important marker of high-risk patients with chest pain. This pattern may also be seen in patients with a right ventricular pacemaker on resumption of native QRS conduction. Intermittent LBBB is a less obvious cause of a similar ECG pattern that may mimic anterior ischemia due to high-grade stenosis.

Cardiac memory during rather than after termination of left bundle branch block

An 83-year-old woman with chronic left bundle branch block and remote history of pacemaker implantation for intermittent AV block was hospitalized for fatigue and leg swelling. She had no cardiac complaints. Routine 12-lead electrocardiogram showed sinus rhythm with left bundle branch block. There were diffuse negative T waves in the inferior and anterolateral leads that were concordant with the QRS complexes. Echocardiogram was normal and nuclear perfusion heart scan showed no abnormality. It was noted that the negative T waves during left bundle branch block were in the exact same leads as were the deep negative QRS complexes during ventricular pacing. The electrocardiographic changes were consistent with cardiac memory. This case is unique because cardiac memory in patients with intermittent left bundle branch block typically occurs when the QRS complexes normalize and not during left bundle branch block itself. Our findings indicate that memory Ts can develop not only after normalization of wide complex rhythms but also with alternating wide complex rhythms as in the presented case where a ventricular paced rhythm was replaced by left bundle branch block.

Microtubules and angiotensin II receptors contribute to modulation of repolarization induced by ventricular pacing

BACKGROUND

Left ventricular pacing (LVP) in canine heart alters ventricular activation, leading to reduced transient outward potassium current (I(to)), loss of the epicardial action potential notch, and T-wave vector displacement. These repolarization changes, referred to as cardiac memory, are initiated by locally increased angiotensin II (AngII) levels. In HEK293 cells in which Kv4.3 and KChIP2, the channel subunits contributing to I(to), are overexpressed with the AngII receptor 1 (AT1R), AngII induces a decrease in I(to) as the result of internalization of a Kv4.3/KChIP2/AT1R macromolecular complex.

OBJECTIVE

To test the hypothesis that in canine heart in situ, 2h LVP-induced decreases in membrane KChIP2, AT1R, and I(to) are prevented by blocking subunit trafficking.

METHODS

We used standard electrophysiological, biophysical, and biochemical methods to study 4 groups of dogs: (1) Sham, (2) 2h LVP, (3) LVP + colchicine (microtubule-disrupting agent), and (4) LVP + losartan (AT1R blocker).

RESULTS

The T-wave vector displacement was significantly greater in LVP than in Sham and was inhibited by colchicine or losartan. Epicardial biopsies showed significant decreases in KChIP2 and AT1R proteins in the membrane fraction after LVP but not after sham treatment, and these decreases were prevented by colchicine or losartan. Colchicine but not losartan significantly reduced microtubular polymerization. In isolated ventricular myocytes, AngII-induced I(to) reduction and loss of action potential notch were blocked by colchicine.

CONCLUSIONS

LVP-induced reduction of KChIP2 in plasma light membranes depends on an AngII-mediated pathway and intact microtubular status. Loss of I(to) and the action potential notch appear to derive from AngII-initiated trafficking of channel subunits.

Cardiac electrical remodeling in health and disease

Electrical remodeling of the heart takes place in response to both functional (altered electrical activation) and structural (including heart failure and myocardial infarction) stressors. These electrophysiological changes produce a substrate that is prone to malignant ventricular arrhythmias. Understanding the cellular and molecular mechanisms of electrical remodeling is important in elucidating potential therapeutic targets designed to alter maladaptive electrical remodeling. For example, altered patterns of electrical activation lead primarily to electrical remodeling, without significant structural remodeling. By contrast, secondary remodeling arises in response to a structural insult. In this article we review cardiac electrical remodeling (predominantly in the ventricle) with an emphasis on the mechanisms causing these adaptations. These mechanisms suggest novel therapeutic targets for the management or prevention of the most devastating manifestation of heart disease, sudden cardiac death (SCD).

Determinants of CREB degradation and KChIP2 gene transcription in cardiac memory

BACKGROUND

Left ventricular pacing (LVP) to induce cardiac memory (CM) in dogs results in a decreased transient outward K current (I(to)) and reduced mRNA and protein of the I(to) channel accessory subunit, KChIP2. The KChIP2 decrease is attributed to a decrease in its transcription factor, cyclic adenosine monophosphate response element binding protein (CREB).

OBJECTIVE

This study sought to determine the mechanisms responsible for the CREB decrease that is initiated by LVP.

METHODS

CM was quantified as T-wave vector displacement in 18 LVP dogs. In 5 dogs, angiotensin II receptor blocker, saralasin, was infused before and during pacing. In 3 dogs, proteasomal inhibitor, lactacystin, was injected into the left anterior descending artery before LVP. Epicardial biopsy samples were taken before and after LVP. Neonatal rat cardiomyocytes (NRCM) were incubated with H(2)O(2) (50 micromol/l) for 1 hour with or without lactacystin.

RESULTS

LVP significantly displaced the T-wave vector and was associated with increased lipid peroxidation and increased tissue angiotensin II levels. Saralasin prevented T-vector displacement and lipid peroxidation. CREB was significantly decreased after 2 hours of LVP and was comparably decreased in H(2)O(2)-treated NRCM. Lactacystin inhibited the CREB decrease in LVP dogs and H(2)O(2)-treated NRCM. LVP and H(2)O(2) both induced CREB ubiquitination, and the H(2)O(2)-induced CREB decrease was prevented by knocking down ubiquitin.

CONCLUSION

LVP initiates myocardial angiotensin II production and reactive oxygen species synthesis, leading to CREB ubiquitination and its proteasomal degradation. This sequence of events would explain the pacing-induced reduction in KChIP2, and contribute to altered repolarization and the T-wave changes of cardiac memory.

Why T waves change: a reminiscence and essay

The following article is a personal reflection on my study of a subject which has long interested me. The subject is the T wave, and especially the T wave changes occurring as a marker of cardiac memory. My interest evolved over coffees that Mauricio Rosenbaum and I used to share at the Hotel Algonquin during his frequent trips from Buenos Aires to New York. There is something about the Algonquin, whose scarred wooden tabletops carry the imprints of Robert Benchley, Dorothy Parker, and the 1920's New York literati, and there was something about Mauricio-clinician-scientist, friend, and raconteur extraordinaire-that made his repeated challenges to me to "look at cardiac memory before you begin losing your own" irresistible. So began my personal voyage into trying to understand the T wave. My guideposts were the experiments of Wilson and Finch,(1) the astute observations of a host of investigators who followed, and Mauricio's iconoclastic insights. The story is far from over...I doubt I'll see the end of it in my lifetime. But if the beauty of discovery is in the voyage, then it has been - for me - a memorable trip.

Cardiac memory: a work in progress

Cardiac memory is a form of electrophysiological remodeling generally considered benign, although it shares transduction pathways with factors that may be pathological, such as angiotensin II and reactive oxygen species. When induced by electrical pacing, memory provides a window into the mechanisms engaged during cardiac device therapy. Emphasis is placed on the complexity of signaling processes occurring downstream to the simple intervention of cardiac pacing and the relationship of resultant ion channel changes to their expression in action potentials and body surface recordings.

A rate-independent method of assessing QT-RR slope following conversion of atrial fibrillation

INTRODUCTION

Following conversion of atrial fibrillation (AF), QT interval transiently and variably prolongs and can trigger torsades de pointes (TdP). However, quantitative analysis of risk in this setting is difficult because cycle length variability during AF makes rate-corrected QT impossible to calculate. In this study, a newly developed method to study heart rate dependence of the QT interval during AF was applied to assess the QT-RR relationships prior to and following cardioversion in patients with AF.

METHODS AND RESULTS

Cardiac rhythm was digitized for > or = 30 minutes prior to and following elective cardioversion to sinus rhythm (SR) in 12 patients. Each QT interval was placed in a "bin" (50 ms), according to the preceding RR interval. All QT intervals within a bin were averaged and RR bin-specific QT values were derived. The slope of the QT-RR relationship was much flatter in AF (0.058 +/- 0.02) compared with that predicted by conventionally used QT rate corrections (0.130 [Bazett], 0.096 [Fridericia]) and much steeper after cardioversion (0.238 +/- 0.14, P < 0.01 compared with AF). The method also allowed us to establish that QT at any given RR interval prolonged when SR was restored (e.g., at RR interval 800 ms: QT = 0.38 +/- 0.03 second [AF] vs 0.46 +/- 0.05 second [SR], P < 0.01). The longest QT values were in patients receiving sotalol or quinidine.

CONCLUSIONS

The results of this study demonstrate that QT interval can be reliably measured in AF using a method that is independent of heart rate. We also showed that cardioversion of AF acutely increases the QT interval and the steepness of the QT-RR slope.

Cardiac Resynchronization Therapy: A Review of Proarrhythmic and Antiarrhythmic Mechanisms

Available evidence supports the hypothesis that cardiac resynchronization therapy (CRT) results in favorable structural as well as electrical remodeling. Electrical remodeling seems to be related, to a large extent, to structural remodeling, usually referred to as reverse remodeling of left ventricular (LV) dysfunction. This can lead to amelioration of the arrhythmogenic substrate associated with depressed LV systolic function and heart failure. However, a direct electrophysiological effect due to favorable remodeling of repolarization with reduction of the dispersion of repolarization cannot be ruled out. On the other hand, in a small subgroup of patients, CRT could increase the dispersion of repolarization and induce malignant ventricular tachyarrhythmias. Clinical trials have consistently shown improved outcome with CRT-defibrillators (CRT-D) and more trials have demonstrated the benefits of the defibrillator in the population with depressed LV function. However, some physicians argue that implanting the less expensive and less complicated CRT-pacemaker (CRT-P) may be appropriate in certain groups of patients. Before this position is accepted, it is imperative that criteria for the selection of this group of patients with presumably low risk for sudden arrhythmic death as well as the proarrhythmic effect of CRT be clearly defined.

Biventricular Pacing Has an Advantage over Left Ventricular Epicardial Pacing Alone to Minimize Proarrhythmic Perturbation of Repolarization

INTRODUCTION

Cardiac resynchronization therapy (CRT) by simultaneous biventricular pacing is now widely accepted as a new therapeutic option for patients with severe congestive heart failure (CHF). Recent studies have shown comparable hemodynamic benefits of left ventricular (LV) pacing alone. The clinical usefulness of CRT, however, might be compromised by potential exaggeration of arrhythmogenic substrates through a modification of ventricular repolarization.

METHODS AND RESULTS

We compared ECG parameters during sinus rhythm (SR), atrioventricular synchronous pacing at the right ventricular apex (RV(end)P), at LV epicardium (LV(epi)P), and at both sites (BiVP) in acute homodynamic studies of 14 CHF patients scheduled for CRT (QRS duration = 144 +/- 23 msec, LVEF = 27 +/- 10%). The maximum rate of increase in LV pressure (LVdp/dt(max)) was decreased significantly during RV(end)P, whereas it was increased similarly during LV(epi)P and BiVP compared with SR. QTc was increased during RV(end)P (by 10.2%) and LV(epi)P (by 26.1%). QTc dispersion (QTc(max)-QTc(min) in the six precordial leads) was also increased during LV(epi)P (by 66.5%). These parameters were unaffected during BiVP. JTc was unchanged, and the interval from the peak to the end of the T wave (Tc(peak-end)) was increased slightly (by 19.3%) during RV(end)P. Both JTc and Tc(peak-end) were increased dramatically during LV(epi)P (by 18.2% and 55.4%, respectively), but increased only modestly during BiVP (by 6.6% and 15.8%, respectively).

CONCLUSIONS

LV(epi)P causes much greater increase in spatial dispersion of ventricular repolarization than BiVP in CHF patients. BiVP may have a substantial advantage over LV(epi)P to minimize the proarrhythmic perturbation of ventricular repolarization in association with CRT.

Molecular/genetic determinants of repolarization and their modification by environmental stress

Although a variety of factors, inherited or environmental, can influence expression of ion channel proteins to impact on repolarization, that environment can affect genetic determinants of repolarization for intervals of varying duration is a concept that is not as generally appreciated as it should be. In the following pages we review the molecular/genetic determinants of cardiac repolarization and summarize how pathologic events and environmental intrusions can affect these determinants. Understanding the chains of events involved should yield insights into both the causes and potential avenues of treatment for abnormalities of repolarization.

Correlation of Electrotonic Monophasic Action Potential Shortening with Short-Term Memory in Human Atrium

To determine the presence of memory in human atria, we recorded monophasic action potential (MAP) at the high right atrium (HRA) in 21 patients. After reaching a steady state at 600 ms, HRA pacing was switched to the coronary sinus (CS) pacing to alter the activation sequence. After 20 minutes of CS pacing, pacing was continued at HRA to record the memory effect of CS pacing. Atrial memory was defined as the change in HRA MAP duration (MAPd) after 20 minutes of altered activation sequence. Baseline MAPd was 229 +/- 31 ms, which was shortened to 226 +/- 24 ms immediately after CS pacing. After 20 minutes of CS pacing, HRA MAPd during HRA pacing was 220 +/- 28 ms, which was significantly shorter than the baseline MAPd (P = 0.003). The degree of atrial memory was associated with the degree of initial electrotonic MAPd changes caused by the altered activation sequence. These results suggest that memory phenomenon exists in human atria, and it can be expressed as a change in MAPd.

Phobic memory and somatic vulnerabilities in anorexia nervosa: a necessary unity?

Anorexia nervosa is a clinically significant illness that may be associated with permanent medical complications involving almost every organ system. The paper raises a question whether some of them are associated with premorbid vulnerability such as subcellular ion channel abnormalities ('channelopathy') that determines the clinical expression of the bodily response to self-imposed malnutrition. Aberrant channels emerge as a tempting, if rather speculative alternative to the notion of cognitively-driven neurotransmitter modulation deficit in anorexia nervosa. The concept of channelopathies is in keeping with some characteristics of anorexia nervosa, such as a genetically-based predisposition to hypophagia, early onset, cardiac abnormalities, an appetite-enhancing efficacy of some antiepileptic drugs, and others. The purpose of this article is to stimulate further basic research of ion channel biophysics in relation to restrictive anorexia.

Pro- and antiarrhythmic effects of fast cardiac pacing in a canine model of acquired long QT syndrome

Increasing the heart rate is one option for suppressing bradycardia-dependent polymorphic ventricular tachycardias (PVTs). The mechanisms underlying preventive pacing in acquired forms of the long QT syndrome (LQTs) are still not fully understood. Using two needle electrodes, local effective refractory periods (ERPs) were determined in the left (LV) and right ventricle (RV) in 20 dogs with acute AV node ablation before continuous pacing, during a 20-min period of continuous fast pacing (Cl 300 ms, fastpac) and during a 35-min recovery period with slow (Cl 500 ms) pacing. This protocol was applied to control dogs (5 dogs) and dogs with pretreatment of the IKs blocking agent chromanol 293b (5 dogs, LQTs1), the IKr-blocking agent dofetilide (5 dogs, LQTs2) or a combination thereof (5 dogs). Fastpac resulted in a significant abbreviation of ERPs in control dogs and dogs receiving dofetilide or chromanol 293b. During recovery, shortening of ERPs persisted in the control group, but diminished in dogs with acquired LQTs. In dogs with LQTs2 fastpac could not suppress inhomogeneity of refractoriness during recovery. With pretreatment of dofetilide and chromanol 293b in combination, MAP duration during fastpac significantly increased (first beat: 256+/-6 ms vs. sixth beat: 278+/-9 ms, p<0.05) and fastpac-induced PVTs were evident. ERP shortening and reduced inhomogeneity of refractoriness might be one antiarrhythmic action of fastpac in dogs with acute AV-block. However, in the acquired LQTs1 and 2 beneficial effects of fastpac diminished and in a combination thereof fastpac-induced PVTs are likely.

Electrotonic load triggers remodeling of repolarizing current Ito in ventricle

A change in activation sequence electrically remodels ventricular myocardium, causing persistent changes in repolarizing currents (T-wave memory). However, the underlying mechanism for triggering activation sequence-dependent remodeling is unknown. Optical action potentials were mapped with high resolution from the epicardial surface of the arterially perfused canine wedge preparation (n = 23) during 30 min of baseline endocardial stimulation, followed by 40 min of epicardial stimulation, and, finally, restoration of endocardial stimulation. Immediately after the change from endocardial to epicardial stimulation, phase 1 notch amplitude of epicardial cells was attenuated by 74 +/- 8% (P < 0.001) compared with baseline and continued to diminish during the period of epicardial pacing, suggesting progressive remodeling of the transient outward current (Ito). When endocardial pacing was restored, notch amplitude did not immediately recover but remained attenuated by 23 +/- 10% (P < 0.001), also consistent with a remodeling effect. Peak Ito current measured from isolated epicardial myocytes changed by 12 +/- 4% (P < 0.025), providing direct evidence for Ito remodeling occurring on a surprisingly short time scale. The mechanism for triggering remodeling of Ito was a significant reduction (by 14 +/- 4%, P < 0.001) of upstroke amplitude in epicardial cells during epicardial stimulation. Reduction in upstroke amplitude during epicardial pacing was explained by electrotonic load on epicardial cells by fully repolarized downstream endocardial cells. These data suggest a novel mechanism for triggering electrical remodeling in the ventricle. Electrotonic load imposed by a change in activation sequence reduces upstroke amplitude, which, in turn, attenuates Ito according to its known voltage-dependent properties, triggering downregulation of current.

Transmural action potential changes underlying ventricular electrical remodeling

INTRODUCTION

Although it is well established that alterations in heart rate or activation sequence induce electrical remodeling in the atria, electrical remodeling in the ventricle is poorly understood.

METHODS AND RESULTS

To determine the changes in cellular repolarization that underlie ventricular electrical remodeling caused separately by altered heart rate and activation sequence, optical action potentials were recorded simultaneously from 256 sites spanning the transmural wall of the arterially perfused canine wedge preparation (n = 15). Action potentials were compared from the same sites under identical conditions [endocardial pacing, cycle length (CL) = 1,000 msec], before and after an intervening 20- to 60-minute period of remodeling induced by (1) rapid pacing (CL = 300 msec) with no change in activation sequence; (2) altered activation sequence (epicardial pacing) with no change in rate; or (3) no change in rate or activation sequence (control). Action potential duration (APD) shortened by 24.8 +/- 4.8 msec following a period of rapid heart rate (P < 0.05) but prolonged (by 12.7 +/- 1.8 msec) following a period of altered activation sequence (P < 0.05). Hence, even after restoration of baseline heart rate and activation sequence, there were persistent changes in APD from baseline, indicative of electrical remodeling. Moreover, the orientation of the maximum APD gradient across the transmural wall changed more significantly following heart rate remodeling (by 27.7 degrees +/- 4.9 degrees, P < 0.05) than following activation sequence remodeling (by 12.3 degrees +/- 2.4 degrees, P < 0.05).

CONCLUSION

Persistent changes in ventricular repolarization can be induced by surprisingly short periods of altered rate or activation sequence. In contrast to atrial remodeling, electrical remodeling in the ventricle can result in prolonged APD (with altered activation sequence) or reversal of APD gradient orientation (with rapid rate), suggesting that the nature of ventricular electrical remodeling induced by these two perturbations is different.

The pharmacology of cardiac memory

Cardiac memory is an altered T wave during sinus rhythm that is induced by a period of ventricular pacing or arrhythmia. The T wave is characterized by a vector that tracks that of the previously paced or arrhythmic QRS complex. Although initially considered a clinical oddity, cardiac memory is of interest both as an example of the general biological property of memory - as studied most extensively in neural tissues - and because of its implications regarding the control of cardiac rhythm. Signal transduction of cardiac memory appears to involve an angiotensin II-regulated pathway initiated by altered stress/strain patterns in the myocardium. The end result is altered density and kinetics of the transient outward current and perhaps other ion currents as well, and an altered transmural gradient for repolarization. The altered repolarization pattern is accompanied by altered responses to specific antiarrhythmic drugs that may be anti- or proarrhythmic.

Gradient of sodium current across the left ventricular wall of adult rat hearts

1. Gradients of ion channels across the left ventricular (LV) wall have been well characterized and it has been shown that disruption of such gradients leads to altered rates of repolarization across the wall, which is associated with the generation of arrhythmias. 2. We have hypothesized that a transmural gradient of I(Na) is present and have directly measured this current in adult rat myocytes isolated from both the epicardial and endocardial layers of the left ventricle. Currents were also recorded in right ventricular (RV) myocytes for comparison. 3. Peak inward I(Na) currents, at -30 mV, were -49.7 +/- 2.5 pA pF(-1) (n = 22), -32.9 +/- 3.2 pA pF(-1) (n = 16) and -49.7 +/- 3.7 pA pF(-1) (n = 24) for RV, LV epicardial and LV endocardial myocytes, respectively. No differences in the voltage dependence of inactivation, the voltage dependence of steady-state inactivation, or reactivation were reported. 4. Our results demonstrate that a gradient of sodium current density is present across the LV wall of adult rat hearts.

Activation-recovery intervals of 12-lead electrocardiograms before and after catheter ablation in patients with Wolff-Parkinson-White syndrome

Preexcitation in Wolff-Parkinson-White syndrome (WPW) has been reported to induce long-lasting changes in ventricular recovery properties. However, there has not been a report concerning changes in the activation-recovery interval (ARI) in 12-lead ECGs before and after catheter ablation (CA) in patients with WPW syndrome. The present study compared changes in ARIs from 12-lead ECGs with those from body surface unipolar leads before and after CA to examine whether ARIs from limb leads of 12-lead ECGs provide useful information on changes in recovery properties in addition to the ARIs from precordial leads. The study population consisted of 27 manifest WPW patients with a left- (n=18, group A) or right-sided accessory pathway (n=9, group B). ARIs in leads I, II, and III were strongly correlated with those in unipolar leads over the left lateral, left lower, and right lower chest, respectively. ARIs in leads aVR, aVL, and aVF showed a significant correlation with those in unipolar leads over the right upper, left upper, and lower anterior chest, respectively. These correlations were maintained before and after CA. Furthermore, in group A, ARIs in lead V1 tended to increase on day 7 post CA compared with before CA and on day 1. In group B, ARIs in lead III significantly decreased on day 7 compared with before CA and on day 1. These findings suggest that ARIs from the limb leads of 12-lead ECGs may represent those from unipolar leads of a particular area over the body surface, and that ARIs from 12-lead ECGs may provide useful quantitative information on changes in recovery properties before and after CA in patients with manifest WPW syndrome.

Comparison of vectorcardiographic and 12-lead electrocardiographic detections of abnormalities in repolarization properties due to preexcitation in patients with Wolff-Parkinson-White syndrome: proposal of a novel concept of a "remodeling gradient"

Repolarization abnormalities after radiofrequency ablation in patients with manifest Wolff-Parkinson-White syndrome (WPW) have been attributed to cardiac memory of pre-existing changes in repolarization properties. We compared spatial ventricular gradient (VG) from vectorcardiograms with QRST values of 12-lead ECG in 41 patients with WPW (group A, manifest WPW due to left-sided accessory pathway (n = 20); group B, manifest WPW due to right-sided accessory pathway (n = 12); group C, concealed WPW (n = 9)) before and after ablation. Group N (n = 607) served as control. In groups A and B, the abnormalities of spatial VG and QRST values of 12-lead ECG that existed before and 1 day after ablation significantly decreased 1 week after ablation. In group C, spatial VG and QRST values of 12-lead ECG showed no significant changes. The diagnostic ability of spatial VG is almost equivalent to that of the QRST value of ECG in detecting repolarization abnormalities in patients with WPW before and after ablation. We propose a new concept of a "remodeling gradient" directing from the preexcited area to the opposite side of the ventricle as a result of preexcitation-induced electrical remodeling.

Persistent T-wave changes after radiofrequency catheter ablation of an accessory connection (Wolff-parkinson-white syndrome) are caused by "cardiac memory"

BACKGROUND

The purpose of this study was to determine the incidence and origin of T-wave changes after ablation of an accessory atrioventricular connection (AC), which could either be a sign of damage to the coronary circulation or a result of persistent abnormal repolarization secondary to previously abnormal ventricular activation ("cardiac memory").

METHODS AND RESULTS

Ninety of 107 consecutive patients (33 women and 57 men, mean age 36 +/- 5 years) undergoing successful catheter ablation of an AC were studied. Patients with bundle branch block or more than 1 AC were excluded. Sixty-four patients had manifest preexcitation (group 1) and 26 had a concealed AC (group 2). Immediately after loss of preexcitation, 38 (59%) patients with a manifest AC showed T-wave abnormalities. In contrast, none of the patients with a concealed AC had T-wave abnormalities after ablation (P <.05). The T-wave changes (1) did not correlate with the number or duration of energy applications or with markers of tissue injury; (2) correlated with the location of the AC and the degree of preexcitation, respectively; and (3) completely resolved over a period of weeks to months. None of the patients had recurrence of preexcitation or tachycardia during a mean follow-up of 16 +/- 7 months.

CONCLUSIONS

T-wave changes after ablation are most likely caused by "cardiac memory" and are not a sign of myocardial or coronary injury.

Cardiac memory after radiofrequency ablation of accessory pathways: the post-ablation T wave does not forget the pre-excited QRS

INTRODUCTION

Normalization of the pre-excited QRS following ablation is accompanied by repolarization changes but their directional relationship to changes in ventricular activation has not been well characterized.

METHODS

Accordingly, we measured QRS and T wave vectors and QRS-T angles from 12 lead ECG recordings immediately before and after accessory pathway (AP) radiofrequency ablation in 100 consecutive patients. Patients with bundle branch block, intraventricular conduction defect or intermittent pre-excitation were excluded, leaving a study group of 45 patients: 35 with pre-excitation and 10 with concealed APs.

RESULTS

With AP ablation, changes occurred in the QRS and T wave vectors and QRS-T angles that were essentially equal and opposite, so that the newly normalized QRS complex and QRS vector were accompanied by a T wave whose vector approximated that of the pre-ablation QRS vector. This tended to maintain a large QRS-T angle: 72 degrees +/- 50 degrees before, and 54 degrees +/- 34 degrees after QRS normalization (p = NS). A QRS-T angle >40 degrees was found before and after ablation in 22/35 patients (63%) with baseline pre-excitation; but never in patients with a concealed AP (p = 0.001). The angle between the pre-excited QRS and the post-ablation T wave was 35 degrees +/- 37 degrees, and </=40 degrees in 25/35 patients (71%). The change in T wave axis with QRS normalization correlated in magnitude with the QRS-T angle before ablation (r = 0.73, p < 0.0001). The change in QRS axis correlated with the QRS-T angle after ablation (r = 0.37, p < 0.03). Shorter AP effective refractory periods (ERPs) correlated with wider QRS-T angles after ablation (r = -0.39, p < 0.03). The ECG leads manifesting these changes depend on AP location.

CONCLUSION

T-wave changes after ablation of APs (1) are dependent on anterograde AP conduction at baseline and are not observed with concealed APs; (2) correlate in magnitude directly with the change in QRS axis and inversely with the anterograde AP-ERP; (3) are related to AP location. With termination of pre-excitation secondary repolarization changes immediately disappear and the post ablation T wave axis approximates that of the pre-excited QRS. Recognition of this sequence may prevent unnecessary clinical interventions.

A role for the renin-angiotensin system in the evolution of cardiac memory

INTRODUCTION

We studied the role of the cardiac renin-angiotensin II system in the genesis of cardiac memory, in which T wave changes induced by ventricular pacing (VP) accumulate and persist during subsequent sinus rhythm.

METHODS AND RESULTS

Anesthetized dogs were instrumented via a thoracotomy and three 20-minute runs of VP were interspersed with periods of normal sinus rhythm sufficient to permit T wave recovery to 90% of control. Memory was quantified as the change (delta) in T wave vector angle showing accumulation over the three monitoring periods. In five control dogs T wave vector = -27 +/- 49 degrees, and this shifted by 104 degrees (P < 0.05) over the three postpacing recovery periods. In seven dogs infused with the receptor blocker saralasin, five infused with the angiotensin-converting enzyme inhibitor captopril, and four infused with the tissue protease inhibitor chymostatin, there were significant reductions in the incidence and the accumulation of memory. In four other experiments, we used isolated, blood-perfused canine hearts to demonstrate that VP used to induce memory alters the contractile pattern of the left ventricle.

CONCLUSIONS

We propose that the alteration in myocardial stretch induced by pacing activates angiotensin II synthesis by cardiac cells. We propose, further that the endogenous cardiac renin-angiotensin II system (blocked by saralasin, captopril and by chymostatin) is an important contributor to the induction of memory.

Regional differences in effects of 4-aminopyridine within the sinoatrial node

4-Aminopyridine (4-AP)-sensitive transient outward current (Ito) has been observed in the sinoatrial node, but its role is unknown. The effect of block of Ito by 5 mM 4-AP on small ball-like tissue preparations (diameter approximately 0.3-0.4 mm) from different regions of the rabbit sinoatrial node has been investigated. 4-AP elevated the plateau, prolonged the action potential, and decreased the maximum diastolic potential. Effects were greater in tissue from the periphery of the node than from the center. In peripheral tissue, 4-AP abolished the action potential notch, if present. 4-AP slowed pacemaker activity of peripheral tissue but accelerated that of central tissue. Differences in the response to 4-AP were also observed between tissue from more superior and inferior regions of the node. In the intact sinoatrial node, 4-AP resulted in a shift of the leading pacemaker site consistent with the regional differences in the response to 4-AP. It is concluded that 4-AP-sensitive outward current plays a major role in action potential repolarization and pacemaker activity in the sinoatrial node and that its role varies regionally.

Changes in cardiac repolarization following short periods of ventricular pacing

INTRODUCTION

"Cardiac memory" (primary T wave change) is thought to occur after 15 minutes to several hours of right ventricular (RV) pacing. The two components of the temporal change in repolarization are memory and accumulation. The purpose of this study was to examine quantitatively the effect of short periods of ventricular pacing on the human cardiac action potential, using monophasic action potential (MAP) recordings.

METHODS AND RESULTS

Thirty-one patients (ages 43+/-14 years) with structurally normal hearts undergoing a clinically indicated electrophysiologic procedure were enrolled. Catheters were placed in the right atrium (RA) and RV, and a MAP catheter was positioned at the RV septum. APD90 was calculated from digitized MAP recordings. MAP morphology comparisons were performed using the root mean square (RMS) of the difference between complexes. All pacing was at 500-msec cycle length. There were four pacing protocols: (1) RA pacing was performed for approximately 15 minutes to evaluate temporal stability of the MAP recordings (5 pts); (2) to evaluate the memory phenomenon, four successive 1-minute episodes of RV pacing were interspersed with 2 minutes of RA pacing (5 pts); (3) the accumulation phenomenon was evaluated by assessing the effects of 1, 5, 10, and 15 minutes of RV pacing on the MAP during RA pacing (16 pts); and (4) 20 minutes of RV pacing was followed by 10 minutes of RA pacing to correlate visually apparent T wave changes with changes in MAP recordings (5 pts). In the control patients, no changes in APD90 or RMS analysis were noted during 14.9+/-1.4 minutes of RA pacing. In the second protocol, RMS of the difference between the baseline MAP complexes and the signal average of the first 50 beats following each of four 1-minute RV pacing trains demonstrated progressively greater differences in morphology after successive episodes of RV pacing. In protocol 3, RMS analysis identified a progressively greater difference between the baseline MAP recording and the average of the first 50 beats after 1, 5, 10, and 15 minutes of RV pacing. In protocol 4, visually apparent changes in T waves occurred in parallel with the RMS of the difference between the baseline MAP recordings and the average of the first 50 beats after 20 minutes of RV pacing. Similar changes also were demonstrated by APD90 analysis.

CONCLUSION

This study is the first to demonstrate that episodes of abnormal ventricular activation as short as 1 minute in duration may exert lingering effects on the repolarization process once normal ventricular activation resumes.

Relationship between QRS duration and repolarization abnormalities in patients with Wolff-Parkinson-White syndrome

Marked T wave abnormalities in 12-lead electrocardiograms often appear after radiofrequency ablation in patients with Wolff-Parkinson-White (WPW) syndrome. Durations of the QRS complex before ablation have been reported to be significantly greater in patients with repolarization abnormalities after ablation than in those with normal repolarization. However, there has been no report concerning the relationship between QRS duration and repolarization abnormalities before ablation. It has been reported that QRST isointegral maps are dependent on local cellular repolarization properties but largely independent of activation sequence, and that they provide quantitative information about repolarization abnormalities. Isointegral maps were constructed from data recorded in 34 patients with WPW syndrome and QRS durations of 0.1 second or longer (21 patients with left-sided accessory pathways and 13 with right-sided pathways) in order to investigate the relationship between QRS duration and abnormalities in repolarization properties during preexcitation. Body surface ECGs were recorded with an 87-lead system at a sampling interval of 1 ms. The QRST values (mean +/- 2SD) from 607 normal individuals were taken to represent the normal range. The area with abnormally low QRST values was designated as the -2SD area and the sum of the QRST values (sigma QRST) in this area was calculated. The QRS duration was found to be significantly related to sigma QRST. These results demonstrate that the patients with WPW syndrome had abnormalities in local repolarization properties that were significantly related to QRS duration during preexcitation. The degree of preexcitation may be important in producing these abnormalities in patients with manifest WPW syndrome. This may result in T wave abnormalities after ablation of the accessory pathway attributable to cardiac memory.

Body surface distribution of significant changes in QRST time-integral values after radiofrequency catheter ablation in patients with Wolff-Parkinson-White syndrome

We analyzed 87-lead body surface QRST time-integral values (QRST values) in 29 patients with Wolff-Parkinson-White syndrome (group A, 17 patients with manifest left-sided accessory pathway; group B, 6 patients with manifest right-sided accessory pathway; and group C, 6 patients with concealed left-sided accessory pathway), before, 1 day after, and 1 week after radiofrequency catheter ablation (RCA). The number of leads with abnormal QRST values was significantly lower 1 week after RCA compared with those before RCA and 1 day after RCA in groups A and B (p < 0.05); there was no significant difference in QRST values before and 1 day after RCA in groups A and B. The QRST values over areas with preexisting repolarization abnormalities were significantly altered 1 week after RCA compared with before and 1 day after RCA in groups A and B (p < 0.01). However, there was no significant difference in the QRST values over areas without preexisting abnormalities before RCA. In group C, there were no significant differences in the QRST values or the number of leads with abnormal QRST values before, 1 day and 1 week after RCA. In conclusion, RCA did not significantly influence repolarization properties over areas without preexisting abnormalities, but gradually reduced preexisting repolarization abnormalities, which were closely related to the location of the accessory pathway in patients with manifest Wolff-Parkinson-White syndrome. Our results suggest that body surface QRST values are useful for assessment of repolarization abnormalities during the periablation period.

Transient T wave abnormalities after cessation of ventricular preexcitation: memory of what?

(1) Ventricular preexcitation causes both secondary and primary T wave changes. The secondary changes disappear immediately after cessation of preexcitation (ablation of accessory pathways) and unmask the primary T wave changes that regress within days, weeks, or months. (2) The pattern of primary T wave change produced by ventricular preexcitation depends on the location of the accessory pathway connections. The septal and posterior connections are associated with more prominent anteriorly directed T wave deflections and deviation of the T wave vector superiorly. The left lateral connections are associated with rightward deviation of the T wave vector in the frontal plane. (3) The primary T wave abnormalities are believed to be caused by local lengthening of repolarization, but the site of the postulated abnormalities needs to be established. (4) The persistence and slow dissipation of the primary T wave change induced by ventricular pacing, left bundle branch block, and presumably ventricular preexcitation have been attributed to the memory of past events. The nature of these events is not known. Several in vitro models demonstrated phenomena of gradual adjustment of ventricular action potential duration to change in cycle length, or to altered pattern of stimulation, but none of such models has mimicked the long-lasting regression of T wave abnormalities. (5) The terms T wave memory and pseudoprimary repolarization changes lack specificity and are unnecessary additions to the electrocardiographic vocabulary.

Cardiac arrhythmias and antiarrhythmic drugs: recent advances in our understanding of mechanism

The purpose of this review is to consider our understanding of the mechanisms of action of cardiac antiarrhythmic drugs, as well as the status of our comprehension of arrhythmias and their therapy. The approach will be to review the basis for normal electric activity of the heart, the mechanisms for cardiac arrhythmias, and our understanding of the mechanisms of drug action, and to distill from these strategies for the future. Immediate strategies in the prevention and treatment of life-threatening arrhythmias will most likely continue to make use of catheter and electrically based therapy, but the longterm treatment of large populations of individuals will still require the search for, and testing and administration of, pharmacologic therapy. It is emphasized that simplistic approaches to the solution of the complex problem of arrhythmias and their management of probably continue to cause problems, and that only by mastering the complexities of pathophysiology may success be best assured.

QRST time integral values in 12-lead electrocardiograms before and after radiofrequency catheter ablation in patients with Wolff-Parkinson-White syndrome

OBJECTIVES

We investigated the usefulness of QRST values obtained from 12-lead electrocardiograms (ECGs) for identification of repolarization abnormalities before and after radiofrequency ablation in patients with Wolff-Parkinson-White syndrome.

BACKGROUND

Marked T wave abnormalities often appear after ablation and have been attributed to a continuation of repolarization abnormalities present before ablation (cardiac memory). However, to our knowledge repolarization properties before and after ablation have not been assessed quantitatively.

METHODS

We calculated the ECG QRST values from 53 patients with Wolff-Parkinson-White syndrome and compared these values before, immediately after and 1 day and 1 week after successful ablation in 25 patients.

RESULTS

QRST values were abnormally high in lead V1 in 7 of 28 patients with a left-sided accessory pathway and abnormally low in leads III and aVF and high in lead aVL in 12, 9 and 10 of 20 patients, respectively, with a right-sided accessory pathway. Preexisting QRST abnormalities were still present immediately and 1 day after ablation but were usually absent by 1 week after ablation. QRST values before, immediately after and 1 day after ablation were not significantly different in any lead. In 14 patients with ablation of a left-sided accessory pathway, QRST values before, immediately after and 1 day after ablation in lead V1 and immediately after ablation in leads I, aVR and V2 were significantly different from QRST values in those leads 1 week after ablation. In six patients with ablation of a right-sided accessory pathway, QRST values before, immediately after and 1 day after ablation in leads III, aVL and aVF and immediately after ablation in lead II were significantly different from QRST values in those leads 1 week after ablation.

CONCLUSIONS

Electrocardiographic QRST values may provide useful quantitative information with respect to repolarization properties before and after ablation in patients with Wolff-Parkinson-White syndrome that is otherwise difficult to obtain by conventional ECG analysis.

Repolarization gradients derived by subtraction of monophasic action potential recordings in the human heart. Studies incorporating altered mechanical loading and ischemia

Information derived from the analysis of the electrocardiographic waveform remains one of the most valuable diagnostic aids in modern cardiology. Paradoxically, although changes in the ST-T segment probably have the widest clinical application, it is the analysis of this repolarization phase that has been surrounded by the greatest difficulties in interpretation.