12-lead Surface ECG Research Articles

Ventricular Tachycardia in Coronary Artery Disease

The diagnosis, definition, localization, and management of postinfarct ventricular tachycardia (VT) in the patient with coronary artery disease depends critically on the surface 12-lead ECG. A systematic analysis of both the sinus rhythm and tachycardia ECGs provides much information that is critical for further decision making. The 12-lead ECG is used to exclude the other differential diagnostic possibilities, outline the substrate for postinfarct VT, define the likely region of VT exit from the scar border, as well as allow for detailed intracardiac analysis using entrainment and pace mapping during catheter ablation procedures.

Does cardiac resynchronization therapy benefit patients with right bundle branch block: cardiac resynchronization therapy has a role in patients with right bundle branch block.

Does cardiac resynchronization therapy benefit patients with right bundle branch block: cardiac resynchronization therapy has a role in patients with right bundle branch block.

Assessment of the relationship between fragmented QRS and cardiac iron overload in patients with beta-thalassemia major.

Objective:Beta-thalassemia major (TM) is a genetic hemoglobin disorder causing chronic hemolytic anemia. Since cardiac insufficiency and arrhythmias are the primary causes of mortality in such patients, monitoring of cardiac iron load is important in management of the disorder. The purpose of this study was to investigate the importance of fragmented QRS (fQRS) and its relation to the cardiac T2* value for the evaluation of cardiac iron load in TM patients.Methods:This retrospective study included 103 TM patients. The patients’ T2* values, measured by cardiac MRI and 12-lead surface ECGs, were interpreted. The cardiac T2* values under 20 were considered as cardiac iron overload. The relationship between the cardiac T2* value and fQRS in ECG was investigated.Results:The median age of the patients was 22.6±6.6 years. All patients were on regular blood transfusions and iron chelators. The patients had no risk factors for coronary artery disease. In 50 (48%) patients fQRS was detected, and in 37 (74%) of these the T2* values were low. 86% of patients with cardiac involvement (37) had fQRS, but 22% of patients with non-involvement (13) had fQRS (p<0.001).Conclusion:Since cardiac involvement is the primary cause of mortality in TM patients, the early diagnosis of cardiac dysfunction is of vital importance. The search for fQRS in the ECGs of these patients, particularly when cardiac T2* values cannot be determined and followed, is a non-expensive and easy-to-attain method for therapy management.

The electrocardiogram in Down syndrome

Down syndrome is the most common chromosomal abnormality, with an incidence of one case in every 650 live births. It is strongly associated with heart disease, which constitutes the main cause of mortality during the first 2 years of life in this population. Most of the cardiac abnormalities in patients with Down syndrome can be suspected by analysing the surface 12-lead ECG. The purpose of this systematic review was to analyse all available published material on surface ECG and cardiac rhythm and conduction abnormalities in patients with Down syndrome to facilitate the search to the clinical cardiologist and paediatrician.

Postmitral Valve Replacement Biatrial, Septal Macroreentrant Atrial Tachycardia Developing After Perimitral Flutter Ablation

Atypical macroreentrant atrial tachycardias are frequently encountered in patients after cardiac surgery, correction of congenital heart disease, or atrial fibrillation ablation. Ablation of one circuit can produce an abrupt change in atrial activation sequence giving rise to another macroreentrant circuit. In this report, we present a unique case of a biatrial septal macroreentrant atrial tachycardia, which developed after perimitral flutter ablation in a patient with mitral valve replacement. Editor’s Perspective see p 175 A 59-year-old man with a mitral valve replacement (bioprosthesis) in 1983 for a rheumatic mitral stenosis and a rereplacement in 1999 (right-sided approach with a vertical incision of the interatrial septum) with a mechanical prosthesis attributable to the degeneration of the former prosthesis was referred for the ablation of a sustained atrial tachycardia with a stable cycle length of 260 ms. The echocardiogram demonstrated a left ventricular ejection fraction of 45% to 50%, a moderately dilated right atrium (RA) as well as left atrium (LA) without signs of a prosthetic malfunction. The baseline surface 12-lead ECG showed an atypical atrial flutter with a regular, monomorphic atrial activity and an irregular atrioventricular conduction (Figure 1A). With broad positive flutter waves in unipolar lead V1 and inferior limb leads II, III and avF but negative flutter waves in limb leads I and avL, the ECG morphology suggested LA localization. Any significant 12-lead isoelectric interval was absent. Endocardial activation mapping with a quadripolar catheter in the RA and a steerable octapolar catheter in the coronary sinus (CS; Bard Medical, Covington, GA) demonstrated a distal to proximal activation sequence in the CS with a baseline cycle length of 260 ms, suggestive of a lateral to septal activation of the LA posterior wall (Figure 1B). An irrigated tip ablation catheter (Navistar Thermocool, Biosense Webster, Diamond Bar) was advanced into the LA via …

Which Patients Are Not Suitable for a Subcutaneous ICD: Incidence and Predictors of Failed QRS‐T‐Wave Morphology Screening

The subcutaneous cardioverter-defibrillator (S-ICD) relies on a pre-implantation QRS-T morphology screening (TMS) of the ECG to assure that it reliably detects the QRS complexes and T waves. The prevalence and clinical characteristics of the patients who fail this TMS is unknown. QRS-TMS was done in 230 consecutive ICD outpatients (75% male, age 57 ± 15 years) without an indication for cardiac pacing, using an ECG simulating the 3 sensing vectors of the S-ICD (TMS-ECG). Patients were defined suitable when at least 1 sensing vector was considered appropriate in both supine and standing position. In total, 7.4% of patients, who were all male, were considered not suitable for a S-ICD according to the TMS-ECG. Independent predictors for TMS failure were hypertrophic cardiomyopathy (HCM; odds ratio [OR] 12.6), a heavy weight (OR 1.5), a prolonged QRS duration (OR 1.5) and a R:T ratio <3 in the lead with the largest T wave on a standard 12-lead surface ECG (OR 14.6). In patients without an indication for pacing, 7.4% would have been not suitable for a S-ICD according to the TMS. HCM, a heavy weight, a prolonged QRS duration and a R:T ratio <3 in the ECG lead with the largest T wave were independently associated with TMS failure. These data might alert physicians that selection of patients for a S-ICD should be considered with special caution in certain patient groups, because they may not satisfy ECG criteria for adequate sensing.

Abstract 18004: Diagnosis of Obstructive Sleep Apnea in Patients With Congenital Long QT Syndrome

Introduction: Obstructive sleep apnea (OSA) is a common health problem which affects about a quarter of US adults. OSA is increasingly linked to cardiovascular diseases including hypertension, heart failure, myocardial infarction, cardiac arrhythmias and sudden cardiac death (SCD). Congenital long QT syndrome (LQTS) is a common cause of SCD in children and young adults during exercise and sleep. LQT3 (SCN5A) and LQT2 (HERG) genotypes are particularly at increased risk for SCD during sleep. We tested the hypothesis that increased numbers of patients with congenital LQTS have OSA compared to controls matched for age gender and BMI. Methods: A complete medical history and a standard 12-lead surface ECG were obtained in LQTS and controls. Polysomnography (PSG) was conducted in 32 LQTS patients (20 LQT1 and 12 LQT2) and 40 controls matched for age, gender and BMI. Blinded interpretation of the sleep studies were carried out by a single investigator board certified in Sleep Medicine. OSA was defined by the presence of AHI ≥5 events/hour for adults (≥18 years) and &gt;1 event/hour for children (&lt;18 years). Results: The PSG results show that 16 LQTS patients (50%) have clinically significant OSA compared to 6 controls (15%) in the controls. There are 7 LQTS patients who have history of early childhood adenotonsillectomy and only 2 of them have OSA on the PSG results. Considering very close relationship between adenotonsillar hypertrophy in children and OSA, these children might have OSA in early childhood. Therefore, total 21 LQTS patients (65%) have OSA on the PSG and/or adenotonsillectomy. Presence of OSA is equally distributed in LQT1 and LQT2 genotypes. Conclusion: OSA is more common in patients with congenital LQTS compared to healthy matched controls. Apneic events during sleep are associated with exaggerated sympathetic responses which might be potential mechanisms for triggering arrhythmias and thus increased risk of SCD during sleep.

Dependence of P-wave dispersion on mean arterial pressure as an independent hemodynamic variable in school children

Introduction:The relationship between diastolic dysfunction and P-wave dispersion (PWD) in the electrocardiogram has been studied for some time. In this regard, echocardiography is emerging as a diagnostic tool to improve risk stratification for mild hypertension.Objective:To determine the dependence of PWD on the electrocardiogram and on echocardiographic variables in a pediatric population.Methods: Five hundred and fifteen children from three elementary schools were studiedfrom a total of 565 children. Those whose parents did not want them to take part in the study, as well as those with known congenital diseases, were excluded. Tests including 12-lead surface ECGs and 4 blood pressure (BP) measurements were performed. Maximum and minimum P-values were measured, and the PWD on the electrocardiogram was calculated. Echocardiography for structural measurements and the pulsed Doppler of mitral flow were also performed.Results: A significant correlation in statistical variables was found between PWD and mean BP for pre-hypertensive and hypertensive children, i.e., r= 0.32, p &lt;0.01 and r= 0.33, p &lt;0.01, respectively. There was a significant correlation found between PWD and the left atrial area (r= 0.45 and p &lt;0.01).Conclusions: We highlight the dependency between PWD, the electrocardiogram and mean blood pressure. We also draw attention to the dependence of PWD on the left atrial area. This result provides an explanation for earlier changes in atrial electrophysiological and hemodynamic characteristics in pediatric patients.

Assessment of QRS duration and presence of fragmented QRS in patients with Behçet’s disease

QRS prolongation and the presence of QRS fragmentation in 12-lead ECG are associated with increased mortality and sudden cardiac death in the long term. In this study we aimed to assess QRS duration and fragmentation in patients with Behçet's disease (BD). A total of 50 patients (mean age 42.7±12.0 years) previously diagnosed with BD were recruited. In addition, a control group consisting of 50 healthy people (mean age 39.4±12.5 years) was formed. The longest QRS duration was measured in surface 12-lead ECG and QRS complexes were evaluated in terms of fragmentation. Serum C-reactive protein levels were also obtained. QRS duration and corrected QT duration were significantly longer in patients with BD compared with controls (102.75±11.91 vs. 96.99±10.91 ms, P=0.007; 438.55±30.80 vs. 420.23±28.06 ms, P=0.003, respectively). Fragmented QRS (fQRS) pattern was more common in patients with BD than controls [n=27 (54%) vs. n=16 (32%), P=0.026]. Disease duration was longer in patients with BD with fQRS compared with those without (12.67±8.68 vs. 7.09±7.06 years, P=0.010). Furthermore, C-reactive protein level was higher in patients with BD with fQRS compared with those without (6.53±4.11 vs. 4.97±6.32 mg/dl, P=0.043). Correlation analysis revealed no association between disease duration and QRS duration (r=0.219, P=0.126). QRS duration is greater and fQRS complexes are more frequent in patients with BD. These findings may indicate subclinical cardiac involvement in BD. Given the prognostic significance of ECG parameters, it is reasonable to evaluate patients with BD with prolonged and fQRS complexes more in detail such as late potentials in signal averaged ECG in terms of cardiac involvement.

Relación entre la dispersión de la onda P,el índice de masa ventricular izquierda y la tensión arterial

The study of arterial hypertension risk factors in children guarantees the establishment of health policies to avoid complications associated with this illness in the future. The highest values of P-wave dispersion during sinus rhythm are pointed as predictors of atrial fibrillation in adulthood since there is an association between arterial hypertension, P-wave dispersion and left ventricular hypertrophy. The aim of this study was to determine the relationship between blood pressure, left ventricular mass index and P-wave dispersion in the pediatric population. In the frame of the PROCDEC II project, children from 8 to 11 years old, without known heart conditions were studied. Arterial blood pressure was measured in all the children; a 12-lead surface ECG and an echocardiogram were done as well. Left ventricular mass index mean values for normotensive (25.21 ± 5.96 g/m²) and hypertensive (30.38 ± 7.39 g/m²) children showed significant differences (p= 0.000). The mean value of the left atrial area was significantly different (p= 0.000) when comparing prehypertensive (10.98 ± 2.23 cm2) and hypertensive (12.21 ± 1.27 cm²) children to normotensive ones (10.66 ± 2.38 cm²). The correlation of P-wave dispersion and the left ventricular mass index showed an r= 0.87 and p= 0.000. P-wave dispersion is increased in pre- and hypertensive children compared to normotensive ones. A dependence of the P-wave dispersion of the left ventricular mass index was found in hypertensive children.

Pseudo-polymorphic Ventricular Tachycardia in a 12-lead Holter Recording

We present an image of pseudo-polymorphic ventricular tachycardia recording on a 12-lead surface ECG Holter. Although at first glance the appearance of the recording resembled polymorphic ventricular tachycardia, careful investigation revealed normal electrocardiographic findings.

The role of acute hyperinsulinemia in the development of cardiac arrhythmias

Patients with perturbed metabolic control are more prone to develop cardiac rhythm disturbances. The main purpose of the present preclinical study was to investigate the possible role of euglycemic hyperinsulinemia in development of cardiac arrhythmias. Euglycemic hyperinsulinemia was induced in conscious rabbits equipped with a right ventricular pacemaker electrode catheter by hyperinsulinemic euglycemic glucose clamp (HEGC) applying two different rates of insulin infusion (5 and 10mIU/kg/min) and variable rate of glucose infusion to maintain euglycemia (5.5 ± 0.5mmol/l). The effect of hyperinsulinemia on cardiac electrophysiological parameters was continuously monitored by means of 12-lead surface ECG recording. Arrhythmia incidence was determined by means of programmed electrical stimulation (PES). The possible role of adrenergic activation was investigated by determination of plasma catecholamine levels and intravenous administration of a beta adrenergic blocking agent, metoprolol. All of the measurements were performed during the steady-state period of HEGC and subsequent to metoprolol administration. Both 5 and 10mIU/kg/min insulin infusion prolonged significantly QTend, QTc, and Tpeak-Tend intervals. The incidence of ventricular arrhythmias generated by PES was increased significantly by euglycemic hyperinsulinemia and exhibited linear relationship to plasma levels of insulin. No alteration on plasma catecholamine levels could be observed; however, metoprolol treatment restored the prolonged QTend, QTc, and Tpeak-Tend intervals and significantly reduced the hyperinsulinemia-induced increase of arrhythmia incidence. Euglycemic hyperinsulinemia can exert proarrhythmic effect presumably due to the enhancement of transmural dispersion of repolarization. Metoprolol treatment may be of benefit in hyperinsulinemia associated with increased incidence of cardiac arrhythmias.

Diastolic Dysfunction and Severity of Cirrhosis in Nonalcoholic Cirrhotic Patients

Background. In this study, we evaluated the association between diastolic dysfunction severity and severity of cirrhosis in nonalcoholic cirrhotic patients. Methods. This cross-sectional study was conducted on all nonalcoholic cirrhotic patients who were admitted in Rasht Razi hospital the Cancer of Guilan Province, north of Iran, from January 2011 to March 2012. Severity of cirrhosis was evaluated by Child-Pugh score. A 12-lead surface ECG and echocardiographic studies were performed. We used a HDI 3000 (Philips ATL, Bothell, WA, USA) equipped with 2 to 4 MHz probes. Diastolic function was determined by an expert cardiac sonographer. Data were analyzed by SPSS for win (version16). A P value less than 0.05 was considered significant. Results. Sixty-tree percent of patients were male. The mean age of patients was 52.78 ± 15.2 years. 22%, 38%, and 40% of patients were considered as child class A, B, and C, respectively. There was a significant relation between diastolic dysfunction and disease duration (P = 0.001), female gender (P = 0.004), age > 60 years (P = 0.045), and severity of cirrhosis (P = 0.048). On multivariate analysis, decreased E/A ratio (P = 0.03) and disease duration (P = 0.02) showed an independent significant relation. Conclusion. According to the relation between severity of cirrhosis and diastolic dysfunction, we recommend cardiac assessment in all child B and C cirrhotic patients.

Surface Electrocardiogram Reconstruction From Intracardiac Electrograms Using a Dynamic Time Delay Artificial Neural Network

This study proposes a method to facilitate the remote follow up of patients suffering from cardiac pathologies and treated with an implantable device, by synthesizing a 12-lead surface ECG from the intracardiac electrograms (EGM) recorded by the device. Two methods (direct and indirect), based on dynamic time-delay artificial neural networks (TDNNs) are proposed and compared with classical linear approaches. The direct method aims to estimate 12 different transfer functions between the EGM and each surface ECG signal. The indirect method is based on a preliminary orthogonalization phase of the available EGM and ECG signals, and the application of the TDNN between these orthogonalized signals, using only three transfer functions. These methods are evaluated on a dataset issued from 15 patients. Correlation coefficients calculated between the synthesized and the real ECG show that the proposed TDNN methods represent an efficient way to synthesize 12-lead ECG, from two or four EGM and perform better than the linear ones. We also evaluate the results as a function of the EGM configuration. Results are also supported by the comparison of extracted features and a qualitative analysis performed by a cardiologist.

EVALUATION OF THE EFFICIENCY AND SAFETY OF ADENO-ASSOCIATED VIRUS SEROTYPE 9 MEDIATED SERCA2A GENE TRANSFECTION TO MYOCARDIUM BY THREE CARDIAC GENE DELIVERY METHODS IN RATS

ObjectivesTo assess the efficiency and safety of adeno-associated virus serotype 9 (AAV9) mediated sarcoplasmic reticulum Ca2+ATPase 2a (SERCA2a) gene transfection to myocardium in normal SD rats by three cardiac gene...

A Novel, Minimally-Invasive Surgical Approach for Ablation of Ventricular Tachycardia Originating Near the Proximal Left Anterior Descending Coronary Artery

Idiopathic ventricular tachycardia (VT) arising from the left ventricular (LV) summit can be challenging for catheter-based percutaneous ablation. We present a patient in whom endocardial and percutaneous epicardial ablations were not successful in eliminating VT. Subsequently, a minimally invasive surgical approach with robotic-assisted mapping, followed by minithoracotomy and cryoablation of the myocardium near the region of the proximal left anterior descending (LAD) coronary artery, was successful in eliminating arrhythmia. A 54-year-old man with a medical history significant for hypertension and sleep apnea presented with exertional palpitations associated with lightheadedness. Holter monitoring revealed frequent premature ventricular contractions (PVCs) and nonsustained VT. β-blockers were started (metoprolol 100 mg BID), but sustained VT was demonstrated on exercise stress testing performed while on β-blockers. Physical examination and laboratory evaluation were unremarkable. Coronary angiography documented normal epicardial coronary vessels with a normal LV ejection fraction (64%). Cardiac magnetic resonance imaging revealed mild LV hypertrophy without fibrosis or other structural abnormalities. Despite optimal dose of β-blockers (metoprolol 100 mg BID) and calcium channel blockers (diltiazem CD 120 mg QD), the patient continued to have symptoms of lightheadedness and presyncope and was subsequently brought to the electrophysiology laboratory for further evaluation and treatment. On 12-lead ECG, the morphology of spontaneous PVCs was predominantly positive in the inferior leads with early precordial transition (V2). The ratio of QS complexes in aVL/aVR was <1, suggestive of origin from the inaccessible region of the LV summit.1 (Figure 1) Figure 1. Surface 12-lead ECG showing premature ventricular contractions with inferior axis, early transition suggesting site of origin near the anterosuperior …

Baseline vectorcardiography as a predictor of invasively determined acute hemodynamic response to cardiac resynchronization therapy

Identifying potential responders to cardiac resynchronization therapy (CRT) may be sometimes difficult and time consuming. Searching for a simple method, we chose vectorcardiography (VCG) for our study. The aim was to evaluate whether a VCG parameter can be used to predict invasively measured acute hemodynamic changes after CRT onset. Baseline VCG data were prospectively recorded just before initiation of CRT in a series of 126 consecutive patients (♂74 %, DCMP 60 %, ICMP 40 %, NYHA class III 100 %, QRS width 161 ± 27 ms, LV-EF 25 ± 6.5 %) prior to implantation at our specialized center. The time interval (TI) between the maximum vector and the end of the vector loop (initial description by Koglek W.) was correlated with acute hemodynamic change after CRT onset. Positive response to CRT was defined as an increase in dp/dt max >10 % or pulse pressure >5 %. According to these invasive hemodynamic parameters, 25 patients (20 %) were defined as non-responders. Using ROC analysis, the threshold value of the TI for responders was found to be 64 ms. TI is a predictor of acute hemodynamic response with a sensitivity of 96 %, a specificity of 76 %, a positive predictive value of 94 %, and a negative predictive value of 79 %. More non-responders are identified by TI than by using conventional QRS width in the 12-lead surface ECG. TI is a new method of evaluation based on baseline VCG analysis. It may be a useful diagnostic test for predicting acute hemodynamic response to CRT.

Optimal Atrio-Ventricular Delay in CRT Patients Can Be Approximated from Surface ECG P-Wave Duration

Cardiac Resynchronization Therapy (CRT) is an established treatment for systolic heart failure with ventricular conduction delays. Optimization of the programmed atrio-ventricular delay (AV) may result in better CRT outcomes. Previous studies have shown positive correlation between inter-atrial conduction time (IACT) and optimal AV. We hypothesized that P-wave duration can be used as a surrogate for IACT and, hence, for AV optimization. During CRT device implant (n=33) we measured IACT as the interval from right atrial pacing or sensing to the left atrial activation observed in the electrogram obtained from an electrophysiology catheter inserted in the coronary sinus. P-wave duration (PWd) was measured from 12-lead surface ECG. Within 3 weeks after the implant patients underwent echocardiographic optimization of the sensed (SAV) and paced (PAV) delays using mitral inflow method. Echo-optimal SAV and PAV were 129±19 (range: 100-180 ms) ms and 175±24 ms (range: 130-230 ms) respectively and correlated with PWd and IACT (Table). Paced PWd correlated with IACT better (R=0.84, p<0.0001) than sensed PWd (R=0.54, p=0.001) possibly due to the delay between P-wave onset and atrial sensing. Compared to nominal programming (SAV=100 ms, PAV=130 in Medtronic devices), adjusting AVs using the regression equations for PWd durations would have reduced the proportion of suboptimally programmed patients (>30 ms away from echo-optimal AV) from 39% to 10% during atrial sensing and from 58% to 9% during atrial pacing. Surface ECG P-wave duration is a reasonable surrogate of inter-atrial conduction time and may be used for AV delay adjustment in CRT patients.Tabled 1Correlation With Echo-Optimal AV Delays During Atrial Sensing and PacingParameter (x)Average value (ms)Correlation, RRegression equation, AV = a*x+bp-valueSensed IACT110 ± 240.760.73*x + 52 ms<0.00001Sensed PWd141 ± 220.600.64*x + 43 ms0.0003Paced IACT148 ± 320.750.58*x + 90 ms<0.0001Paced PWd165 ± 320.660.50*x + 93 ms<0.0001 Open table in a new tab

The ECG in Cardiac Resynchronization Therapy: Influence of Left and Right Ventricular Preactivation and Relation to Acute Response

The aims of this study were to compare ECG signs of biventricular electrical resynchronization during cardiac resynchronization therapy (CRT) with various interventricular (VV) delays and to correlate these and other ECG characteristics with the acute hemodynamic benefit of CRT. Thirty-four patients with heart failure and a left bundle branch block (LBBB) pattern were prospectively enrolled. A 12-lead surface ECG and the relative improvement in left ventricular (LV) dP/dt(max) (the maximum rate of pressure rise) were recorded at baseline and during CRT with VV delays varying from 80 ms LV preactivation to 40 ms right ventricular (RV) preactivation. Rightward QRS-axis shift occurred in 71-80% among all VV delays. Activation reversal to dominant negative in leads I/aVL was progressively observed at increasing LV preactivation (53-65%) and less (18-22%) during RV preactivation. Activation reversal to dominant positive in leads V1/V2 was observed in 21-27% during LV preactivation and in 6-15% during RV preactivation. Higher acute response to CRT was independently predicted by a complete LBBB at baseline (regression coefficient B = 7.7 [0.3-15.0], P = 0.042), later timing of LV depolarization within the QRS at baseline (Q-LVsense: B = 0.2 [0.1-0.3], P = 0.002), and biventricular electrical resynchronization during CRT as evidenced by activation reversal in leads I/aVL (B = 9.9 [3.2-16.6], P = 0.005). ECG signs of biventricular electrical resynchronization are present over a wide range of LV preactivated VV delays but to a lesser extent during RV preactivation. The presence of complete LBBB and longer Q-LVsense at baseline and signs of biventricular electrical resynchronization during CRT predict higher acute hemodynamic response.

112 Location of subsidiary atrial pacemakers following ablation of the sinus node in the goat

IntroductionThe development of sinus node dysfunction in patients may be accompanied by the emergence of subsidiary atrial pacemakers (SAPs) and/or junctional escape rhythms. It has been postulated that biological modification...