Origin Of Arrhythmias Research Articles

Visualizing the complex 3D geometry of the perfusion border zone in isolated rabbit heart

Myocardial infarction, caused by a major blockage of a coronary artery, creates a border zone (BZ) between perfused and nonperfused tissue, which is believed to be the origin of fatal cardiac arrhythmias. We used a combination of optical clearing and polarization-sensitive optical coherence tomography to visualize a three-dimensional organization of the BZ in isolated rabbit hearts (n=5) at the microscopic level with a high spatial resolution. We found that the BZ has a complex three-dimensional structure with nonperfused areas penetrating into perfused tissue with finger-like projections. These "fingers" may play an important role in the initiation and maintenance of ventricular arrhythmias.

E Right ventricular origin of arrhythmias inScn5a+/− mice is due to reduced Na+ and higher K+ channel expression and function

<h3>Introduction</h3> Brugada syndrome is associated with ventricular tachycardia originating in the right ventricle (RV); this has been attributed to either depolarisation abnormalities or increased repolarisation heterogeneities. We have used a heterozygotic <i>Scn5a+/−</i> murine model to investigate the underlying mechanisms for the predisposition of the RV to arrhythmias. <h3>Methods and Results</h3> Na_v1.5 mRNA and protein expression were lower in <i>Scn5a+/−</i> than wild-type (WT) hearts, with a further reduction in the RV compared to left ventricle (LV) (Abstract E figure 1A,B, n=4, significant differences: * = WT vs <i>Scn5a+/−</i>; # = LV vs RV). There were higher expression levels of K_v4.2, K_v4.3 and KChIP₂ in RV than LV in both groups. Action potential (AP) upstroke velocity was decreased in <i>Scn5a+/−</i> (RV: 59.43±2.70 V/s to 30.26±4.03 V/s, p&lt;0.0001, n=20), and furthermore was smaller in RV than LV. AP durations were smallest in the RV of <i>Scn5a+/−</i> myocytes. RV transient outward current density (<i>I_to</i>) was greater than LV in both WT and <i>Scn5a+/−</i> (Abstract E figure 1C, n=17), with similar voltage dependence of activation. Time constants of inactivation were larger in RV than LV, and voltage dependence of inactivation was shifted to more negative values in RV compared to LV, but to more positive values in <i>Scn5a+/−</i> compared to WT. Maximum Na⁺ current density (<i>I_Na</i>) was decreased in <i>Scn5a+/−</i>, with a further reduction in the RV (Abstract E figure 2A–C, n=17). Voltage dependence of activation was unchanged, but inactivation was shifted to more negative values in <i>Scn5a+/−</i>. Maximum persistent Na⁺ current density (<i>I_pNa</i>) was decreased in a similar pattern to <i>I_Na</i> (RV: −0.30±0.03 pA/pF, n=15 vs −0.17±0.02 pA/pF, n=22, p=0.0009). <h3>Conclusion</h3> Our findings show preferential upregulation of the single Scn5a gene in the LV of the <i>Scn5a+/−</i> mice compared to RV. The reduced expression of Na⁺ channels in RV leads to smaller <i>I_Na</i>, resulting in slowed conduction, and smaller <i>I_pNa</i>, which in combination with increased <i>I_to</i>, results in shorter AP durations and greater heterogeneity of repolarisation, thus suggesting arrhythmogenesis may be initiated by both abnormal depolarisation and repolarisation in the RV of <i>Scn5a+/−</i> hearts. Insight into the molecular mechanisms of arrhythmias could prove crucial in planning possible new pharmacological therapies for a disease where the mainstay of treatment is cardioverter-defibrillator implantation.

Intramural Idiopathic Ventricular Arrhythmias Originating in the Intraventricular Septum

Background— Intramural septal idiopathic ventricular arrhythmias have not been described systematically. Methods and Results— In a consecutive group of 93 patients with idiopathic ventricular arrhythmias referred for ablation, the site of origin of ventricular arrhythmias was assessed by activation mapping and pace-mapping. In 7 of 93 patients (8%), an intramural focus in the interventricular septum was identified. All ventricular arrhythmias arising intramurally had a left bundle-branch block morphology with inferior axis. The intramural focus was effectively ablated from both sides of the septum in 4 patients and from within the septum in 1 patient. The ablation procedure of an intramural focus near the His bundle failed in 2 of 7 patients. ECG and mapping characteristics of the patients with intramural septal ventricular arrhythmias differentiated intramural arrhythmias from other sites of origin. Conclusions— Idiopathic septal ventricular arrhythmias can originate from intramural foci. Activation mapping from within a perforator branch within the interventricular septum is helpful in identifying the site of origin of intramural septal arrhythmias. Ablation within the septum or from both sites of the septum may be required to eliminate the targeted arrhythmia.

Electrocardiographic Patterns of Ventricular Arrhythmias in Arrhythmogenic Right Ventricular Dysplasia/Cardiomyopathy

Ventricular arrhythmias in patients with ARVD/C are common. Differentiation between idiopathic ventricular tachycardia and arrhythmogenic right ventricular dysplasia is of utmost importance. Baseline sinus rhythm electrocardiography as well as electrocardiographic differences during ventricular arrhythmias (VT or PVCs) can be helpful in differentiating the two disease states. The pathological fibrofatty myocyte replacement in ARVD/C as well as ventricular arrhythmia origin are likely responsible for these differences.

Abstract 9250: Endocardial Electrogram Characteristics Indicating an Epicardial Origin of Focal Ventricular Arrhythmias

Introduction: While most ventricular arrhythmias (VA) can be ablated successfully using an endocardial (ENDO) approach, epicardial (EPI) mapping and ablation is sometimes required. There may be clues on the surface electrocardiogram related to intrinsicoid deflection and QRS width; however, identification of an EPI origin of VA with certainty remains problematic, and there are no reported ENDO electrogram (EGM) characteristics that may direct ablation strategy. Methods: All patients referred for ablation of ventricular tachycardia or frequent ventricular ectopy from June 2006 through July 2010 were evaluated. Only patients with completed electroanatomical activation maps of a focal VA from ENDO and EPI were included. EGMs recorded by a bipolar mapping catheter in the area of earliest ENDO activation were analyzed and compared to the area of early EPI activation. Results: There were 17 patients with completed ENDO and EPI electroanatomical maps of a focal VA identified. We identified 3 characteristics from ENDO mapping that consistently indicated an EPI VA origin: 1) Diffusely early activation (&gt; 2cm2 region of sites with equally earliest activation within 10 msec; figure); 2) Sequence of a far-field EGM followed by a near-field EGM in the region of earliest ENDO activation; and 3) Inability to capture the far-field component of the earliest ENDO EGM (stimulus-QRS &lt; egm-QRS time) or reproduce the PVC or VT QRS complex morphology with pacing at the earliest ENDO activation site. Conclusions: The presence of a diffuse area of early activation and inability to capture a far-field electrogram from the endocardium indicates an epicardial origin of a focal ventricular arrhythmia.

Relationship between electroanatomical voltage mapping characteristics and breakout site of ventricular activation in idiopathic ventricular tachyarrhythmia originating from the right ventricular outflow tract septum

To assess the electrophysiological characteristics of the breakout site of ventricular activation using electroanatomical voltage mapping (EVM) and its relation to the optimal ablation site in idiopathic ventricular tachyarrhythmias originating from the outflow tract of the (RVOT) septum. Twenty-eight patients with symptomatic drug-refractory premature ventricular complexes (PVCs) and/or ventricular tachycardia (VT) originating from the RVOT septum and 5 control subjects with WPW syndrome were included. Low-voltage areas (LVAs) were defined as signal amplitudes between 0.1 and 1.5 mV. The borderline between the normal area and the LVA was defined as "border," and the distance from the LVA to the border (length of LVA) was measured. In all 28 patients and control subjects, there was an LVA below the pulmonary valve. There was no significant difference in length of LVA between patients with idiopathic ventricular arrhythmias and control subjects (2.0 ± 0.6 vs. 1.9 ± 0.1 cm). In 19 of the 28 patients, the optimal ablation site was identical to the border area. In all 11 patients who had pre-potentials at the successful ablation site, there were two cases with polymorphic VT and/or ventricular fibrillation associated with PVCs. In these two cases, length of LVA was longer than in other patients (4.0 and 3.9 cm vs. 1.8 ± 0.5 cm (n = 26)), and the optimal ablation site was located at the border area. The border area, including the LVA, tends to be the breakout site and/or origin of ventricular arrhythmias in idiopathic ventricular tachyarrhythmia originating from the RVOT septum.

The site of origin of torsade de pointes

ObjectiveThe electrocardiographic (ECG) characteristics and mode of onset of torsade de pointes (TdP) are well described. Less is known about the site of onset of this arrhythmia. This study was...

Teaching Points With 3-Dimensional Mapping of Cardiac Arrhythmias

Before creating a detailed 3-dimensional map of an arrhythmia, the electrophysiologist should already have a reasonable idea regarding which cardiac chamber contains either the focal site of origin of an automatic tachycardia or the relevant substrate for reentry. Typically, a combination of careful review of the ECG during tachycardia and knowledge of the location of abnormal substrate (such as myocardial infarction, atriotomy scar, etc) will allow focused mapping in the appropriate chamber. Prior teaching points have already discussed1,2 the fact that an isolated “early site of activation” is essentially meaningless for guiding ablation of macroreentry. However, in some circumstances, even for a focal “automatic” tachycardia, the apparently early site is not a suitable site to target for ablation. After constructing the activation map during tachycardia before ablation, especially if the earliest site of activation obtained does not appear to be particularly early compared with the surface ECG reference, the following should be considered. ### Overlapping Cardiac Structures Mapping a chamber other than the actual chamber where the tachycardia originates will clearly lead to a wrong conclusion. For example, when mapping premature ventricular tachycardias or monomorphic ventricular tachycardia in a structurally normal heart, a detailed map of the right ventricular outflow tract may show the “earliest site” of activation to be in the posterior wall of the right ventricular outflow tract. The true site of origin may, however, be in a coronary cusp or the subvalvar anterior left ventricular outflow tract. The posterior right ventricular outflow tract may appear to be early because a far-field signal is detected on the mapping electrode or because of breakthrough in the right ventricular outflow tract from the wave front originating on the other side of the region.3,4 After mapping the left ventricle and coronary cusps and combining the maps, the earliest activation …

Atrial Tachycardia as a Proarrhythmic Effect of Radiofrequency Catheter Ablation for Atrioventricular Nodal Reentrant Tachycardia

Radiofrequency catheter ablation is now the first line treatment for atrioventricular nodal reentrant tachycardia. The success rate is high with a low incidence of complications. However, a possible proarrhythmic effect of radiofrequency energy has been rarely reported and no study has demonstrated a direct correlation between the anatomic site of the radiofrequency application and the origin of a new post-ablation arrhythmia. We present a case of a focal atrial tachycardia that occurred after slow pathway radiofrequency catheter ablation for atrial nodal reentrant tachycardia and originating close to the previous ablation site. This tachycardia was successfully treated with a second ablation session.

Establishment of the mouse ventricular conduction system

The ventricular conduction system represents the electrical wiring responsible for the co-ordination of cardiac contraction. Defects in the circuit produce a delay or conduction block and induce cardiac arrhythmias. Understanding how this circuit forms and identification of the factors important for its development thus provide insights into the origin of cardiac arrhythmias. Recent advances, using genetically modified mouse models, have contributed to our understanding of how the ventricular conduction system is established during heart development. Transgenic mice carrying different reporter genes have highlighted the conservation of the anatomy and development of the ventricular conduction system between mice and humans. Lineage tracing and retrospective clonal analysis have established the myogenic origin of the ventricular conduction system and determined properties of conductive progenitor cells. Finally, gene knock-out models reproducing human cardiac defects have led to the identification of transcription factors important for the development of the ventricular conduction system. These transcription factors operate at the levels of both conduction system morphogenesis and differentiation by controlling the expression of genes responsible for the electrical activity of the heart. In summary, defects in the ventricular conduction system are a major cause of arrhythmias, and deciphering the molecular pathways responsible for conduction system morphogenesis and the differentiation of conductive myocytes furthers our understanding of the mechanisms underlying heart disease.

Assessment of a prototype equipment for cuffless measurement of systolic and diastolic arterial blood pressure

the action potential was correctly reconstructed, allowing determining at what time the stimulation was given. If this technique will be successfully extrapolated to a model of a 2-dimensional myocardial tissue, such a reconstruction will indicate locations of propagation irregularities, such as wavebreaks or ectopic foci, thus allowing understanding the origins of a possible arrhythmia or fibrillatory conduction.

Epicardial Outflow Tract Ventricular Tachycardia: Distal Great Cardiac Vein and Coronary Cusp Origin

The origin of outflow tract ventricular arrhythmia (OT-VA) can be predicted by ECG analysis. Recently, we devised a method to identify an epicardial OT-VA using the peak deflection index (PDI) in an inferior ECG lead. We will present our method of epicardial OT-VA identification and introduce how we determine the ablation site. Methods: An epicardial origin (10[14%] of the 70 patients) indicates that the successful ablation site of the OT-VA was in the distal great cardiac vein (GCV) (n=3) or on the coronary cusps (n=7). PDI is determined in the inferior lead presenting the tallest R wave by dividing the time from QRS onset to peak QRS deflection by total QRS duration. Results: A PDI of >0.6 predicted epicardial cases with a 90% sensitivity and a 95% specificity. In the 7 patients with coronary cusp ventricular arrhythmia (CC-VA), a discrete pre-potential (DPP) was recorded in 4 patients (57%). The DPP recorded at the successful ablation site on the coronary cusp preceded QRS onset by 63±16 ms (range, 50–84 ms). In those patients, excellent pace mapping was not always necessary. Conclusions: A PDI of >0.6 can be predictive of cases of epicardial OT-VA ablation in which the OT-VA origin is the distal GCV or the coronary cusps. In CC-VA, a DPP with activation time of ≥50 ms may be an indicator of successful ablation.

Gender and Age Differences in Candidates for Radiofrequency Catheter Ablation of Idiopathic Ventricular Arrhythmias

The prevalence, gender- and age-related differences, ablation success rate and inter-relationship between the origins of the idiopathic ventricular arrhythmias (I-VA) have not been clarified. A total of 625 consecutive patients with symptomatic, drug resistant I-VA (315 males and 310 females; mean age, 54 ± 17 years; 218 ventricular tachycardias, 407 premature ventricular contractions) who underwent catheter ablation were studied. The patients were divided into 5 groups based on the VA origin: (1) outflow tract (OT)-VA, consisting of right ventricular (RV) OT-VA and left ventricular (LV) OT-VA; (2) inflow tract (IT)-VA, consisting of tricuspid annulus (TA)-free wall (FW)-VA, IT-septum-VA, and mitral (MA)-FW-VA; (3) LV-inferoseptum-VA; (4) LV-other-VA; and (5) RV-other-VA. RVOT-VA in women were 1.5 times more frequent than in men, while LVOT-VA were more frequent in men. The prevalence of LVOT origin I-VA increased with age compared to that for the RVOT. The mean age of MA-FW-VA patients (62 ± 14 years) was higher than that of TA-FW-VA patients (51 ± 18 years; P = 0.03). The ablation success rate for RVOT-VA (88%) was higher than that for LVOT-VA (58%; P<0.0001). A multivariate analysis revealed that the patient age was one of the valuable predictors of a successful ablation (odds ratio=0.97; 95% confidence interval: 0.95-0.99; P=0.007). Distinct gender and age differences were found in the incidence of I-VA according to their site of origin.

Novel Transitional Zone Index Allows More Accurate Differentiation between Idiopathic Right Ventricular Outflow Tract and Aortic Sinus Cusp Ventricular Arrhythmias

Background: Although several ECG algorithms have been proposed for differentiating the origins of outflow tract ventricular arrhythmia (OT-VA), their accuracy is still limited in cases with cardiac rotation.Objective: The purpose of this study was to assess whether a novel “cardiac rotation-corrected” transitional zone (TZ) index would be a useful marker for differentiating right ventricular outflow tract (RVOT) origin from aortic sinus cusp (ASC) origin.Methods: Surface ECGs of OT-VAs with left bundle branch block morphology and inferior axis in 112 patients who were successfully ablated in the RVOT (n=87) or the ASC (n=25) were analyzed. According to the site of R-wave transition, TZ score was graded with 0.5-point increments (e.g. V2=2-point, V3–V4=3.5-point, V5=5-point) and TZ index was defined as follows: TZ score of OT-VA minus TZ score of sinus beat.Results: The TZ index was significantly lower in the ASC origin than in the RVOT origin (−1.2±0.9 vs. 0.3±0.7, p<0.0001). A cutoff value of the TZ index <0 predicted the ASC origin with 88% sensitivity and 82% specificity. The previously reported R-wave duration index ≥50% had a high specificity of 85% but a low sensitivity of 44%, and R/S-wave amplitude index ≥30% had 68% sensitivity and 79% specificity. The area under the curve by receiver operating characteristic curve analysis was 0.90 for the TZ index, which was significantly higher than the R-wave duration index and R/S-wave amplitude index of 0.74 and 0.76, respectively.Conclusion: This novel TZ index can be a more useful marker for differentiating RVOT origin from ASC origin.

The Importance of the Spatial Relationship between the Position of the Non-contact Mapping Balloon Array and the Arrhythmogenic Target Sites for Successful Catheter Ablation

Back ground: Three‐dimensional mapping systems such as the non‐contact mapping system (EnSite) have been utilized for radiofrequency catheter ablation (RFCA) in cases with various kinds of arrhythmias.Methods: An EnSite system was utilized for RFCA in 12 patients with right‐sided atrial tachycardia (AT). The patients were classified into two groups according to the focus of the AT in the right atrium (RA). The patients in whom the EnSite array was positioned near the focus of the AT were defined as group A, whereas those patients in whom the EnSite array was located less near the focus were defined as group B. RF energy was applied under the guidance of the mapping with the EnSite array. We investigated the relationship between the position of the EnSite array and the focus of the AT in terms of the mapping accuracy in both groups.Results: Even though the accuracy of the mapping of the breakout site and arrhythmia origin was comparable between groups A and B, the distance between the successful CA sites and the presumed AT focus according to the EnSite mapping was significantly shorter in group A than group B.Conclusions: As the location of the focus of the AT becomes closer to the proximal and distal ends of the ESB, the mapping accuracy deteriorates.

Novel transitional zone index allows more accurate differentiation between idiopathic right ventricular outflow tract and aortic sinus cusp ventricular arrhythmias

Although several ECG algorithms have been proposed for differentiating the origins of outflow tract ventricular arrhythmia (OT-VA), their accuracy still is limited in cases with cardiac rotation. The purpose of this study was to assess whether a novel "cardiac rotation-corrected" transitional zone (TZ) index would be a useful marker for differentiating right ventricular outflow tract (RVOT) origin from aortic sinus cusp (ASC) origin. Surface ECGs of OT-VAs with left bundle branch block morphology and inferior axis in 112 patients who were successfully ablated in the RVOT (n = 87) or the ASC (n = 25) were analyzed. The TZ index was defined according to the site of R-wave transition of sinus beats and OT-VAs. The TZ index was significantly lower in the ASC origin than in the RVOT origin (-1.2 ± 0.9 vs 0.3 ± 0.7, P <.0001). A cutoff value of the TZ index <0 predicted the ASC origin with 88% sensitivity and 82% specificity. The previously reported R-wave duration index ≥ 50% had a high specificity of 85% but a low sensitivity of 44%, and R/S-wave amplitude index ≥ 30% had 68% sensitivity and 79% specificity. The area under the curve by receiver operating characteristic curve analysis was 0.90 for the TZ index, which was significantly higher than the R-wave duration index and R/S-wave amplitude index of 0.74 and 0.76, respectively. This novel TZ index can be a more useful marker for differentiating RVOT origin from ASC origin.

A Couplet of PVCs with Different QRS Morphologies Arising from a Single Origin in the Left Ventricular Outflow Tract

A 59-year-old man with two different premature ventricular contractions (PVCs) forming a couplet underwent electrophysiological testing. Although pacing from the aorto-mitral continuity (AMC) produced an excellent pace map of one type of PVCs, a radiofrequency application within the right coronary cusp (RCC) eliminated all the PVCs. This case demonstrates that a single origin with two breakout sites in the left ventricular ostium (LVos) may result in a couplet consisting of different PVCs and preferential conduction from the RCC to AMC may also occur. These possibilities should be kept in our mind when predicting sites of origin of LVos ventricular arrhythmias.

The Fourth Dimension

Radiofrequency ablation is now a cornerstone in the management of ventricular tachycardia (VT). VT ablation plays a palliative role in decreasing shocks and improving the quality of life in patients with structural heart disease and is often curative in treating VT in patients with normal hearts.1,2 When compared with other types of ablation, however, VT procedures have lower success rates, have a propensity for complications, and are technically challenging. A recognized cause for difficulty is the need to address the 3-dimensional pathological substrate (endocardial, midmyocardial, epicardial). At present, combined endocardial and epicardial approaches3 have largely addressed this problem and, along with a larger electrode and irrigation-based ablation, may allow success for the midmyocardial substrate as well. See article p 324 Recently, a novel syndrome of VT arising from the papillary muscles (PMs) has been described.4,–,6 This arrhythmia, along with VT arising from other endocavitary structures (moderator band, false tendon),7 has brought to light a fourth dimension that the interventional electrophysiologist has to appreciate and navigate during ablation. In this issue of Circulation: Arrhythmia and Electrophysiology , Yamada et al8 report electrophysiological findings in 19 patients who underwent successful ablation of PM VT. We learn from their study the problems related to pace mapping the potential for multiple morphologies arising from a single substrate and the unique mapping and ablation-related difficulty with this entity. When analyzing their findings, we are compelled to address important issues related to the specific mechanism of this novel syndrome, as well as assessing our present general limitations of how we map and ablate VT. The premise that pacing at the site of a focal arrhythmia origin will reproduce the QRS morphology of the tachycardia is a commonly used strategy with ablation.9,10 Yamada …

The role of local voltage potentials in outflow tract ectopy

Discrete, fragmented, local voltage potentials (LVPs) have been observed in electrograms recorded at the ablation site in patients undergoing radiofrequency ablation for arrhythmias originating in both the right and left ventricular outflow tract; however, the incidence and the significance of the LVP with respect to arrhythmogenesis is uncertain. We studied 25 patients with outflow tract arrhythmias referred for radiofrequency catheter ablation and recorded high-amplified intracardiac electrograms close to the site of origin of the arrhythmia. Ten patients undergoing ablation for supraventricular arrhythmias served as controls. During sinus rhythm, LVPs were recorded in 24 of the 25 patients, 10-85 ms (41 +/- 19 ms) after the onset of the QRS complex, duration 33 +/- 11 ms, voltage 2.0 +/- 1.5 mV. The same potential was recorded 10-52 ms (mean 37 +/- 11 ms) prior to the V potential in the ventricular premature beats. In 10 patients, ventricular parasystole was suggested by varying coupling intervals >100 ms, and fusion beats allowing for the estimation of the least common denominator of R-R intervals. In 23 of the 25 patients, the 12-lead electrocardiogram (ECG) and intracardiac contact mapping located the arrhythmias to an area of 3-4 cm(2) in the septal region of the right ventricular outflow tract; in two patients, the site of origin was in the left coronary cusp. Radiofrequency ablation carried out in 24 of the 25 patients was successful in 21 patients, and after successful ablation, the LVP could still be recorded in all these 21 patients. The LVP was not present in 10 controls. Local potentials are recorded close to the site of origin of ventricular ectopy in >90% of patients with idiopathic outflow tract ectopy and imply successful ablation. The potentials may reflect an area of depressed conductivity known to be a prerequisite for experimental ventricular ectopy including parasystole.

Ventricular arrhythmias originating from papillary muscles in the right ventricle

Premature ventricular complexes (PVCs) and ventricular tachycardia (VT) with origin in the left ventricular papillary muscle have recently been described. There are no prior studies describing the characteristics of the ventricular arrhythmias (VAs) arising from the right ventricular papillary muscles (RV PAPs). Among 169 consecutive patients who underwent a catheter ablation of a VA, eight patients with RV PAPs were identified (seven men, mean PVC burden 17.0% +/- 20%). A control group consisted of 10 consecutive patients with arrhythmias originating from the right ventricle (10 women, mean PVC burden 13.9% +/- 12.8%). All patients underwent cardiac magnetic resonance imaging (MRI). Intracardiac echocardiography was used to identify the site of origin of the RV PAP arrhythmias. The site of origin of a total of 15 distinct PAP arrhythmias was mapped to the following papillary muscles: posterior (n = 3), anterior (n = 4), or septal (n = 8). Postablation echocardiograms did not reveal new tricuspid regurgitation. During a mean follow-up of 8 +/- 9 months, there were no adverse outcomes. The PVC burden was reduced from 17% +/- 20% preablation to 0.6% +/- 0.8% postablation in the RV PAP group and from 13.9% +/- 12.8% to 0.3% +/- 0.4% in the control group. The QRS complex was broader in the RV PAP group compared with in the control group (163 +/- 21 ms vs. 141 +/- 22 ms; P = .02). RV PAP arrhythmias originating from the posterior or anterior RV PAPs more often had a superior axis with late R-wave transition (>V4) compared with septal RV RAP arrhythmias, which more often had an inferior axis with an earlier R-wave transition in the precordial leads (<or=V4; P <.05). PVCs and VT may originate in the RV PAPs. Radiofrequency ablation is effective in eliminating these arrhythmias.