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Mapping and localizing presystolic Purkinje potentials are crucial for determining the optimal ablation site for fascicular premature ventricular contractions (PVCs). Here we present a case of PVCs originating from the distal left anterior fascicle (LAF). Activation mapping using a multipolar catheter with small electrodes demonstrated early presystolic Purkinje potentials during the PVCs. A moderately good pace-map match was also obtained near the successful ablation site. This case demonstrates the activation pattern of PVCs originating from the distal LAF and the usefulness of multipolar catheters with small electrodes for the mapping of fascicular PVCs.

A 38-year-old woman with a structurally normal heart was referred for catheter ablation due to symptomatic, monomorphic, high burden (12%) premature ventricular complexes (PVC) refractory to medical therapy. The PVC's ECG morphology suggested an origin in the proximal left anterior fascicle (LAF). During procedure PVCs were mechanically suppressed. Consequently, selection of the ablation target site was based on pace-mapping. This case illustrates how ablation from the right coronary cusp (RCC) for PVC arising from the proximal LAF could be accurately guided by pace-mapping. At this location, pacing can result in both a selective and a non-selective capture of the proximal LAF.

Left bundle branch pacing (LBBP) is emerging as an alternative to His bundle pacing that overcomes the latter's limitations. Several studies have reported on the safety, efficacy, and electrophysiological properties of LBBP, while postoperative success rates range from 80.5% to 94%. The left posterior fascicle is composed of broad bands of fibers coursing inferiorly and posteriorly toward the papillary muscle, while the anterior fascicle is a thin, tendon-like structure. We report a case of a 70-year-old man in whom left posterior fascicular pacing was done after LBBP failed. We were able to demonstrate all the features of left posterior fascicular capture, including fascicular potential and a left anterior hemiblock pattern, using surface 12-lead electrocardiography. Left posterior fascicular pacing could be an alternative technique when attempts to deploy LBBP fail.

A 16-year-old female patient was hospitalized due to narrow QRS tachycardia suggestive of fascicular ventricular tachycardia. Initially, the differential diagnosis with supraventricular tachycardia can be challenging. The tachyarrhythmia is well controlled with medication, but electrophysiological study and ablation may be necessary in patients who remain symptomatic.

A 32‐year‐old male received catheter ablation of frequent ventricular extrasystoles (VEs). His electrocardiogram showed monomorphic VEs with an inferior axis and early precordial transitional zone. During electrophysiological testing, a 10‐pole catheter positioned in the left ventricular outflow tract recorded sharp pre‐potentials just before the ventricular activation during VEs as well as sinus beats. Three‐dimensional mapping was performed by annotating the sharp pre‐potentials to reveal that the earliest activation site was deemed to be close to the left anterior fascicle. A cryoablation catheter was introduced into the left ventricle and freezing for 240 seconds successfully eliminated the clinical VEs without any complications., A 32‐year‐old male received catheter ablation of frequent ventricular extrasystoles (VEs). During the electrophysiological study, a 10‐pole catheter positioned in the left ventricular outflow tract recorded sharp pre‐potentials just before the ventricular activation during the VEs as well as sinus beats. A cryoablation catheter was introduced into the left ventricle and freezing for 240 seconds on the blue tag successfully eliminated the clinical VEs without any complications.

A 33-year-old man had verapamil-sensitive ventricular tachycardia (VT) with a right bundle branch block (RBBB) and right axis deviation. Programmed stimulation from the para-Hisian region induced ventricular tachycardias (VT1 or VT2). VT1 was entrained during pacing from the para-Hisian region. A single para-Hisian stimulation antidromically captured the proximal portion of the left anterior fascicle (LAF), but the cycle length of VT2 remained unchanged. This observation indicated that the upper limb of the LAF was a bystander of the reentry circuit. We have clarified this mechanism with applying a single premature stimulation from the para-Hisian region.

A 17‐year‐old woman presented with frequent palpitations and shortness of breath and was diagnosed with drug‐refractory ventricular parasystole. We predicted that the parasystole originated from the left anterior fascicle (LAF). Detailed activation maps of both conduction systems, including the LAF, during sinus rhythm and ventricular parasystole were obtained using a parallel mapping system. We confirmed the earliest fascicular potential of the parasystole and performed catheter ablation with no complications. This novel mapping algorithm for simultaneous acquisition of multiple maps aided effective treatment of ventricular parasystole originating from the LAF., Ventricular parasystole originating from the left anterior fascicle can be effectively eliminated by using this novel mapping algorithm of parallel mapping and LAT hybrid mapping. Parallel mapping makes it possible to obtain both activation maps during ventricular parasystole and sinus rhythm simultaneously, decreasing the procedure time while also increasing efficacy. LAT hybrid mapping also makes it possible for precise positioning during parasystole ablation.

Belhassen ventricular tachycardia (BVT), also known as verapamil-sensitive ventricular tachycardia, is an infrequent finding that can be fatal unless recognized early and treated in a prompt manner. Most patients have insignificant presentation suggestive of the disease, but on electrocardiography (EKG), BVT is characterized by a complete right branch block (RBB) and a right axis deviation (RAD). In this case report, we describe an unusual case of a 35-year-old male patient who presented to the emergency department (ED) complaining of acute palpitations of two-hour duration; subsequent diagnostic testing revealed BVT in the patient.

The history dependence of force is an intrinsic property of muscle whereby a muscle actively shortened or lengthened to an isometric steady-state produces less (residual force depression; rFD) or more force (residual force enhancement; rFE), respectively, than a purely isometric contraction at the same muscle length and level of activation. Previous studies on the modifiability of the history dependence of force have been inconclusive, and none have attempted to modify rFD and rFE through isometric resistance training biased to short versus long muscle-tendon unit (MTU) lengths. We tested maximal voluntary rFD and rFE in 7 males and 6 females before and after 8 weeks of maximal isometric dorsiflexion training 3 days/week. Participants trained one leg at 0° of plantar flexion (short-MTU training) and one at 40° of plantar flexion (long-MTU training). Ultrasonography of the tibialis anterior assessed resting muscle architecture. Tibialis anterior fascicle length decreased by ~3% following short-MTU training (P = 0.03) and increased by ~4% following long-MTU training (P = 0.01). rFD did not change following training at either MTU length (absolute rFD: P = 0.53; percent rFD: P = 0.51), nor did rFE (absolute rFE: P = 0.78; percent rFE: P = 0.80), with no relationships between the change in fascicle length and the change in percent rFD (R2 = 0.01, P = 0.62) nor rFE (R2 = 0.001, P = 0.88). Our data indicate that voluntary rFD and rFE were not modified by isometric training and not related to the fascicle length adaptations we observed.

Background: Premature ventricular complex (PVC) with narrow QRS duration originating from proximal left anterior fascicle (LAF) is challenging for ablation. This study was performed to evaluate the safety and feasibility of ablation from right coronary cusp (RCC) for proximal LAF-PVC and to investigate this PVC’s characteristics. Methods: Mapping at RCC and left ventricle and ECG analysis were performed in 20 patients with LAF-PVC. Results: The earliest activation site (EAS), with Purkinje potential during both PVC and sinus rhythm, was localized at proximal LAF in 8 patients (proximal group) and at nonproximal LAF in 12 patients (nonproximal group). The Purkinje potential preceding PVC-QRS at the EAS in proximal group (32.6±2.5 ms) was significantly earlier than that in nonproximal group (28.3±4.5 ms, P =0.025). Similar difference in the Purkinje potentials preceding sinus rhythm QRS at the EAS was also observed between proximal and nonproximal groups (35.1±4.7 versus 25.2±5.0 ms, P P =0.002, and 3.9±0.8 versus 15.7±7.8 mm, P 5 , and V 6 ; lower R wave in leads I, aVR, aVL, V 1 , V 2 , and V 4 ; and smaller q wave in leads III and aVF. The QRS duration difference (PVC-QRS and sinus rhythm QRS) Conclusions: PVCs originating from proximal LAF, with unique electrocardiographic characteristics, could be eliminated safely from RCC.

We thank Yamada et al1 for their interest in our recent article. We wish to address the points raised by their letter. First, Yamada et al raise concerns about the location of the left anterior fascicle as depicted in Figures 1, 3, and 5. It should be pointed out that Figures 1 and 5 represent purely schematic depictions of the fascicular, papillary, and annular anatomy. To compress 3-dimensional anatomy into a 2-dimensional figure, we arbitrarily placed the left anterior fascicle along the septal aspect of the annular ring. Although the left anterior fascicle courses anteriorly and laterally after branching from the left bundle, we intentionally elected not to mark …

ee t as, 2 At the atrial level, no P waves can be identified indicating complete sinoatrial block. 2. The first 3 QRS complexes have the same R-R interval (950 ms) and are narrow compatible with an atrioventricular (AV) junctional origin. QRS complexes 5 and 9 have the same QRS configuration. 3. Of interest are the wider QRS complexes occurring after a shorter R-R interval (complexes 4, 6, 8, and 10). QRS complex 4 is 80 ms wide and shows an incomplete right bundle branch block and a pattern of left axis duration. It could have its origin in the AV junction with aberration, with delay in the right bundle branch and the left anterior fascicle owing to premature activation of the His bundle. It could also have an origin shortly after the takeoff of the

A 56-year-old man in hypertrophic cardiomyopathy had an electrical storm caused by ventricular fibrillation (VF). Mapping during the initiation of the VF triggered by a premature ventricular contraction (PVC1), with right bundle branch block (RBBB)-like morphology and superior axis, demonstrated a prominent Purkinje–muscle junction (PMJ) delay at the distal portion of the left posterior fascicle. Delivery of radiofrequency (RF) energy to this area abolished the VF triggered by the PVC1. However, VF emerged by triggering another PVC (PVC2) with RBBB-like morphology and inferior axis. Similarly, the initiation of VF was associated with the PMJ delay at the peripheral left anterior fascicle, where RF delivery completely suppressed the VF. The PMJ delay and subsequent Purkinje–muscle reentry-like activity could be essential for the initiation of the Purkinje-related VF.

BACKGROUND The distal insertion of right atriofascicular pathways remains a source of debate. Moreover, there are various morphologies of preexcited QRS complexes involving atriofascicular pathways that have been poorly characterized. OBJECTIVE To characterize the distal insertion of atriofascicular accessory pathways and to provide a mechanism for the change in QRS morphology observed between short and Long ventricuto-His (V-H) antidromic atrioventricular reentrant tachycardias (AVRTs) in the same patient. METHODS Thirteen patients with atriofascicular pathways and preexcited AVRT with short V-H and long V-H intervals were studied. For each patient, the tachycardia cycle Length, V-H interval, QRS width, and axis were compared. A baseline His-ventricular interval was also recorded. RESULTS The baseline His-ventricular interval was significantly Longer than the V-H interval during antidromic AVRT (median 50 ms vs 10 ms; P

Background Decrement of glomerular filtration rate leads to many serious complications that cause both functional and structural impairments of the other organs. Long-term clinical observations of children and teenagers with end-stage renal disease (ESRD) showed that more than one third of those patients manifested various cardio-vascular conditions. The aim of the study was to analyze possible disturbances in the heart ventricular conduction system by using a technique of ventricular activation time (VAT) differences in ESRF children on peritoneal dialysis (PD) with normal electrocardiogram (ECG) examinations. Material and methods The study group comprised 10 ESRD children (mean age: 13.6 ± 2.31 years) on peritoneal dialysis – group I. The control group (group II) consisted of 26 age-matched healthy children with no clinical evidence of renal or cardiac disease and with normal 12-lead ECG recordings. Each of the ESRD patients was also subjected to the standard ECG examination. In order to capture possible heart conduction abnormalities, body surface potential mapping (BSPM) recordings were performed in PD patients between the successive dwells (‘on empty abdomen’) with a HPM-7100 Fukuda Denshi system. Based on the source ECG data, the original technique of a VAT difference map was then applied. Results Differences between VAT values for the two examined groups of children, controls and ESRD patients on PD, were significantly pronounced in the region of the right upper anterior thorax, the entire left thorax and nearly in the total back. Such a pattern of VAT delays indicates a pathological electric transmission in the intraventricular conduction system of the left anterior fascicle of His bundle. Conclusion 1. VAT maps (isochrone maps) can be useful to detect abnormal spreading and depolarization through the heart ventricles. 2. Map of VAT value differences makes it possible to identify early disturbances in the left His bundle branch in ESRD children treated with peritoneal dialysis regardless of normal 12-lead ECG. 3. Further studies on a larger group of children with ESRD on PD are required to verify the preliminary observations presented herein.

This study examined the associations between the fluctuations of foot acceleration during shortening and lengthening contractions with the electromyographic (EMG) activity of lower leg muscles and ultrasound measures of tibialis anterior fascicle length and pennation angle. Young (24.9 ± 4.17 years) and old (74.8 ± 3.31 years) adults lifted and lowered a submaximal load with the foot at different speeds (3°/s–50°/s). The standard deviation (SD) of foot acceleration normalized to the load lifted was similar for young (12.2 ± 7.22 cm s−2/kg) and old adults (14.3 ± 8.03 cm s−2/kg; P = 0.093). The changes in tibialis anterior muscle fascicle length and pennation angle were similar for young and old adults (P ≥ 0.233), but greater for shortening (fascicle length: 0.937 ± 0.633 cm, pennation angle: 1.61 ± 0.918o) than for lengthening contractions (fascicle length: 0.806 ± 0.521 cm, pennation angle: 0.966 ± 0.632o; P ≤ 0.014). The changes in fascicle length and pennation angle were not associated with the SD of foot acceleration (r 2 ≤ 0.031; P ≥ 0.092). The surface EMG of tibialis anterior was greater for the shortening contractions than for the lengthening contractions (P

A 72-year-old woman developed incessant interfascicular (IF) ventricular tachycardia immediately after successful right bundle branch (RBB) catheter ablation for the treatment of sustained bundle branch reentrant tachycardia. Catheter ablation of the left bundle branch and the left anterior fascicle was successful in eliminating the tachycardia (in 2 different sessions). This report discusses the direct link between the creation of an RBB block and the development of IF tachycardia, in our case, and in prior cases of IF reentry reported in the literature.

SummaryWe report a 12-year-old boy with hypertrophic cardiomyopathy presenting with syncope. His electrocardiogram showed first-degree atrioventricular block, complete right bundle branch block, conduction delay in the anterior fascicle of the left bundle branch, and intermittent complete atrioventricular block. We detected hypertrophic cardiomyopathy in the mother. The relationship between the diseases is discussed, and interpreted in the light of previous descriptions.

Coexistence of supraventricular tachycardia and ventricular tachycardia is rare. A patient with no structural heart disease and wide QRS complex tachycardia with a right bundle block configuration and right-axis deviation underwent electrophysiological examination. A concealed left atrioventricular pathway (AP) was found, and atrioventricular reciprocating tachycardia (AVRT) and left ventricular tachycardia (VT) originating in or close to the anterior fascicle of the left ventricle were both induced. Radiofrequency (RF) catheter ablation of the concealed left AP was successfully performed. Ten months later, VT recurred and was successfully ablated using a local Purkinje potential as a guide. Coexistent AVRT and idiopathic VT originating from within or near the left anterior fascicle were successfully ablated. (Jpn Circ J 1999; 63: 223 -227)

Radiofrequency catheter ablation has been used to treat idiopathic left ventricular tachycardia with high success rates. The majority of reported cases have exhibited the typical findings of right bundle branch block morphology with left axis deviation and originate from within or near the left posterior fascicle. We report a case of idiopathic left ventricular tachycardia originating from within or near the left anterior fascicle, which was successfully ablated using a local Purkinje potential as a guide.

Background Cardiac blocks (CBs) (atrioventricular blocks, left bundle branch block, left anterior fascicle block ± right bundle block) are known to reflect myocardial fibrosis in patients with Systemic Sclerosis (SSc). Their prevalence has been already assessed in EUSTAR cohort on 3656 patients (1). Nevertheless, only a few associated features were investigated. Objectives To assess the prevalence of CBs in a larger series and investigate associated clinical and therapeutic features. Methods Data from 10183 SSc patients (87% females, 13% males; 31% diffuse disease, 69% limited disease); aged from10-91 years-median age 56; with a disease duration ranging from (0.83-76 years - median 9 years) entered in the EUSTAR MEDS-online system, the largest online SSc database in the world, from 2003 to July 2012 were analyzed retrospectively. CBs as well as other epidemiological, clinical and therapeutic aspects were deduced from Minimal Essential Data Set charts. Results CBs were detected at enrollment in 968 patients (10%). In univariate analysis CBs were found to be associated with epidemiological [ male sex ( OR 1.6, 1.4-1.9); age Conclusions We confirm the already reported association of CCBs with anti-Scl-70 positivity. The detected association with CCB and ACE is likely to reflect confounding for indication. References Walker UA, Tyndall A, Czirjak L. Ann Rheum Dis 2007; 66:754-63 Disclosure of Interest None Declared

Ablation of an Anterior Fascicular Idiopathic VT. Introduction: Idiopathic ventricular tachycardia (VT) originating in or close to the anterior fascicle of the left bundle is rare. A patient with no structural heart disease and VT with a right bundle branch block configuration and right-axis deviation underwent an electrophysiologic examination. Methods and Results: Both endocardial activation mapping during VT and pacemapping were performed via a transseptal approach to localize the site of origin of the VT. Endocardial recordings of the His bundle and the posterior and anterior fascicles of the left bundle branch revealed an origin of the VT in or close to the anterior fascicle. The Purkinje potential at that site preceded the QRS complex by 20 msec, with pacemapping showing an optimal match between the paced rhythm and the clinical VT. RF energy delivered at this site terminated the VT. A left anterior nemiblock appeared after RF ablation. Ten months later, the patient is free from recurrences of VT. Conclusions: Idiopathic VT originating in or close to the anterior fascicle was cured by RF ablation. A Purkinje potential preceding the QRS during tachycardia and an optimal pacemap were used to guide RF ablation.

The ligaments of the ankle are superficial and easily accessible at ultrasonography. Surprisingly, the reliability of this technique has never been proven. With this goal in mind, ten ankles were subjected to a ultrasono-anatomic comparison. The five principle ligamentous fascicles (three on the lateral side and two on the medial side) measured at ultrasonography and the values verified after dissection. This study shows that the ligaments of the ankle are analyzed with ultrasonography and that the measures done are valid and have a precision of 2 mm for the anterior fascicle and the lateral fascicle of the lateral ligamentous plane Due to its simplicity and its low price, ultrasonography appears to be an important method in evaluating the ligaments and the degree of seriousness of ankle sprains.

A 45-year-old man presented to the emergency room after three syncopes. ECG showed sinus rhythm with complete right bundle branch block and left anterior fascicle block. Echocardiography and 24 h ECG monitoring were normal. Chest radiography showed small patchy infiltrations and spiro-ergometry tests showed normal carbon monoxide transfer factor but a reduction in physical capacity (maximum oxygen consumption 70%) associated with an effort-related grade II atrioventricular block. An MRI scan …

Total body surface maps from 15 subjects with left bundle branch block and normal axis (LBBB-NA) and 10 subjects with left bundle branch block and left axis (LBBB-LA) were analyzed and compared with maps from normal subjects. In 19 of the 25 subjects with LBBB, the timing of early upper sternal positivity was similar to that of normal subjects, indicative of timely but oppositely directed septal activation. The right ventricular breakthrough was normally located in all, but was earlier after the onset of QRS than expected in some. The initial portion of the positivity produced by left ventricular activation was located in the upper anterior chest in both LBBB-NA and LBBB-LA, but its onset was generally delayed compared with that in normal subjects, presumably because of the time taken by the right-to-left septal activation. Also, the total duration of this positivity was longer than in normal subjects and extended considerably beyond 90 msec, indicating prolonged activation of the anterior free wall of the left ventricle. In LBBB-NA, this upper anterior positivity remained anterior throughout depolarization, but in LBBB-LA it moved toward the left shoulder and the left upper back, presumably due to the posterior orientation of the terminal portion of depolarization. This terminal orientation in patients with LBBB-LA was thought to be due to the additional delay in the activation of the anterobasal portion of the left ventricle caused by selective involvement of the left anterior fascicle.

This report describes the clinical and electrocardiographic features in 30 cases of complete right bundle branch block associated with a block of the anterior fascicle of the left bundle branch, 7 of which also featured a block of the posterior fascicle of the left bundle branch (trifascicular block). The majority of the patients suffered from coronary atherosclerotic heart disease and/or hypertensive heart disease. Complete right bundle branch block associated with fascicular block of the left bundle branch constitutes a special electrocardiographic pattern. The prognosis of the patients presenting this pattern is poor, since it may develop into trifascicular block, i.e., complete atrioventricular block, often necessitating the implantation of artificial pacemakers.

To clarify the distribution pattern of the left bundle branch (LBB) in the human heart, the AV conduction system was studied in 13 autopsied hearts obtained from subjects aged 50 to 80 years. Vertical serial sections (7 micron) of the bundle of His and LBB were prepared and every 20th section was stained alternately with hematoxylin-eosin (HE) or by the elastica van Gieson (EVG) method and examined by light microscopy. Reconstruction was performed using a two-dimensional system in order to histologically differentiate the bundle cells from Purkinje cells. The LBB bifurcated into the anterior and posterior radiations and the cells in the septal portion were almost all Purkinje cells except in two cases showing a septal branch between the two radiations. The LBB usually branched widely from the bundle of His. An extremely anterior fascicle of the LBB was found in all cases. The distribution of the LBB at the top of the ventricular septum was divided into network and continuous types. Purkinje cells were present on both the atrial and apical sides of the two main radiations. It was suggested that these findings resulted from the fact that we morphologically differentiated the bundle cells from Purkinje cells by light microscopy.

A 43-year-old female with a chief complaint of palpitation was subjected to clinical electrophysiological studies. Initial standard 12-lead ECG revealed that her palpitation tvas caused by fascicular parasystole firing at the basic cycle length of 1.25–1.40 seconds, and that both sinus and parasystolic beats were associated with left anterior fascicular block and tachycardia-dependent RBBB. His-bundle electrocardiogram suggested that the parasystolic focus was located in the proximal portion of the anterior fascicle of the left bundle branch and that the site of tachycardia-dependent conduction block was located in the main right bundle branch. These findings suggest that diffuse pathological changes in the intraventricular conducting system were responsible for both the conduction block and automatic impulse formation in the present case.

Isolated left posterior fascicular block in the absence of associated right bundle-branch block is a rare electrocardiographic finding. In view of its anatomy and the fact that it receives a dual blood supply, the posterior fascicle of the left bundle branch appears to be less vulnerable than the anterior fascicle or the right bundle. Mechanical disruption of the posterior fascicle can produce isolated left posterior fascicular block. This has been demonstrated in animal models. However, such occurrence has not been noted in humans. We present two cases of inferior wall myocardial infarction, complicated by rupture of the inferior septum, resulting in isolated left posterior fascicular block. The development of isolated left posterior fascicular block complicating myocardial infarction may, therefore, serve to alert to the possible underlying septal rupture.

Serial sectioning of the interventricular septum was carried out in 16 hearts, 8 from elderly subjects with no conduction disturbance and 8 from patients with chronic left anterior hemiblock. The histologic slides were studied stereologically, and the relative density of fibrosis was quantitatively assessed by the point counting technique at various levels of the main subdivisions of the left bundle branch system. Statistical analysis revealed the following: (1) Although some fibrosis was found in the control hearts, the density of fibrosis was consistently and significantly greater throughout the conduction system in patients with left anterior hemiblock. (2) In the group with hemiblock, the relative density of fibrosis tended to increase significantly from the posterior ramification to the midseptal fibers and, finally, to the anterior fascicle. (3) Among the eight patients with hemiblock, fibrosis appeared to be evenly distributed throughout the conduction system in four. It was predominantly located in the anterior and midseptal fibers in one patient and showed an increasing severity from the posterior to the midseptal and anterior fibers in the remaining three patients. From this quantitative study, it is concluded that left anterior hemiblock is a reliable sign of left bundle branch disease but that the underlying lesions are more widely distributed than would be from the expected electrocardiographic terminology since they were found predominantly in the anterior ramifications in only half of the studied cases.

Summary To assess whether it is appropriate to require small Q waves in Leads I and aV L for the diagnosis of left anterior fascicular block (LAFB), routine electrocardiograms from 348 patients were reviewed. Cases with inferior or lateral myocardia infarction, pregnancy, marked obesity, obstructive pulmonary disease, or unusual chest cage deformity were excluded. We found that tracings with Q waves in both Leads I and aV L occurred less frequently with a normal QRS axis of 0 degrees to +90 degrees (54 of 200, 27 per cent), than with a leftward axis of −1 degree to −80 degrees (72 of 148, 49 per cent; p L alone in 43 per cent, in both Leads I and aV L in 30%, and in neither Lead I nor aV L in 27 per cent. Taken in conjunction with currently available histopathological and electrophysiological information, our findings suggest that LAFB may occur in the presence or absence of "septal" Q waves, depending on both the direction of initial forces present prior to the development of LAD and on pathological involvement of portions of the left intraventricular conduction system other than the left anterior fascicle. Once other recognizable causes of LAD are excluded, it would seem reasonable to allow an electrocardiographic diagnosis of left anterior fascicular block to be made on the basis of marked left axis deviation, regardless of the direction of the initial QRS forces.

premature beats in patients with conduction disease in the left bundle branch (Fig. 1). The second part of the question was why does the QRS complex following the first sinus beat in V1–V6 have a different QRS morphology than the other QRS complexes during sinus rhythm? Most likely this beat is a fusion beat, since the QRS complexes in leads V4–V6 are nearly identical with the ectopic focus from the diseased left anterior fascicle. Answer