Pathological Study of an Explanted Heart Due to Intractable Ventricular Fibrillation

Pathology of the Explanted Heart. A 35-year-old male had multiple admissions for polymorphic sustained ventricular tachycardia (VT) associated with cardiac arrest, uncontrolled by beta blockers and antiarrhythmic drugs including amiodarone. Electro-physiologic testing was negative and there was no evidence for conduction system abnormalities. Retrograde atrioventricular (AV) conduction was present. The left ventricular ejection fraction was 68% with normal left ventricular size. Multiple myocardial biopsies were reported normal except for one suggesting myocarditis. Atrial pacing (rates > 90) and high-dose isoproterenol (> 300 grams/min) helped suppress VT. A DDD pacer was implanted but VT still recurred. An internal cardioverter defibrillator was implanted with attempted selective ventricular sympathetic denervation. Six months later, he had a recurrent cardiac arrest that did not respond to internal defibrillator shocks. Multiple external shocks returned him to sinus rhythm. He underwent heart transplantation despite normal left ventricular function and no heart failure. Pathology of the explanted heart without the atria revealed a weight of 442 grams. Both* ventricles were hypertrophied and enlarged. Serial section examination of the conduction system revealed chronic myocarditis of the approaches to the AV node, the AV node, and beginning of the right bundle branch. The AV node was in part within the central fibrous body, and the AV bundle showed fibro-fatty change and was left sided. There was marked fibrosis of the left bundle branch, chronic epicarditis, arteriolosclerosis of the summit of the ventricular septum, and fibrosis on both sides of the heart. Conclusions: (1) The above findings suggest that myocarditis of a smoldering type and/or fibrosis of the ventricular septum probably caused the intractable VT and fibrillation; and (2) A new indication for cardiac transplantation may include intractable VT associated with cardiac arrest. (J Cardiovasc Electrophysiol. Vol. 3, pp. 437–441, October 1992)     

Electrovectorcardiographic Diagnosis of Left Septal Fascicular Block: Anatomic and Clinical Considerations

Several publications considering anatomical, histological, pathological, electrocardiographic, vectorcardiographic, and electrophysiologic studies have shown that the left bundle branch splits into three fascicles or in a “fan‐like interconnected network” in the vast majority of human hearts. The left His system is trifascicular with a left anterior, a left posterior, and a left septal fascicle (LSF). Consequently, the classic term “hemiblock,” to describe the block of one of the fascicles, established several decades ago by the Rosembaum's school, should be updated. Electrovectorcardiographic changes resulting from conduction abnormalities of the left anterior and left posterior fascicles are commonly diagnosed, mainly by their changes in the frontal plane. However, the existence of conduction defects of the LSF remains controversial. The ECG/VCG hallmark of LSF block is prominent anterior QRS forces (PAF) on the horizontal plane. This ECG/VCG phenomena should be distinguished from other conditions that also produce anterior QRS shift in the HP as: normal variants, right ventricular enlargement, misplaced precordial leads, lateral myocardial infarction, right bundle branch block, Wolff‐Parkinson‐White, obstructive and nonobstructive forms of hypertrophic cardiomyopahty, diastolic left ventricular enlargement, endomiocardial fibrosis, Duchenne muscular dystrophy, and dextroposition. The two highly frequent etiologies of LSFB are ischemia (coronary artery disease (CAD) with critical proximal obstruction of the left anterior descending coronary artery) and, in Latin America, Chagas’ cardiomyopathy. The aims of this review are to revise the evidence of the existence of a trifascicular left Hissian system and to help in the ECG/VCG recognition of the LSFB. Ann Noninvasive Electrocardiol 2011;16(2):196–207     

Cardiac resynchronization therapy in patients with heart failure and conduction abnormalities other than left bundle-branch block: analysis of the Multicenter InSync Randomized Clinical Evaluation (MIRACLE)

BACKGROUND: Cardiac resynchronization therapy (CRT) has been proposed as a treatment for patients with congestive heart failure (CHF) and prolonged QRS durations. Previous studies have predominantly included patients with left bundle-branch block (LBBB). The Multicenter InSync Randomized Clinical Evaluation (MIRACLE) investigators assessed the efficacy of CRT in patients with CHF with QRS durations > or = 130 ms and found that CRT lead to improvement in several measures of functional capacity and exercise tolerance. HYPOTHESIS: We designed this retrospective study to determine whether patients with CHF who have conduction abnormalities other than LBBB also respond favorably to CRT. METHODS: We divided patients enrolled in the MIRACLE trial into three subgroups according to conduction abnormality--LBBB, right bundle-branch block (RBBB), and nonspecific interventricular conduction delay (IVCD)--and compared the response among and within these groups to CRT or no CRT at baseline and 6-months' follow-up. RESULTS: We found 313 patients with LBBB, 43 with RBBB, and 35 with IVCD. When they received CRT, significant improvement was achieved in functional class (p = 0.001) by patients with RBBB, and in quality of life (p = 0.038) by patients with IVCD. Patients in the RBBB and IVCD groups showed improvement in exercise time and peak oxygen consumption after CRT. Most patients with RBBB (82%) also had either left anterior fascicular block or left posterior fascicular block. CONCLUSIONS: Patients with CHF with RBBB and IVCD do benefit from CRT. Improvement with CRT in patients with RBBB may be due to concomitant left-sided conduction abnormalities. Further subgroup analyses of other CRT trials are necessary to validate these results.     

Accessory atrioventricular pathway, supra-, and infrahisian conduction impaired due to mitral annulus calcification

Disorders of conduction occurring simultaneously in both normal and accessory pathways of patients with Wolff-Parkinson-White (WPW) syndrome have only rarely been observed. To our knowledge this is the first report of impaired conduction in both pathways in WPW syndrome due to mitral annulus calcification (MAC). This case of WPW syndrome type A presented the following conduction abnormalities: (1) right bundle-branch block; (2) transient second-degree AV block with prolonged PR interval of the conducted beats; (3) during electrophysiological study, induction of tachycardia, dependent (phase 3) second-degree AV block, and occasionally conduction of two consecutive beats, the second showing an increased H-V interval (from 25 to 60 ms) and left bundle-branch block (LBBB) pattern, due to (4) infrahisian conduction abnormality.     

Alternate Patterns of Ventricular Activation during Supraventricular Bigeminy

Several investigators have previously noted that in the presence of bigeminal atrial extrasystoles, the premature beats may exhibit an alternate pattern of ventricular excitation either in the form of alternating left and right bundlebranch block, or alternating right bundle-branch block and normal intraventricular conduction. However, the association of alternating intraventricular conduction with other types of supraventricular bigeminy has rarely been documented. In this report we present five diverse forms of supraventricular bigeminy exhibiting the phenomenon of alternating ventricular excitation on the early beats. Our findings suggest that the exact mechanism of supraventricular bigeminy is irrelevant in terms of subsequent ventricular events. Practically any type of supraventricular bigeminy may result in an alternate pattern of ventricular activation.     

Left bundle branch block: a continuously evolving concept

Eppinger and Rothberger in 1909 and 1910 first acknowledged the importance of the conduction system, yet a confusion of the pattern of left bundle branch block with right bundle branch block resulted which persisted for 25 years. In left bundle branch block, right ventricular endocardial activation begins before, and is often completed before, initiation of left ventricular endocardial activation. Most likely, right to left septal activation then follows, resulting in left ventricular endocardial activation. Although it is hazardous to make definitive diagnoses of infarction in the presence of left bundle branch block, clues do exist. Benign left bundle branch block is rare; usually disease becomes manifest. Electrocardiographic criteria of hypertrophy are not as helpful in older patients with chronic left bundle branch block (mainly because of the very high incidence of left ventricular hypertrophy) as in younger patients with block of nonatherosclerotic origin. Left bundle branch block is often associated with other abnormalities of the conduction system. Fascicular blocks may mask or mimic myocardial infarction. Left posterior fascicular block is most often an indicator of left ventricular myocardial deficit if right ventricular enlargement is eliminated. Mortality is higher in patients with associated left axis deviation than in those with a normal axis, although the incidence of progression of atrioventricular (AV) block is low. In symptomatic patients with prolonged His to ventricular intervals, the incidence of progression of AV block is higher (12%). Preexisting left bundle branch block in the absence of clinical evidence of heart disease is rare, yet carries with it a slightly increased mortality. Newly acquired left bundle branch block carries a 10-fold increase in mortality; the incidence of sudden death as the first manifestation of heart disease is increased 10-fold.     

Complete Heart Block From Chronic Marijuana Use

Marijuana is the most commonly used illicit drug in the world. Over the last decade, the potency of marijuana has increased tremendously. Its use is associated with harmful health consequences including adverse cardiovascular effects, such as arrhythmias, myocardial infarction, cardiomyopathy and stroke. It has been reported to cause bradycardia. This report describes the case of a 51-year-old female with no significant past medical history who presented with complete heart block due to chronic marijuana use, requiring a permanent pacemaker. To our knowledge, this is the first reported case of complete heart block due to chronic marijuana use. Advanced conduction system abnormalities can be a potential complication of chronic marijuana use, which the physicians need to be aware of. With increasing push for medical marijuana, physicians are likely to encounter more of such cases.     

A computer heart model incorporating anisotropic propagation: II. Simulations of conduction block

This study describes the simulation of the more common types of conduction blocks with a computer model of the heart incorporating anisotropic propagation. The rationale was to test the model as to its ability to simulate these blocks by physiologically justifiable adjustments of the conduction system alone. The complete blocks were generated by simply blocking conduction totally at selected sites in the proximal conduction system, and the incomplete blocks by slowing down the conduction velocity in the proximal system. Also simulated were the left fascicular blocks and the bilateral blocks. All simulated electrocardiograms, vectorcardiograms, body surface potential maps, and epicardial isochrones for these blocks were similar to clinically observed data, with the exception of the left posterior hemiblock, which was slightly atypical. This could be because such blocks are usually accompanied by other cardiac pathologies not included in our simulations. The model also supports van Dam's observation that during left bundle branch block the passage of activation from right to left occurs via slow myocardial activation with no evidence of a local delay due to a septal barrier. Finally, the model suggests that a left bundle branch block with a normal frontal plane QRS axis may simply represent a case of an incomplete left bundle block, whereas one that exhibits a left axis QRS deviation in the frontal plane represents a more severe complete left bundle branch block.     

His Bundle pacing for congenital complete AV block: An attempt to fix a broken heart?

Congenital complete atrioventricular block (CCAVB) is usually due to failure of atrioventricular nodal conduction with preservation of the His‐Purkinje system. Most patients with CCAVB ultimately require pacemaker therapy to restore physiologic heart rates, dealing with the detrimental effects of chronic right ventricular (RV) pacing on cardiac structure and function. The ideal stimulation pattern aims to mimic the normal conduction to restore electromechanical coupling, preventing the harmful effects of lack of atrioventricular and inter‐intraventricular synchrony. This can be done through conduction system pacing. Using His bundle pacing (HBP) for cardiac resynchronization therapy in two complete congenital atrioventricular block patients, we have reported better exercise tolerance and echocardiographic improvements related to reversible left ventricular dysfunction that can be corrected by restoration of the normal activation pathway via the His‐Purkinje network.     

Right and left ventricular activation sequence in patients with heart failure and right bundle branch block: a detailed analysis using three-dimensional non-fluoroscopic electroanatomic mapping system

Three-dimensional mapping in RBBB and heart failure. INTRODUCTION: Recently, right bundle branch block (RBBB) was proved to be an important predictor of mortality in heart failure (HF) patients as much as left bundle branch block (LBBB). We characterized endocardial right ventricular (RV) and left ventricular (LV) activation sequence in HF patients with RBBB using a three-dimensional non-fluoroscopic electroanatomic contact mapping system (3D-Map) in order to provide the electrophysiological background to understand whether these patients can benefit from cardiac resynchronization therapy (CRT). METHODS AND RESULTS: Using 3D-Map, RV and LV activation sequences were studied in 100 consecutive HF patients. Six of these patients presented with RBBB QRS morphology. The maps of these patients were analyzed and compared post hoc with those of the other 94 HF patients presenting with LBBB. Clinical and hemodynamic profile was significantly worse in RBBB group compared to LBBB. Patients with RBBB showed significantly longer time to RV breakthrough (P<0.001), longer activation times of RV anterior and lateral regions (P<0.001), and longer total RV endocardial activation time (P<0.02) compared to patients with LBBB. Time to LV breakthrough was significantly shorter in patients with RBBB (P<0.001), while total and regional LV endocardial activation times were not significantly different between the two groups. CONCLUSIONS: Degree of LV activation delay is similar between HF patients with LBBB and RBBB. Moreover, patients with RBBB have larger right-sided conduction delay compared to patients with LBBB. The assessment of these electrical abnormalities is important to understand the rationale for delivering CRT in HF patients with RBBB.     

Incessant slow bundle branch reentrant ventricular tachycardia in a young patient with left ventricular noncompaction

A 15-year-old girl was admitted to the cardiology outpatient clinic due to mild palpitations and documented incessant slow ventricular tachycardia (VT) with left bundle branch block (LBBB) pattern. The baseline electrocardiogram revealed first-degree atrioventricular block and intraventricular conduction defect. Transthoracic echocardiography showed prominent trabeculae and intertrabecular recesses suggesting left ventricular noncompaction (LVNC), which was confirmed by cardiac magnetic resonance imaging. During electrophysiological study, a sustained bundle branch reentrant VT with LBBB pattern and cycle length of 480 ms, similar to the clinical tachycardia, was easily and reproducibly inducible. As there was considerable risk of need for chronic ventricular pacing following right bundle ablation, no ablation was attempted and a cardioverter-defibrillator was implanted. To the best of our knowledge, no case reports of BBR-VT as the first manifestation of LVNC have been published. Furthermore, this is an extremely rare presentation of BBR-VT, which is usually a highly malignant arrhythmia.     

Visualizing anatomical evidences on atrioventricular conduction system for TAVI

Visualizing the anatomy of the atrioventricular (AV) conduction axis substantiates that there is remarkable inter-individual variation at the macro- and microscopic levels, and that the atrioventricular bundle and left bundle branch are located more anteriorly, distally, and cranially and much closer to the aortic root complex than previously thought. The AV conduction system may therefore be compromised during implantation of a transcatheter aortic valve prosthesis, which may account for the relatively high incidence of new cardiac conduction abnormalities when conventional prosthetic valves are used. The design of the newer JenaValve® may afford advantages over more conventional valves by avoiding the high-risk implantation area and the potential for coronary ostia obstruction.     

Homozygous SCN5A mutation in Brugada syndrome with monomorphic ventricular tachycardia and structural heart abnormalities.

AIMS: To describe a patient showing monomorphic ventricular tachycardia, ECG aspect of Brugada syndrome, and structural heart abnormalities due to a homozygous missense mutation in SCN5A. METHODS AND RESULTS: Thirteen subjects (six males, seven females, mean age 46 +/- 22 years) belonging to the same family underwent physical examination, basal biochemical marker detection, 12-lead ECG, Holter ECG, signal-averaged ECG, echocardiogram and genetic analysis. The proband underwent a stress test together with left and right ventricular angiography and electrophysiological study. Three subjects (the proband, his mother, and one brother) showed on ECG an ST-segment elevation in the right precordial leads with coved type aspect. Moreover, the proband presented a sustained monomorphic ventricular tachycardia (left bundle branch block aspect with superior axis), whereas all other family members were asymptomatic. Imaging techniques documented right ventricular structural abnormalities only in the proband. Mutation screening in SCN5A gene was performed in the proband and in available family members. The proband carries a novel SCN5A mutation, R814Q, in homozygous, whereas the parents and four siblings were heterozygous carriers of the same mutation. CONCLUSION: This study provides the first evidence of a homozygous missense mutation in SCN5A associated with atypical ventricular arrhythmias and right structural abnormalities.     

Prognostic effect of bundle branch block related to coronary artery bypass grafting

The incidence and prognostic effect of the development of new perioperative ventricular conduction abnormalities were examined in all patients undergoing coronary artery bypass surgery at Duke University Medical Center between 1976 and 1981. Of the 913 patients included, transient (resolved before discharge) ventricular conduction abnormalities developed in 156 (17%) and persistent (until discharge) changes developed in 126 (14%). Complete right bundle branch block (BBB) was the most frequent type of new ventricular conduction abnormality, followed by left anterior hemiblock and incomplete right BBB (found in 60%, 26%, and 9%, respectively, of all patients with transient changes and 29%, 33% and 26% of all patients with persistent changes). Development of new ventricular conduction abnormalities was most strongly related to date of operation (p less than 0.0001, univariate chi 2 = 122), increasing from 2% transient and 7% persistent in 1976 to 36% transient and 22% persistent in 1981. The incidence was also higher in older patients. Preoperative ejection fraction and number of diseased vessels were related to development of perioperative ventricular conduction abnormalities but were not independently related after adjustment for other baseline characteristics. Contrary to findings in other studies, development of new perioperative ventricular conduction abnormalities, including isolated new left BBB, did not worsen the survival rate in patients followed up to 3 years after surgery.     

The electrocardiogram in systemic sclerosis (scleroderma). Study of 102 consecutive cases with functional correlations and review of the literature

The electrocardiographic findings in 102 consecutive patients with scleroderma were reviewed to determine the frequency and nature of the electrocardiographic abnormalities associated with this disease. Septal infarction pattern unassociated with QRS prolongation was present in 10 percent, compared with none of 96 control subjects (p less than 0.001). Ventricular conduction abnormalities were present in 17 percent. A normal electrocardiogram was obtained in 49 percent. A subset of 48 patients underwent detailed cardiopulmonary evaluation including exercise thallium scintigraphy, rest and exercise radionuclide ventriculography, pulmonary function tests, and chest roentgenography. Functional correlations of the electrocardiographic findings were examined in this subset. Septal infarction pattern (five of 48) and ventricular conduction abnormalities (10 of 48) were both associated with septal or anteroseptal thallium perfusion abnormalities (10 of 15 versus six of 33 of the remainder, p less than 0.005), which were present despite normal coronary angiographic results. Thallium defect scores were greater in patients with septal infarction pattern or ventricular conduction abnormalities compared with the remainder (defect scores 3.0 +/- 2.6 versus 1.4 +/- 2.2, respectively, p less than 0.025). In patients with ventricular conduction abnormalities, both left bundle branch block and right bundle branch block with left anterior fascicular block were associated with abnormal left ventricular function, whereas isolated right bundle branch block or left anterior fascicular block was associated with normal left ventricular function. A normal electrocardiographic finding (19 of 48) was associated with normal left ventricular function at rest (19 of 19). However, 11 of 19 (58 percent) had thallium perfusion defects and four of 19 (21 percent) had an abnormal response to exercise, although in none was the peak ejection fraction less than 50 percent. It is concluded that both septal infarction pattern and ventricular conduction abnormalities are electrocardiographic abnormalities associated with scleroderma heart disease; they appear to be a result of myocardial fibrosis. Some degree of myocardial fibrosis may be present with a normal electrocardiographic result, but significant left ventricular dysfunction is unlikely. Septal infarction pattern and ventricular conduction abnormalities, when present, are indicators of more advanced fibrosis.     

Electrocardiographic patterns of left bundle-branch block caused by intraventricular conduction impairment in working myocardium: a model study

By definition, the electrocardiographic (ECG) patterns of left bundle-branch block (LBBB) represent distinctive changes in duration and shape of the QRS complex caused by intraventricular conduction delay in the left ventricle (LV) due to structural abnormalities in the His-Purkinje conduction system and/or ventricular myocardium. However, impaired conduction in the working myocardium is not taken into consideration in the practical ECG diagnosis.Because the degree of LV myocardium impairment could be of importance for clinical evaluation of patients, we studied the effects of blocked and of delayed onsets of activation in the LV to simulate complete and incomplete LBBBs and slowed conduction in the LV myocardium by applying an analytical computer model.We demonstrated that typical LBBB patterns were caused both by block or delay in the onset of the LV activation, as well as by impaired conduction in the myocardium itself while maintaining the location and onset of the LV activation. The most important difference was the absence of initial anteriorly oriented electrical forces in cases of the simulated complete LBBB and of incomplete LBBB if the onset of LV activation was delayed (≥6 milliseconds). Under the conditions defined in this model that did not consider myocardial infarction, the presence of initial anteriorly oriented electrical forces was indicative of preserved conduction in the left bundle and of impaired conduction in LV working myocardium.

Conclusion

The elucidation of the participation of working myocardium impairment in the intraventricular conduction delay in the LV could be of vital significance for the clinical management of patients with LBBB patterns, for example, indicated for resynchronization therapy.     

Hereditary bundle branch system defect. A new genetic entity?

A familial survey demonstrated mendelian inheritance in three large kindreds with conduction abnormalities and heart block. The trait was autosomal dominant, with varying expressivity and penetrance, apparent male preponderance, and congenital onset. Manifestations included right bundle branch block, left axis deviation, and right bundle branch block associated with left axis deviation. Complete heart block proved almost always to be a late event, and developed in all documented cases from bilateral bundle branch block. An r' pattern, most likely representing a right ventricular conduction delay, is discussed.     

Embryonic conduction tissue: a spatial correlation with adult arrhythmogenic areas

INTRODUCTION: The occurrence of arrhythmias in adult patients may arise preferentially in anatomic regions derived from the specialized cardiac conduction system. To examine this hypothesis, we performed a detailed analysis of the developing cardiac conduction system using the recently described CCS-lacZ transgenic mouse strain. METHODS AND RESULTS: Transgenic embryos (E9.5-15.5) were stained for beta-galactosidase activity and co-stained with the myocardial marker HHF35. Results were reconstructed three dimensionally. CCS-lacZ expression was observed in the sinoatrial node, left and right venous valves, septum spurium, right and left atrioventricular ring, His bundle, bundle branches, and right ventricular moderator band. Furthermore, lacZ-positive cells could be demonstrated for the first time in the left atrium, in the posterior wall surrounding the pulmonary venous orifice. and, in later stages, surrounding the pulmonary venous wall. These cells were continuous with the left venous valve in the right atrium. LacZ-positive tissue also could be identified in Bachmann's bundle, running retro-aortically between the right atrium and left atrium. CONCLUSION: Known arrhythmogenic areas including Bachmann's bundle, the pulmonary veins, and sinus venosus derived internodal structures, demonstrate lacZ expression. These data support the hypothesis that areas derived from the developing cardiac conduction system may contribute to the arrhythmogenic substrate in adult hearts.     

Cure of Interfascicular Reentrant Ventricular Tachycardia by Ablation of the Anterior Fascicle of the Left Bundle Branch

Ablation of Interfascicular Reentrant Tachycardia. Introduction: Fascicular reentrant ventricular tachycardia (VT) using the anterior fascicle of the left bundle anterogradely is rare and may produce identical QRS morphology during sinus rhythm and VT. Catheter ablation of this type of VT has not been described in detail.
Methods and Results: In a postinfarct patient with dilated left ventricle and recurrent VT (showing a QRS configuration of right bundle branch, left posterior fascicular block), endocardial recordings from the His-Purkinje system showed that VT was due to interfascicular reentry. Induction of VT occurred after progressive retrograde conduction delay on increasing the prematurity of the extrastimulus. Anterograde conduction occurred exclusively over the left anterior fascicle, which caused identical QRS morphology during sinus rhythm and VT. During VT, the left posterior fascicle was used retrogradely. The usual target for bundle branch reentry ablation, the right bundle, did not participate in the reentrant circuit. While performing left ventricular endocardial mapping, VT was interrupted when positioning the catheter on the left anterior fascicle, and "reversed" nonsustained bundle branch reentry occurred with anterograde conduction over the posterior fascicle and retrograde conduction over the anterior fascicle. Ablation of conduction in the anterior fascicle led to cure of the VT.
Conclusion: Interfascicular reentrant VT with right bundle branch block, right-axis QRS configuration can be cured by catheter ablation of anterior fascicle conduction.