Microwave ablation of the atrioventricular junction in open-chest dogs

The use of microwave energy for ablation of the atrioventricular (AV) junction was examined in open-chest dogs. Using a specially designed microwave catheter and a 2450 MHz generator, microwave energy was delivered to the AV junction according to one of two protocols. In protocol 1, increasing amounts of energy were delivered until irreversible AV block occurred. In protocol 2, only two applications of energy were used, one at low energy and the other at an energy found to be high enough to cause irreversible AV block. Each dog received between one and six applications of microwave energy. The amount of energy delivered per application ranged from 25.6 to 311.4 J. No AV block was seen at 59.4 ± 28.3 J. Reversible AV block was seen with an energy of 120.6 ± 58 J. Irreversible AV block was seen at 188.1 ± 75.9 J. Irreversible AV block could be achieved in each animal. There was no difference in the energy required to cause irreversible AV block between the two protocols. The tissue temperature measured near the tip of the microwave catheter was correlated with both the amount of energy delivered and the extent of AV block caused. Histologic examination demonstrated coagulation necrosis of the conduction system. Microwave energy is a feasible alternative energy source for myocardial ablation. Since tissue damage is due exclusively to heating and the resulting rise in temperature can be measured, microwave energy may have advantages over currently existing energy sources in terms of both titrating delivered energy and monitoring the extent of tissue destruction. © 1995 Wiley-Liss, Inc.     

Hypothyroidism as the cause of atrioventricular block in an elderly patient

Syncope is a common problem in the older patient. Sometimes syncope is caused by extreme bradycardia secondary to atrioventricular (AV) block. We describe a case in which a 90-year-old woman presented with complete AV block due to severe hypothyroidism. After suppletion with levothyroxine, AV conduction was restored. (Neth Heart J 2008;16:57-9.)     

Morning preference in onset of symptomatic third-degree atrioventricular heart block

The aim of this study was to examine 24h patterning in the symptoms indicative of third-degree atrio-ventricular (AV) heart block. We found a total of 227 cases (126 men and 101 women) of third-degree AV block that had been diagnosed by the Emergency Medical Department of the St. Anna Hospital in Ferrara, Italy between 1990 and 2001. Determination of the hour of onset of symptomatic third-degree AV block, however, was possible and listed in the records of only 161 or 70.9% of the cases (92 men and 69 women). The onset time of every event was categorized into one of four 6h spans of the 24h: night (00:00-05:59h), morning (06:00-11:59h), afternoon (12:00-17:59h), and evening (18:00-23:59h). The onset of the symptoms of third-degree AV block in the sample of 161 cases was significantly greater in the morning between 06:00 and 11:59h than any other 6h span of the day and night (chi2-test; p < 0.001). The same phenomenon was substantiated in the subgroup of the 92 males (chi2; p < 0.0001), although it could not be detected for the smaller subgroup of 69 women. The 24h pattern, with morning preference, in the onset of symptomatic third-degree AV block is similar to the one in sudden cardiac death and cardiogenic cardiac arrest. The etiology of the 24h pattern in symptomatic AV block is unknown; it may be an expression of intrinsic biological rhythmicity within the heart tissue or its control system, and/or the timing of environmental triggers resulting in coronary ischemia.     

An unusual case of complete atrioventricular block causing Takotsubo syndrome

Complete atrioventricular (AV) block in association with Takotsubo syndrome (TS) has been well recognized, but the cause and effect relationship has not been elucidated. We describe a 78-year-old female who presented with complete AV block but one week later developed new-onset, diffuse T-wave inversions, QT prolongation, and acceleration of junctional escape rate. Left ventriculogram revealed features typical of TS. One year after permanent pacemaker implantation, complete AV block persisted despite the reversal of wall motion defects implying that conduction abnormality was the trigger of TS rather than its consequence.     

Unusual Pauses In Sinus rhythm And Intermittent 2 to 1 AV Block In A Patient With Concealed His Extra Systoles - A Rare Cause Of Bradycardia

A 56 year old male with a past medical history of hypertension and dyslipidemia presented with recurrent dizziness. Routine EKG was performed, which suggested frequent junctional extra systoles with compensatory pauses. During telemetry periods of 2:1 block with effective ventricular rate of 34 bpm was observed. His bundle study suggested frequent His extra systoles causing functional AV block. Treatment with anti-arrhythmic medication, paradoxically improved AV block and symptoms in our patient.     

Second Degree Heart Block Associated with QT Prolongation

Pseudo 2:1 AV block when sinus intervals are shorter than the ventricular refractory period has been reported with long QT syndrome (LQTS). We report the characteristics and treatment of a patient suffering from congenital LQTS with episodes of true 2:1 AV block. The pseudo 2:1 AV block relates to the extreme prolongation of ventricular refractoriness. Several histologic studies have documented abnormalities within the conduction system, including apoptosis. Because of the rare occurrence and poor prognosis of the LQTS with impaired AV conduction, international guidelines for diagnosis and treatment are needed.     

Relationship between hair elements and severity of atrioventricular block in horses

The aim of this study was to investigate the relationships between the mean concentrations of trace elements and the severity of the seconddegree atrioventricular (AV) block in the mane hair of horses. Electrocardiographs of horses were continually recorded for 6 h using a holter cardiac monitor to determine dropped ventricular beats (DVBs) which can be used as an indicator of the severity of the AV block. Mane hair Ca, Cu, Mg, and Zn concentrations were measured by the particle-induced X-ray emission method. The Zn/Cu ratio and Ca concentration in mane hair were significantly and positively correlated with the hourly DVBs in horse with a second-degree AV block (p<0.01, r2=0.485; p<0.05, r2=0.351, respectively). Proposed diagnostic cutoff points for hair Ca concentration and Zn/Cu ratio based on receiver operating characteristics curves analysis in detecting second-degree AV block were set at 1536 μg/g and 26.0, respectively. Those results with horse hair suggest that the evaluation of the Ca, Cu, Mg, and Zn status in mane hair by this method is strongly related to the severity of second-degree AV block and might predict the susceptibility of an individual much before the development of the symptom.     

猫冠状动脉缺血与再灌注对房室传导的影响

急性下壁心肌梗塞常引起房室传导功能障碍,然而这种障碍与心肌缺血的内在联系并不很清楚,本实验在去植物性神经传出纤维的猫上进行,通过模板匹配方法从Ｈｉｓ束电图检测Ａ,Ｈ,Ｖ波并测量两心房间期（ＡＡ）,心房波与Ｈｉｓ波间期（ＡＨ）,Ｈｉｓ波与心室波间期（ＨＶ）和心房波与心室波间期（ＡＶ）。结果如下：结扎右冠状动脉后,２０只动物的ＡＨ间期１４只出现增加（Ａ组）６只未出现增加（Ｂ组）对Ｂ组进行快速心房起博和     

News and Views

The aim of this study was to examine 24h patterning in the symptoms indicative of third-degree atrio-ventricular (AV) heart block. We found a total of 227 cases (126 men and 101 women) of third-degree AV block that had been diagnosed by the Emergency Medical Department of the St. Anna Hospital in Ferrara, Italy between 1990 and 2001. Determination of the hour of onset of symptomatic third-degree AV block, however, was possible and listed in the records of only 161 or 70.9% of the cases (92 men and 69 women). The onset time of every event was categorized into one of four 6h spans of the 24h: night (00:00–05:59h), morning (06:00–11:59h), afternoon (12:00–17:59h), and evening (18:00–23:59h). The onset of the symptoms of third-degree AV block in the sample of 161 cases was significantly greater in the morning between 06:00 and 11:59h than any other 6h span of the day and night (χ²-test; p<0.001). The same phenomenon was substantiated in the subgroup of the 92 males (χ²; p<0.0001), although it could not be detected for the smaller subgroup of 69 women. The 24h pattern, with morning preference, in the onset of symptomatic third-degree AV block is similar to the one in sudden cardiac death and cardiogenic cardiac arrest. The etiology of the 24h pattern in symptomatic AV block is unknown; it may be an expression of intrinsic biological rhythmicity within the heart tissue or its control system, and/or the timing of environmental triggers resulting in coronary ischemia.     

Development of a model of complete heart block in rats

Atrioventricular(AV) block is a useful substrate for the study of cardiacphysiology. The objective of this investigation was todevelop a straightforward and reproducible model of permanent AV blockin rats. Working through a sternotomy, we used an epicardial fat padbetween the aortic root and the right atrial wall of the rat as alandmark for the site for injection of 70% ethanol (5-10 µl)into the myocardium 3 mm below the epicardial surface. Stable, completeheart block was produced in 23 of 28 rats (82%) with a success rate of100% in the last 16 rats of the series. Saline injection produced noheart block in 15 rats. A separate group of 14 animals was allowed torecover. Chronic heart block was achieved in all ethanol-injectedanimals for up to 7 days before death. The survival rate in therecovered rats was 90% in the ethanol-injected group and 100% in thesaline-injected control group. Acute hemodynamic changes following theproduction of heart block consisted of an increase in central venouspressure, a decrease in systolic blood pressure, a decrease in leftventricular pressure, and a decrease in change in pressure overtime. Chronic hemodynamic changes demonstrated a return tobaseline of the central venous pressure, a persistent decrease insystolic blood pressure, and a decrease in left ventricular pressure.After the rats were killed and the hearts were dissected, discreteareas of myocardial damage were identified histologically in the atrialseptum near the AV conduction axis tissue in the ethanol-injectedhearts. Complete heart block was associated only with lesions extendinginto the specialized muscle of the AV node or His bundle. Focal mildhemorrhage, inflammation, and damaged myocardial fibers were observedin the acute stage, whereas healing lesions were characterized bygranulation tissue and fibrosis replacing conduction tissue. The simpletechnique described provides a reproducible model for permanent,complete heart block and the study of cardiac function.

     

The Spread of Excitation in the Embryonic Chick Heart

The spread of excitation in embryonic chick hearts, ranging in age from 7 to 20 days, was studied with both intracellular and extracellular electrodes. Evidence that the delay in ventricular excitation could be attributed to the cells of the entire atrioventricular (AV) ring was obtained, in part, from sagittal sections of the heart. In the intact preparation, uniform propagation occurred throughout the atrial roof at an apparent conduction velocity of 0.4 to 0.5 meter/sec. Delay of impulse propagation was localized in a very narrow band of tissue which extended across the AV ring. The apparent conduction velocity of this tissue was between 0.003 and 0.005 meter/sec. Both normal and retrograde propagation revealed the spread of conduction across the AV ring to be decremental in nature. This finding was supported by high frequency stimulation experiments which gave rise to AV block localized in the cells of the AV ring. Cardiac rhythmicity and AV transmission were responsive to acetylcholine and norepinephrine in much the same manner as in the adult mammalian heart. The present findings are in support of the hypothesis that the embryonic AV ring is the functional counterpart of the adult AV node.     

Ventriculo-atrial gradient due to first degree atrio-ventricular block: a case report

Background

Isolated, asymptomatic first degree AV block with narrow QRS has not prognostic significance and is not usually treated with pacemaker implantation. In some cases, yet, loss of AV synchrony because of a marked prolongation of the PR interval may cause important hemodynamic alterations, with subsequent symptoms of heart failure. Indeed, AV synchrony is crucial when atrial systole, the "atrial kick", contributes in a major way to left ventricular filling, as in case of reduced left ventricular compliance because of aging or concomitant structural heart disease.

Case presentation

We performed a trans-septal left atrium catheterization aimed at evaluating the entity of a mitral valve stenosis in a 72-year-old woman with a marked first-degree AV block, a known moderate aortic stenosis and NYHA class III symptoms of functional deterioration. We occurred in a deep alteration in cardiac hemodynamics consisting in an end-diastolic ventriculo-atrial gradient without any evidence of mitral stenosis. The patient had a substantial improvement in echocardiographic parameters and in her symptoms of heart failure after permanent pacemaker implantation with physiological AV delay.

Conclusion

We conclude that if a marked first degree AV block is associated to instrumental signs or symptoms of heart failure, the restoration of an optimal AV synchrony, achieved with dual-chamber pacing, may represent a reasonable therapeutic option leading to a consequent clinical improvement.     

Comparison of arrhythmia detection by conventional Holter and a novel ambulatory ECG system using patch and Android App,over 24 h period

BackgroundAmbulatory electrocardiogram (AECG) is done for evaluation of arrhythmia. Commonly used AECG system is 24 h Holter. Patch based second generation AECG monitoring devices, which can record for longer periods, are now available.ObjectiveAndroid App based WebCardio using WiPatch is a new AECG system which records ECG in two leads for 72 h. Our study compared the arrhythmia detection by WebCardio and conventional Holter by simultaneously connecting both for 24 h in patients having indication for AECG.MethodsThe AECG of patients who had simultaneous recording with WebCardio and conventional Holter, in the department of Cardiology, Medical College, Thrissur were evaluated. Ability to detect any of the 6 arrhythmias :1) atrial fibrillation (AF), 2) atrioventricular (AV) block, 3) sinus pause of ≥3 s (SP), 4) supraventricular tachycardia (SVT), 5) premature ventricular complex (PVC) and 6) ventricular tachycardia (VT)/ventricular fibrillation (VF) was compared. Detection of each arrhythmia was also compared.Results141 patients had simultaneous recordings by both systems of AECG. The WebCardio picked up at least one of the 6 arrhythmias; AF, AV block, SP, SVT, PVC or VT/VF in 98 cases compared to 88 in the Holter (McNemars test, two tail P = 0.006). In eleven cases WebCardio detected an arrhythmia where Holter could not. In one case Holter identified an arrhythmia and WebCardio could not. Individual arrhythmias; AF, SP, SVT and VT/VF were detected equally by both systems. AV block (23 Vs 18, p = 0.0625) and PVCs (83 Vs 74, p = 0.0636) were detected in more number of cases in WebCardio. In the five cases where WebCardio alone identified AV block, four had poor quality of P wave in the Holter.ConclusionArrhythmia was picked up in more number of patients by the WebCardio compared to Holter. This was due to higher pickup of AV block and PVCs by WebCardio. Difference in AV block identification was due to better quality of P in WebCardio. WebCardio is a good alternative to Holter for AECG.     

Left Ventricular Dysfunction Caused by Unrecognized Surgical AV block in a Patient with a Manifest Right Free Wall Accessory Pathway

A 24-year-old male with Wolff-Parkinson-White syndrome developed systolic cardiomyopathy and severe heart failure following membranous ventricular septal defect repair and tricuspid valve replacement. Following successful catheter ablation of a right anterolateral accessory pathway (AP), complete AV block with junctional escape rhythm was noted. Patient subsequently underwent implantation of a biventricular ICD. Heart failure symptoms significantly improved soon after and left ventricular systolic function normalized 3 months post-procedure. In this case, surgically acquired AV block likely explains development of postoperative cardiomyopathy by facilitating ventricular activation solely via the AP and thereby increasing the degree of ventricular dyssynchrony.     

A partial agonist of the A(1)-adenosine receptor selectively slows AV conduction in guinea pig hearts

The use of full agonists of the A(1)-adenosine receptor (A(1)-ADOR) as antiarrhythmic agents is limited by their actions to cause high-grade atrioventricular (AV) block, profound bradycardia, atrial fibrillation, and vasodilation. It may be possible to avoid these undesired actions by use of partial agonists. We determined the effects of CVT-2759, a potential partial agonist of A(1)-ADORs, on guinea pig hearts. CVT-2759 (0.1-100 microM) increased the S-H interval of the isolated heart from 45 +/- 1 to 60 +/- 3 ms (P < 0. 01) with a half-maximal effect at 3.1 microM. CVT-2759 did not cause second-degree AV block. CVT-2759 significantly attenuated the actions of the full agonists N(6)-cyclopentyladenosine and adenosine. CVT-2759 caused a moderate slowing of atrial rate by 10 microM. In contrast, CVT-2759 was a full agonist to decrease cAMP content of rat adipocytes and Fischer rat thyroid line 5 cells. Results of radioligand binding assays indicated that CVT-2759 stabilized a high-affinity, G protein-coupled state of the A(1)-ADOR in membranes prepared from rat adipocytes but not in membranes prepared from the guinea pig brain. The results suggest that a weak A(1)-ADOR agonist, such as CVT-2759, may be useful to slow AV nodal conduction and thereby ventricular rate without causing AV block, bradycardia, atrial arrhythmias, or vasodilation.     

Arrhythmia and sudden death associated with elevated cardiac chloride channel activity

The identification and analysis of several cationic ion channels and their associated genes have greatly improved our understanding of the molecular and cellular mechanisms of cardiac arrhythmia. Our objective in this study was to examine the involvement of anionic ion channels in cardiac arrhythmia. We used a transgenic mouse model to overexpress the human cystic fibrosis transmembrane conductance regulator (CFTR) gene, which encodes a cAMP-regulated chloride channel. We used RNase protection and in situ hybridization assays to determine the level of CFTR expression, and radiotelemetry and in vivo electrophysiological study in combination with pharmacological intervention to analyse the cardiac function. Cardiac CFTR overexpression leads to stress-related sudden death in this model. In vivo intracardiac electrophysiological studies performed in anaesthetized mice showed no significant differences in baseline conduction parameters including atrial-His bundle (AH) or His bundle-ventricular (HV) conduction intervals, atrioventricular (AV) Wenckebach or 2:1 AV block cycle length and AV nodal functional refractory period. However, following isoproterenol administration, there was marked slowing of conduction parameters, including high-grade AV block in transgenic mice, with non-sustained ventricular tachycardia easily inducible using programmed stimulation or burst pacing. Our sudden death mouse model can be a valuable tool for investigation of the role of chloride channels in arrhythmogenesis and, potentially, for future evaluation of novel anti-arrhythmic therapeutic strategies and pharmacological agents.     

Laser endoscopic destruction of the atrioventricular junction of the heart conduction system in an experiment

Feasibility and degree of local AV junction destruction were studied prior to the induction of complete transversal block on the model of 18 isolated perfused dog hearts, using endoscopic laser device, employing cardiofibroscope and laser Ne: YAG. Morphological pattern in the destruction zone is presented. The technique and device can be used for transvenous AV junction destruction.     

Discovery of a persistent left superior vena cava during pacemaker implantation

An 83-year-old male was admitted to the coronary care unit because he had developed a total atrioventricular (AV) block after he had undergone a transurethral resection of the prostate for benign prostate gland hypertrophy.     

Resting Sinus Heart Rate and First Degree AV block: Modifiable Risk Predictors or Epiphenomena?

Simple and cost-effective tools that identify patients at increased risk for adverse cardiovascular events are actively sought. High resting sinus heart rate and first degree AV block are easily recognized and commonly encountered findings in a cardiology practice. A growing body of epidemiological and clinical evidence has been shown them to be independent predictors of all-cause and cardiovascular mortality, both in the general population and in patients with structural heart disease. This paper reviews the important role of heart rate and first degree AV block in predicting cardiovascular outcomes, examines the pathophysiological mechanisms underlying this increased risk, and discusses the effectiveness of available therapies to favorably modify these risk factors.     

Parasympathetic effects on cardiac electrophysiology during exercise and recovery

Depressed parasympathetic tone is associated with an increased risk of sudden cardiac death. Exercise and the postexercise recovery period, which are associated with parasympathetic withdrawal, are high risk periods for sudden death. However, parasympathetic effects on cardiac electrophysiology during exercise and recovery have not been described. Electrophysiology studies were performed using noninvasive programmed stimulation (NIPS) in nine subjects (age 59 +/- 18 yr) with implanted dual-chamber devices and normal left ventricular function during multiple bicycle exercise sessions. NIPS was performed at rest, during exercise, and in the early recovery period both before and after parasympathetic blockade with atropine. Parasympathetic effect was defined as the value of the parameter of interest in the absence of atropine minus the value of the parameter in the presence of atropine. During exercise, sinus cycle length, atrioventricular (AV) block cycle length, AV interval, and ventricular effective refractory period shortened; in recovery, the values were intermediate between the rest and exercise values (P < 0.0001 by ANOVA). Parasympathetic effects on sinus cycle length, AV block cycle length, AV interval, and ventricular effective refractory period were 247 +/- 140, 58 +/- 20, 76 +/- 20, and 8.6 +/- 7.5 ms at rest, 106 +/- 20, 37 +/- 14, 24 +/- 13, and 2.6 +/- 7.8 ms during exercise, and 209 +/- 114, 50 +/- 23, 35 +/- 21, and 9.5 +/- 11.8 ms during recovery, respectively. There was poor correlation among the parasympathetic effects noted at the sinus node, AV node, and ventricle. Further work evaluating parasympathetic effects on cardiac electrophysiology during exercise and recovery in patients with heart disease is required to elucidate its role in modulating the risk of sudden cardiac death noted at these times.