Showing papers on "QRS complex published in 1978"

Recurrent sustained ventricular tachycardia. 2. Endocardial mapping.

Abstract: Endocardial ventricular mapping of 21 ventricular tachyardias (VT) in 17 patients was performed using electrode catheters. Activation at multiple left and right ventricular sites was utilized to determine the site of origin of the VT. Eleven VT had a left bundle branch block pattern (VT-LBBB) and 10 VT had right bundle branch block pattern (VT-RBBB). In all VT-RBBB the earliest site of activation was in the LV or septum. In VT-LBBB the earliest site was RV (4/11), LV (5/11) and septum (2/11). All ventricular tachycardias with QRS less than 140 msec arose in the septum. In patients with an aneurysm, the site of origin of ventricular tachycardia was always in the aneursm. All VT-LBBB arising from the left ventricle originated in an aneurysm involving the septum. QRS changes during ventricular tachycardia were associated with alterations in the patterm of ventricular activation without alteration of the site of origin. In three patients the site of origin predicted by endocardial ventricular mapping was confirmed intraoperatively by epi- and/or endocardial mapping. We conclude that endocardial ventricular mapping demonstrates the limitations of the surface electrocardiogram in localizing the site of origin of ventricular tachycardia. The method may provide important data upon which the surgical therapy of ventricular tachycardia is based.

Clinical, electrocardiographic and electrophysiologic observations in patients with paroxysmal supraventricular tachycardia.

Abstract: Seventy-nine patients without ventricular preexcitation but with documented paroxysmal supraventricular tachycardia were analyzed. Electrophysiologic studies suggested atrioventricular (A-V) nodal reentrance in 50 patients, reentrance utilizing a concealed extranodal pathway in 9, sinus or atrial reentrance in 7 and ectopic automatic tachycardia in 3. A definite mechanism of tachycardia could not be defined in 10 patients (including 7 whose tachycardia was not inducible). The three largest groups with inducible tachycardias were compared in regard to age, presence of organic heart disease, rate of tachycardia, functional bundle branch block during tachycardia and relation of the P wave and QRS complex during tachycardia. A-V nodal reentrance was characterized by a narrow QRS complex and a P wave occurring simultaneously with the QRS complex during tachycardia. Reentrance utilizing a concealed extranodal pathway was characterized by young age, absence of organic heart disease, fast heart rate, presence of bundle branch block during tachycardia and a P wave following the QRS complex during tachycardia. Sinoatrial reentrance was characterized by frequent organic heart disease, a narrow QRS complex and a P wave in front of the QRS complex during tachycardia. In conclusion, a mechanism of paroxysmal supraventricular tachycardia could be defined in most patients. Observations of clinical and electrocardiographic features in these patients should allow prediction of the mechanism of the tachycardia.

Recording from the body surface of arrhythmogenic ventricular activity during the S-T segment.

Abstract: Recent experimental reports have documented the delay of epicardial potentials beyond the QRS complex as a result of infarction, and the degree of delay was directly associated with the onset of ventricular arrhythmias. This study describes a method using high amplification, band pass filtering and signal averaging for recording from the body surface these delayed potentials presaging ventricular arrhythmias. This technique, has been used for recording low level cardiac potentials masked by noise. In 10 dogs control records of the electrocardiogram and surface averaged lead were obtained during sinus rhythm, atrial pacing and premature atrial beats. Subsequently, the left anterior descending coronary artery was ligated in each dog. Nine dogs survived the surgical procedure and underwent similar recordings 3 to 6 days after infarction. Electrocardiographic changes were consistent with a recent infarction. During the pacing protocol discrete multiphasic wave forms appeared during the S-T segment of the surface averaged lead, and concomitant changes in the terminal portions of the QRS complex were observed in seven dogs. In five of these dogs ventricular arrhythmias were observed at the faster pacing rates or after closely coupled premature atrial beats. The chest was then reopened and the pacing procedure repeated during recording of direct epicardial electrograms with a multicontact bipolar electrode. This electrogram validated the existence of potentials during the S-T segment in all but one dog and late activity that was not repeatable on a beat to beat basis in another. Thus, when late activity was confirmed with the epicardial electrogram, seven of eight dogs showed a corresponding change in the surface averaged lead. This technique may prove to be a sensitive indicator of abnormal electrical activity preceding ventricular arrhythmias.

Evaluation of R wave amplitude changes versus ST-segment depression in stress testing.

Abstract: Exercise ECGs and coronary angiograms were reviewed in 266 patients (81 normals and 185 with significant coronary artery disease). Thirty-three false positive and 96 false negative ST responses to stress testing were purposely chosen to determine if the R wave could reduce the number of false ST responses. R wave amplitude changes were measured in the control and in the immediate postexercise period. An increase or no change in R wave was taken as evidence of an abnormal response, while a decrease in the R wave was a normal response. The sensitivity by ST segment was 48% and the specificity was 59%. These values were low because of the large number of false positive and negative ST responses in the study. It was our purpose to determine if these lowered values could be significantly improved by the R wave. Using R wave criteria, the sensitivity was 63% (P is less than 0.01) while the specificity was 79% (P is less than 0.01). The sensitivity and specificity of stress testing can be significantly improved using R wave changes.

Inverse calculation of QRS-T epicardial potentials from body surface potential distributions for normal and ectopic beats in the intact dog.

Abstract: Inverse epicardial potential distributions were calculated from potential distributions measured from the body surface in 12 intact dogs, divided into six pairs. The calculation procedure made use of measurements from the initial dog of each pair, giving the geometric location of each epicardial and body surface electrode and the approximate variance of the epicardial potentials and of the body surface noise. The same calculation procedure subsequently was applied to the other dog of the pair. For all dogs, inverse solutions were calculated throughout QRS-T for several sequences of excitation and repolarization which were produced by stimulating singly and in pairs any of eight ventricular sites. All calculated inverse results were checked by detailed quantitative comparison to the corresponding measured epicardial potential distributions, which were obtained from chronically implanted epicardial electrodes. The root mean square (RMS) numerical differences between the inverse computed and the measured epicardial distributions were a substantial fraction of the RMS measured epicardial voltages, often 0.7 or more, and the correlation coefficients between measured and computed epicardial distributions were in the range 0.6-0.8. Nonetheless, the major epicardial electrical events of excitation and repolarization easily were seen in all of the inverse maps in the initial dogs of each pair, and with only slightly less clarity in the subsequent dogs. Events readily observed included the initial minimum around the stimulus site as excitation began, the movement of the zero contour line across the epicardium as excitation progressed, and the characteristic pattern of repolarization with a maximum near the stimulus site. The results demonstrated that specific physical features of epicardial potential distributions can be determined from body surface measurements and can be verified by comparison with direct epicardial measurements.

Cardiovascular effects of tricyclic and tetracyclic antidepressants.

Abstract: Cardiovascular effects of therapeutic doses of tricyclic or tetracyclic antidepressants (TCA) were examined in 66 patients. After three weeks of therapy, heart rate and PR interval were increased ( P P c time and the QRS interval did not reach significant levels. We observed significant flattening of T waves ( P P ( JAMA 239:213-216, 1978)

Sustained ventricular tachycardia: Evidence for protected localized reentry

Abstract: The components of the reentrant circuit were evaluated in 26 patients in whom sustained ventricular tachycardia could be reproducibly initiated or terminated, or both. Observations suggesting that the proximal His-Purkinje system was not a requisite component included (1) lack of requirement for retrograde His-Purkinje delay or bundle branck reentry, or both, for initiation of the tachycardia: (2) anterograde depolarization of the His bundle during ventricular tachycardial without alteration of the QRS configuration or cycle length; and (3) the presence of random retrograde His potentials during the tachycardia. Evidence that the reentrant circuit was localized to a small area of the ventricles included (1) the ability to capture large segments of the ventricles transiently or continuously with occurrence of intermittent or continuous supraventricular capture either spontaneously or with atrial pacing without effect on the tachycardia. These findings suggest that the reentrant circuit must be small, electrocardiographically silent and relatively protected.

Relationships among ventricular arrhythmias, coronary artery disease, and angiographic and electrocardiographic indicators of myocardial fibrosis.

Abstract: This study was performed to determine the relationships among angiographic, hemodynamic, clinical, and electrocardiographic data and premature ventricular contractions (PVCs). Arrhythmias were analyzed by 24 hour Holter monitor in 244 patients evaluated for chest pain by coronary angiography and left ventriculography. Using a categorical linear model, the presence of myocardial fibrosis as indicated by both abnormal left ventricular contraction (LVC) and abnormal initial QRS on electrocardiogram was found to be the only independent predictor of both frequent and complex ventricular arrhythmias (P less than .0001). All other descriptors, including the number of diseased vessels (greater than or equal to 75% obstruction), were dependent upon abnormal LVC in their association with PVCs. When the right anterior oblique view of the left ventriculogram was divided into nine segments to allow automated quantiative analysis of LVC, the prevalence of frequent PVCs was directly related to the number of abnormally contracting segments. Of patients with 0 abnormal segments, 11% had greater than or equal to 2 PVC/hr, in contrast to 44%, 73% and 100% of patients with 1-3, 4-6, and 7-9 abnormal wall segments, respectively (P less than 0.01). A similar quantitative relationship was found between premature ventricular contractions and abnormal initial forces indicating previous myocardial infarction on the electrocardiogram.

Atypical ventricular tachycardia as a manifestation of disopyramide toxicity

Abstract: An unusual ventricular tachyarrhythmia developed in a 57 year old woman with recurrent ventricular tachycardia and toxic disopyramide plasma concentrations. The rhythm was similar to the patient's previous ventricular tachycardia, but the rate was slower and the QRS complex was markedly widened, mimicking the electrocardiographic changes associated with electrolyte abnormalities. Disopyramide, which has electrophysiologic properties similar to those of quinidine, probably caused the arrhythmia and should be added to the list of drugs associated with atypical ventricular tachycardia.

Electrophysiologic characteristics of concealed bypass tracts: Clinical and electrocardiographic correlates

Abstract: Twelve of 60 consecutively studied patients undergoing electrophysiologic study for paroxysmal supraventricular tachycardia had atrioventricular (A-V) bypass tracts functioning as the retrograde limb of the reentrant circuit. None had evidence of preexcitation in the surface electrocardiogram, but in two patients anterograde preexcitation could be produced by pacing from the coronary sinus. In all 12 patients with concealed bypass tracts the retrograde atrial activation sequence or effect of left bundle branch block aberration during the tachycardia, or both, confirmed the left-sided bypass tract. A negative P wave in lead I during the tachycardia was also diagnostic of a left-sided bypass tract. Dual A-V nodal pathways were found in five patients with concealed bypass tracts but were unrelated to the development of the tachycardia. When compared with supraventricular tachycardia due to A-V nodal reentry, clinical findings suggestive of a concealed bypass tract included: (1) P wave following the QRS complex (12 of 12 versus 12 of 40), (2) negative P wave in lead I during the tachycardia, and (3) bundle branch block aberration during the tachycardia (8 of 12 versus 3 of 40). Other characteristics of patients with concealed bypass tracts that were of less value in individual cases were shorter cycle lengths of tachycardia, younger patient age and lesser incidence of organic heart disease.

Natural history of Wolff-Parkinson-White syndrome discovered in infancy.

Abstract: The prognosis of 20 infants with a diagnosis of Wolff-Parkinson-White syndrome under 1 year of age is presented Children were followed up from 1 to 19 years (mean 9 years) Seven patients had associated congenital heart disease Analysis of the associated arrhythmias revealed episodes of supraventricular tachycardia in 18 (90 percent) During paroxysmal supraventricular tachycardia the QRS complex was normal in seven and wide in nine children Categorizing patients into groups according to the width of the QRS complex and the presence or absence of a delta wave during tachycardia helps in understanding and planning therapy Eighteen patients had a stable or improved course with growth but two patients with tetralogy of Fallot died postoperatively with resistant supraventricular tachycardia The high prevalence rate of supraventricular tachycardia during infancy which later decreases or disappears could be explained by the different electrophysiologic responses between normal and accessory pathways during the fast heart rate characteristic of this young age Invasive electrophysiologic studies are indicated in children older than 1 year of age who remain symptomatic and in all children being conconsidered for cardiac surgery regardless of the effectiveness of the preoperatlve therapy

Experimental basis for QRS and T wave potentials in the WPW syndrome. The relation of epicardial to body surface potential distributions in the intact chimpanzee.

Abstract: The WolfT-Parkinson-White (WPW) syndrome was experimentally mimicked by stimulating seven different ectopic (pre-excitation) sites in intact chimpanzees. The objective was to determine how to differentiate one ectopic site from another possible ectopic site close by. The approach used was to obtain a direct picture of total cardiac electrical activity in the form of epicardial potential distributions to understand the cardiac origin of the surface potentials throughout ventricular depolarization and repolarization. QRS-T wave body surface maps were interpreted by visually comparing them directly with the associated measured epicardial potential distributions and by quantitative comparison with those produced by adjacent ectopic sites. During early QRS (delta wave) all sites produced a body surface maximum within the same small area on the anterior chest; however, the position of the minimum was markedly different and was related spatially to the position of the ectopic site. The epicardial measurements showed that during early excitation there was a minimum of large magnitude at the ectopic site while the nearby maximum was of much lower magnitude. The body surface maxima and minima during QRS provided an easy way to distinguish between ectopic sites on one ventricle vs. the other, but between adjacent sites on the same ventricle there was frequently little change in the pattern of the QRS maximum and minimum. However, adjacent sites produced distinct changes in the distant low level potential areas. The combined analysis of QRS and T waves showed that subepicardial ectopic sites 2-3 cm apart produced detectable differences in the body surface distributions. Furthermore, the T wave patterns were as useful as or more useful than those during QRS for predicting the ectopic pre-excitation site. On the epicardium, the positions of the repolarization maximum and minimum were the same as those of the earliest and latest areas of ventricular excitation, a feature which resulted in a better indication of cardiac electrical events on the body surface during ST-T waves than during QRS.

Spectrum of regular tachycardias with wide QRS complexes in patients with accessory atrioventricular pathways.

Abstract: Reciprocating tachycardia and atrial flutter or fibrillation are the rhythm disorders most frequently documented in patients with accessory atrioventricular (A-V) pathways. Reciprocating tachycardia typically results in a regular tachycardia (140 to 250/min) with a normal QRS pattern, although on occasion bundle branch block aberration occurs. Atrial flutter or fibrillation may result in an irregular ventricular response, with the QRS configuration being normal or exhibiting bundle branch block or various degrees of ventricular preexcitation, or both. Although much less common than either reciprocating tachycardia or atrial flutter/fibrillation, regular tachycardias with a wide QRS complex suggestive of ventricular preexcitation are observed in patients with accessory pathways. Excluding functional or preexisting bundle branch block, several arrhythmias may cause these electrocardiographic findings which may mimic those of ventricular tachycardia. In the present study a variety of arrhythmias that resulted in tachycardias with a wide QRS complex were examined in 163 patients with accessory pathways who underwent clinical electrophysiologic study for evaluation of recurrent tachyarrhythmias. Twenty-six patients (15 percent) manifested a regular tachycardia with a wide QRS complex suggesting ventricular preexcitation. Atrial flutter with 1:1 anterograde conduction over an accessory pathway (15 of 26 patients, 58 percent) was the most frequent arrhythmia and was usually associated with a heart rate of 240/min or greater (12 of 15 patients). Reciprocating tachycardia with conduction in the anterograde direction over an accessory pathway (antidromic reciprocating tachycardia) occurred in 7 of 26 patients (27 percent), and resulted in a slower ventricular rate than atrial flutter (217 ± 22 versus 262 ± 42, P In this study the clinical electrophysiologic diagnostic features of several arrhythmias which cause tachycardias with a wide QRS compex suggesting ventricular preexcitation are outlined. It is apparent that definitive arrhythmia diagnosis during these tachycardias is often complex and usually requires careful study using intracardiac electrode catheter techniques.

Value of the QRS complex in assessing left ventricular ejection fraction.

Abstract: The relation between electrocardiographic findings and the angiographic left ventricular ejection fraction and the augmented ejection fraction after a premature ventricular contraction was investigated in 73 patients with documented chronic coronary artery disease The patients were separated into four groups according to the presence or absence of abnormal Q waves Twenty-four patients had diaphragmatic myocardial infarction, 21 had anterior myocardial infarction, 15 had both and 13 had no myocardial infarction There were no statistically significant differences in cardiac index, left ventricular end-diastolic pressure or number of coronary vessels showing critical narrowing in the four groups The sum of R waves (in mv) in leads aVL, aVF and V1 to V6 (ΣR) was correlated with the ejection fraction (EF) and the augmented ejection fraction (EFa) EF in percent = 66 ΣR mv + 94 (no = 73, r = 061); and EFa in percent = 86 ΣR mv + 110 (no = 73, r = 077) Among patients with ΣR of less than 40 mv, augmented ejection fraction was less than 045 in 73 percent; among patients with ΣR of 40 mv or more the augmented ejection fraction was greater than 045 in 93 percent (P < 0001) Thus, the ΣR, calculated from six precordial and two augmented leads in patients with chronic coronary artery disease, correlated with both ejection fraction and augmented ejection fraction The electrocardiogram in patients with coronary artery disease may prove useful as a simple, readily available and noninvasive guide in the assessment of left ventricular function in patients with coronary artery disease

Inexcitable right ventricle and bilateral bundle branch block in Uhl's disease.

Abstract: A 29-year-old female with Uhl's anomaly developed complete atrioventricular (A-V) block. His bundle studies revealed block distal to the His bundle recording site with narrow QRS complexes. Right ventricular capture could not be obtained and despite successful left ventricular epicardial pacing, the patient died. Autopsy revealed absence of myocardium in most areas of the right ventricle and the right side of the ventricular septum with a normal tricuspid valve. Conduction system examination revelaed total destruction of both bundle branches. This is the first case where bilateral bundle branch block is shown to be present in Uhl's anomaly. Narrow QRS complexes probably reflected the absence of right ventricular forces.

The electrocardiographic recognition of cardiac states at high risk of ventricular arrhythmias. An experimental study in dogs.

Abstract: SUMMARY Recognition of states in which the heart is vulnerable to arrhythmia would be a helpful guide to prophylaxis. The possibility of recognizing such states from the ECG is suggested by the already established relations between abnormally disparate recovery to both vulnerability to arrhythmia and ECG waveform. In this study, canine QRS, T, and QRST isoarea maps were determined from ECGs recorded at 192 body sites during control states and conditions of enhanced susceptibility to arrhythmia. Vulnerable states were produced by ouabain intoxication, hypothermia, premature beats, and epinephrine infusion. A hypothetical series of QRST isoarea maps that would be expected to occur without increased local inequalities of recovery was derived by adding the control QRS isoarea map to a fraction (a) of the control T isoarea map and allowing the fraction to vary from a = 1 to a = — 1. One QRST isoarea map selected from the derived series was subtracted from a QRST isoarea map during each state of enhanced arrhythmia vulnerability. Derived maps were selected to minimize the average amplitude of the residual maps. RMS values of the residual maps systematically increased with increasing prematurity of depolarization, with time after a toxic injection of a dose of ouabain, with increasing hypothermia, and during the first 3 minutes of epinephrine infusion. Also, the RMS values of the residual maps decreased in hypothermic dogs during rewarming. Our findings suggest that states of vulnerability to arrhythmia due to increased disparity of recovery can be identified by analysis of ECG waveforms recorded from lead systems sensitive to electrical activity in local cardiac regions.

Noninvasive recording of His-Purkinje activity in man by ORS-triggered signal averaging.

Abstract: Mobile instrumentation and a clinically applicable method have been developed for external His bundle recording. High gain signal amplification (10)(5) filtering (30--300 HZ) and averaging (128 or 256 consecutive cycles) are used. Acquisition of signals arising in the P-R interval is triggered by the patient's QRS signal at the end of that interval. The precordial bipolar electrodiogram is digitized at 5k HZ with 8 bit resolution and transferred to a 1,024 word, 18 bit signal averager. The averaged signal is then displayed on an oscilloscope and photographed. Good correlations were obtained between direct intracardiac and precordial recordings in experimental animals and in humans. Noise level after averaging was below 0.3 microV, and there was good elimination of asynchronous atrial and ectopic ventricular activity. With averaging of 128 or 256 consecutive cycles, the signal attenuation after propagation to the chest wall was in the range 1:2000 to 1:4000 in comparison with the directly recorded His bundle activity deflections. The noninvasive method may be of value in follow-up of acute and chronic disturbances of atrioventricular conduction, as well as in studies of effects of pharmacologic interventions.

Cardiac complications of protein-sparing modified fasting.

Abstract: Cardiovascular abnormalities developed in a patient during a proteinsparing modified fasting diet. Syncope was the complaint at the time of examination. Hypotension, persistent QTcinterval prolongation, and a low QRS voltage were observed before the development of refractory ventricular tachycardia. At autopsy, antemortem thrombi were attached to the left ventricular endocardium and a fenestrated aortic valvule. Strick proteinsparing modified fasting is not without risk of sudden death even with close medical supervision. (JAMA240:120-122, 1978)

Experimental studies and clinical report on the electrical alternans of ST segment during myocardial ischemia.

Abstract: During myocardial ischemia produced in 43 dogs by occlusion of left coronary artery, electrical alternans developed in 34 experiments. The most common was alternans of ST-T complex. Surface and intracellular electrograms were recorded simultaneously from contiguous sites in the ischemic area. The alternans of ST-T complex in the surface electrogram corresponded to that of the rate of repolarization of the membrane action potential. The development of this alternans is localized in 2 relatively small area and transient. This may be the reason why electrical alternans of ST-T is clinically rare. A clinical case showing electrocardiographic changes of electrical alternans of ST-T complex without any change in the QRS complex is reported. Myocardial infarction and hypokalemia is considered as a cause of the alternans. The present results support the hypothesis that the mechanism of electrical alternans will be an alternation of the rate and extent of the ions transported across the myocardial cell membrane.

Method and apparatus for monitoring electrocardiographic waveforms

Abstract: Apparatus for the recognition of ventricular premature beats by an identifying width of a QRS complex by dividing the area by the height and further noting when the width measurements is at least 40% wider than the average width of the immediately preceding several QRS complexes. Additional apparatus for indicating ventricular premature beats by determination of an early width determination which exceeds the average width by at least 20% and is additionally followed by the compensatory pause as determined by interbeat interval measurement.

QRS voltage change with adriamycin administration.

Abstract: A decrease in the electrocardiographic limb lead QRS voltage of greater than or equal to 30% was highly correlated with the development of congestive heart failure in patients treated with adriamycin (ADM). It is felt that if a decrease in limb lead QRS voltage greater than or equal to 30% were detected in a patient receiving ADM, cardiomyopathy might be avoided or ameliorated by discontinuation of the drug.

Pronounced dependence of ventricular endocardial QRS potentials on ventricular volume.

Abstract: To evalulate the relation between ventricular endocardial potentials (QRS amplitude) and ventricular dimensions, left and right ventricular endocardial potentials were recorded with hook electrodes in anaesthetised open-chest dogs during transfusion and withdrawal of blood Left ventricular end-diastolic diameter was measured by ultrasonic crystals, and end-diastolic volume was determined by thermodilution In each dog, left ventricular endocardial potentials, whether recorded from anterior or posterolateral walls, decreased linearly as left ventricular end-diastolic diameter or volume increased, and vice versa With an average increase in left ventricular end-diastolic diameter from 401 +/- 17 to 446 +/- 18 mm, left ventricular endocardial potentials decreased from 328 +/- 25 to 235 +/- 23 mV (P less than 0001); and for an increase in left ventricular end-diastolic volume from 136 "/- 125 to 343 +/- 058 ml/kg left ventricular endocardial potentials decreased from 362 +/- 66 to 149 +/- 43 mV (P less than 0001) Changes in right ventricular endocardial potentials paralleled the changes in left ventricular endocardial potentials These findings indicate that acute changes in ventricular dimensions influence endocardial potentials considerably, and suggest a potential clinical application for detecting acute changes in ventricular volume

ECG alterations with progressive left ventricular hypertrophy in spontaneous hypertension.

Abstract: Although many ECG criteria exist for diagnosis of left ventricular hypertrophy (LVH) in hypertensive man, little is known of which specific ECG changes accompany progression of LVH with duration of hypertension. The spontaneously hypertensive rat (SHR) provides the best animal model thus far developed for studying this process since these animals demonstrate a progressive increase in left ventricular/body weight ratio with age. Electrocardiograms were performed under light ether anesthesia in four age groups of SHR and two nonnotensive Wistar strains (NR and WKY). Analysis of variance for two factors (rat strain and age) revealed progressively increased QRS and P-wave duration and delay in intrinsicoid deflection in SHR (p<0.001). Bipeak P-wave notching was also noted in SHR similar to left atrial abnormality in hypertensive man. Thus, specific ECG indices can be identified in association with the known progressive increase in left ventricular mass in SHR and should provide a better means to understand ev...

Incidence of Different Types of A-V Block and their Localization by his Bundle Recordings

Abstract: The recordings of the His bundle electrogram in cases of atrioventricular block has demonstrated the inability of the surface electrocardiogram to localize exactly the site of the conduction disturbance, especially when the QRS complexes, of either conducted or escape beats, are widened.

Re-entry via Mahaim fibres as a possible basis for tachycardia.

Abstract: Paroxysmal tachycardia with widened QRS complexes was recorded in a 21-year-old man. In sinus rhythm there was no evidence of pre-excitation. His bundle studies revealed an abnormally short HV interval of 30 ms. Premature atrial stimuli produced an increased PR interval. At short coupling intervals the His bundle activity became incorporated within the QRS complex. Concurrently, a left bundle-branch block pattern appeared identical to that seen during tachycardia. Closely coupled ventricular extrastimuli initiated a tachycardia identical to the initial episode. A re-entry mechanism via anterograde Mahaim fibres and retrograde His bundle -AV node pathway is postulated.