The role of left ventricular conduction in the electrogenesis of left ventricular hypertrophy. An electrophysiologic study in man

A case report of different degrees of the left anterior, septal and posterior fascicular branch block

We present a rare case of various conduction defects involving the left anterior, septal, and posterior branch in one patient. The different degrees of block of anterior, septal, and posterior fascicular of the left bundle branch indicate pathological changes in left ventricle. However, the values of this electrocardiographic presentation indicating the left ventricular function still need more investigations.

Electrocardiographic criteria of left ventricular hypertrophy in general population

The question on whether the electrocardiographic criteria are reliable for detection of left ventricular hypertrophy (LVH) and play a role in predicting outcome is open. Answer can only proceed from population-based studies over unselected people followed up for years. In this study, 1,699 subjects from general population underwent echocardiogram and standard electrocardiogram (ECG) codified for LVH with Minnesota code and with other five methods. Other items were also recorded and used as covariables. Left ventricular mass index (LVMI) was 127.6 +/- 44.9 g m(-2) in men and 120.8 +/- 41.2 g m(-2 )in women, and correlated directly with age in both genders. Prevalence of echocardiographic LVH was 36.6% in men and 53.4% in women. LVMI correlated directly with the Sokolow-Lyon score in both genders at any age, with the Romhilt-Estes, Cornell and R(aVL) scores in all subjects but elderly men, and with the Lewis score in men and women aged < or =69 years. Sensitivity and the predictive value of electrocardiographic tests, as well as the prevalence of LVH diagnosed with electrocardiographic criteria, were always low. Specificity was high for all the tests, and in particular for the Cornell index. Only when diagnosed with echocardiogram or with the Sokolow-Lyon criterion, LVH was an independent predictor of mortality. We conclude that electrocardiographic tests cannot be used as a surrogate of echocardiogram in detecting LVH in the general population because their positive predictive value (PPV) is unacceptably low. On the contrary, they could replace echocardiography in the follow up and for prediction of outcome, when LVH has previously been correctly diagnosed with other methods.

High-resolution analysis of the surface P wave as a measure of atrial electrophysiological substrate

BACKGROUND

At present atrial electrophysiology can only be assessed by invasive study. This limits available data in humans concerning atrial electrophysiologic changes in disease and in response to intervention. Indirect evidence suggests that the signal-averaged P wave (SAPW) may provide noninvasive markers of atrial electrophysiology but no direct evaluations that measure both refractoriness and conduction time have been reported.

METHODS

We investigated 9 patients attending for diagnostic electrophysiological studies (4 male; mean age 35.7 years). A 20-pole catheter was positioned in the right atrium; a decapole catheter was placed in the coronary sinus. Atrial effective refractory period (AERP) and conduction times were measured at the lateral and septal right atrium and the left atrium during sinus rhythm (SR) and at pacing cycle lengths of 600, 500, and 400 ms. Simultaneous SAPW recordings were taken during SR and pacing at 600 ms. Intravenous flecainide (2 mg/kg) was given after which the protocol was repeated.

RESULTS

Flecainide slowed conduction significantly at all sites (P < 0.05). During baseline measurements, rate adaptation of AERP was observed (P < 0.02 at the septum). Flecainide increased filtered P wave duration (P < 0.05) and reduced P wave energies (P < 0.05). Negative correlation was observed between P wave energies and conduction time with an inverse relationship between high-frequency energy and left atrial AERP.

CONCLUSIONS

The SAPW provides a noninvasive marker of atrial electrophysiology.

Clinical significance of QS complexes in V1 and V2 without other electrocardiographic abnormality

BACKGROUND

In the absence of other electrocardiographic (ECG) abnormalities, QS deflections simultaneously in both of the leads V1-V2 may have multiple possible causes. Despite much information in the literature indicating that this is an unlikely pattern for pure septal infarction, such an ECG diagnosis is frequently given.

METHODS

Ninety-nine cases having QS deflections in both leads V1 and V2 but no other ECG abnormality were compared to 99 other patients with entirely normal ECGs, to whom they were matched by age, gender, and the presence or absence of septal Q waves. Retrospective analysis of medical records was performed to determine the nature of any cardiovascular disease in these two groups, and to find a possible explanation for the ECG abnormality.

RESULTS

Because of its intermittence in subjects with multiple ECGs, QS deflections in leads V1-V2 appeared most often to be an artifact of precordial lead placement. Prior myocardial infarction, or presence of clinical coronary disease was present in only about 20% of the cases. Neither the intermittence of Q wave in V2 on repeated ECGs nor the absence of septal Q waves was useful in distinguishing between those with and without coronary heart disease.

CONCLUSIONS

This ECG pattern is a sign of prior myocardial infarction in only a minority of cases, and in the latter, infarction limited to the interventricular septum is exceptional. This ECG finding should be interpreted as a nonspecific QRS abnormality with multiple possible causes. Clinical correlation and repeat tracings with attention to lead placement will help to clarify its significance.

In search of left septal fascicular block

BACKGROUND

In most humans, the left bundle branch divides into 3 fascicles. Electrocardiographic changes resulting from conduction abnormalities of the left anterior and left posterior fascicles are well described and commonly diagnosed. Existence of conduction defects of the left septal fascicle is controversial, without generally accepted criteria for diagnosis.

METHODS

Approximately 26,000 electrocardiograms were reviewed to find examples consistent with left septal fascicle block according to criteria derived from review of the literature.

RESULTS

Electrocardiograms meeting proposed criteria were found in about 0.5% of tracings. Illustrative examples are shown with discussion of reasons for their selection.

CONCLUSIONS

Left septal fascicle block seems to exist, is polymorphic, and may explain some previously inadequately understood electrocardiographic abnormalities.

Spectrotemporal and spectral turbulence analysis of the signal-averaged P wave in paroxysmal atrial fibrillation

Patients with paroxysmal atrial fibrillation (AF) have greater overall P wave magnitude than control subjects, but the temporal localization of the increased energy is unknown. P wave spectral turbulence has not been investigated in such patients, and the optimum methodology for studying P wave signals has not been defined. This study, therefore, applied both spectrotemporal and spectral turbulence analyses to the signal-averaged P waves of patients with paroxysmal AF and to representative control subjects. Group A, 58 persons without cardiopulmonary disease (24 patients with paroxysmal AF, 34 control subjects), and group B, 57 with such disease (31 patients with paroxysmal AF, 26 control subjects), were studied. Spectral analysis was performed on a windowed 64-ms data segment that was advanced through the P wave in 2-ms steps. Spectral turbulence was measured from differentiated 24-ms data segments, by either cross-correlation between adjacent spectra, or differentiation of adjacent spectral coefficients over time (SV, spectral velocity). Patients had greater maximum P wave energy than control subjects, between 80-150 Hz for group A (means, 0.9 vs 0.7 microV2 x s), and 20-150 Hz for group B (means, 22.4 vs 16.3 microV2 x s). Spectral velocity was greater in patients with paroxysmal AF than in control subjects in both groups (group A: Peak SV, 11.6 vs 7.4 microV2 and group B: Peak SV, 12.0 vs 7.6 microV2). Increased energy and SV were reported in the central P wave. Spectrotemporal analysis suggested abnormal atrial activation in the central P wave associated with paroxysmal AF. A localized abnormality in atrial electrophysiology may cause the electrogenesis of the arrhythmia.

Effect of low dose sotalol on the signal averaged P wave in patients with paroxysmal atrial fibrillation

OBJECTIVE

To investigate the effects of low dose sotalol on the signal averaged surface P wave in patients with paroxysmal atrial fibrillation.

DESIGN

A longitudinal within patient crossover study.

SETTING

Cardiac departments of a regional cardiothoracic centre and a district general hospital.

PATIENTS

Sixteen patients with documented paroxysmal atrial fibrillation. The median (range) age of the patients was 65.5 (36-70) years; 11 were men.

MAIN OUTCOME MEASURES

Analysis of the signal averaged P wave recorded from patients not receiving antiarrhythmic medication and after 4-6 weeks' treatment with sotalol. P wave limits were defined automatically by a computer algorithm. Filtered P wave duration and energies contained in frequency bands from 20, 30, 40, 60, and 80 to 150 Hz of the P wave spectrum expressed as absolute values (P20, P30, etc) and as ratios of high to low frequency energy (PR20, PR30, etc) were measured.

RESULTS

No difference in P wave duration was observed between the groups studied (mean (SEM) 149 (4) without medication and 152 (3) ms with sotalol). Significant decreases in high frequency P wave energy (for example P60: 4.3 (0.4) v 3.3 (0.3) microV2.s, P = 0.003) and energy ratio (PR60: 5.6 (0.5) v 4.7 (0.6), P = 0.03) were observed during sotalol treatment. These changes were independent of heart rate.

CONCLUSIONS

Treatment with low dose sotalol reduces high frequency P wave energy but does not change P wave duration. These results are consistent with the class III effect of the drug and suggest that signal averaging of the surface P wave may be a useful non-invasive measure of drug induced changes in atrial electrophysiology.

Electrogenesis of the S1S2S3 electrocardiographic pattern. A study in humans based on body surface potential and right ventricular endocardial mapping

To study the electrogenesis of the S1S2S3 pattern, seven patients had body surface potential mapping and endocardial mapping of inflow tract, outflow tract, and apex of the right ventricle. QRS duration was longer in S1S2S3 versus controls (94 +/- 14 vs. 84 +/- 14 msec). Surface mapping was similar in S1S2S3 patients and in controls during the first 30-40 msec of QRS, but S1S2S3 patients subsequently presented the following differences: (1) earlier time of onset (34 +/- 3 vs. 44 +/- 6 msec) and a lower voltage (1,242 +/- 468 vs. 1,649 +/- 31 mV) of peak positive anterior maximum; (2) earlier dorsal migration (45 +/- 3 vs. 55 +/- 7 msec) of the maximum; (3) a second peak positive maximum at 58 +/- 3 msec, located on the dorsal spine; (4) the appearance of a right subclavicular positive area at 51 +/- 6 msec, which in controls was absent or appeared later (66 +/- 7 msec). At the end of QRS, the maximum was located in all but two S1S2S3 cases on the upper sternum. Right ventricular endocardial mapping showed a similar activation time of the apex in S1S2S3 patients and controls, but in the former a significant inflow (56 +/- 21 vs. 36 +/- 9 msec) and outflow tract (79 +/- 13 vs. 39 +/- 8 msec) activation delay was documented. The data obtained using body surface potential mapping suggest that an anomalous wavefront rightward and superiorly oriented is present in the S1S2S3 pattern, which is able to oppose the electrical forces of ventricular free walls.(ABSTRACT TRUNCATED AT 250 WORDS)

Diagnostic body surface potential map patterns in left ventricular hypertrophy during PQRST

Body surface potential maps were recorded from 117 thoracic sites and 3 limb electrodes in 173 normal subjects older than 30 years of age and 122 patients with clinically "pure" left ventricular (LV) hypertrophy. Typical LV hypertrophy map patterns were identified at successive instants during the PQRST waveform by removing from sequential LV hypertrophy maps the corresponding normal variability range at each electrode site. The presence in individual patients of 1 or more patterns typical in time and location of LV hypertrophy allowed retrospective assignment to the LV hypertrophy group. The most consistent discriminant patterns were excessive negative voltages in the anterior torso with reciprocal excess of positive voltages in the upper right chest during the second half of the P wave, excessive negative voltages in the lower right anterior torso at mid-QRS and excessive negative voltages in the left precordium with reciprocal excess of positive voltages in the upper right chest throughout ST-T. Best classification results were achieved with ST-T features, followed by features from the P wave, the QRS waveform and the PR segment. Cumulative use of ST-T and P features yielded a specificity of 94% with a sensitivity of 88%. Little improvement was obtained by the addition of QRS and PR information. The discriminant map criteria were applied to body surface potential maps from 169 new subjects (77 normal subjects ages 20 to 30 years and 92 patients with complicated LV hypertrophy). Little modification in specificity (93%) and sensitivity (90%) was observed. The performance of commonly used standard lead criteria was also tested.(ABSTRACT TRUNCATED AT 250 WORDS)

Body surface maps in left bundle branch block uncomplicated or complicated by myocardial infarction, left ventricular hypertrophy or myocardial ischemia

We provided a topographic and quantitative description of body surface maps (BSM) during the entire QRST interval in seven uncomplicated LBBBs and 31 LBBBs complicated by: myocardial infarction (MI, seven cases), left ventricular hypertrophy (LVH, eight cases), myocardial ischemia (IS, seven cases), MI + LVH (six cases) and LVH + IS (three cases). In all patients we observed abnormal map configurations attributable to the LBBB. We were unable to identify consistent effects of the complicating heart condition(s) on the general pattern of chest potentials. Conversely, the surface voltages were generally decreased by MI and IS and increased by LVH. By considering the 38 patients as a preliminary learning set we applied a stepwise discriminant analysis to 77 voltage-related variables derived from BSM to produce a model for discriminating between LBBBs with and without MI. We properly allocated more than 90% of the patients. We also attempted to classify the patients into four groups: pure LBBB, LBBB + MI, LBBB + LVH and LBBB + IS, with a percentage of correct classification of about 80%. The two classifying procedures were applied to ten new LBBB patients with results similar to those obtained in the 38 of the study group.

Electrophysiological mechanisms of the SI SII SIII electrocardiographic morphology

We studied three groups of individuals by means of spatial-velocity electrocardiograms and thallium-201 myocardial imaging to figure out the electrophysiological explanation of the SI SII SIII electrocardiographic morphology. We studied twelve healthy individuals without SI SII SIII, seven healthy individuals with SI SII SIII and fifteen patients with chronic obstructive pulmonary disease with SI SII SIII. The average values of the QRS-E and QRS-F intervals were higher in the second (P less than 0.05 and P less than 0.005) and third groups (P less than 0.01 and P less than 0.001) than in the first. One patient of the second group and thirteen of the third showed right ventricular enlargement. The slowing down of the right ventricular conduction explained the SI SII SIII morphology in normal individuals in more than half the cases. In patients with chronic obstructive pulmonary disease with SI SII SIII the conduction delay plays an important part in the electrogenesis of the right ventricular enlargement electrocardiographic morphology. We think that these observations can give further data about the electrophysiologic mechanism of the SI SII SIII morphology.

Electrocardiographic diagnosis of chamber enlargement

The purpose of this article is to review the changing role of the electrocardiogram in the diagnosis of cardiac chamber enlargement. Electrocardiographic criteria for the diagnosis of ventricular hypertrophy and atrial enlargement are reviewed in relation to autopsy, angiographic, echocardiographic and imaging findings. The electrocardiographic theory underlying the recognition of hypertropphy or dilation incorporates a number of sound physical principles that may lead to meaningful correlations with the tissue mass, chamber diameter and intracardiac blood volume. However, there are limiting factors related to the variable orientation of the heart in the chest, variable extracardiac factors and nonspecificity of each depolarization and repolarization abnormality used in the diagnosis of hypertrophy or dilation. This explains the superiority of the new noninvasive methods, in particular echocardiography, in the diagnosis of hypertrophy. Echocardiography is superior to electrocardiography in the detection of mild hypertrophy, and is more useful in the serial follow-up of changes during progression or regression of chamber enlargement.

Diagnostic implications of figure-of-eight and clockwise QRS loop rotation on the horizontal vectorcardiogram in chronic aortic valve disease

In chronic aortic valve disease the left ventricular (LV) volumes, mass and ejection fraction (EF), as well as selected Frank ECG measurements of patients with a normal counterclockwise rotation (Type A) of the horizontal QRS vector loop are compared with those of patients showing an abnormal figure-of-eight or clockwise configuration (Type B) to investigate whether the different QRS patterns reflect ventriculographic alterations or depends on a conduction delay. In aortic stenosis (AS,n = 21) and combined AS and aortic insufficiency (AS + AI,n = 23) the Type B vectorcardiograms (VCGs) correlate with significantly increased LV end-diastolic volumes (p. .01, .01, respectively) and depressed EF (p .07, .009, respectively). In pure AI (n = 39) LV volumes, mass and EF do not differ between the Type A and Type B patterns. As compared to Type B VCGs of AS (n = 6), the LV end-diastolic volume index is clearly higher in Type A VCGs of pure AI (n = 21)(p .028). The only ECG change which is significant at the p .01 level in each group is the increase of the R peak time in lead X in the Type B VCGs. This can be related to greater volume and mass only in AS and AS+ AI, but is not substantiated by equivalent ventriculographic alterations in pure AI. The findings indicate that Type B VCGs are very likely caused by a left ventricular conduction delay since they cannot be strictly correlated with increases in LV volume and mass alone.

Possible role of a ventricular conduction disturbance in the electrogenesis of the ECG-VCG signs of myocardial infarction

The typical QRS patterns of myocardial infarction (MI-QRS) are commonly attributed to myocardial cellular death. However, observation of a transient appearance of MI-QRS during coronary insufficiency, the disappearance of MI-QRS after coronary by-pass surgery and the appearance of MI-QRS after intracranial hemorrhage suggest that a different electrophysiological mechanism may be at work. There is a single convincing explanation for all these observations. It seems possible, at least theoretically, that a localized conduction disturbance can generate or contribute to the generation of the MI-QRS. The results obtained in nine out of 194 cases studied by means of premature right atrial stimulation (PRAS) in our laboratory seem to confirm this hypothesis. In five of them we observed typical MI-QRS in the aberrant beats which were absent in the basal tracings. In the other four cases, MI-QRS which were present in basal tracings disappeared in the aberrant beats. In three of these a reduction in the duration of QRS was also observed, while in the fourth the duration of QRS did not change. In no case could the alterations of QRS (induction or disappearance of MI-QRS) be explained by a classical conduction disturbance, preexcitation or by a premature ventricular beat. While the induction of MI-QRS was clearly due to an aberrant conduction in the supraventricular beats, the disappearance of basal MI-QRS changes in premature supraventricular beats is more difficult to explain. One possible electrophysiological mechanism could be a supernormal phase conduction. If this is the case, the basal MI-QRS could be due to a ventricular conduction disturbance. In conclusion, our results suggest that MI-QRS can be generated, at least in our cases, by a localized conduction disturbance.

Left bundle branch block: a predictor of poor left ventricular function in coronary artery disease

Clinical, coronary arteriographic, and hemodynamic studies were performed in 55 patients with left bundle branch block (LBBB) and coronary artery disease and were compared with 110 patients consecutively matched for age and sex with ischemic heart disease but without LBBB. No significant differences were found in duration of symptoms or frequency of prior myocardial infarction, hypertension, or diabetes mellitus; however, the LBBB patients had a significantly (p less than 0.001) higher frequency of congestive heart failure (38.2% vs 11.8%) and cardiomegaly (63.6% vs 25.5%). An evaluation of severity of the coronary disease on the basis of subtotal vs total obstructive lesions, number of vessels involved, total coronary score, and individual coronary arteries involved revealed no significant differences between the groups. The LBBB patients had significantly (p less than 0.001) greater impairment of left ventricular function as reflected by the end-diastolic volume (107 +/- 43 vs 79 +/- 30 ml/m2), ejection fraction (0.35 +/- 0.19 vs 0.59 +/- 0.18), and frequency of an abnormal contractile pattern (91% vs 61%). Evaluating the LBBB patients on the basis of the QRS width and axis revealed no significant intragroup differences in clinical profile, severity of coronary disease, or left ventricular dysfunction. A prolonged PR interval (greater than or equal to 0.20 second) was associated with more severe coronary artery disease and an enlarged heart. This study indicates that coronary artery disease associated with LBBB identifies patients with severe left ventricular dysfunction.

Correlation between electrical and echocardiographic data in hypertrophic cardiomyopathy

We have studied 38 patients with clinical and echocardiographic evidence of hypertrophic cardiomyopathy. We tried to correlate the electrical findings of hypertrophy in electrocardiographic and vectorcardiographic tracings with the anatomical data supplied by M-mode echocardiography of septal and posterior wall thickness and left ventricular diameters.

Epicardial activation of the human ventricle: effects of left ventricular hypertrophy

To determine the effects of left ventricular hypertrophy on epicardial activation of the human heart, intraoperative epicardial mapping of 40 to 66 points was performed in 10 patients undergoing aortic valve replacement. Mean calculated left ventricular mass was 364 +/- 98 g. All patients had normal left ventricular contraction. Earliest epicardial activation occurred in the anterior right ventricle in all patients. In 9 patients, it was the only epicardial breakthrough point. One patient had a single inferior left ventricular breakthrough point. Epicardial activation spread from the right ventricle towards the left ventricle in both the anterior and inferior direction. Latest epicardial activation occurred at the base of the left ventricle in 9 patients and the base of the right ventricle in 1. When compared with patients with coronary artery disease, normal ventricular contraction, and no left ventricular hypertrophy, patients with hypertrophy had fewer left ventricular breakthrough points (p less than 0.001) and were more likely to have latest activation at the left ventricular base (p less than 0.0010. We conclude that left ventricular hypertrophy is associated with marked changes in the pattern of epicardial activation. These changes may reflect delay in spread from endocardium due to the increased wall thickness.

Negative U wave: a highly specific but poorly understood sign of heart disease

A negative U wave is highly specific for the presence of heart disease and is associated with other electrocardiographic abnormalities in more than 90 percent of patients. The three most common conditions associated with a negative U wave are systemic hypertension, aortic and mitral regurgitation and ischemic heart disease. The U wave vector is directed opposite to the QRS axis in the horizontal plane in patients with both left and right ventricular hypertrophy. In patients with ischemic heart disease, the U wave vector tends to be directed away from the site of the akinetic or dyskinetic region. The change from a negative to an upright U wave after a reduction in blood pressure, renal transplantation, insertion of a valve prosthesis or a coronary arterial bypass graft procedure is associated with a decrease in the QRS amplitude but with no consistent changes in T wave polarity. The timing of the U wave apex is dependent on the duration of ventricular repolarization but not on the duration of the QRS complex. This finding and other electrocardiographic observations are explained better by the ventricular relaxation than by the Purkinje fiber repolarization theory of U wave genesis.

Reliability of echocardiographic and electrocardiographic parameters in assessing serial changes in left ventricular mass

A reliable noninvasive index of left ventricular mass would be useful in following patients with valvular heart disease and left ventricular hypertrophy. We reviewed concurrent electrocardiograms and echocardiograms from 54 subjects, 39 patients with aortic or mitral valve disease and 15 normal subjects. Pre- and early postoperative echocardiographic estimates of left ventricular mass in 17 patients who had valve replacements correlated well (r = 0.96, p less than 0.001) and demonstrated little change in mean values despite altered left ventricular dimensions. Echocardiographic estimates of left ventricular mass were, therefore, used as a standard for evaluating other noninvasive indices. Precordial electrocardiographic voltage showed a weak correlation with left ventricular mass in the study group as a whole (r = 0.59, p less than 0.001), but no correlation in patients with volume overload (r = 0.36, p = NS). In 18 patients who had preoperative and three separate postoperative studies at least eight weeks apart, changes in left ventricular cross-sectional area (an index of left ventricular mass which corrects for changes in left ventricular volume) closely followed alterations in left ventricular mass. However, changes in posterior wall and interventricular septal thickness often resulted from altered ventricular volume and did not accurately reflect directional changes in left ventricular mass. Serial changes in electrocardiographic voltage were similarly unreliable. We conclude that left ventricular mass and cross-sectional area by echocardiography allow accurate noninvasive assessment of left ventricular mass, whereas wall thickness and electrocardiographic changes do not.

The anterior displacement of the QRS loop as a right ventricular conduction disturbance. Electrophysiologic and vectorcardiographic study in man

Anterior displacement (AD) of the QRS horizontal loop (Frank VCG method) was induced by programmed right atrial stimulation (PRAS) in 15 cases. When AD occurred we noticed changes of the terminal QRS vectors and of the T loop similar to those observed in incomplete right bundle branch block (RBBB). The increasingly anticipated extrastimuli induced progressively the AD and then progressive degrees of RBBB. The anterior shifting of the efferent limb never appeared after the induction of RBBB. A left conduction disturbance never appeared after the AD. In cases of supposed incomplete left bundle branch block (i.e. left ventricular hypertrophy) the QRS duration decreased when the AD was induced. Therefore, the AD induced by PRAS and probably those observed in some clinical cases are due to a right ventricular conduction disturbance.