Peri-infarction block; electrocardiographic abnormality occasionally resembling bundle branch block and local ventricular block of other types

The Primary Alteration of Ventricular Myocardium Conduction: The Significant Determinant of Left Bundle Branch Block Pattern

Intraventricular conduction disturbances (IVCD) are currently generally accepted as ECG diagnostic categories. They are characterized by defined QRS complex patterns that reflect the abnormalities in the intraventricular sequence of activation that can be caused by pathology in the His-Purkinje conduction system (HP) or ventricular myocardium. However, the current understanding of the IVCD's underlying mechanism is mostly attributed to HP structural or functional alterations. The involvement of the working ventricular myocardium is only marginally mentioned or not considered. This opinion paper is focused on the alterations of the ventricular working myocardium leading to the most frequent IVCD pattern-the left bundle branch block pattern (LBBB). Recognizing the underlying mechanisms of the LBBB patterns and the involvement of the ventricular working myocardium is of utmost clinical importance, considering a patient's prognosis and indication for cardiac resynchronization therapy.

Peri-infarction block, a marker for VT risk?

We present a monomorphic ventricular tachycardia (VT) in a patient with a history of myocardial infarction and syncope. The ECG shows an acceleration-dependent peri-infarction block inferiorly. The authors suggest that this old (but forgotten) ECG-entity may serve as a marker for assessing the risk of post-infarction VT.

Value of leads V7-V9 in diagnosing posterior wall acute myocardial infarction and other causes of tall R waves in V1-V2

Left posterolateral chest leads (V7, V8, V9) helped distinguish the multiple causes of tall R waves in V1 and/or V2, diagnosed true posterior myocardial infarction when standard leads did not, and identified the presence or absence of posterior injury in patients with inferior infarction.

Clinical significance of terminal QRS abnormalities in the setting of inferior myocardial infarction

To ascertain the clinical relevance of terminal electrocardiographic (ECG) QRS prolongation in the setting of inferior myocardial infarction, 32 patients were studied by radionuclide ventriculography to evaluate regional left ventricular contractility. Of the 32 patients, 16 had evidence of terminal QRS prolongation and notching associated with inferior myocardial infarction, and 16 had isolated ECG evidence of inferior myocardial infarction without terminal QRS prolongation. The regional ejection fraction in the posterolateral and inferoapical regions of patients with terminal conduction delay was lower than those without this conduction delay. This group also demonstrated a lower global ejection fraction than those patients with ECG evidence of inferior myocardial infarction without terminal QRS changes. Terminal QRS abnormalities are important qualitative predictors of left ventricular dysfunction in the setting of inferior myocardial infarction.

Relation of peri-infarction block to ventricular late potentials in patients with inferior wall myocardial infarction

This study explores the relation of the presence of peri-infarction block to ventricular late potentials in patients with inferior wall myocardial infarction (MI). The hypothesis was that both the gross peri-infarction block pattern and subtle low-level ventricular late potentials are expressions of conduction abnormality associated with infarction. The consequent question arose whether peri-infarction block may have the same association with sustained ventricular arrhythmias that has been demonstrated in postinfarction patients with ventricular late potentials. Seventy patients with documented Q-wave MI were divided into those with (23) and those without (47) peri-infarction block. Signal-averaged electrocardiograms were obtained. Analysis of the vectormagnitude complex revealed that the total duration of that complex and the duration of terminal potential under 40 microV in the peri-infarction group exceeded that in the group without peri-infarction block (p less than 0.0001). The voltage in the last 40 ms of the vectormagnitude complex was also significantly less in the peri-infarction group (p less than 0.0005). There were 13 instances of sustained ventricular tachycardia, ventricular fibrillation or sudden death occurring subsequent to infarction not associated with the acute ischemic event, 11 of which occurred in the peri-infarction group. The significantly higher incidence of late potentials along with the significantly higher incidence of sustained ventricular arrhythmias in the peri-infarction block on the surface electrocardiogram may provide another marker for identifying persons at increased risk for these arrhythmias subsequent to MI.

Depolarization changes early in the course of myocardial infarction: significance of changes in the terminal portion of the QRS complex

Studies of patients during variant angina have revealed that there are specific changes in the terminal part of the QRS complex that provide information regarding the location of the ischemia. Extending these studies to acute myocardial infarction, the electrocardiogram (ECG) obtained from 32 patients within 5 h of the onset of chest pain was analyzed to determine if similar inferences could be made. A preinfarction ECG was available from each patient for comparison and 30 patients underwent coronary arteriography within 3 weeks of the infarction. The 10 patients with anterior infarction had a decrease (p less than 0.05) in the S wave in leads V2 (0.80 +/- 0.50 mV) and V3 (0.65 +/- 0.43 mV). In 23 patients with inferior infarction an increase (p less than 0.05) in the R wave of lead III (0.47 +/- 0.35 mV), S wave of lead aVL (0.31 +/- 0.23 mV) and R wave of lead aVF (0.37 +/- 0.30 mV) occurred. A strong positive correlation between the R wave changes in leads III and aVF and the S wave in lead aVL (r = 0.94 and 0.91, respectively) suggests that the R and S wave changes in these leads are expressions of the same phenomenon and indicates that the terminal QRS complex is chiefly affected. Eight of 23 patients with inferior infarction and ST depression in the anterior precordial leads had a normal left anterior descending coronary artery. All had an increase in S wave amplitude in leads V2 and V3. Eight patients had inferior infarction, ST depression in anterior leads and severe lesions in the left anterior descending artery or anterior wall motion abnormalities.(ABSTRACT TRUNCATED AT 250 WORDS)

The degree to which myocardial infarct site and size determine the electrocardiographic axis. Analysis of correlative data by computational modeling

The spatial electrical QRS axis was determined for 428 twelve-lead electrocardiograms from patients subsequently shown by postmortem dissection to have ventricular myocardial fibrosis or necrosis. Four 16-segment ventricular models of the heart were used to "predict" the spatial electrical QRS axis from known ventricular mass and deficit. The raw model I in ideal anatomic position and vectors perpendicularly outward for each muscle segment showed a mean correlation value of -0.494; model II was rotated in the chest to produce best fit with a correlation of 0.638, but the anatomic orientation was not reasonable; model III maintained original position and orientation but the vectors were scaled (correlation 0.780); and model IV, with nonperpendicular vectors, yielded a mean correlation of 0.793. The exceptions to good predictability formed a distinct subset largely composed of electrocardiograms with some form of variant intraventricular conduction (slight QRS widening, fascicular block patterns and "indeterminate frontal-plane axis").

Importance of the terminal portion of the QRS in the electrocardiographic diagnosis of inferior myocardial infarction

The scalar electrocardiograms of 64 patients with inferior wall myocardial infarction (MI) and 87 normal subjects were quantitatively analyzed to determine the respective contributions of the initial and terminal portions of the QRS to the diagnosis of inferior MI. Of the 10 best individual electrocardiographic criteria for inferior MI, 7 were Q-wave criteria and 3 were criteria that consisted of delayed termination of the QRS in leads II or III. Combining the best terminal QRS criterion (the QRS in lead III ending at least 20 ms later than the QRS in lead I) with the 7 best Q-wave criteria and the best Q-wave criterion (Q wave 40 ms or longer in lead aVF) with the 3 best terminal QRS criteria, resulted in criteria with better sensitivities and overall diagnostic performances than those of the individual criteria. Analyzing the vectorcardiograms that were also available in 26 of the patients with inferior MI and 34 of the normal subjects showed that the delayed inscription of the end of the QRS in leads II and III in patients with inferior MI is due to redirection of the terminal forces of ventricular depolarization. The terminal portions of the QRS complexes in the limb leads, considered both alone and in conjunction with traditional measurements of Q waves, contain information that is useful for diagnosing inferior MI.

Rate-dependent variation in the duration of the QRS complex with left anterior fascicular block

The case of a 67-year-old man with combined ischemic and valvular heart disease is presented. Electrocardiographic abnormalities included left anterior fascicular block with a variable duration of the QRS complex. The width of the QRS complex was dependent on the length of the cycle, being broader with short than with long preceding R-R intervals. This is interpreted as a tachycardia-dependent focal block coexisting with a fixed delay in fascicular conduction.

TQ-ST segment mapping: critical review and analysis of current concepts

Controversy and confusion surround many aspects of TQ-ST segment mapping today. Technical standards pertaining to the recording and measurement of the TQ-ST deflection have not been uniformly established nor has the correlative value of the deflection as an indicator of myocardial injury been clearly ascertained. The TQ-ST deflection is believed to originate primarily although not exclusively as a result of extracellular potassium accumulation in the ischemic region and subsequent establishment of a transmembrane potential gradient during diastole and systole at the ischemic boundary. Nonspatial factors (including electrolytes, antiarrhythmic agents, heart rate) influence the TQ-ST deflection by altering this gradient. Spatial factors (including ischemic area and shape, electrode location) alter the relative position of the ischemic boundary to the electrode site and as such can be analyzed with the solid angle theorem. Further study of the complex behavior of the TQ-ST segment deflection, particularly in the presence of pharmacologic intervention, is necessary before mapping techniques can be used reliably in clinical studies designed to quantitate and modify ischemic damage.

Physiopathological and diagnostic hypotheses in peripheral block

Delays and conduction blocks may occur in Purkinje fibers, junctions and muscular cells. Since such blocks may take place everywhere in the ventricles and not only in the free walls, we prefer to use the term peripheral instead of parietal block. The electrophysiologic problems connected with such blocks are discussed. The localization of the ventricle affected by the block is usually simple using VCG recording and is based on the orientation of terminal vectors. It is more difficult to recognize the ventricular walls affected by the block, the intraparietal localization and the source of the block: Purkinje fibers, junctions or muscular fibers. We maintain the concept that peripheral blocks alter not only the terminal phases of ventricular depolarization, but sometimes also the initial ones, in that the Purkinje-junction-muscular fibers system can be damaged in the septum with the major conduction pathways remaining intact. Several discrepancies found between the prescence of electric patterns of septal necrosis and autopsy data may be explained by peripheral blocks localized in the left septum.

Left ventricular parietal block: diagnostic and clinical study

Fifty-five patients with widened QRS complexes due to the presence of slurred S waves or of terminal slurrings on R waves, in more than three leads, with no infarction or bundle branch and fascicular blocks, were studied with the usual clinical examinations as well as vectorcardiographic recording. A parietal block of the left ventricle was diagnosed when, in the presence of a normal development of ventricular depolarization in the initial and middle phases, the terminal QRS loop was delayed, sometimes irregular and displaced leftward and posteriorly. When this delay was directed to the right, the ventricular localization was puzzling. The comparison of the electrocardiographic (ECG) and vectorcardiographic (VCG) data on the terminal part of ventricular depolarization showed some discrepancies and revealed the greater importance of VCG investigation for the study and the localization of parietal blocks. The pathogenesis of such minor conduction disturbances is not yet clear, since the experimental data on the anatomical-functional structures are different: the Purkinje network, Purkinje fiber-muscle junction or common myocardium. In some cases we think it is possible to localize the structure concerned; in any case we can always localize it at the level of the free ventricular wall.

On the relationship between heart weights, fibrosis, and QRS duration

This study analyzed the effects of heart weights, myocardial fibrosis, sex, and body length upon the duration of the QRS complex. A positive correlation was found between presence or absence of fibrosis and duration of the QRS complex. A positive correlation was also found between weights of the heart and QRS duration, but this correlation appeared to be spurious and due to the tendency of fibrosed hearts to be heavier than those with normal myocardium.

Alternation of the Heart

Alteration of the heart occurs whenever any of its tissues, contractile or conductive, fail to function during alternate beats. This results in a diversity of 2:1 conduction blocks with electrical alternation and myocardial blocks that produce alternation of the pulse. In a general way, the more distal blocks, involving bundle branches, arborization, and myocardium are the more ominous, implying serious underlying heart disease. They can occur normally, however, at rapid heart rates.

Another type of alternation involving atrial as well as ventricular waves is sometimes seen in serious pericardial disease with effusion. It is believed to be due to an unusual rotary oscillation of the heart released from its normal inhibitory mediastinal restraints by the surrounding effusion. This is an anatomic rather than a cellular form of alternation and can exhibit other mechanical disorders such as alternating friction sounds.