Borys Surawicz

AHA/ACCF/HRS recommendations for the standardization and interpretation of the electrocardiogram: part III: intraventricular conduction disturbances: a scientific statement from the American Heart Association Electrocardiography and Arrhythmias Committee, Council on Clinical Cardiology; the American College of Cardiology Foundation; and the Heart Rhythm Society: endorsed by the International Society for Computerized Electrocardiology.

The present article introduces the second part of “Recommendations for Standardization and Interpretation of the Electrocardiogram.” The project was initiated by the Council on Clinical Cardiology of the American Heart Association and has been endorsed by the American College of Cardiology

AHA/ACCF/HRS Recommendations for the Standardization and Interpretation of the Electrocardiogram

The present article is the fourth in a series of 6 documents focused on providing current guidelines for the standardization and interpretation of the electrocardiogram (ECG). The project was initiated by the Council on Clinical Cardiology of the American Heart Association. The rationale for this

The Measurement of the Q-T Interval of the Electrocardiogram

The sources of error in determination of the beginning of QRS and the end of T during measurement of the Q-T duration are analyzed. An important error is confusion of an elevated U wave with the T wave, resulting in the diagnosis of a prolonged Q-T. In such cases, some of the precordial leads usually show a notch or kink between T and U which indicates approximately the end of T. If these criteria are used, the true corrected Q-T duration in hypopotassemia without hypocalcemia is not prolonged, but normal or shortened, corresponding to an earlier appearance of the second heart sound.

AHA/ACCF/HRS Recommendations for the Standardization and Interpretation of the Electrocardiogram. Part III: Intraventricular Conduction Disturbances A Scientific Statement From the American Heart Association Electrocardiography and Arrhythmias Committee, Council on Clinical Cardiology; the American College of Cardiology Foundation; and the Heart Rhythm Society

The present article is the fourth in a series of 6 documents focused on providing current guidelines for the standardization and interpretation of the electrocardiogram (ECG). The project was initiated by the Council on Clinical Cardiology of the American Heart Association. The rationale for this project and the process for its implementation were described earlier.1 Abnormalities in the ST segment, T wave, and duration of the QT interval reflect abnormalities in ventricular repolarization. These abnormalities are common and often difficult to interpret. The U wave most likely represents an electricmechanical phenomenon that occurs after repolarization is completed. However, it is frequently included in discussions of repolarization and is discussed in this section. The ST segment corresponds to the plateau phase of the ventricular transmembrane action potential. Under normal conditions, the transmembrane voltage changes slowly during this phase and remains at approximately the same level in all ventricular myocardial cells. As a result, only small voltage gradients are present. This absence of pronounced voltage gradients is similar to that which occurs during electric diastole, ie, from the end of repolarization to the onset of the next depolarization, when ventricular myocardial cells are at their resting transmembrane potential of approximately 85 mV. This corresponds to the TP segment on the ECG. The absence of significant voltage gradients in ventricular myocardial cells during these 2 phases of the cardiac cycle explains why the ST and TP segments are normally nearly flat and at approximately the same level; that is, they are isoelectric. The T wave corresponds to the phase of rapid ventricular repolarization (phase 3) of the ventricular action potential.

Long QT: Good, bad or indifferent?

A survey of current literature suggests an increasing interest in both the desirable and undesirable implications of a prolonged QT interval, the former perceived to be the beneficial effect of antiarrhythmic drugs that prolong the duration of ventricular action potential, and the latter considered to be a potential marker for sudden cardiac death in patients with ischemic heart disease. In addition, there has been an increasing interest in the congenital long QT syndrome associated with an apparent dysfunction of the autonomic nervous system and serious, potentially lethal ventricular arrhythmias. Circumstantial evidence suggests that these arrhythmias are due to increased dispersion of repolarization which may be aggravated by psychologic and emotional perturbations. In this review, the associations between the long QT interval, autonomic nervous system, dispersion of repolarization, antiarrhythmic drugs and ventricular arrhythmias are examined. Attention is directed to the difficulties of accurate QT measurement, problems related to the correction of the QT interval for heart rate and sex (QTc), the wide range of normal values and the modest QT alterations after various manipulations of the autonomic nervous system. Clinical conditions associated with marked, moderate and occasional QT lengthening are listed and discussed briefly in relation to the disturbances of nervous system, dispersion of ventricular repolarization and ventricular arrhythmias. It is proposed that the absence of relevant animal models of neurogenic or psychogenic QT prolongation hinders the investigation of the neurogenic factors associated with QT lengthening. QT prolongation is most often induced by antiarrhythmic drugs and ischemic heart disease. However, it is not known whether the occurrence of torsade de pointes type of ventricular tachycardia in patients treated with antiarrhythmic drugs is related to a critical drug dose or a critical degree of QTc prolongation. There is no conclusive evidence that QT lengthening has any predictive value either during the acute phase or during convalescence after myocardial infarction. Also, a serious deficiency in current knowledge is the lack of an established relation between the prolonged QT interval and the dispersion of ventricular repolarization. It is concluded that the number of unanswered questions discussed in this review still makes it difficult to judge when a prolonged QT interval is good, bad or indifferent.

Task force I: Standardization of terminology and interpretation

The development of a soundly based, widely acceptable uniform terminology for electrocardiographic interpretation is difficult. Physicians frequently disagree about the classification of features in an individual record, and similar disagreements occur in reports generated by different computer programs.‘-1s Some disagreement results from technical error, but the remainder arises from differences in measurement technique, terminology and criteria. Standard rules for measurement, classification and description of electrocardiographic features appear desirable to improve patient care by improving the consistency and quality of the report as well as communication between the interpreter and the user. The standards should be flexible enough to provide for continuing incorporation of improvements in electrocardiographic diagnoses, for classification of features from different populations and for different categories of users. Standards for medical procedures are more readily accepted if they are logical, easily understandable and auth0ritative.l’ However, significant variability in electrocardiographic classification persists even when physicians agree to use identical criteria.44 Imprecise identification of the onset and offset of electrocardiographic deflections is one source of variability in classification procedure, but this type of error can be minimized by proper selection of criteria.lzJs There is no comprehensive list of definitions and criteria designed for the use of electrocardiographic interpreters. The New York Heart Association monograph on nomenclature14 focuses on comprehensive cardiac diagnosis rather than the electrocardiographic report. One of the best known digital coding systems, the Minnesota Code, has precisely defined criteria for classifying electrocardiographic features but is more useful in large scale clinical studies than in the interpretation of routine clinical reports.15J6 Types of interpretive statements: Selecting criteria for each electrocardiographic interpretive statement may be more difficult than selecting terminology. Statements can be divided arbitrarily into three types: (1) Type A refers to an anatomic lesion or pathophysiologic state that can be verified by nonelectrocardiographic evidence; this includes hypertrophy, infarction, ischemia, pulmonary disease and drug and metabolic effects. Selection of optimal criteria for type A statements depends on confirmatory nonelectrocardiographic information, which is limited in many instances at present. (2) Type B refers to an anatomic or functional disturbance that is detectable by the electrocardiogram itself (including special intracardiac leads). Criteria for these statements are based on characteristic features, and pertain mostly to arrhythmias and conduction disturbances. (3) Type C refers to electrocardiographic features that do not fit into type A and B categories. These include electrical axis, nonspecific T wave abnormalities, “premature repolarization,” and unusual voltage. It appears reasonable to define interim standards for types B and C statements at this time, with the understanding that they may be modified by additional information. Selection of criteria: For any type of electrocardiographic statement criteria should be selected with regard to sources of uncertainty that determine the accuracy of the statement; this principle is common to all medical diagnoses. 11~17-21 With respect to electrocardiographic diagnosis, numerous sources of uncertainty include physiologic variations from complex to complex or from day to day, variations in recording equipment or technique, recognition and measurement of the recorded wave forms, morphologic and etiologic classification of electrocardiographic features, and inadequate communication between the interpreter and user of the report.2,22*23 Criteria for classification into different categories should not depend on a difference between measurements resulting from chance variations.zJ4 Borderline regions should be defined on the basis of total precision for both the measurement and the criteria. The definition of pathologic states responsible for the electrocardiographic changes is not necessarily precise. This may complicate establishment of valid criteria. The problem of classifying “microinfarcts” in a correlative study of electrocardiographic criteria is one example of this situation.25 Variations in electrocardiographic measurements associated with age and other constitutional factors make it imperative that all comparisons be made between similar population samples. Collection of data from large samples of healthy and diseased populations

Prevalence of male and female patterns of early ventricular repolarization in the normal ECG of males and females from childhood to old age

OBJECTIVESnThis study was designed to establish the cause of electrocardiographic (ECG) pattern differences between genders.nnnBACKGROUNDnThe male and female patterns of early ventricular repolarization in normal ECGs differ from each other. The male pattern displays a higher J-point amplitude and increased ST angle. The distribution of these patterns between genders has not been studied.nnnMETHODSnNormal ECGs of 529 males and 544 females, age 5 to 96 years, were subdivided into nine age groups in each gender. We designated the pattern as female if the J point was <0.1 mV in each of the leads V(1) to V(4), and as male if the J point was > or =0.1 mV and the ST angle > or =20 degrees in at least one of the V(1) to V(4) leads; the pattern was indeterminate if the J point was > or =0.1 mV and the ST angle was <20 degrees.nnnRESULTSnDistribution of patterns was significantly different between genders (p < 0.001). In females, the patterns were distributed similarly from puberty to advanced age with about 80% prevalence of the female pattern. In males, the male pattern prevalence increased at puberty, reached 91% in the age group of 17 to 24 years and declined gradually with advancing age to 14% in the oldest males. The prevalence of indeterminate pattern was about 10% in both genders. Patterns were unchanged in 95% of 493 subjects who had ECGs recorded at separate times or at different heart rates.nnnCONCLUSIONSnGender differences in early ventricular repolarization were caused by age-dependent changes in prevalence of the male pattern.

The electrocardiographic pattern of hypopotassemia with and without hypocalcemia.

Detailed analysis of the electrocardiogram in patients with hypopotassemia without hypocalcemia showed that the Q-U interval and its components (Q-oT, Q-aT, Q-T, and Q-aU) have essentially the same duration as in normal subjects for the same heart rate and sex. The typical hypopotassemia pattern is characterized by progressive depression of S-T, lowering and inversion of T and increase of U in left precordial leads. In hypopotassemia with hypocalcemia S-T and Q-T, but not Q-U, are prolonged, causing an increased degree of merging between T and U. Three methods of differentiation between completely merged T and U waves and true T waves of long Q-T duration are given.

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.

The duration of the Q-U interval and its components in electrocardiograms of normal persons☆

Abstract 1. 1. In fifty normal men and fifty normal women the synchronous standard limb and precordial leads as well as the heart sounds were registered at rest. The following intervals were measured: the intervals from the beginning of the QRS complex to the end of this complex (QRS), to the origin of the T wave (Q-oT), to the apex of the T wave (Q-aT) to the end of the T wave (Q-T), to the “halfway point of T” (Q-T/2), to the apex of the U wave (Q-aU), and to the end of the U wave (Q-U). The origin of the T wave or the end of the RS-T segment was defined as the point most distant from a straight line connecting the RS-T junction with the apex of T. The relation of the beginning of the second heart sound to the apex and end of T and to the apex of U was also studied. All values were correlated with the heart rate and the age and sex, and in some cases also with the body height. 2. 2. The QRS duration, when measured from the earliest to the latest points in synchronous leads, is greater than when measured in separate limb leads. It increases slightly with decreasing heart rate but shows the greates relation to the body size. Men have a greater QRS duration than women, but in the same height groups the values were equal for both sexes. The upper limit for a height up to 5 feet 6 inches was 0.10 second, that for a height from 5 feet 6 inches to 6 feet was 0.11 second, and that for a height from 6 feet to 6 feet 6 inches was 0.12 second. Of nine persons over 6 feet tall, seven had a QRS exceeding 0.11 second. 3. 3. The Q-T duration increases with decreasing heart rate; at all heart rates women had on the average a 7 per cent longer Q-T duration than men. The components of Q-T (Q-oT and Q-aT) showed the same dependence on the heart rate as the entire Q-T interval. When expressed as a percentage of the Q-T interval expected for the heart rate, Q-oT ranged between 49 and 63 per cent, while Q-aT ranged between 62 and 92 per cent, independently of the heart rate and sex. Of all the components of Q-T, the RS-T segment was the most elastic, showing the greatest differences between the sexes and at high and low heart rates. QRS was the most rigid component. 4. 4. The interval from the end of T to the apex of U was practically independent of the heart rate and sex; it averaged 0.10 second. The Q-aU interval expected for a certain heart rate can be easily determined, therefore, by adding 0.10 second to the Q-T interval expected for this rate. The interval from the apex to the end of U was influenced by the heart rate more than any other interval, but as the determination of the end of U especially at high heart rates was difficult, this observation should be interpreted with caution. 5. 5. The second heart sound began within 0.03 second before or after the end of the T wave, 0.06 to 0.12 after the apex of T and 0.04 to 0.14 second before the apex of the U wave. At lower heart rates it tended to begin up to 0.01 second earlier. 6. 6. The electrocardiogram of women is characterized not only by a longer duration of Q-T and its components Q-oT and Q-aT but also by a longer and more horizontal RS-T segment than that of men. The point when the T wave reaches one-half of its final amplitude is situated nearer to the apex of T in women than in men. These characteristics make it possible, in most normal cases, to distinguish the electrocardiogram of a woman from that of a man.