Clinical vectorcardiography in adults. Part 2

Emergency vectorcardiographic study of acute aortic dissection

There has been no report in the literature of emergency vectorcardiographic study in patients with acute aortic dissection. A total of 135 consecutive patients with suspected coronary artery disease was studied. On admission to the intensive-care unit through the emergency service, each patient was given electrocardiographic and vectorcardiographic examinations, which were repeated at intervals of 24 hours. Fourteen patients (9 type I, 2 type II, and 3 type III according to DeBakey's classification) had acute aortic dissection indicated by clinical symptoms and proven by angiography. The electrocardiograms all revealed abnormal T-wave inversion in limb or precordial leads except 3 patients. Nine (64%) of the 14 patients had abnormal length/width (L/W) ratios of the T-loop in 2 planes of the emergency vectorcardiogram. Two (22%) among these 9 patients died of ventricular tachyarrhythmia. The inscription direction of the T-loop showed abnormality in 4 (29%) of the 14 patients; 2 (50%) among these 4 patients died of ventricular tachyarrhythmia. The de novo occurrence of sustained ventricular tachyarrhythmia after emergency cardiac surgery in patients with acute aortic dissection has been documented in this report. Furthermore, patients with acute aortic dissection who have (1) an abnormal sense of inscription direction of the T-loop in at least 1 of either the horizontal or left sagittal plane, and (2) an abnormal L/W ratio in at least 2 planes in the preoperational emergency vectorcardiogram, have altered ventricular repolarization and thus are at high risk of postoperationally unexpected ventricular tachyarrhythmia. This information is not available from the electrocardiogram.

Spatial vectorcardiogram in acute inferior wall myocardial infarction: its utility in identification of patients prone to complete heart block

Spatial vectorcardiography was performed in 28 (22 males, 6 females; age 36-78 years) consecutive cases of acute inferior wall myocardial infarction during sinus rhythm within 24 hours of admission. Orthogonal leads using the corrected Frank lead system were recorded at a paper speed of 100 mm/sec. Qualitative analysis consisted of study of QRS loop inscription in all 3 orthogonal planes. Additional quantitative analysis using the spherical coordinate system was undertaken to measure the magnitude and angular direction (azimuth and elevation angle) of spatial R maximum cardiac vector. During the hospital course, 15 patients developed transient complete heart block and 13 patients did not. The direction of the QRS loop inscription in the 3 planes did not differ between the two groups. The spatial R maximum magnitude and azimuth angle did not differ between the patients who developed complete heart block and those who did not. Values for elevation angle were markedly different between the two groups. The spatial R maximum elevation angle ranged from 0 to -35 degrees and was negative (superiorly directed) in 14 of the 15 patients with complete heart block, whereas it ranged from -10 degrees to +/- 75 degrees and was negative (superiorly directed) in only 2 of the 13 patients without this complication. Thus it appears that negative elevation angle of spatial R maximum cardiac vector in patients with inferior wall myocardial infarction may indicate proneness to complete heart block.

When is the vectorcardiogram superior to the scalar electrocardiogram?

The clinical usefulness of the vectorcardiogram is well documented by the numerous reports published in the last 3 decades. It has been found more reliable than the electrocardiogram for the diagnosis of atrial enlargement and right ventricular hypertrophy. It is more sensitive than the electrocardiogram in the recognition of myocardial infarction, especially if the infarction is inferior or if it occurs in the presence of left bundle branch block or left anterior hemiblock. It is helpful in the diagnosis of ventricular pre-excitation and in the localization of the bypass tract. Some repolarization abnormalities are more clearly demonstrated by the vector display. However, some information, such as that on cardiac chamber size and myocardial damage, can also be obtained by other noninvasive tests that are often performed on the same patients. With the increasing awareness of cost-effectiveness of various laboratory procedures in medicine, the vectorcardiogram should no longer be considered a routine cardiac test and should be requested only for a specific clinical purpose. When properly utilized, vectorcardiography should remain a valuable diagnostic as well as teaching tool.

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.

Improved electrocardiographic criteria for the diagnosis of left anterior hemiblock

New electrocardiographic (ECG) criteria for the diagnosis of left anterior hemiblock are proposed. The proposed criteria are based upon the relation between portions of the vectorcardiographic (VCG) QRS loop in the frontal plane and the corresponding portions of the ECG QRS complexes recorded by the limb leads. The application of the proposed criteria requires that the tracings be obtained with 3-channel ECG machines so that the temporal relation between the QRS complexes in simultaneously recorded limb leads can be inspected. This type of analysis of the electrocardiogram permits prediction of features of the VCG QRS loop that are important for the diagnosis of left anterior hemiblock. The proposed ECG criteria for the diagnosis of left anterior hemiblock are (1) the QRS complexes in leads aVR and aVL each end in an R wave (terminal R wave), and (2) the peak of the terminal R wave in lead aVR occurs later than the peak of the terminal R wave in lead aVL. The sensitivity and specificity of the proposed criteria were empirically evaluated using series of electrocardiograms obtained under clinical circumstances during which the occurrence of left anterior hemiblock was, respectively, likely and unlikely. The performance of the proposed criteria was statistically superior to that of 2 sets of frontal plane QRS axis criteria.