The precordial lead in 104 normal adults

For the precordial lead the right arm electrode is placed on the anterior chest, just to the left of the sternum about the level of the apex, and the second electrode is on the left leg. The record is then taken as one usually derives Lead II of the standard electrocardiogram. This method is simpler than that of placing one electrode on the front and the other on the back of the chest.A simple glass electrode is described for obtaining precordial leads.It is suggested that the electrodes of the precordial lead be reversed so that P, R and T will be positive and only S inverted, just as they are in the standard electrocardiogram of normal adults.The precordial chest lead in 104 normal individuals is summarized. In this series the P-wave is shown to be negative, is not more than ?1.5 mm. and is usually followed by an end deflection above the isoelectric level. The P-Q interval averages 0.15 second. The QRS group is always diphasic, and never notched or slurred. Its duration is 0.09 second. The absence of the Q-wave or of the R-wave is definitely abnormal. The Q-wave averages ?5.3 mm. in size and the R-wave, +10.7 mm. No Q-wave less than ?1.5 mm. and no R-wave less than +2.5 mm. in size was ever observed. The R-T transition is below the isoelectric level, occasionally just isoelectric. A positive R-T transition or one that is more than 2 mm. below the isoelectric is definitely abnormal. The T-waves are always inverted and usually are less than ?6.0 mm. in size.The precordial lead may prove of service in interpreting which T-wave inversions of the third lead are abnormal.Left ventricular preponderance in the standard electrocardiogram of normal adults does not change the form of the precordial lead.     

History of precordial leads in electrocardiography.

Precordial leads were first used by Waller, whose capillary electroscope was too insensitive to detect the electric forces emanating from the human heart unless the electrode was placed over the precordium as near to the heart as possible. When Einthoven developed the elegant, reliable and sensitive string galvanometer, he could record the electric forces of the heart from the hands and feet of the subject without even undressing him. When Einthoven's great galvanometer became available, only the three standard limb leads were used. Thomas Lewis and others experimented with precordial direct leads and made many important discoveries in electrocardiography and cardiology. Wolferth and Wood, in 1932, introduced the first precordial lead in clinical, diagnostic cardiology. The recordings were 'upside-down', i.e. positive deflections were down and negative ones up. They called this the 4th lead (lead IV). The precordial electrode was placed on the chest over the apex of the heart, regardless of where the apex was located. This immediately opened new avenues of study in infarction, ventricular hypertrophy, bundle branch block, and all other cardiac states. Then CL, CR, CF, CB and V leads were introduced. The points considered best for placing the 'exploring' or precordial electrode became an issue, and much confusion prevailed until Wilson and his associates developed the central or isopotential terminal and until the American Heart Association and the Heart Society of Britain and Ireland met in London and published the standards for recording precordial leads in 1938. There followed, for obvious reasons, a slow settling of the confusion until the V1 through V6 precordial leads became standard procedure all over the world, as exists today. Goldberger introduced the augmented unipolar limb leads (aVR, aVL and aVF) which have resulted in the standard 12-lead electrocardiogram of routine use today. No one would consider an electrocardiographic evaluation adequate in a cardiac study at present unless the 12-lead ECG were recorded.     

Congenital dextrocardia complicated by hypertension,coronary artery disease and myocardial infarction

The case record of a seventy-three year old man with congenital dextrocardia and situs inversus viscerum complicated by hypertension, coronary artery disease and myocardial infarction is presented. Electrocardiographic recordings of the limb leads, with and without reversal of the arm lead wires, and of the precordial leads of the V series derived from both right and left chest areas are presented. In this instance the electrocardiographic findings in precordial leads taken over the right chest point to fresh anteroseptal infarction; those leads recorded from the left chest were not informative. This serves to emphasize the fact that precordial leads should be recorded from the right side of the chest rather than the left in order that the exploring precordial electrode may overlie the area of cardiac damage, and thus manifest maximal changes in the electrocardiogram. We agree that the electrocardiogram may best be interpreted by application of the usual criteria to the limb leads taken with the arm lead wires reversed although in this case the limb leads yielded no information of diagnostic significance.     

Lack of benefit of an active pectoral pulse generator on atrial defibrillation thresholds

INTRODUCTION: Atrial defibrillation can be achieved with standard implantable cardioverter defibrillator leads, which has led to the development of combined atrial and ventricular devices. For ventricular defibrillation, use of an active pectoral electrode (active can) in the shocking pathway markedly reduces defibrillation thresholds (DFTs). However, the effect of an active pectoral can on atrial defibrillation is unknown. METHODS AND RESULTS: This study was a prospective, randomized, paired comparison of two shock configurations on atrial DFTs in 33 patients. The lead system evaluated was a dual-coil transvenous defibrillation lead with a left pectoral pulse generator emulator. Shocks were delivered either between the right ventricular coil and proximal atrial coil (lead) or between the right ventricular coil and an active can in common with the atrial coil (active can). Delivered energy at DFT was 4.2 +/- 4.1 J in the lead configuration and 5.0 +/- 3.7 J in the active can configuration (P = NS). Peak current was 32% higher with an active can (P < 0.01), whereas shock impedance was 18% lower (P < 0.001). Moreover, a low threshold (< or = 3 J) was observed in 61% of subjects in the lead configuration but in only 36% in the active can configuration (P < 0.05). There were no clinical predictors of the atrial DFT. CONCLUSION: These results indicate that low atrial DFTs can be achieved using a transvenous ventricular defibrillation lead. Because no benefit was observed with the use of an active pectoral electrode for atrial defibrillation, programmable shock vectors may be useful for dual-chamber implantable cardioverter defibrillators.     

Optimum bedside cardiac monitoring

Correct electrode placement is critical to obtaining accurate information from any monitoring lead. The choice of lead should be based on the goals of monitoring for a specific patient population and on the individual patient's clinical situation. When using a 5-wire monitoring cable, arm electrodes should be placed on the shoulders; leg electrodes, on the lower thorax or hip area; and the chest electrode, in the desired V lead position. When using a 3-wire system, lead placement depends on which lead is desired for monitoring. If arrhythmia diagnosis is the goal of monitoring, lead V1 is the best lead; lead V6 is the next best lead. If ST segment monitoring for ischemia or reocclusion following percutaneous coronary interventions is the goal, the best lead depends on the coronary artery involved. Multiple lead monitoring is superior to single lead monitoring. If two leads are available, V1 and lead III or aVF (or a limb lead with maximal ST segment displacement) are good choices. If three leads are available, leads V1, III, and aVF are the best choices. Continuous 12-lead monitoring is available and offers several advantages.     

Clinical predictors of atrial defibrillation thresholds with a dual-coil, active pectoral lead system.

OBJECTIVES: The purpose of this study was to identify clinical predictors of atrial defibrillation thresholds (DFTs) with standard implantable cardioverter-defibrillator (ICD) leads. BACKGROUND: Atrial defibrillation can be achieved with active pectoral, dual-coil transvenous ICD lead systems. If clinical predictors of atrial defibrillation efficacy with these lead systems were identified, they could be used to predict which patients may require more complex lead systems for atrial defibrillation, such as a coronary sinus electrode. METHODS: This was a prospective study of 135 consecutive patients undergoing initial ICD implant for standard indications. The lead system evaluated was a transvenous defibrillation lead with coils in the superior vena cava (SVC) and right ventricular apex (RV), and a left pectoral pulse generator emulator (CAN). The shocking pathway was RV-->SVC+CAN. Atrial DFT was measured using a step-up protocol. Clinical and echocardiographic parameters were evaluated as predictors of atrial DFT and multiple linear regression was performed. RESULTS: Mean atrial DFT was 4.6 +/- 3.8 J. Atrial DFT was < or =3 J in 70 patients (52%) and < or = 10 J in 97% of patients. The highest atrial DFT was 20 J (one patient). Left atrial size (r = 0.21, P = .01) and left ventricular end-diastolic diameter (r = 0.19, P = .02) were independent predictors of atrial DFT. However, these two predictors accounted for only 6% of the variability in atrial DFT. CONCLUSIONS: Clinical parameters are of limited use in predicting atrial DFT with a dual-coil, active pectoral ICD lead system. Because the RV--> SVC + CAN shocking pathway provides reliable atrial and ventricular defibrillation, this configuration should be preferred for combined atrial and ventricular ICDs.     

How many ECG leads do we need?

The number of leads needed in clinical electrocardiography depends on the clinical problem to be solved. The standard 12-lead ECG is so well established that alternative lead systems must prove their advantage through well-conducted clinical studies to achieve clinical acceptance. Certain additional leads seem to add valuable information in specific patient groups. The use of a large number of leads (eg, in body surface potential mapping) may add clinically relevant information, but it is cumbersome and its clinical advantage is yet to be proven. Reduced lead sets emulate the 12-lead ECG reasonably well and are especially advantageous in emergency situations.     

Evaluation of the ECG recording in abnormal positions of the heart in the thorax

Abnormal localization of the heart in the chest is a rare congenital developmental disorder (1,10). Even if the heart is in these instances normally developed, its abnormal position leads in case of its affection by disease to diagnostic and therapeutic difficulties, in particular when an invasive procedure must be used. With regard to the entirely different position of individual cardiac departments it is necessary to differentiate carefully between dextrocardia and dextroversion (15). Dextroposition is only a marginal problem. A very satisfactory diagnostic method in these anomalies is the ECG tracing, where we encounter quite typical pictures. Dextrocardia and dextroversion are characterized by a similar mirror image reversed tracing in the leads from the extremities. It differs, however, fundamentally in the chest lead tracings. In dextrocardia during tracing of standard thoracic leads we follow the predominant negative QRS complex in all leads; when including the dextrolateral thoracic leads the curve "becomes normal". In dextroversion, with regard to the anterior position of the left ventricle the dominating finding is a high R wave in all leads from the left and right side of the chest.     

Precordial electrocardiographic mapping after exercise in the diagnosis of coronary artery disease.

A technique is described for recording the precordial electrocardiographic body surface map before and after exercise. The technique provides an extra dimension to the conventional exercise electrocardiogram because a measurement can be made of the area and severity of S-T segment changes that are projected onto the front of the chest. Sixteen lead isopotential surface maps were recorded before and after exercise in 109 patients with angina who subsequently underwent coronary arteriography. In addition, exercise electrocardiograms were obtained in 53 of these patients using three orthogonal leads and in all patients using a single chest unipolar chest lead. Precordial surface mapping after exercise was found to have a greater sensitivity (95 percent) than electrocardiography using either the orthogonal leads (68 percent) or a single chest lead (64 percent) (P less than 0.01). The specificity of the three techniques did not differ significantly (P greater than 0.05). The technique of precordial surface mapping after exercise improves the ability to diagnose coronary artery disease and can easily be applied to clinical practice.     

A self-retaining skin contact electrode for chest leads in electrocardiography

A new skin contact electrode for electrocardiographic work is presented. This electrode is of small surface, completely insulated, of low resistance and is self-retaining. It is hoped that it will facilitate in particular the study of chest leads in electrocardiography.     

Effects of limb electrode placement on the 12- and 16-lead electrocardiogram

The effects of three common limb electrode placement configurations on ECG signal morphology were examined, including the standard electrode placement of the electrodes on the extremities, the Mason-Likar placement, and the Lund placement. A non-traditional asymmetric configuration of placing the LA electrode on the upper arm with the RA electrode on the torso (below the clavicle) was also investigated. A series of 16-lead ECGs were acquired from 150 subjects representing a broad range of diseases. Effects of the limb electrode placement on axis measurements, QRS amplitudes, ST levels, and infarctions were studied. On average, the P, QRS, and T axes all exhibited rightward shifts as the electrodes were moved away from the extremities, but more generally, the axis became more vertical, with the largest shifts occurring when the standard ECG axis measurement was close to 0 degrees and tending to exhibit leftward shifts for ECGs with a standard axis measurement between 0 and –90 degrees. Voltage changes were consistent with axis shifts in the frontal plane (decreased lateral and increased inferior lead voltages), with the largest mean change a reduction in R wave amplitude of lead I going from the standard to the Mason-Likar configuration. In the precordial leads, Q and/or S magnitudes decreased in right-sided leads (V4r, V1, V2, V3) and R magnitudes increased in lateral leads (V3 – V9) as the arm electrodes moved toward the trunk, suggesting a posterior shift in the mean QRS axis. ST deviations in the lateral and posterior precordial leads tended to be mimicked in lead III when the electrodes were moved from the extremities to the torso. Over half (13 of 25) of the ECGs exhibiting criteria for inferior infarct in the standard configuration had that criteria erased when the electrodes were moved to the Mason-Likar positions. The largest single effect on the ECG resulted from moving the LA electrode from the shoulder to the clavicle. The asymmetric configuration with the RA electrode on the torso and the LA electrode on the upper arm may offer some compromise between noise and faithfulness to the standard configuration in noisy environments such as exercise testing or monitoring.     

Evaluation of 3 chest leads CM5, CC5, and CL5 and factors which influence the results

In recent few years, many authors had discussed the possibilities of using bipolar precordial leads to replace lead V5 in diagnosing anterior wall myocardial ischemia. But there still remains some problems to be solved: (1) Are there any difference between bipolar precordial leads and lead V5 in wave forms? (2) What kind of factors influence the ST deviation? 36 patients were studied by comparing unipolar lead V5 with respect to three different bipolar chest leads CM5, CC5, CL5 both in lying and sitting positions. We found that: (1) The differences is least significant between bipolar CC5 and lead V5 while it is most significant between bipolar lead CM5 and lead V5. (2) The deviation of ST segment in bipolar leads is affected both by potential at negative electrode as well as potential at positive electrode. Statistical analysis revealed that ST segment is positively related to the potential on positive electrode and negatively related to the potential on negative electrode. For this reason, therefore, in the view point of most comparable ST deviation with lead V5 for monitoring of myocardial ischemia, it is advisable to locate the negative electrode at the site on chest with least potential. Usually we place the negative electrode on V6R to compose a bipolar lead CC5.     

Role of Echocardiography in the Emergency Department for Identifying Patients with Myocardial Infarction and Ischemia

Echocardiography is a valuable, noninvasive diagnostic tool that can provide information on systolic function and valvular abnormalities and can provide alternative explanations for causes of chest pain. Experimental as well as clinical studies have shown that wall motion abnormalities have a high sensitivity for predicting myocardial infarction. More recent studies, performed in the emergency department on patients evaluated for myocardial ischemia, have reported similar results. An important aspect is that necrosis is not necessary to cause wall motion abnormalities; therefore, echocardiography can also be used to identify patients with ischemia without infarction. Importantly, sensitivity is significantly higher than that for electrocardiography and is comparable to that for myocardial perfusion imaging. Newer developments, such as digital transmission over telephone lines, may lead to more widespread routine use in the emergency department. Acute emergency department echocardiography appears to be a promising tool when used in the evaluation of patients with chest pain.     

常规导联及头胸导联心电图与核素显像对急性下壁心肌梗死诊断的比较

目的：观察心电图与核素显像对急性下壁心肌梗死（AIMI）定位诊断的价值。方法：以90例冠状动脉造影的资料（其中AIMI患者50例,正常人40例）为标准,与同步记录的常规导联心电图,头胸导联心电图,和核素显像检测的结果进行比较。结果：对AIMI诊断,常规导联心电图的准确率为84.4%,敏感性为86.0%,特异性为82.5%;头胸导联心电图的诊断准确率为97.8%、敏感性为96.0%,特异性为100.0%;核素显像的诊断准确率为94.4%、敏感性为92.0%,特异性为97.5%。头胸导联心电图诊断AIMI的准确率、敏感性和和特异性均明显高于常规导联心电图（P〈0.05）,且高于核素显像但差异无显著性（P〉0.05）。结论：对于急性下壁心肌梗死的定位诊断头胸导联心电图准确率、敏感性和和特异性好于常规心电图,与核素显像无显著差异,但检测方便,有推广价值。     

Computer-aided electrocardiography

The three principal forms of medical electrocardiography are the standard 12 lead electrocardiogram (ECG), the exercise ECG and the long-term ambulatory ECG. The volume of use of the 12 lead ECG is 10 to 20 times greater than that of the exercise test or the ambulatory test, and it has received correspondingly more developmental and marketing attention. A great increase in the rate of adoption of computerized electrocardiography was brought about when large scale integration of computer hardware made it possible to place the entire computational package within a standard-sized ECG cart. Exercise ECG testing involves processing a data sample minutes in duration. Only a very few diagnostic possibilities are examined; emphasis is on measurements of the ST segment and on non-ECG observations. Ambulatory electrocardiography currently involves only one or two ECG leads and these are tested for only a few diagnostic possibilities; however, duration of the data sample is relatively long, usually 24 hours. Computer processing involves examination of about 100,000 cardiac cycles for RR interval, QRS shape and ST segment deviation.     

Superiority of a vertical sternal lead for detection of arrhythmias during ambulatory electrocardiographic monitoring.

In a preliminary study comparing 7 sets of bipolar leads with standard modified V1 and V5 leads, a vertical sternal lead system with the negative lead just below the suprasternal notch, and the positive lead over the xiphoid had the greatest P-wave area. In the current study, the vertical sternal and modified V1 leads were obtained simultaneously using 2-channel ambulatory electrocardiographic recorders in 50 consecutive patients undergoing diagnostic ambulatory electrocardiography for suspected arrhythmias. The vertical sternal lead provided tracings with a larger P-wave area compared with that of the modified V1 (0.58 +/- 0.44 vs 1.23 +/- 0.69 mm2; p less than 0.0001), and a greater QRS complex (9.23 +/- 4.16 vs 11.78 +/- 4.90 mm; p = 0.006). During premature atrial contractions and supraventricular tachycardia, P-wave visibility was significantly better in the sternal lead than in V1 (p less than 0.001). Furthermore, sternal lead tracings were superior with regard to overall quality and noise level. It is suggested that the vertical sternal lead replace the currently used modified V1 during ambulatory electrocardiographic monitoring. This lead system in conjunction with the standard modified V5 lead should be useful in the differential diagnosis of atrial arrhythmias.     

Toward the optimal lead system and optimal criteria for exercise electrocardiography

To define the optimal lead system for exercise electrocardiography, data of the whole body surface potential distribution were analyzed in 25 normal subjects and in 25 patients with coronary artery disease at rest and during exercise. All patients had a normal electrocardiogram at rest. The sensitivity of the standard chest leads was 60 percent; it improved to 84 percent with the body surface map whereas both methods had a 100 percent specificity. On the basis of these data, and reports from other centers, it is concluded that a single bipolar lead from the right subclavian area to lead V₅ is adequate in those laboratories that are restricted to testing subjects with a normal electrocardiogram at rest. In patients with a previous infarction or other abnormalities in the electrocardiogram at rest three (pseudo) orthogonal leads or several standard leads are necessary.

Recommendations for optimal measurements from the exercise electrocardiogram are based on quantitative computer analysis of selected leads in larger groups of patients. Best results were obtained with a combination of S-T amplitude, S-T slope and heart rate. The improvement in sensitivity from 50 percent with visual analysis to 85 percent with computer was similar to that obtained with body surface mapping. Changes of the P wave and QRS complex during exercise appeared to be of little diagnostic value. The pathophysiologic mechanisms that contribute to the changes of the electrocardiogram during exercise are discussed.     

The Utility of a Lewis Lead for Distinguishing Atrioventricular Reentrant Tachycardia from Typical Atrioventricular Nodal Reentrant Tachycardia

Objective The Lewis lead configuration is an alternative bipolar chest lead and it can help detect atrial activity. The utility of the Lewis lead to distinguish orthodromic atrioventricular reentrant tachycardia (AVRT) from typical atrioventricular nodal reentrant tachycardia (AVNRT) by visualizing the apparent retrogradely conducted P waves was investigated. Methods Forty-four patients with paroxysmal supraventricular tachycardia (PSVT) were included in this study. All patients had PSVT documented by an electrocardiogram (ECG) and underwent an electrophysiological study (EPS). During tachycardia, an ECG recording was performed using a Lewis lead with the electrode on the right aspect of the sternum at the second intercostal space instead of the right arm and the electrode on the fourth intercostal space instead of the left arm. The ECG parameters during tachycardia were compared between AVRT and AVNRT. Results Fourteen patients were diagnosed with AVRTs and 30 with typical AVNRTs on EPS. The positive P wave could be seen in the Lewis lead configuration in 9 of 14 patients with AVRTs and 21 of 30 patients with AVNRTs. P waves were more often visible in the Lewis lead configuration than in the standard leads (66% vs. 45%). The RP interval was significantly longer for AVRTs than for AVNRTs (88±17 vs. 154±34 ms, p<0.001), which yields 89% sensitivity and 71% specificity for distinguishing these 2 tachyarrhythmias with a cut-off point of 100 ms. Conclusion A Lewis lead configuration may help to make an accurate diagnosis among the reentrant supraventricular tachycardias prior to procedures, owing to its ability to locate P waves.     

Chest‐lead ST‐J amplitudes using arm electrodes as reference instead of the Wilson central terminal in smartphone ECG applications: Influence on ST‐elevation myocardial infarction criteria fulfillment

Background

“Smartphone 12‐lead ECG” for the assessment of acute myocardial ischemia has recently been introduced. In the smartphone 12‐lead ECG either the right or the left arm can be used as reference for the chest electrodes instead of the Wilson central terminal. These leads are labeled “CR leads” or “CL leads.” We aimed to compare chest‐lead ST‐J amplitudes, using either CR or CL leads, to those present in the conventional 12‐lead ECG, and to determine sensitivity and specificity for the diagnosis of STEMI for CR and CL leads.

Methods

Five hundred patients (74 patients with ST elevation myocardial infarction (STEMI), 66 patients with nonischemic ST deviation and 360 controls) were included. Smartphone 12‐lead ECG chest‐lead ST‐J amplitudes were calculated for both CR and CL leads.

Results

ST‐J amplitudes were 9.1 ± 29 μV larger for CR leads and 7.7 ± 42 μV larger for CL leads than for conventional chest leads (V leads). Sensitivity and specificity were 94% and 95% for CR leads and 81% and 97% for CL leads when fulfillment of STEMI criteria in V leads was used as reference. In ischemic patients who met STEMI criteria in V leads, but not in limb leads, STEMI criteria were met with CR or CL leads in 91%.

Conclusion

By the use of CR or CL leads, smartphone 12‐lead ECG results in slightly lower sensitivity in STEMI detection. Therefore, the adjustment of STEMI criteria may be needed before application in clinical practice.     

Electrocardiographic estimate of peak systolic pressure gradient in children with aortic stenosis

In children with congenital aortic stenosis a modified mapping system was created to explore the electrocardiographic potentials on the chest surface from the left sternal edge (direct anterior), left axillary line (direct lateral) and midchest (45 degrees anterior to the lateral lead) in the third through the seventh intercostal spaces. Potentials were normalized according to chest size based on elliptical and cylindrical models of the chest with the heart at the center. The unadjusted and adjusted potentials were correlated with the peak systolic gradients across the left ventricular outflow tract and equations to predict the gradients were derived by stepwise multiple regression analysis. The best equation was: Gradient = -15.0 +(3.845 X MCT 4) +(0.474 X CD X LSS 3) + (0.138 X CD X MCS 3) where MCT 4 = T wave amplitude in the lead in the fourth interspace in the midclavicular line CD = AP chest diameter in cm LSS 3 = S wave amplitude in the lead in the third interspace at the left sternal border MCS 3 = S wave amplitude in the lead in the third interspace in the midclavicular line (R = 0.84, SEE = 24.3) There are areas on the chest surface that are unexplored by standard electrocardiography. The electrocardiographic potentials from these areas, when normalized for chest size, yield better estimates of transaortic gradients than previous estimates from the routine electrocardiogram.