EKG Lead Placement ================== On Thu, 9 May 1996, Stephen A. Mitchell wrote: >........ > I was taught that the precordial leads are placed as follows: > Lead V1: at 4th intercostal space just right of the sternum > Lead V2: at 4th intercostal space just left of the sternum > Lead V3: midway between V4 and V4 on top of the 5th rib > Lead V4: midclavicular line in the 5th intercostal space > Lead V5: anterior axillary line at the same level as V4 > Lead V6: midaxillary line at the same level as V4 > > The hospital's ED staff diagrams showing the above placements, but the > actual placements used by the staff is as follows: > Lead V1: at 2nd intercostal space just right of the sternum > Lead V2: at 2nd intercostal space just left of the sternum > Lead V3: at 5th intercostal space just left of the sternum > Lead V4: midclavicular line in the 5th intercostal space > Lead V5: anterior axillary line at the same level as V4 > Lead V6: midaxillary line at the same level as V4 > The 6 limb leads, of course, are not affected by the positioning of the unipolar chest leads, so those will be identical in both cases. Leads V3 through V6 likewise are essentially identical above and so will look the same. Only V1 and V2 are positioned differently. The original idea behind the chest leads is that, by cancelling out the limb leads the unipolar electrode will more acurately reflect the depolarization of the myocardium immediately adjacent to the lead. Nevertheless, in reality, they all reflect total myocardial depolarization with, perhaps,a slight disproportionate contribution from the myocardium underlying the electrode. A study done recently positioning V1 at the right 2nd ICS found significant changes in QRS and T wave morphology. Whether the diagnosis of acute ateroseptal MI would be obscured by this change is open to question. Most studies have been done by modifying limb lead positions from the conventional limb to truncal locations. It is clear that QRS morphology is affected by this, however, the effect on ST segment changes appears minimal (2). The bottom line is that modifying the position of V1 and V2 as you indicate would not affect the diagmosis of inferior, high lateral, or extensive anterior MI. It might, conceivably, affect the diagnosis of anteroseptal or posterior wall MI in a few cases, however, by altering the magnitude of the ST segment above or below the 0.2 mV criteria. H. Louzon MD (1) Koehler NR [Changes in electrocardiogram in V1 by precordial electrode malposition] Arq Bras Cardiol 1993 Aug;61(2):99-101 PURPOSE--To evaluate changes in the electrocardiogram (ECG) with incorrect positioning of the chest lead for V1, placed in the second and third right intercostal spaces. METHODS--Two hundred and five patients were studied after a conventional ECG, with the record of tracings where the chest electrode for V1 was placed at the second and third right intercostal spaces at the right sternal border. These tracings were then compared with the former one and changes observed in the P wave, QRS complex and T wave registered and submitted to statistical analysis. Patients age ranged from 6 to 89 years, mean 46. Whites comprised 79%, black 6% and mulattos 15%. Women totalized 62% and men 38% of the sample. Clinical diagnosis were arterial hypertension (50%), no apparent cardiac disease (41%), coronary atherosclerotic heart disease (4%), mitral valve prolapse and other organic heart disease (5%). RESULTS--Negativation or accentuation of negative terminal forces of P wave were present in 84% of the patients, alterations in the QRS complex in 75% of the cases, and in the T wave in 66% of the cases, with confidence intervals of 0.7898 to 0.8901; 0.6907 to 0.8092; and 0.6163 to 0.7437, respectively. CONCLUSION--Important changes in the ECG record may occur with high probability if the chest electrode for lead V1 is placed above the standard place. (2) Krucoff MW, Loeffler KA, Haisty WK Jr, Pope JE, Sawchak ST, Wagner GS, Pahlm O Simultaneous ST-segment measurements using standard and monitoring-compatible torso limb lead placements at rest and during coronary occlusion. Am J Cardiol 1994 Nov 15;74(10):997-1001 Electrocardiographic recordings used to assess ST-segment deviation are performed using both standard and torso limb lead positions, where bony prominences give more artifact-free signal. Whereas significant QRS artifact can be introduced by such changes in lead location, the impact on ST-segment measurements has never been assessed. Digital electrocardiographic recordings were performed in 29 patients throughout elective angioplasty balloon inflation in the left anterior descending (n = 12), right coronary (n = 14), and circumflex (n = 3) arteries. In all cases, unipolar leads V1, V4, and V6 were affixed to the torso lead positions, allowing reconstruction of simultaneously acquired standard and modified 9-lead electrocardiograms (ECGs). ST levels in the 26 patients who had ST deviation during angioplasty were compared at both baseline and peak ischemia of up to 1,046 microV in the anterior, and 551 microV in the inferior leads. Differences in recorded ST levels for modified versus standard lead locations were all < 100 microV, even at peak ischemia. Although ST-segment elevation in the inferior leads appeared to show slightly more pronounced differences between lead sets than did anterior elevation, all differences were < 100 microV. Thus, measurement of ST-segment levels appears unlikely to be importantly affected by the intermixture of ECGs recorded with standard lead positions and ECGs recorded with monitoring-compatible lead positions on the torso. Recalibration of ST-segment measurements may be necessary for meticulous quantification of ischemia, infarct size, or other measurements that might be affected by variations < 100 microV.