All about leads

Electrode placement is different for each lead, and different leads provide different views of the heart. A lead may be chosen to highlight a particular part of the ECG complex or the electrical events of a specific cardiac cycle.

Although leads II, V1, and V6 are among the most commonly used leads for monitoring, you should adjust the leads according to the patient’s condition. If your monitoring system has the capability, you may also monitor the patient in more than one lead.

Going to ground

All bipolar leads have a third electrode, known as the ground, which is placed on the chest to prevent electrical interference from appearing on the ECG recording.

Heeeere’s lead I

Lead I provides a view of the heart that shows current moving from right to left. Because current flows from negative to positive, the positive electrode for this lead is placed on the left arm or on the left side of the chest; the negative electrode is placed on the right arm. Lead I produces a positive deflection on ECG tracings and is helpful in monitoring atrial rhythms and hemiblocks.

Introducing lead II

Lead II produces a positive deflection. Place the positive electrode on the patient’s left leg and the negative electrode on the right arm. For continuous monitoring, place the electrodes on the torso for convenience, with the positive electrode below the lowest palpable rib at the left midclavicular line and the negative electrode below the right clavicle. The current travels down and to the left in this lead. Lead II tends to produce a positive, highvoltage deflection, resulting in tall P, R, and T waves. This lead is commonly used for routine monitoring and is useful for detecting sinus node and atrial arrhythmias.

Next up, lead III

Lead III produces a positive deflection. The positive electrode is placed on the left leg; the negative electrode, on the left arm.

Along with lead II, this lead is useful for detecting changes associated with an inferior wall myocardial infarction.

The axes of the three bipolar limb leads—I, II, and III—form a triangle around the heart and provide a frontal plane view of the heart. (See Einthoven’s triangle, page 28.)

The six unipolar precordial leads are placed in sequence across the chest and provide a view of the heart’s horizontal plane. (See Precordial views, page 30.) These leads include:

A positive option

MCL6 may be used as an alternative to MCL1. Like MCL1 it monitors ventricular conduction changes. The positive lead in MCL6 is placed in the same location as its equivalent, lead V6. The positive electrode is placed at the fifth intercostal space at the midaxillary line, the negative electrode below the left shoulder, and the ground below the right shoulder.

Electrode basics

A threeor five-electrode (or leadwire) system may be used for cardiac monitoring. (See Leadwire systems, page 32.) Both systems use a ground electrode to prevent accidental electrical shock to the patient.

A three-electrode system has one positive electrode, one negative electrode, and a ground.

The popular five-electrode system uses an exploratory chest lead to monitor any six modified chest leads as well as the standard limb leads. (See Using a five-leadwire system, page 33.)

This system uses standardized chest placement. Wires that attach to the electrodes are usually color-coded to help you to place them correctly on the patient’s chest.

One newer application of bedside cardiac monitoring is a reduced lead continuous 12-lead ECG system (EASI system), which uses an advanced algorithm and only five electrodes uniquely placed on the torso to derive a 12-lead ECG. The system allows all 12 leads to be simultaneously displayed and recorded. (See Understanding the EASI system, page 34.)

How to apply electrodes

Before you attach electrodes to your patient, make sure he knows you’re monitoring his heart rate and rhythm, not controlling them. Tell him not to become upset if he hears an alarm during the procedure; it probably just means a leadwire has come loose.

Explain the electrode placement procedure to the patient, provide privacy, and wash your hands. Expose the patient’s chest and select electrode sites for the chosen lead. Choose sites over (Text continues on page 34.)

OBTAINING A RHYTHM STRIP

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