ECGs in Emergency Medical Services

ECGs are not only used in outpatient and in-hospital diagnostics on a daily basis. In emergency medicine, an ECG can help ensure that serious heart disease is detected promptly. That can save lives.

WEINMANNhas been developing reliable, user-friendly emergency medical equipment for over 45 years.MEDUCORE Standard² is a compact monitor and defibrillator that optimizes the generation and evaluation of 6- and 12-lead ECGs directly at the emergency site.

What is an ECG?

ECG stands for ElectroCardioGram. An electrocardiogram traces the electrical currents of the heart – or more precisely, the electrical activity of the heart muscle fibers. It is also referred to as a cardiac current curve, or cardiac voltage curve.

The measurement of these cardiac currents is termed electrocardiography. It is performed by an electrocardiograph (or ECG device).

Background and meaning

The contractions of the heart are triggered by an electrical pulse that originates in the sinus node and propagates through the heart’s excitation conduction system to all the heart muscle cells. This change in electrical potential can be measured using electrodes on the skin, and then recorded over time. If the ECG is normal, the result is almost always a uniformly recurring curve.

An ECG is a non-invasive procedure that provides indications as to the characteristics and health of the heart. They include:

It should, however, also be considered that an ECG reflects the electrical activity of the heart muscle, but does not indicate the actual ejection rate of the heart. Therefore, complementary examinations such as echocardiography may be necessary to provide comprehensive information as to heart health and to make diagnoses.

ECG leads: How is an ECG obtained?

The electrical potentials generated during conduction of excitation through cardiac muscle cells can be measured in a variety of ways. The measured changes in potential are called derivatives. Measurements are taken by means of two lead electrodes connected to the ECG device, which are stuck to the skin at two points - the so-called lead points. There are 12 standard leads. They are distinguished essentially by the type of polarity and by the location on the body where the electrodes are attached. 

In terms of polarity, there are:

1. Bipolar leads: Bipolar leads measure the change in potential between two equal points on the body surface, such as between the right and left arms.
2. Unipolar leads: Unipolar leads measure the electrical voltage between a differential and an indifferent, or reference, electrode. The reference electrode, as the zero point, is generated by interconnecting two lead points via a resistor.

Depending on the location on the body where the electrodes are attached, a distinction is made between:

1. Extremity leads
2. Chest leads 
3. Other leads

Bipolar extremity lead

The bipolar extremity lead for an ECG originated with Einthoven. It determines changes in electrical potential in the frontal plane.

Einthoven’s bipolar limb leads measure voltage using 3 electrodes placed at the following locations:

• Right arm (RA)
• Left arm (LA)
• Left foot (LF)

This records 3 derivatives:

• Einthoven I: between right and left arm (RA – LA)
• Einthoven II: between right arm and left foot (RA – LF)
• Einthoven III: between left arm and left foot (LA – LF)

Unipolar extremity lead

Unipolar limb lead derivation according to Goldberger also records changes in electrical potential in the frontal plane. The locations of the 3 electrodes are the same as for Einthoven’s bipolar limb leads:

• Right arm (RA)
• Left arm (LA)
• Left foot (LF)

A unipolar limb lead records the change in potential between a differential electrode and two lead points interconnected as an indifferent electrode. 3 derivatives are recorded:

• aVL (augmented voltage left): LA – RA and LF
• aVR (augmented voltage right): RA – LA and LF
• aVF (augmented voltage foot): LF – LA and RA

Bipolar chest lead

The bipolar chest lead according to Nehb detects changes in electrical potential in the posterior wall of the heart, and is also referred to as the small heart triangle.

In bipolar chest lead derivation, the 3 Einthoven lead points are shifted to the chest wall near the heart:

• Right sternal base of the second rib (N_st)
• 5th intercostal space, left mid-clavicular line (_Nap)
• 5th intercostal space, left posterior axillary line (N_ax)

3 derivatives are recorded:

• Nehb A (anterior): between N_st and N_ap
• Nehb I (inferior): between N_ax and N_ap
• Nehb D (dorsal): between N_st and N_ax

Unipolar chest lead

Unipolar chest lead derivation according to Wilson detects changes in potential in the horizontal plane. In unipolar chest wall lead placement, 6 – or electively 9 – lead electrodes are routinely placed on the chest wall near the heart:

• V1: 4th intercostal space, right sternal edge
• V2: 4th intercostal space, left sternal edge
• V3: 5th left rib, between V2 and V4
• V4: 5th intercostal space, left mid-clavicular line
• V5: anterior axillary line at the same level as V4
• V6: mid-axillary line at the same level as V4
• V7: posterior axillary line, at the same level as V4–V6
• V8: scapular line, at the same level as V4–V6
• V9: paraspinal border, at the same level as V4–V6

The voltage of leads V1 to V6 is measured against the extremity electrodes interconnected as an indifferent electrode according to Goldberger. 

The ECG curve

The ECG curve comprises multiple segments composed of specific waves and intervals:

The P wave on the ECG results from excitation propagation in the atria. The QRS complex reflects the excitation propagation in the ventricles. The T wave corresponds to the excitation regression in the ventricles. The subsequent U wave occurs inconstantly, and can have various causes. The PQ interval extends from the beginning of the P wave to the beginning of the Q spike. It describes the transition of the electrical pulse from the atria to the ventricles. The QT interval comprises the total intraventricular excitation time. It extends from the beginning of the Q wave to the end of the T wave. The interval of the ST segment represents the recovery of the heart muscle. The ST segment begins with the zero line in the ECG, and ends with the repolarization of the heart.

Irregularities in the ECG

Systematic evaluation of the curve can reveal a variety of different irregularities that can provide indications for diagnosis. The following are just a few examples:

Indications: When is an ECG performed?

Key indications for an ECG include thoracic complaints, such as chest pain or retrosternal burning. An ECG is also indicated in cases of dizziness, fainting and unclear syncope. An ECG is used to diagnose various diseases:

• Cardiac arrhythmias, such as extrasystole, atrial fibrillation or bradycardia
• Disturbances in conduction and propagation of excitation, such as bundle branch block or AV block
• Coronary heart disease
• Acute or recent myocardial infarction (STEMI, NSTEMI)
• Pulmonary embolism
• Myocardial hypertrophy
• Abnormal right and left loads
• Pericarditis
• Myocarditis
• Electrolyte disorders
• Adverse drug reactions

In most cases, these symptoms and illnesses occur as an emergency.

ECGs in emergency medical services with WEINMANN MEDUCORE Standard²

MEDUCORE Standard² from WEINMANN intuitively and reliably supports users in generating and analyzing an ECG as part of patient monitoring, and in performing defibrillation. As a portable ECG device, MEDUCORE Standard² is used in emergency medical, hospital and military medical corps services.

In Basic Life Support (BLS) mode, the compact monitor/defibrillator generates a 6-lead ECG with either Einthoven bipolar limb leads (I, II, III) or Goldberger unipolar limb leads (aVR, aVL, aVF).

For advanced ECG diagnostics, a 12-lead ECG can be performed in Advanced Life Support (ALS) mode. Advanced Life Support also enables manual defibrillation and cardioversion.

The ECG can be analyzed immediately on the display, and the trace can be e-mailed or printed out via a Bluetooth® connection to a mobile printer, as required.

The display of MEDUCORE Standard² has a night mode featuring inverted colors to ensure clarity and maximize safety even in complete darkness. The practical replay view allows all recorded ECG curves and measured values to be retraced retroactively when the patient is handed over at the hospital. The professional alarm system featuring warning tones, LED lights and adjustable alarm limits provides users with prompt and unambiguous alerts in the event of any change in vital signs.