Using an algorithm to easily interpret basic cardiac rhythms

AORN Journal, Nov, 2005 by Denise Atwood

Every nurse should be able to recognize basic electrocardiogram (ECG) rhythms, such as normal sinus rhythm, sinus tachycardia, atrial fibrillation, atrial flutter, heart blocks, ventricular fibrillation, and asystole. To interpret basic ECG rhythms, nurses must understand the normal conduction pathways of the heart, as well as the basic pathophysiology of abnormal rhythms. This article presents an algorithm that is designed to help health care providers rapidly interpret primary ECG rhythms. Fred Killingbeck, RN, EMT-P, CEN, CCRN, the creator of the algorithm, describes this as the CRISP (ie, cardiac rhythm identification for simple people) method of ECG interpretation.

NORMAL PHYSIOLOGY OF CARDIAC IMPULSE CONDUCTION

Cardiac impulses are conducted through the conduction system, which consists of the sinoatrial (SA) node, atrioventricular (AV) junction and AV node, bundle of His, right and left bundle branches, and Purkinje fibers (Figure 1). (1) Normal conduction of a cardiac impulse is generated in the SA node located in the upper portion of the right atrium. The SA node is the natural pacemaker of the heart, and it produces a heart rate between 60 and 100 beats per minute (bpm). The impulse spreads through the right and left atria via the internodal pathways. (1)

[FIGURE 1 OMITTED]

The impulse then travels to the AV junction located in the lower portion of the right atrium. The impulse is delayed for 0.08 to 0.12 seconds in the AV junction, which gives the atria time to contract (ie, depolarize). The AV node is located in the AV junction. If the SA node fails to function, the AV node is the next in line in the conduction pathway, and it takes over as the heart's pacemaker. The AV node produces a heart rate between 40 and 60 bpm. (1)

The impulse spreads from the AV junction to the bundle of His and down the interventricular septum. The bundle of His divides into the right and left bundle branches in the ventricles, which end in the Purkinje system (ie, a network of fibers that spread throughout both ventricles and papillary muscles). The cardiac impulse terminates with a contraction (ie, ventricular depolarization) when these fibers are stimulated by an impulse. (1)

ELEMENTS OF AN ECG

An ECG gives a picture of the electrical activity that causes the different parts of the heart to beat and relax. An ECG consists of segments or intervals (ie, P wave, PR interval, QRS complex, ST segment, T wave, QT interval) that help determine where an impulse was generated and assess the length of time it takes an impulse to travel through the heart (Figure 2). (2)

[FIGURE 2 OMITTED]

Atrial depolarization produces the P wave on an ECG. The presence of P waves indicates that impulses are being generated in the SA node. The PR interval represents the amount of time the impulse takes to travel from the beginning of atrial depolarization to the beginning of ventricular depolarization. The QRS complex correlates with depolarization (ie, contraction) of the ventricles. The interval from the end of ventricular depolarization to the beginning of ventricular repolarization is represented by the ST segment. The T wave corresponds to repolarization of the ventricles. The total time for both ventricular depolarization and repolarization is represented by the QT interval.

CALCULATING HEART RATE

To calculate heart rate, a nurse should count the number of QRS complexes in a six-second strip. He or she should then multiply the number of QRS complexes by 10 (Figure 3).

[FIGURE 3 OMITTED]

ASSESSING THE PATIENT

Before beginning analysis of a suspected ECG abnormality, a perioperative nurse first must rapidly assess the patient, including checking the patient's level of consciousness, vital signs, skin color and temperature. After determining that the patient is stable, the nurse should rule out non-medical explanations for ECG irregularities (eg, patient movement, integrity of electrodes). The nurse then should assess the patient's lung sounds, presence of chest pain, and medical history. Chest pain can be assessed and documented using the PQRST method.

* P (ie, provocation)--What activities elicit pain?

* Q (ie, quality)--What does the pain feel like? Do other symptoms occur simultaneously?

* R (ie, region, radiation)--Where is the pain? Does the pain radiate? If so, where?

* S (ie, severity)--How does the pain rate on a scale of 0 to 10?

* T (ie, timing, treatment)--When did the pain begin? How long did it last? What did you do to relieve the pain, and was it effective? (2)

If the patient is not stable, the nurse should proceed to step 1 of the CRISP algorithm (Table 1) to begin the process of determining the patient's heart rhythm.

STEP 1--ARE QRS COMPLEXES PRESENT?

A nurse should begin using the algorithm at step 1 by asking, "Are QRS complexes present?" If the answer is "no" the rhythm is ventricular fibrillation or asystole (Figure 4).

[FIGURE 4 OMITTED]

The pathophysiology of ventricular fibrillation occurs when areas of normal myocardium in the ventricle alternate with areas of ischemic, injured, or infracted myocardium. (3) This causes a chaotic pattern of ventricular depolarization. Ventricular fibrillation looks like a wavy line on an ECG.