Management of tachyarrhythmias in the emergency room

Introduction

Epidemiology

Almost 2% of the admissions to the emergency room are due to tachyarrhythmias.

Narrow-QRS tachyarrhythmias are by far the commonest finding (~ 90%). Among them, atrial fibrillation (AF) (45%), paroxysmal supraventricular tachycardia (35%) and atrial flutter (AFl) (8%) are the most frequent ones. A wide-QRS tachyarrhythmia is present in the remaining 10% of the patients: about half of them have a ventricular tachycardia.

General considerations

The arrhythmia can often be terminated in the first-aid department and many patients may be discharged after a short observation time. Therefore, the principal exams needed to make clear the kind of the arrhythmia and the possible underlying diseases should be performed in this setting.

It is, indeed, important to keep in mind that physician’s primary objective is to treat the patient and not only the arrhythmia, which has always to be evaluated in the global clinical contest.
In fact, the arrhythmia could be secondary to cardiac, pulmonary or dysmetabolic diseases and the correct treatment must be directed not only to the arrhythmia, but - when present - to its cause.

We believe that in a first-aid department the "load and go" practice has to be changed in a "stay and play (or fight)" one.
Nevertheless, in this setting there is no space for time consuming procedures. That is why, in this paper, we suggest guidelines for a rapid diagnosis and for a therapeutic approach aimed to stabilize the patient and to get out the emergency phase. We emphasize the use of transthoracic DC shock for the interruption of ventricular or supraventricular arrhythmias, as a safe and rapid technique with virtually no contraindications and few drawbacks. On the contrary, we consider transoesophageal pacing as often too time consuming in a first-aid department.

Diagnostic procedures

By convention, a tachyarrhythmia is a rhythm disorder determining a heart rate over 100 beats per minute (bpm).
However, atrial tachyarrhythmias with depressed atrio-ventricular conduction could result in ventricular rates below 100 bpm.

Every patient presenting with a tachyarrhythmia - except than in very critical situations - must have a complete 12-lead ECG and a long ECG strip recorded, particularly during interruption attempts. It is also mandatory to get a venous access and to perform some basic laboratory tests (electrolytes, enzymes, blood urea and blood-cell count).

In patients with haemodynamic failure (cardiogenic shock, low blood pressure, pulmonary edema) possibly precipitated by the arrhythmia, an interruption attempt has to be carried out as soon as possible. Synchronous DC shock is the treatment of choice and a precise diagnosis regarding the nature of the arrhythmia, if not immediately clear, can be deferred.

If no haemodynamic impairment is present, a correct diagnosis - based on anamnesis, clinical examination and ECG - must precede any treatment (fig. 1).

Figure 1. First steps in the management of any tachyarrhythmia (narrow or wide QRS)

The first approach to the electrocardiographic diagnosis is based on two simple parameters: the duration and the regularity of the QRS.

a) QRS duration

narrow-QRS arrhythmias (QRS < 120 msec) have always a supraventricular origin (fig. 2);

Figure 2. Narrow-QRS tachycardias, listed in order of frequency

wide-QRS arrhythmias (QRS > 120 msec) may rise from a ventricular (40-50%) or supraventricular site. In this latter case, an aberrancy due to a bundle branch block (either preexisting or rate-dependent) or an accessory atrio-ventricular pathway is present (fig. 3).

Figure 3. Supraventricular tachycardias with wide-QRS

A. nodal reentry tachycardia with right bundle branch block
B. antidromic atrioventricular reentry tachycardia: activation goes to the ventricles through the accessory pathway and comes back to the atria through the AV node

b) The regularity of the ventricular rhythm allows a further diagnostic step (fig. 3-4).

Figure 4. Wide-QRS tachycardia, listed in order of frequency

Vagal stimulation maneuvers are the third important diagnostic tool (tab. I-II). They can have three effects on the arrhythmia: (1) interruption, (2) slowing of the ventricular rate, (3) no modification.
In the first case both, the therapeutic goal and an important insight into the tachycardia origin, are obtained. In fact, we can infer that atrio-ventricular node was part of the reentrant circuit maintaining the arrhythmia (as in nodal or atrio-ventricular reentry tachycardias). In the second case, vagal stimulation does not interrupt the arrhythmia but induces a transient modification of the atrio-ventricular conduction, indicating its atrial origin. Besides, the atrial activity may become evident, unveiling the arrhythmia type (AF, atrial flutter, atrial tachycardia).

Vagal stimulation techniques (tab. I).

The most efficient is the Valsalva’s maneuver, even though it requires the patient’s collaboration and it is often difficult to perform by the elderly. The "Diving reflex" - evocated by keeping a surgical glove full of ice and cold water on the face - is indicated in children. The carotid sinus stimulation is the most frequently performed. In order to obtain an effective vagal stimulation, the carotid sinus has to be exactly located. After having identified the carotid artery under the sternocleido-mastoid muscle, digital pressure has to be performed on it at the mandibolar angle level, beginning from the right site and, if unsuccessful, repeating it on the other side. In the elderly, the presence of carotid murmur dissuades from this maneuver.

Vagal stimulations may not be effective in presence of a high level of sympathetic drive: the faster they are performed, the better it is.

Table I. Vagal stimulation maneuvers

Table II. Effects of vagal stimulation on supraventricular tachycardias

Home page MANAGEMENT OF TACHYARRHYTHMIAS IN THE EMRGENCY ROOM
Home page MANUALS ON CARDIAC ARRHYTHMIAS
Home page EINTHOVEN