is based on the QRS pattern. If the QRS pattern is regular or nearly regular in any unstable patient with a tachydysrhythmia and a palpable pulse, synchronized cardioversion with 100 J should be used, followed by stepwise energy increases to 200 J with a biphasic device or 360 J with a monophasic device, if necessary. Some rhythms may require less energy, but attempts to titrate this lifesaving therapy for unstable patients is of little practical benefit. Synchronized countershock is recommended to avoid postcountershock ventricular fibrillation (VF). However, sensing problems often make reliable identification of the QRS complex needed for synchronization impossible. We recommend an unsynchronized shock promptly if any sensing problem occurs. Any patient without pulses and an irregular tachydysrhythmia should be immediately given a high‐energy unsynchronized countershock.
Patients with internal pacemakers or automatic implantable cardioverter defibrillators (AICDs) are still at risk of cardiac dysrhythmias. Although meant to cardiovert dysrhythmias, AICDs do not always convert these rhythms, and sometimes these devices deliver shocks inappropriately. If a patient has an unstable tachydysrhythmia and the AICD is not firing or is ineffective, externally cardiovert as previously recommended, with pads in the anterior‐posterior configuration and 10 cm away from the internal device pouch. Postconversion care with medical therapy will be unaffected.
If an AICD is repeatedly firing absent a ventricular dysrhythmia, a magnet held over the device may inactivate it, simplifying patient care and improving patient comfort (see Chapter 11). Fortunately, these are rare events.
If countershock fails in an unstable patient with a wide‐complex tachycardia, give either IV amiodarone (150 mg or 5 mg/kg) or lidocaine (100 mg or 1‐2 mg/kg) as a bolus and repeat the countershock. The ALIVE trial and recent American Heart Association guidelines recommend amiodarone as the first‐line agent in unstable, and especially pulseless, wide‐complex tachydysrhythmia [1, 9]. Lidocaine is still the easiest to deliver quickly, but is considered a second‐line agent due to variable success in terminating ventricular tachycardia (VT).
If the QRS complexes are chaotic, the most common diagnosis is atrial fibrillation. When chaos and a QRS duration of more than three small boxes appear together, atrial fibrillation with altered conduction is the diagnosis. All unstable fast chaotic rhythms should be cardioverted with 100 J, attempting to synchronize first, recognizing that synchronization may fail and an unsynchronized countershock may be required. As always, titrate energy up as needed. No postcountershock medications are needed.
One practical point, if regularity versus irregularity cannot be established during assessment of a patient with an unstable wide or narrow tachydysrhythmia, 100 J remains an appropriate starting energy level for countershock. Similarly, if simplicity of treatment protocols is sought, 100 J is reasonable for all unstable nonsinus tachycardias, because the extra energy delivered to the rapid atrial fibrillation patient is unlikely to cause harm or worsen discomfort compared to 50 J.
Step four: focus actions to evaluate stable but symptomatic and borderline patients
Up to this point, little specific history and only a few basic physical examination and ECG reading skills have been required. This is intentional, so as not to clutter the field evaluation for those who need it the most (i.e., the unstable patient) or do not need it at all (i.e., the asymptomatic patient). The remaining patients are those with symptoms, albeit none clearly identifying instability. Here, a few questions and actions can help to direct the appropriate prehospital care.
History
EMS clinicians should focus on previous cardiac‐related problems in stable patients. For example, a patient who presents with new‐onset wide‐complex tachydysrhythmia with a history of previous myocardial infarction is much more likely to have VT than a supraventricular rhythm with abnormal conduction. Similarly, one with a history of a previous dysrhythmia who presents with similar symptoms again is likely to have recurrence rather than a new dysrhythmia. Neither of these clinical rules is infallible, but this information can help guide therapy. Other points are also helpful. For instance, a patient with a history of poorly controlled hypertension presenting with a lowered but “normal” blood pressure suggests a dramatic change, prompting treatment that is more intensive.
History can influence the dosing of field agents. Subjects with liver or heart failure, and those aged 65 years and older, should receive lower lidocaine infusions or follow‐up boluses. Those patients with renal failure are at risk for hyperkalemia and rhythm changes. The current medications can provide a clue to any previous conditions or guide field drug therapy. A patient treated with digoxin or a beta‐blocker plus an anticoagulant for palpitations may have atrial fibrillation. Finally, although rare, a brief search for drug allergies or intolerances (“Has any heart drug been bad for you?”) may help avoid a complication. The key is to take a focused history, looking for information regarding heart disease and other specific conditions.
Physical examination
In addition to a search for signs of instability, some manipulations can help when assessing and managing tachycardias. Specifically, actions that alter atrioventricular node conduction (“vagal maneuvers”) can help terminate or uncover a specific dysrhythmia [2, 10]. In a patient less than 50 years old, carotid body massage can help, although many fear doing this in the field because of poorly documented concerns about embolization. The Valsalva action can be used with carotid body (not carotid artery) massage in young patients or as the sole maneuver in those over 50 years old. We do not recommend other maneuvers, including ocular and rectal massage, ice packs or cold‐water dunking, or rapid inflation of pneumatic antishock garments.
Stable narrow‐complex tachydysrhythmias
In patients who are symptomatic but stable or who have one borderline symptom of instability (e.g., dizzy or anxious with a low blood pressure), certain actions may aid. Patients with regular narrow‐complex tachydysrhythmias between 120 and 140 per minute are likely to have sinus tachycardia and require no antidysrhythmic treatment. Stable patients with regular narrow‐complex tachydysrhythmias at 140 per minute or greater should have vagal stimulating maneuvers performed to assess and hopefully terminate the rhythm. Sometimes, this maneuver uncovers sinus P waves, clarifying the sinus or atrial etiology. When P waves are seen, treatment is directed at the cause, not the rhythm.
Those with minor symptoms (e.g., isolated subjective dizziness or palpitations) do not require field treatment beyond vagal maneuvers. For those with symptoms that are more prominent and with regular narrow‐complex tachydysrhythmias at 140 per minute or greater, give adenosine (6‐12 mg as a rapid IV bolus from a mid‐arm or more proximal site, followed with a flush) [1–3, 8]. The smaller initial dose (6 mg) is effective about 60% of the time. It should be repeated within 2 minutes at the higher dose if no effect is seen. If adenosine causes slowing followed by a return to tachycardia, repeat or larger doses will not help. The cause is a non‐reentrant source, often an atrial rhythm, either atrial tachycardia, fibrillation, or flutter.
Adenosine is effective in 85% to 90% of patients with regular narrow‐complex tachydysrhythmias. The drug has a duration of effect of 20 seconds or less, and recurrence of a narrow‐complex tachydysrhythmia may occur in 10% to 58% of cases. Patients commonly complain of transient chest pain, dyspnea, or flushing during adenosine treatment. Some patients may experience bradycardia or asystole after adenosine. It usually lasts only seconds, but it may require temporary external pacing if prolonged. Contrary to popular belief, adenosine can occasionally terminate VT, although most such patients are unaffected [11].
Verapamil (2.5‐5 mg IV initially, followed by 5–10 mg in 15 minutes, if unsuccessful) and diltiazem (0.15 mg/kg initially, followed by 0.20‐0.25 mg/kg in 15 minutes, if unsuccessful) will terminate 85% to 90% regular narrow‐complex tachydysrhythmias [12, 13]. However, both can cause hypotension and congestive heart failure, though diltiazem may have slightly lower rates of this in equipotent doses. Because of these disadvantages, many prefer to use adenosine in the