Paroxysmal Atrial Tachycardia With Block

KEY FEATURES

ESSENTIALS OF DIAGNOSIS

• Atrial rate of 150–250 bpm

• Atrioventricular (AV) block of 2:1

• Often associated with digitalis toxicity

GENERAL CONSIDERATIONS

• Increasingly seen in advanced organic heart disease and severe pulmonary disease

• Digoxin toxicity must be suspected

• A ventriculophasic response is often seen (P-P intervals containing QRS complexes are shorter than those that do not)

• May be secondary to automaticity or triggered activity

• Exacerbated by hypokalemia, particularly when associated with digoxin excess

CLINICAL PRESENTATION

SYMPTOMS AND SIGNS

• Related underlying cardiac disease and ventricular rate

• Shortness of breath

• Rarely chest pain

• Palpitations

• Gastrointestinal symptoms secondary to digitalis toxicity

PHYSICAL EXAM FINDINGS

• Varying S₁

• Disproportionate jugular a waves compared with pulse (2:1)

• Carotid sinus massage may slow pulse rate (not advised in digitalis toxicity owing to induction of serious ventricular arrhythmia)

DIFFERENTIAL DIAGNOSIS

• Other forms of atrial tachycardia

• Atypical AV nodal reentrant tachycardia

• Atrial flutter

DIAGNOSTIC EVALUATION

LABORATORY TESTS

• CBC, basic metabolic panel

• Serum digoxin level (may not correlate with toxicity, which is a clinical diagnosis)

• Arterial blood gas analysis if there is evidence of advanced lung disease

ELECTROCARDIOGRAPHY

• Shows atrial tachycardia usually with 2:1 AV block

• The ventricular rate is often within the normal range

• Varying block may also be noted

IMAGING STUDIES

• Echocardiogram to assess underlying heart disease

DIAGNOSTIC PROCEDURES

• None required

TREATMENT

CARDIOLOGY REFERRAL

• When secondary to digitalis toxicity usually can be managed by a generalist

• When tachycardia is persistent with advanced heart disease, cardiology referral is required

HOSPITALIZATION CRITERIA

• Almost all patients require hospitalization secondary to advanced nature of underlying disease

MEDICATIONS

• Withdraw digoxin when appropriate

• In life-threatening conditions, consider digoxin (Digibind) 228 mg (6 vials); life-threatening ingestions may require more

• Correct electrolyte abnormalities

• Therapies targeted at abolishing the arrhythmia are unrewarding

• In persistent cases, AV block with medication may be achieved to control ventricular rate

THERAPEUTIC PROCEDURES

• If the tachycardia is secondary to advanced heart disease and not related to digitalis toxicity, then radiofrequency ablation may be attempted with a mapping (contact or noncontact) system

SURGERY

• Usually not required

MONITORING

• ECG monitoring in hospital

• Digoxin level monitoring during Digibind therapy

DIET AND ACTIVITY

• Related to underlying heart disease

ONGOING MANAGEMENT

HOSPITAL DISCHARGE CRITERIA

• Resolution of arrhythmia

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