Tachyarrhythm ias Approach to Tachyarrhythmias
GENERAL PRINCIPLES
• Tachyarrhythmias are encountered in both inpatient and outpatient settings.
• Recognition and stepwise analysis of these rhythms facilitate appropriate management.
• Clinical decision-making is guided by patient symptoms and signs of hemodynamic stability.
Definition
Cardiac rhythms whose ventricular rate exceeds 100 beats per minute (bpm).
Classification
Broadly classified into the following based on the width of the QRS complex on the ECG:
• Narrow-complex tachyarrhythmia (QRS pulse, then suggestive of an AV nodal reentrant tachycardia (AVNRT), AV reentrant tachycardia (AVRT), or a junctional tachycardia (JT), all leading to retrograde atrial activation occurring simultaneously with ventricular contraction.
Diagnostic Testing
LABORATORIES
Serum electrolytes, complete blood count (CBC), thyroid function tests, serum level of digoxin (if applicable), and urine toxicology screen should be considered for all patients.
ELECTROCARDIOGRAPHY
• Twelve-lead ECG, in the presence of the rhythm abnormality and in normal sinus rhythm (NSR), is the most useful initial diagnostic test.
• If the patient is clinically stable, obtain 12-lead ECG and continuous rhythm strip with leads that best demonstrate atrial activation (e.g., V1, II, III, aVF).
• Examine ECG for evidence of conduction abnormalities, such as preexcitation or bundle branch block, or signs of structural heart disease such as prior myocardial infarction (MI).
• Comparison of ECG obtained during arrhythmia with baseline can highlight subtle features of QRS deflection that indicate superposition of atrial and ventricular depolarization.
• Rhythm strip is useful to document response to interventions (e.g., vagal maneuvers, antiarrhythmic drug therapy, or electrical cardioversion).
IMAGING
CXR and transthoracic echocardiogram (TTE) can help provide evidence of structural heart disease that may make ventricular arrhythmias more likely.
OTHER DIAGNOSTIC TESTING
• Continuous ambulatory ECG monitoring
î Aids in outpatient diagnosis of tachyarrhythmias.
î A 24- or 48-hour Holter monitor; useful for documenting arrhythmias that occur with sufficient frequency.
î Useful for assessment of patient's heart rate response to daily activities or antiarrhythmic drug treatment.
î Correlation between patient-reported symptoms in a time-marked diary and heart rhythm recordings is key to determining if symptoms are attributable to arrhythmia.
• Event recorders
î Weeks to months of ambulatory monitoring; useful for documenting symptomatic transient arrhythmias that occur infrequently.
î Loop recorder—worn by the patient and continuously records the cardiac rhythm. When activated by the patient or via autodetection, a rhythm strip is saved with several minutes of preceding data.
î Implantable loop recorder (ILR)—SC monitoring device used to provide an automated or patient- activated recording of significant arrhythmic events that occur very infrequently or for patients who are unable to activate external recorders.
• Exercise ECG
Useful for studying exercise-induced arrhythmias or assessing sinus node response to exercise.
• Inpatient telemetry monitoring
Mainstay of surveillance monitoring during hospitalization for cardiac arrhythmia patients, especially those who are seriously ill or experiencing life-threatening arrhythmias.
• Electrophysiology study (EPS)
î Invasive catheter-based procedure used to study susceptibility to arrhythmias or investigate the mechanism of a known arrhythmia.
î EPS can be combined with catheter ablation for management of many arrhythmias.
î Capability of EPS to induce and study arrhythmias is highest for reentrant mechanisms.
TREATMENT
Refer to treatment of individual tachyarrhythmias for hemodynamically unstable patients and advanced cardiac life support (ACLS) algorithm for tachycardias in Appendix C.