A patient presents with regular narrow QRS tachycardia. A 12-lead electrocardiogram (ECG) demonstrates an r' in lead V1 that was not seen on ECG when the patient was in sinus rhythm. An esophageal electrode shows a 1:1 atrial-to-ventricular relationship during tachycardia. The ventriculoatrial (VA) interval is measured as 55 milliseconds.
Which of the following is the most likely diagnosis?
AV nodal reentrant tachycardia (AVNRT). Atrial tachycardia and PJRT are long RP tachycardias and, therefore, would not have such a short VA interval. PJRT is a special type of orthodromic AVRT that involves a posteroseptal accessory pathway with decremental (AV nodal-like) conduction properties and, hence, has a long RP (long VA) interval. Because of the time required to reach the accessory pathway for the retrograde portion of the arrhythmia circuit, orthodromic AVRT generally has a VA interval longer than 70 milliseconds. Therefore, a VA interval shorter than 70 milliseconds excludes orthodromic AVRT and makes AVNRT the most likely diagnosis. A small r' wave (pseudo r' wave) can sometimes be seen at the terminal portion of the QRS (usually best in lead V1 ). This deflection represents retrograde activation of the atrial (a retrograde P wave) occurring shortly after the QRS complex.
A 17-year-old patient who is known to have Wolff-Parkinson-White syndrome presents with a regular narrow complex tachycardia with a cycle length of 375 milliseconds (160 bpm) that occurred with a sudden onset. You note that there is a 1:1 atrial-to-ventricular relationship and that the RP interval is 100 milliseconds.
The best initial treatment is:
Vagal maneuvers. A sudden onset of a regular narrow complex tachycardia with a cycle length of 375 milliseconds and an RP interval of 100 milliseconds is a short RP tachycardia (the PR interval would be 375 milliseconds – 100 milliseconds = 275 milliseconds, so the RP is shorter than the PR). This patient most likely presents with orthodromic AVRT, a reciprocating tachycardia circuit that involves antegrade conduction through the AV node and retrograde conduction through the accessory pathway (however, AVNRT is also possible). As the AV node is a necessary component of the arrhythmia circuit, AV nodal blockade effectively terminates this type of tachycardia. Vagal maneuvers, such as Valsalva, coughing, or carotid sinus massage, may be quite effective and avoid the potential risks associated with administration of medications. Verapamil and other drugs that block AV conduction, such as β-blockers and adenosine, may be quite useful for termination of AVRT. This should not be confused with the management of AFib in the setting of Wolff-Parkinson-White syndrome, in which administration of AV nodal blocking drugs, such as verapamil, is contraindicated due to a concern for uninhibited and thus rapid AV conduction of the AP, which if rapid enough can induce ventricular fibrillation. When AV conduction is occurring through both the AV node and AP, retrograde, concealed conduction into the AP can limit its antegrade conduction properties. If preexcited, AFib with IV procainamide or DC cardioversion is the correct management. A precautionary note regarding the use of adenosine for regular narrow QRS tachycardia in patients with WolffParkinson-White syndrome: Adenosine may precipitate AFib and result in a very rapid ventricular response (preexcited tachycardia). Atropine has no role in the treatment of these types of arrhythmia. Catheter ablation is not generally an acute treatment option for this arrhythmia, although this approach may be an excellent option for chronic treatment (cure).
A 25-year-old patient presents with the sudden onset of tachycardia and is found to have a regular narrow QRS tachycardia with a cycle length of 340 milliseconds (176 bpm). An ECG appears to show P waves visible just after each QRS complex. You place an esophageal electrode and confirm a 1:1 atrial-to-ventricular relationship with a VA interval of 110 milliseconds. During the tachycardia, there is spontaneous development of left bundle branch block (LBBB), and a slower tachycardia with a VA interval of 150 milliseconds is now seen.
What is the most likely diagnosis for the second tachycardia?
Orthodromic AVRT using a left-sided accessory pathway. A regular narrow QRS tachycardia that has VA interval prolongation with the development of bundle branch block is most consistent with an orthodromic AVRT using an accessory pathway ipsilateral to the bundle branch. During AVRT, the antegrade limb of the circuit is the AV node and HisPurkinje/bundle branch system, and the retrograde limb is the accessory pathway. Block in a bundle branch ipsilateral to an accessory pathway creates a larger circuit, as the antegrade limb must now use the contralateral bundle branch, and therefore, the VA interval increases. This results in an increase in the tachycardia cycle length (a slower tachycardia). Of note, a slower tachycardia with bundle branch block itself does not necessarily have the same significance. Other types of tachycardia may slow because of a change in conduction of other components of the tachycardia circuit, such as the conduction through the AV node (A–H interval). Thus, it is important to demonstrate VA interval prolongation during bundle branch block to implicate an ipsilateral accessory pathway participating in AVRT.
A 65-year-old man presents after an arrest while eating at a local restaurant. On arrival, paramedics documented ventricular fibrillation (VF), and he was successfully resuscitated. He has a history of myocardial infarction (MI) and congestive heart failure (CHF). Serum electrolytes are remarkable only for mild hypokalemia. MI is ruled out by ECG and serial blood tests of myocardial enzymes. Subsequent evaluation includes cardiac catheterization, which shows severe three-vessel coronary artery disease (CAD) and severe left ventricular (LV) systolic dysfunction. A nuclear myocardial perfusion scan shows a large area of myocardial scar without significant viability in the territory of the left anterior descending coronary artery. The decision is made to treat the CAD medically.
Which of the following is the best management strategy for his arrhythmia?
ICD implantation. Cardiac arrest with VT or VF in the absence of reversible causes (e.g., MI, severe electrolyte or metabolic disorders) is a class I indication for ICD implantation. ICD implantation for such patients is superior to amiodarone drug therapy, as demonstrated in the Antiarrhythmics Versus Implantable Defibrillator (AVID) trial. The Canadian Implantable Defibrillator Study examined a similar population of patients and, although not statistically significant, showed a strong trend for the superiority of ICDs. Demonstration of inducible VT or VF in these types of patients is not necessary.
A 55-year-old woman has CAD and moderately severe LV systolic dysfunction (LV ejection fraction, 34%). Routine ambulatory Holter monitoring shows asymptomatic frequent ventricular ectopy with PVCs and occasional runs of nonsustained VT.
Which of the following statements about the management of this patient is true?
Implantation of an ICD is indicated if an EP study shows inducible VT. The Multicenter Automatic Defibrillator Implantation Trial (MADIT) evaluated patients with CAD, ischemic cardiomyopathy with an LV ejection fraction of <35%, and nonsustained VT. This study showed that for patients with inducible VT at baseline EP study and after administration of IV procainamide, treatment with an ICD was superior to treatment with antiarrhythmic drugs. A follow-up study, MADIT II, assessed the role of ICD implantation in patients with an ischemic cardiomyopathy and an ejection fraction ≤30%. Nonsustained VT was not required to undergo ICD implant, nor was an EP study. The study was terminated early after an average follow-up of 20 months because the ICD significantly reduced allcause mortality (14.2% versus 19.8% for conventional therapy). This study helped expand ICD implant indications. This is a class I indication for ICD implantation.
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