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How can clinicians diagnose a patient who has had regular episodes of heart palpitations over the past year, when the symptoms always resolve before reaching the hospital? That's the question facing Ramanathan Velayutham, MD, of the Jawaharlal Institute of Postgraduate Medical Education and Research in Puducherry, India, and colleagues in .

The patient, in their 40s, told clinicians that the palpitations -- which varied in frequency from weekly to less than once a month -- came on suddenly, lasted for several minutes, and ended abruptly on their own. The episodes were not associated with fainting or giddiness. Clinicians could not identify any contributory history.

Findings from a cardiovascular examination at the time of presentation were normal; the patient was in sinus rhythm with a pulse rate of 100 beats/minute and a blood pressure of 126/80 mm Hg. A 12-lead ECG showed intermittent loss of preexcitation with sinus beats and an accessory pathway that suggested a posteroseptal pathway.

"Preexcited beats had a short PR interval (90 milliseconds), a QRS duration of 100 milliseconds, and discordant ST-segment and T-wave changes. Delta waves were negative in leads V1, III, and aVF and positive in leads V2, I, and aVL, suggestive of a posteroseptal pathway," Velayutham and team noted.

They noted that on surface ECG, intermittent preexcitation is generally believed to be related to slower ventricular rates during atrial fibrillation compared with persistent preexcitation; this is because accessory pathway effective refractory periods (APERPs) are longer in patients with intermittent preexcitation, they explained.

Since lower ventricular rates are associated with comparatively lower likelihood of a patient degenerating into ventricular fibrillation, intermittent preexcitation helps identify an accessory pathway with a low risk for sudden cardiac death, they said.

Results of a transthoracic echocardiogram suggested that the patient's heart was structurally normal, with normal left ventricular systolic function. The patient's frequent symptom recurrence prompted clinicians to recommend an electrophysiological assessment, which might detect possible high-risk characteristics not revealed by the surface ECG.

This assessment identified the presence of a posteroseptal accessory pathway with an effective refractory period of 240 milliseconds. "Tachycardia could be successfully induced with a single atrial extrastimulus, and the tachycardia rate was 220 beats/min," Velayutham and colleagues noted.

Based on the patient's recurrent episodes of palpitations, the short APERP, and the fact that atrial extrastimulus testing induced tachycardia, clinicians considered the accessory pathway to be high risk and it was successfully ablated. Following ablation, there was no ECG evidence of delta waves.

Discussion

Of several algorithms that use surface ECG findings to localize the accessory pathways, the "well-established Arruda algorithm suggested the presence of a posteroseptal accessory pathway in this patient," the authors wrote.

They noted that determining the risk associated with accessory pathways requires identification of markers for sudden cardiac death, which include:

• An APERP less than 250 milliseconds
• Shortest preexcited R-R intervals of less than 250 milliseconds during atrial fibrillation
• The presence of multiple accessory pathways
• Ebstein anomaly
• Familial Wolff-Parkinson-White syndrome

Conversely, bypass tracts with longer refractory periods are associated with sudden loss of preexcitation during treadmill testing and sporadic preexcitation on the surface ECG, Velayutham and colleagues noted.

"The coronary sinus pathway is associated with coronary sinus aneurysm, which is found to have a rapid conduction time and thereby high risk of fast ventricular rate and sudden cardiac death during atrial fibrillation episodes," they added.

Development of atrial fibrillation is thought to be preceded by an increasing burden of atrial high rate episodes. Notably, the IMPACT substudy on the in patients with implantable defibrillators found that manifest atrial fibrillation developed without any preceding atrial high rate episodes in 34% of patients.

According to research on , "during atrial fibrillation, the ventricular rate is often very fast, most complexes will usually have a delta wave configuration and there is a risk of ventricular fibrillation when the minimum interval between delta waves is less than 250 milliseconds." In these cases, researchers observed that digoxin and verapamil may be dangerous, and recommended using a drug which slows conduction in the accessory pathway, such as sotalol or flecainide.

Velayutham and colleagues observed that intermittent preexcitation on the surface ECG tends to occur with pathways associated with less risk of ventricular fibrillation and sudden cardiac death; they cited a study on surface ECG in 52 patients with Wolff-Parkinson-White syndrome in which 50% demonstrated intermittent loss of preexcitation.

Furthermore, longer APERPs, as well as longer shortest preexcited R-R intervals during atrial fibrillation, were observed in patients with intermittent preexcitation, as opposed to those with persistent preexcitation, the group noted; this implies a low risk of developing fast ventricular rate in cases of atrial fibrillation.

They also cited a study on 328 which noted longer APERPs in the 12.5% with intermittent versus persistent preexcitation. Those investigators reported that the incidence of pathways with refractory periods ≤250 milliseconds was not significantly different.

As this case demonstrated, intermittent preexcitation on the surface ECG does not always indicate a low-risk pathway, Velayutham and team noted. For instance, among 56 patients with Wolff-Parkinson-White syndrome and ventricular fibrillation, four patients had on the resting ECG. In of 295 children with preexcitation, the frequency of high-risk pathways was comparable in patients with intermittent preexcitation and those with persistent preexcitation.

"One of the probable explanations for this phenomenon can be a higher catecholamine sensitivity of the accessory pathway in some patients with intermittent preexcitation," Velayutham and colleagues wrote. They in which a 50-year-old man with intermittent preexcitation at baseline showed marked sensitivity to adrenergic stimulation, as indicated by observation of 1:1 preexcitation at peak exercise and with isoproterenol administration.

The authors suggested that in the patient reported in their case, a treadmill test could have supported this theory, but was not performed. Their patient's symptoms resolved about 6 months after undergoing radiofrequency ablation, and regular follow-up is ongoing.

They concluded that "risk stratification of an accessory pathway depends on how rapidly it conducts during atrial fibrillation." They recommended an invasive electrophysiological study for risk assessment in symptomatic patients with manifest preexcitation, "even if the noninvasive assessment suggests otherwise."

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