Question

A 61-year-old woman describes intermittent attacks of a rapid, irregular heartbeat associated with mild dizziness. These episodes have occurred unpredictably over the past several months, with many symptom-free days between attacks. She is asymptomatic during her clinic appointment, and a resting 12-lead ECG demonstrates normal sinus rhythm.

Which investigation is most appropriate to establish the diagnosis?

A. 48-hour Holter monitoring
B. Exercise stress ECG
C. Transthoracic echocardiography
D. Event recorder electrocardiogram
E. Ambulatory blood-pressure monitoring

Answer

D. Event recorder electrocardiogram

Explanation

This history suggests paroxysmal atrial fibrillation (AF) or another intermittent tachyarrhythmia. Because the patient is currently in sinus rhythm, a single resting ECG cannot exclude paroxysmal AF.

The key MRCP principle is to choose ambulatory ECG monitoring according to how frequently symptoms occur:

• Episodes <24 hours apart → 24-hour ambulatory ECG (Holter).
• Episodes >24 hours apart → longer-term ambulatory monitoring/event recorder.

Here, the episodes are separated by several days, so a 24-hour Holter has a significant chance of recording nothing. An event recorder ECG provides monitoring over a longer period and therefore has a better chance of capturing the rhythm during symptoms.

A treadmill ECG is primarily useful when symptoms or arrhythmias are exercise-related or when exercise-induced myocardial ischaemia is being investigated. Ambulatory blood-pressure monitoring is used mainly for diagnosing or assessing hypertension. Echocardiography can identify structural heart disease but does not usually establish the rhythm responsible for infrequent palpitations.

Atrial fibrillation classification

Paroxysmal AF: episodes terminate spontaneously or with intervention within 7 days.

Persistent AF: AF is continuously sustained beyond 7 days and generally requires intervention for termination.

Permanent AF: AF is accepted by the patient and clinician, and no further attempts to restore or maintain sinus rhythm are planned.

A useful distinction is that “permanent” AF describes a management decision, rather than simply an episode that has lasted for a particularly long time.

Summary for quick exam revision

Paroxysmal atrial fibrillation may not be visible on a routine 12-lead ECG because the patient can be in normal sinus rhythm between attacks. In a patient with intermittent palpitations, the frequency of symptoms determines the most appropriate ambulatory ECG investigation. If suspected AF episodes occur less than 24 hours apart, a 24-hour ambulatory ECG is appropriate. If episodes occur more than 24 hours apart, longer-term ambulatory ECG monitoring or an event recorder is preferred. This increases the likelihood of obtaining symptom-rhythm correlation. Therefore, a patient who has palpitations only every few days should not rely on a single 24-hour Holter recording. Event recorder ECG is the best answer in this question. Exercise ECG is mainly useful when symptoms are precipitated by exercise or exercise-induced ischaemia is suspected. Ambulatory blood-pressure monitoring is for evaluating hypertension rather than intermittent arrhythmia. Echocardiography assesses cardiac structure but does not usually capture an intermittent rhythm disturbance. Paroxysmal AF terminates within 7 days, usually much sooner. Persistent AF is continuously sustained for more than 7 days. Permanent AF means that the patient and clinician have accepted AF and are no longer pursuing rhythm restoration. For MRCP questions, remember the central rule: frequent symptoms → short Holter; infrequent symptoms → prolonged monitoring/event recorder.