Uncovering The Electrifying Truth Of A Racing Heart

Palpitations are a common cardiac symptom, but elucidating the cause is notoriously challenging.

Most episodes are sporadic and short-lived, making it difficult to obtain a heart rhythm recording during such occurrences. Without a symptom-heart rhythm correlation, physicians will not be able to prescribe definitive therapy. With the advent of technology, devices are now available to assist physicians in being able to make that formerly elusive diagnosis.

Most individuals have experienced palpitations at some point in their lifetime. The sensation of palpitations varies from person to person. Patients may report rapid and/or strong heart beats that may be regular or irregular, and associated with skipped or missed beats. Identifying the cause of the palpitations is never easy and at times, despite multiple investigations, the cause is still unknown. The crux of the approach to palpitations is to obtain a symptom-heart rhythm correlation. To this end, several devices have proven useful, and will be discussed in this article.

12-Lead Electrocardiography (ECG )

ECG presents the simplest method of capturing and analysing a patient's heart rhythm. It provides a snapshot of the heart's surface electrical activity when the 12 electrodes are attached to the patient. If no significant arrhythmia is identified on the ECG whilst the patient experiences palpitations, one can conclude that the palpitations are not secondary to malignant heart rhythms.

However, the challenge lies in performing ECG on a patient during palpitations. Most patients experience short-lived, self-limiting palpitations, and by the time they reach the clinic or emergency department, the palpitations would have resolved.

Ambulatory ECG Monitors

Compared to standard 12-lead ECG machines, ambulatory ECG monitors are more useful for recording heart rhythms during symptoms. There are a myriad of such devices available, but the most common one being employed in restructured hospitals, is the 24-hour Holter monitor.

The 12 ECG leads are secured over the patient's chest/torso and connected to a portable monitor. The patient is allowed to leave the hospital or clinic with the monitor, but needs to return 24 hours later for leads removal and data analysis.

The main drawback of the Holter monitor is its limited recording period of 24 hours. Therefore, it is only suitable for patients with frequent symptoms, especially those who experience daily palpitations. Patients' activities are also restricted by the monitor and leads. Some individuals may develop rashes as a result of prolonged skin exposure to the ECG electrodes.

Implantable Loop Recorders (ILR)

To circumvent the limited recording period of external monitors, ILRs may be implanted in the left chest, next to the sternum, with recording capabilities of two to three years. These days, ILR has been miniaturised to a mere 4.5cm by 0.6cm by 0.4cm, allowing implantation via an "injector" system under local anaesthesia (See Figure 1).

The ILR provides continuous monitoring of the heart rhythm and records arrhythmias based on pre-programmed parameters. Patients can also manually instruct the ILR to record the heart rhythm during palpitations using a handheld activator. Data recorded on the ILR is downloaded and analysed during regular clinic reviews or remotely via transmitters from a patient’s home.

Cardiac Electrophysiology Study

Under appropriate circumstances, patients with palpitations may be recommended to undergo a cardiac electrophysiology study. This entails the introduction of catheters via the femoral vein into the heart, to study the intracardiac electrical signals in order to elucidate the pathophysiology of the palpitations. If abnormal foci of electrical activity are detected, radiofrequency ablation of these foci may be performed in the same setting, providing a possible cure to the palpitations.

Conclusion

The tools all serve to provide a recording of the heart rhythm during symptoms, but they should not replace proper history-taking. A thorough history of the nature and frequency of the palpitations provides vital clues to the underlying etiology. The choice of investigative modality will then depend on the features elicited.

 

Adjunct Assistant Professor Chia Pow-Li is a Consultant from the Cardiology Department and Director of the Coronary Care Unit at Tan Tock Seng Hospital. He obtained his basic medical degree and Masters of Medicine (Internal Medicine) from the National University of Singapore. He is a Member of the Royal College of Physicians (Edinburgh) and a Fellow of the Academy of Medicine (Singapore). He completed a one year fellowship at St Vincent's Hospital, Sydney in cardiac electrophysiology and pacing in 2011.