Dr Tushar Salukhe BSc MBBS MRCP MD is a cardiologist at Bupa Cromwell Hospital and a cardiac electrophysiologist and honorary senior lecturer at the Royal Brompton Hospital and National Heart Lung Institute, Imperial College.
The treatment of arrhythmia has been transformed over the last two decades from the drudgery of working through a cascade of antiarrhythmic agents, each with their own array of side effects, to a low risk day-case procedure with an expectation of a long-term, drug-free cure. This progress has been largely due to enormous technical advances in cardiac electrophysiological study and ablation such that, in experienced hands, virtually all tachyarrhythmias are amenable to ablation.
Ablation is the accurate destruction of discrete regions of endocardial tissue responsible for the propagation of arrhythmia using radiofrequency energy delivered via endocardial catheters. The cardiac chambers are typically instrumented with the ablation catheters introduced through pinhole incisions in the femoral vessels. The ablation and preceding electrophysiological study are varied in terms of technique, risk profile and outcomes, all of which depend on the arrhythmia being treated. Appropriate patient counselling and procedural planning is therefore critically dependant on achieving a diagnosis accurately and in a timely manner. To this end, early referral to a cardiac electrophysiologist may deliver treatment to patients more efficiently.
Early referral, early diagnosis, early treatment
Seldom do patients present to the general practitioner with complete absence of clinical signs. However, this is usual in patients with palpitations who typically do not exhibit any signs on physical examination in the surgery. Indeed, their 12-lead ECG at the time of consultation is also often normal. Thus, in the absence of the all important ECG during symptoms the diagnosis can be challenging and particular attention must be paid to the history. Presenting features of arrhythmia may range from no symptoms to transient loss of consciousness without premonition. The broad range of presenting symptoms reflects the breadth of arrhythmias which the physician must consider. This task is made even more challenging by tremendous subjectivity with which patients interpret their symptoms in terms of onset, offset, rate and regularity. What is rarely unclear, however, is the impact it has on the patient’s quality of life and peace of mind. Thus, with potentially curative treatments readily available, early referral to the cardiac electrophysiologist should not be delayed for seeking the oft elusive diagnostic ECG. Capturing the ECG during symptoms is very important, but can be a frustrating process, particularly if symptoms are few and far between. Asking the patient to attend an emergency department during symptoms for an ECG is a useful measure.
When faced with a patient with ongoing symptoms, a normal ECG, no documented arrhythmia and a very suggestive history, the electrophysiologist may proceed to offer that patient a diagnostic electrophysiolgical study (EPS) with a view to proceeding to ablation if necessary. The purpose of the diagnostic EPS is to describe the electrical properties of the heart and to provoke arrhythmia through programmed stimulation of the atria and ventricles. This low risk procedure (<0.5% complication risk) is typically performed under local anaesthetic to maximise chances of arrhythmia provocation and also to enable the electrophysiologist to match the arrhythmia to the patient’s symptoms. The EPS has excellent sensitivity and specificity for common SVT.
Who and when to refer directly to the electrophysiologist
Narrow complex tachycardia
The differential diagnoses for common narrow complex tachycardias, defined as greater than 100 bpm with QRS duration <120ms, includes common atrial flutter, atrioventricular nodal re-entry tachycardia AVNRT, atrioventricular re-entry tachycardia (AVRT) utilising an accessory AV connection and atrial fibrillation. All are amenable to ablation with a very low procedural complication risk of <1%. Atrial fibrillation will be discussed separately later.
Common atrial flutter (Figure 1a) is notoriously difficult to control pharmacologically and has an excellent and accessible target for ablation. The cavo-tricuspid isthmus, a muscular band of tissue which lies between the septal leaflet of the tricuspid valve and the inferior vena cava, is the target for ablation which is curative for common atrial flutter in 98% of patients. Ablation for symptomatic recurrent or persistent atrial flutter would, by most electrophysiologists, be considered first-line treatment.
Atrioventricular nodal re-entry tachycardia, AVNRT, typically manifests in the third to sixth decades, but can occur in any age group. The tachycardia circuit is confined to the AV node and results in near simultaneous atrial and ventricular activation, hence classically, during tachycardia the P wave is inscribed on the terminal end of the QRS complex during tachycardia (Figure 1b) while the sinus rhythm ECG is normal. The ablation target is very close to the AV node but can be safely ablated with < 1% risk of AV node injury requiring permanent pacemaker implantation. Long-term single procedure cure is about 95%. Ablation is also considered first-line treatment for recurrent AVNRT.
When AVRT is associated with evidence of an accessory pathway on the sinus rhythm ECG called “pre-excitation” (seen typically a short PR interval and delta wave) then this defines the Wolf-Parkinson-White syndrome (Figure 1c). Depending on the location of the accessory connection (which is highly variable), ablation is curative in 90-95% of patients after a single procedure. Ablation is offered as first-line treatment so referral to an electrophysiologist would be very appropriate. In young patients, when the accessory connection is found to lie very close to the AV node or His bundle at the EPS, and the risk of AV node injury exceeds 1-2%, then ablation may be differed after antiarrhythmics have failed to control symptoms.
Occasionally pre-excitation on the ECG may be found incidentally in asymptomatic patients. Although opinion is somewhat divided, most electrophysiologists would offer such patients an EPS to assess the safety and location of the accessory connection and thus the merits of ablation. Referral of such patients to an electrophysiologist would be appropriate.
Broad complex tachycardia
Documented broad complex tachycardia, defined as >100 bpm with QRS duration >120 ms, should be considered as a ventricular arrhythmia until proven otherwise and prompt urgent referral to an electrophysiologist should be made. When tachycardia is manifest and the patient is conscious immediate treatment should be sought in an emergency department. In the elective and out-patient setting, useful additional investigations should include an ECG and echocardiogram to document left ventricular function, but neither should delay referral to an electrophysiologist.
Indicators of potentially malignant arrhythmia
Myocardial infarction or impaired left ventricular function
Patients complaining of palpitations with a history of myocardial infarction, heart failure or known impaired left ventricular function, should be referred to the electrophysiologist very early, particularly if syncope or pre-syncope is an associated symptom, or if the QRS duration on the resting 12-lead ECG is greater than 120ms. There is a wealth of evidence from several randomised clinical trials that large proportions of patients with myocardial infarction and depressed ventricular function are vulnerable to sudden arrhythmic cardiac death and have a clear survival advantage if implanted with an automated cardioverter defibrillator when identified appropriately. Early referral to an electrophysiologist is strongly recommended.
Family history, Long QT and Brugada
Syncope or palpitations in patients with a family history of early, premature and unexpected sudden death should also be referred for early assessment even if initial examination is normal. Long QT and Brugada syndromes are becoming increasingly recognised and in patients appropriately selected to be at risk of sudden arrhythmic death. In such patients the electrophysiologist may, after initial consultation, recommend family screening.
Syncope, pre-syncope or palpitations in conjunction with an abnormal ECG, particularly of the Long QT or Brugada phenotype (see Figures 1d and 1e for examples) are a clear indication for early referral to the electrophysiologist. However, an incidental discovery of an abnormal ECG without symptoms or family history may not necessarily imply syndrome phenotype.
Despite being the most common arrhythmia in humans, effective ablation for AF has come to the fore relatively recently compared to other less common arrhythmias. Indeed, mechanism for the persistent or chronic (non-paroxysmal) forms of AF is still under scientific scrutiny. The emergency management of AF and anticoagulation with warfarin, or newer, recently NICE approved agents, are are beyond the scope of this article. Instead, the focus will be on elective ablative treatments available.
The natural history of AF in the majority of patients begins with short self-terminating paroxysms lasting typically less than 24 hours (but by definition less than 7 days). Untreated, paroxysms become more frequent and longer lasting. Long periods in AF cause the atria to dilate altering their electrophysiological properties and leading to fibrosis; all process which in turn sustain more AF. Early treatment is therefore key to long-term success. Identification and treatment of primary causes of AF such as hypertension, thyroid dysfunction, valvular heart disease and alcohol over consumption remains fundamental prior to considering ablation.
A seminal observation by French cardiac electrophysiologist Michel Haïssaguerre in 1998, reported in the New England Journal of Medicine, showed that the AF in its paroxysmal form was initiated by spontaneous electrical activity from the pulmonary veins. By ablating the left atrial tissue around each pair of pulmonary veins the electrophysiologist can electrically “disconnect” the veins from the left atrial resulting in effective treatment. The procedure is called pulmonary vein isolation (PVI). The procedure is performed on full anticoagulation without need to interrupt warfarin treatment. The overall procedural risk is <1% and is successful in 80% of patients after a single procedure with about 20% of patients needing a repeat procedure due to pulmonary vein reconnection. The European Society of Cardiology guidelines now recommend PVI as first-line treatment for patients with symptomatic recurrent paroxysmal AF once other causes have been excluded.
Ablation for more persistent forms of AF requires further ablation within the body of the left and right atria and the coronary sinus. Although the risk profile for the procedure is similar (<1%) to PVI, the single procedure success rate is lower at 50% with 80% achieving long-term success after two to three procedures. Currently, patients are offered AF ablation if their symptoms are attributable to AF because there is, as yet, no evidence that AF ablation confers any addition prognostic benefit over and above anticoagulation. Whether AF ablation adds to survival or reduces morbidity is the subject of randomised controlled trials such as CABANA, which are currently recruiting. Thus, all patients with symptomatic atrial fibrillation should be referred to an electrophysiologist.