David Ross

Department of Cardiology, Westmead Hospital, Sydney

Recent major advances in cardiac electrophysiology coincide with development of sophisticated 3D mapping displays superimposed on individual patient CT images with the ability to locate the tip of an ablation catheter in 3D space with an accuracy of 1-2mm. This allows better delineation of complex circuits and design of appropriate strategies of ablation. This is especially beneficial for reentrant ventricular tachycardias based on myocardial scarring and complex atrial flutters such as those based on complex congenital heart disease. These technologies also enabled new approaches to atrial fibrillation, the most common and difficult to treat arrhythmia. The pulmonary veins and adjacent atria appear to be triggers for initiating and maintaining AF. RF ablation aiming to isolate the pulmonary veins results in cure rates of 70-80% for paroxysmal AF and 50-70% for chronic AF. However, recurrent arrhythmias are common and repeat procedures are usually required to achieve the above results. These are relatively major procedures and are best performed under general anaesthesia. Prevention of patient movement is important for preserving accuracy of the systems for detecting catheter location in space. Although these are generally safe procedures, complications include pericardial bleeding and tamponade, stroke, emergency cardiac or vascular surgery, creation of pulmonary vein stenosis, phrenic nerve injury and rarely, creation of an oesophago-atrial fistula. RF ablation for AF is becoming increasingly frequent and is moving earlier in the treatment armamentarium. Since the ablation approach is relatively recent, long term follow up over decades is not yet available but results over several years are encouraging.

Ventricular tachycardias occurring in hearts without apparent structural heart disease are now better understood. The most common locations are in the right ventricular outflow tract or involving the Purkinje system of the left ventricular septum. Other ventricular tachycardias arise in the aortic or pulmonary roots or between them, or in the epicardium or cardiac veins. Success rates for ablation of these not uncommon arrhythmias are approximately 90%.

Development of techniques for percutaneous transthoracic access to the pericardial space has been important for mapping and ablation of epicardial arrhythmias.

Implantable defibrillators have become the mainstay of treatment for ventricular tachyarrhythmias based on previous myocardial scars secondary to myocardial infarction or cardiomyopathy. Some patients develop "VT storms" with refractory frequent arrhythmias leading to repeated shocks. These are very debilitating and distressing and usually require RF ablation to target the culprit arrhythmia. This can be ablated in the majority of cases.

Biventricular pacing is useful for patients with congestive heart failure and mechanical dyssynchrony of left ventricular contraction. Placement of an additional pacing lead in a lateral left ventricular vein allows the lateral wall and septum to be paced synchronously and often improves cardiac function and symptoms in patients with heart failure refractory to optimal medical therapy.

A number of recent randomised trials have shown improved survival after defibrillator implantation in patients with severe left ventricular dysfunction with ejection fractions less than 30-35%. A substantial proportions of deaths in these patients are arrhythmic and preventable by an implanted device. This has broadened the indications for these devices but has considerable cost implications.

RF ablation has become the treatment of choice for symptomatic supraventricular tachycardias of almost all mechanisms.

Recent research into cardiac ion channels and genomics have expanded the understanding and detection of diseases such long QT syndrome, Brugada syndrome, and catecholaminergic polymorphic VT and may ultimately lead to new therapies.

In conclusion, there have been major advances in electrophysiology resulting in improved diagnosis and treatment of cardiac arrhythmias.