Left Ventricular Summit Arrhythmias: Mapping And Ablation Challenges

Arrhythmias arising from the left ventricular summit occupy a difficult region at the intersection of ventricular myocardium, the coronary venous system, the aortic root and the proximal coronary arteries. Premature ventricular complexes (PVCs) and ventricular tachycardia (VT) from this area can be highly symptomatic, trigger ventricular fibrillation, or complicate the management of structural heart disease.

The summit is generally described as the superior epicardial aspect of the left ventricle, bounded by the left anterior descending artery and the left circumflex artery. Its location is three-dimensional rather than a simple surface landmark. Some foci are reachable from the coronary venous system or the left ventricular endocardium, while others are shielded by thick myocardium or lie close to structures that make energy delivery hazardous.

Successful treatment depends on integrating the 12-lead ECG, computed tomography (CT), cardiac magnetic resonance (CMR), intracardiac echocardiography and electroanatomic mapping. A single chamber-based strategy can misidentify the true origin, particularly when activation exits through adjacent myocardium and produces a misleadingly distant earliest signal.

For electrophysiologists in Australia, these cases also involve practical decisions about referral pathways, advanced imaging, device availability and procedural volume. A patient from regional Queensland or Western Australia may need transfer to Brisbane, Sydney, Melbourne or Perth for complex mapping, while public and private hospitals may have different access to three-dimensional mapping platforms and hybrid imaging support.

Defining The Left Ventricular Summit

The left ventricular summit is an anatomically complex region near the superior and lateral left ventricular outflow tract (LVOT). Its borders are commonly related to the left main coronary artery bifurcation, the left anterior descending artery, the left circumflex artery and the great cardiac vein. The area is often divided into an accessible inferior portion and a more inaccessible superior portion.

The inferior region may be approached from the endocardial LVOT, aortic cusps or coronary venous branches. The superior region can be protected by epicardial fat, the coronary arteries and the thickness of the myocardium. These boundaries are variable, so terminology should support a procedural map rather than replace it.

An arrhythmic focus may sit within the summit itself or in neighbouring structures, including the aortic sinus of Valsalva, the left coronary cusp, the great cardiac vein, the anterior interventricular vein and the distal coronary sinus. The earliest electrical activation may therefore be recorded at an apparent “exit” rather than at the site of origin.

Electrocardiographic Clues And Their Limits

A summit PVC often has a right bundle branch block or left bundle branch block-like pattern depending on its precise origin and conduction pathway. Inferior axis, early precordial transition and a prominent initial q wave in lead I can suggest a high left ventricular origin. The aVL and aVR relationship, transition zone and QRS width may help distinguish a summit focus from aortic cusp or right ventricular outflow tract activity.

Precordial transition earlier than that seen in sinus rhythm may support a left-sided origin, although this finding is influenced by lead placement, cardiac rotation and the presence of scar. A QS pattern in aVL or a deep S wave in lead V6 can provide additional clues, but no ECG algorithm reliably identifies the ablation target in every patient.

PVC morphology should be interpreted alongside clinical context. Frequent monomorphic ectopy in a patient with apparently normal ventricular function may represent an idiopathic focus, whereas multiple morphologies, reduced ejection fraction or a history of infarction raises concern for scar-related VT. Exercise, electrolyte disturbance and antiarrhythmic drugs can also alter the observed burden and morphology.

Building A Three-Dimensional Anatomical Map

Preprocedural CT angiography can define the relationship between the summit, coronary arteries, aortic root and epicardial fat. CMR is especially valuable when cardiomyopathy or myocardial scar is suspected, because late gadolinium enhancement can identify fibrosis that may form part of a re-entry circuit. Imaging data should be registered carefully, as respiratory motion and differences in cardiac phase can create meaningful spatial error.

During the procedure, mapping usually begins with a systematic survey of the right ventricular outflow tract, pulmonary artery, aortic cusps, LVOT, left ventricle and coronary venous system. Activation mapping seeks the earliest ventricular electrogram and a suitable pace-map match. Fractionated or delayed potentials may indicate diseased substrate rather than the origin of a focal PVC.

Intracardiac echocardiography can support catheter positioning, monitor wall contact and identify pericardial fluid. It also helps define the aortic cusps and ventricular outflow tracts in real time. A combined map of electrical activation and anatomical risk structures is more useful than an electrical map that ignores coronary anatomy.

Choosing The Initial Ablation Route

An endocardial approach is often attempted first when activation is earliest in the LVOT, beneath the aortic valve or within the left coronary cusp. Ablation in the aortic root requires careful attention to the coronary ostia and valve anatomy. Coronary angiography or integrated CT guidance may be used to confirm a safe distance before radiofrequency energy is delivered.

The coronary venous system can provide a direct route to some summit foci. Mapping within the great cardiac vein or anterior interventricular vein may reveal earlier activation than endocardial sites. However, venous calibre, catheter stability, high impedance and proximity to coronary arteries can limit energy delivery. Ethanol infusion into a coronary venous branch has been described in selected refractory cases, but it requires specialised expertise and carries important vascular risks.

When the focus is inaccessible from the endocardium and venous system, percutaneous epicardial access may be considered. This decision should account for prior cardiac surgery, anticoagulation, pericardial adhesions, epicardial fat and the likelihood that the true target is protected by a layer of tissue. An apparently logical epicardial lesion may fail if the arrhythmogenic myocardium lies deep within the ventricular wall.

Coronary Arteries And Procedural Safety

The most serious technical concern is injury to the left main, left anterior descending or left circumflex coronary artery. The operator must establish the position of these vessels in relation to the proposed lesion set, using coronary angiography, CT integration or both. A safe distance cannot be treated as a universal number because catheter orientation, energy settings, tissue thickness and vessel anatomy affect risk.

Radiofrequency application near a coronary artery may cause spasm, dissection, thrombosis or delayed stenosis. Coronary venous ablation can expose a nearby artery to thermal injury even when the catheter is not in direct contact with the vessel. Cooling from blood flow may reduce lesion formation in some settings, while high-power applications can increase the danger of collateral damage.

Epicardial procedures add the risks of pericardial bleeding, phrenic nerve injury and damage to the coronary vasculature. Epicardial fat may prevent adequate tissue contact, and ablation through fat can be inefficient. Haemodynamic monitoring, access to emergency cardiac surgery and a plan for managing coronary complications are essential components of the procedural environment.

Handling Scar-Related Ventricular Tachycardia

In patients with previous myocardial infarction or non-ischaemic cardiomyopathy, summit-region VT may be part of a broader epicardial or intramural scar. The clinical PVC that initiates VT can be less important than the low-voltage channels that sustain re-entry. Substrate mapping in sinus rhythm may therefore reveal targets even when VT is poorly tolerated or cannot be induced.

An approach to post-infarction VT ablation can include scar homogenisation, late-potential ablation, pace mapping and elimination of local abnormal ventricular activities. These strategies must be tailored to the scar’s depth and distribution; an endocardial-only procedure may leave an epicardial or intramural circuit intact.

Cardiac implantable electronic devices complicate mapping but provide valuable diagnostic information. Stored electrograms can clarify the initiating rhythm, cycle length and response to antitachycardia pacing. Defibrillator programming, sedation, haemodynamic support and post-procedure device interrogation should be planned with the same care as the ablation lesions.

Improving Outcomes Through Team-Based Planning

Summit ablation is best managed by a team that includes electrophysiology, imaging, anaesthesia, cardiac nursing and, when required, interventional cardiology or cardiothoracic surgery. Preprocedure review should reconcile ECG findings, imaging, medication use, renal function, anticoagulation and the patient’s goals. CMR may be less suitable for some patients with older devices, while CT contrast exposure matters in people with chronic kidney disease.

Australia’s geography makes case selection and referral particularly important. Patients travelling from Darwin, Hobart or remote communities may need coordinated imaging and several consultations during one metropolitan visit. Public hospital waiting lists, private insurance arrangements and the availability of mapping technology can influence timing, so a clear referral summary reduces duplicated testing and delays.

The regulatory environment also matters. Medicines and many medical devices used in Australia are assessed through the Therapeutic Goods Administration, while local hospital governance determines credentialling, consent processes and procurement. Device choice should be based on clinical evidence, operator experience and institutional capability rather than market availability alone.

High-quality scholarship helps clinicians compare evolving techniques, and the Journal of Arrhythmia provides open-access research, reviews and educational material relevant to electrophysiology practice across the Asia-Pacific region. Its readership includes specialists, trainees and researchers who can apply anatomical and technical insights to local procedural pathways.

Careful follow-up should include symptom assessment, ambulatory monitoring and ventricular function review. PVC suppression may improve a reversible cardiomyopathy, while recurrent VT may signal residual substrate, disease progression or an alternative exit site. Antiarrhythmic medication, heart failure therapy and implantable defibrillator management remain important even after an apparently successful procedure.

Advanced mapping cannot remove every uncertainty from left ventricular summit arrhythmias. It can, however, make uncertainty visible: the likely source, the available routes, the structures at risk and the evidence supporting each lesion. Clinicians can use current open-access research and multidisciplinary planning to refine patient selection, procedural safety and long-term rhythm care.