Catheter Ablation of Ventricular Arrhythmias
Key Points
Key Points
- Ventricular arrhythmias (VAs) are an important cause of morbidity and mortality and come in a variety of forms, from single premature ventricular complexes to sustained ventricular tachycardia and fibrillation.
- Rapid developments in our understanding of, and in our ability to diagnose and treat these arrhythmias, have taken place over the past decade.
Table 1. Definitions
| Clinical Characteristics |
|---|
| Clinical ventricular tachycardia (VT): VT that has occurred spontaneously based on analysis of 12-lead ECG QRS morphology. |
| Hemodynamically unstable VT: causes hemodynamic compromise requiring prompt termination. |
| Idiopathic VT: used to indicate VT that is known to occur in the absence of clinically apparent structural heart disease. |
| Idioventricular rhythm: three or more consecutive beats at a rate of up to 100/min that originate from the ventricles independent of atrial or atrioventricular (AV) nodal conduction. Although various arbitrary rates have been used to distinguish it from VT, the mechanism of the ventricular rhythm is more important than the rate. Idioventricular rhythm can be qualified as “accelerated” when the rate exceeds 40 bpm. |
| Incessant VT: continuous sustained VT that recurs promptly despite repeated intervention for termination over several hours. |
| Nonclinical VT: VT induced by programmed electrical stimulation that has not been documented previously. |
| Nonsustained VT: terminates spontaneously within 30 s. |
| Premature ventricular complex (PVC): an early ventricular depolarization with or without mechanical contraction. We recommend avoiding the use of the terms “ventricular premature depolarization” and “premature ventricular contraction” to standardize the literature and acknowledge that early electrical activity does not necessarily lead to mechanical contraction. |
| Presumptive clinical VT: similar to a spontaneous VT based on rate, limited ECG, or electrogram data available from ICD interrogation, but without the 12-lead ECG documentation of spontaneous VT. |
| PVC burden: the amount of ventricular extrasystoles preferably reported as the % of beats of ventricular origin of the total amount of beats over a 24-h recording period. |
| Repetitive monomorphic VT: continuously repeating episodes of self-terminating nonsustained VT. |
| Sustained VT: continuous VT for 30 s or that requires an intervention for termination (such as cardioversion). |
| Ventricular tachycardia: a tachycardia (rate >100 beats/min) with three or more consecutive beats that originates from the ventricles independent of atrial or AV nodal conduction. |
| VT storm: three or more separate episodes of sustained VT within 24 h, each requiring termination by an intervention. |
| VT Morphologies |
| Monomorphic VT: a similar QRS configuration from beat to beat (Figure 1A). Some variability in QRS morphology at initiation is not uncommon, followed by stabilization of the QRS morphology. |
| Monomorphic VT with indeterminate QRS morphology: preferred over "ventricular flutter", a term that has been applied to rapid VT that has a sinusoidal QRS configuration that prevents identification of the QRS morphology. |
| Multiple monomorphic VTs: more than one morphologically distinct monomorphic VT, occurring as different episodes or induced at different times. |
| Pleomorphic VT: has more than one morphologically distinct QRS complex occurring during the same episode of VT, but the QRS is not continuously changing (Figure 1B). |
| Polymorphic VT: has a continuously changing QRS configuration from beat to beat, indicating a changing ventricular activation sequence (Figure 1C). |
| Right- and left bundle branch block-like VT configurations: terms used to describe the dominant deflection in V1, with a dominant R wave described as “right bundle branch block-like” and a dominant S wave with a negative final component in V1 as “left bundle branch block-like” configurations. |
| Torsades de pointes: a form of polymorphic VT with continually varying QRS complexes that appear to spiral around the baseline of the ECG lead in a sinusoidal pattern. It is associated with QT prolongation. |
| Unmappable VT: does not allow interrogation of multiple sites to define the activation sequence or perform entrainment mapping. This may be due to hemodynamic intolerance that necessitates immediate VT termination, spontaneous or pacing-induced transition to other morphologies of VT, or repeated termination during mapping. |
| Ventricular fibrillation (VF): a chaotic rhythm defined on the surface ECG by undulations that are irregular in both timing and morphology, without discrete QRS complexes. |
| PVC Morphologies |
| Monomorphic PVC: PVCs felt reasonably to arise from the same focus. Slight changes in QRS morphology due to different exit sites from the same focus may be present. |
| Multiple morphologies of PVC: PVCs originating from several different focal locations. |
| Predominant PVC morphology: the one or more monomorphic PVC morphologies occurring most frequently and serving as the target for ablation. |
| Mechanisms |
| Focal VT: a point source of earliest ventricular activation with a spread of activation away in all directions from that site. The mechanism can be automaticity, triggered activity, or microreentry. |
| Scar-related reentry: arrhythmias that have characteristics of reentry and originate from an area of myocardial scar identified from electrogram characteristics or myocardial imaging. Large reentry circuits that can be defined over several centimeters are commonly referred to as "macroreentry." |
Table 2. Anatomical terminology
| Term | Definition |
|---|---|
| RV inflow | The part of the RV containing the tricuspid valve, chordae, and proximal RV. |
| RV outflow tract (RVOT) | The conus or infundibulum of the RV, derived from the bulbus cordis. It is bounded by the supraventricular crest and the pulmonic valve. |
| Tricuspid annulus | Area immediately adjacent to the tricuspid valve, including septal, free wall, and para-Hisian regions. |
| Moderator band | A muscular band in the RV, typically located in the mid to apical RV, connecting the interventricular septum to the RV free wall, supporting the anterior papillary muscle. It typically contains a subdivision of the right bundle branch (RBB). |
| RV papillary muscles | Three muscles connecting the RV myocardium to the tricuspid valve via the tricuspid chordae tendineae, usually designated as septal, posterior, and anterior papillary muscles. The septal papillary muscle is closely associated with parts of the RBB. |
| Supraventricular crest | Muscular ridge in the RV between the tricuspid and pulmonic valves, representing the boundary between the conus arteriosus and the rest of the RV. The exact components and terminology are controversial; however, some characterize it as being composed of a parietal band that extends from the anterior RV free wall to meet the septal band, which extends from the septal papillary muscle to meet it. |
| Pulmonary valves | The pulmonic valve includes three cusps and associated sinus, variously named right, left, and anterior; or anterolateral right, anterolateral left, and posterior sinuses. The posterior-right anterolateral commissure adjoins the aorta (junction of the right and left aortic sinuses). Muscle is present in each of the sinuses, and VA can originate from muscle fibers located within or extending beyond the pulmonary valve apparatus. |
| Sinuses of Valsalva, aortic cusps, aortic commissures | The right (R), left (L), and noncoronary aortic valve cusps are attached to the respective SV. The left sinus of Valsalva (LSV) is posterior and leftward on the aortic root. The noncoronary sinus of Valsalva (NCSV) is typically the most inferior and posterior SV, located posterior and rightward, superior to the His bundle, and anterior and superior to the paraseptal region of the atria near the superior AV junctions, typically adjacent to atrial myocardium. The right sinus of Valsalva (RSV) is the most anterior cusp and may be posterior to the RVOT infundibulum. VAs can also arise from muscle fibers at the commissures (connections) of the cusps, or from myocardium accessible to mapping and ablation from this location, especially from the RSV/LSV junction. |
| LV outflow tract (LVOT) | The aortic vestibule, composed of an infra-valvular part, bounded by the anterior mitral valve leaflet, but otherwise not clearly distinguishable from the rest of the left ventricle (LV); the aortic valve; and a supra-valvular part. |
| LV ostium | The opening at the base of the LV to which the mitral and aortic valves attach. |
| Aortomitral continuity (AMC); aortomitral curtain, or mitral-aortic intervalvular fibrosa | Continuation of the anteromedial aspect of the mitral annulus to the aortic valve; a curtain of fibrous tissue extending from the anterior mitral valve leaflet to the left and noncoronary aortic cusps. The AMC is connected by the left and right fibrous trigones to ventricular myocardium, the right fibrous trigone to the membranous ventricular septum. |
| Mitral valve annulus | Area immediately adjacent to the mitral valve. This can be approached endocardially, or epicardially, either through the coronary venous system or percutaneously. |
| LV papillary muscles | Muscles connecting the mitral valve chordae tendineae to the LV, typically with posteromedial and anterolateral papillary muscles. Papillary muscle anatomy is variable and can have single or multiple heads. |
| LV false tendon (or LV moderator band) | A fibrous or fibromuscular chord-like band that crosses the LV cavity, attaching to the septum, papillary muscles, trabeculations, or free wall of the LV. They may contain conduction tissue and may impede catheter manipulation in the LV. |
| Posterior-superior process | The posterior-superior process of the LV is the most inferior and posterior aspect of the basal LV, posterior to the plane of the tricuspid valve. VAs originating from the posterior-superior process of the LV can be accessed from the right atrium, the LV endocardium, and the coronary venous system. |
| Endocardium | Inner lining of the heart. |
| Purkinje network | The specialized conduction system of the ventricles, which includes the His bundle, RBB and left bundle branches (LBB), and the ramifications of these, found in the subendocardium. The Purkinje system can generate focal or reentrant VTs, typically manifesting Purkinje potentials preceding QRS onset. |
| Interventricular septum | Muscular wall between the LV and RV. |
| Membranous ventricular septum | The ventricular septum beneath the RSV and NCSV, through which the penetrating His bundle reaches the ventricular myocardium. |
| LV summit | Triangular region of the most superior part of the LV epicardial surface bounded by the left circumflex coronary artery, the left anterior descending artery, and an approximate line from the first septal coronary artery laterally to the left AV groove. The great cardiac vein (GCV) bisects the triangle. An area superior to the GCV is considered to be inaccessible to catheter ablation due to proximity of the coronary arteries and overlying epicardial fat. |
| Crux of the heart (crux cordis) | Epicardial area formed by the junction of the AV groove and posterior interventricular groove, at the base of the heart, approximately at the junction of the middle cardiac vein and coronary sinus (CS) and near the origin of the posterior descending coronary artery. |
| Epicardium | The outer layer of the heart—the visceral layer of the serous pericardium. |
| Epicardial fat | Adipose tissue variably present over the epicardial surface around coronary arteries, LV apex, RV free wall, left atrial appendage, right atrial appendage, and AV and interventricular grooves. |
| Pericardial space or cavity | The potential space between the parietal and visceral layers of serous pericardium, which normally contains a small amount of serous fluid. This space can be accessed for epicardial procedures. |
| Parietal pericardium | The layer of the serous pericardium that is attached to the inner surface of the fibrous pericardium and is normally apposed to the visceral pericardium, separated by a thin layer of pericardial fluid. |
| Fibrous pericardium | Thick membrane that forms the outer layer of the pericardium. |
| Subxiphoid area | Area inferior to the xiphoid process; typical site for percutaneous epicardial access. |
| Phrenic nerve | The right phrenic nerve lays along the right atrium and does not usually pass over ventricular tissue. The course of the left phrenic nerve on the fibrous pericardium can be quite variable and may run along the lateral margin of the LV near the left obtuse marginal artery and vein; inferior, at the base of the heart; or anterior over the sternocostal surface over the L main stem coronary artery or left anterior descending artery. |
| Coronary sinus (CS) and branches | The CS and its branches comprise the coronary venous system with the ostium of the CS opening into the right atrium. Tributaries of the CS, which runs along the left AV groove, may be used for mapping. These include the anterior interventricular vein (AIV), which arises at the apex and runs along the anterior interventricular septum, connecting to the GCV that continues in the AV groove to the CS; the communicating vein located between aortic and pulmonary annulus; various posterior and lateral marginal branches or perforator veins; and the middle cardiac vein that typically runs along the posterior interventricular septum from the apex to join the CS or empty separately into the right atrium. The junction of the GCV and the CS is at the vein or ligament of Marshall (or persistent left superior vena cava, when present), and the valve of Vieussens (where present). |
Figure 1. Monomorphic (A), pleomorphic (B), and polymorphic (C) VT
Treatment
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Training and Institutional Requirements and Competencies
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