Frank Bogun, MD
CASE PRESENTATION 1
A 10-year-old boy was seen for a routine physical examination by his primary care physician (PCP). He was found to have an irregular rhythm. A 12-lead ECG showed a bigeminal rhythm with premature ventricular contractions (PVCs) that displayed a left bundle branch block, inferior axis morphology. A 24-hour Holter monitor demonstrated a PVC burden of 32%. An echocardiogram demonstrated normal left ventricular function and dimensions. The boy and his parents were told not to worry about it and to be checked out again when the boy reached 18 years of age. At the age of 18, the boy, still without any symptoms returned to his PCP and got another ECG, which again showed a bigeminal rhythm (Figure 18-1). Holter monitor now showed a PVC burden of 33%, and the echocardiogram showed an EF of 30% with increased LV dimensions. The patient was started on β-blocker therapy and angiotensin-converting enzyme inhibitors and was referred to a pediatric electrophysiologist, who confirmed that the PVC burden was not suppressed by β-blocker therapy. He thereafter was referred to for an ablation procedure. During the ablation procedure, intracardiac echo was used in combination with an electroanatomic mapping system (Figure 18-2). Activation mapping was performed in the right ventricular outflow tract (RVOT) and identified a site in the posterior RVOT that preceded the onset of the PVC-QRS complex by −27 ms (Figure 18-3A). Pacing at this location reproduced a similar but not identical pace-map compared to the spontaneous PVC (Figure 18-3B). Radiofrequency energy was delivered at this location for a total of 2 minutes, and subsequently the PVC was no longer seen. A repeat echocardiogram 3 months postablation showed an ejection fraction of 40% and reduced LV dimensions. Six months postablation, the left ventricular ejection fraction had normalized to an ejection fraction of 60%, and the LV dimensions improved further. A Holter documented the absence of PVCs.
FIGURE 18-1 Shown is a 12-lead ECG with frequent PVCs in a bigeminal rhythm.
FIGURE 18-2 (A) Illustrates a view of the intracardiac echocardiogram with the ablation catheter located in the right ventricular outflow tract (RVOT; green icon) just below the pulmonary valve. (B) Illustrates an electroanatomic activation map of the RVOT from a left anterior oblique view. Brown tags indicate ablation lesions. The pulmonary annulus is marked (PA).
FIGURE 18-3 (A) Shown is the 12-lead ECG tracings and intracardiac recordings from the earliest endocardial site obtained during activation mapping of the PVC in the RVOT. (B) Shown is the 12-lead of the pace-map when pacing is performed from this location.
Triggered activity via delayed after depolarizations is the most likely mechanism of frequent PVCs, although reentry, especially in patients with structural heart disease and frequent PVCs, has been suggested as a possible mechanism as well.1 Reentry as a mechanism for PVCs has thus far only been demonstrated in animal models.2
PVC CARDIOMYOPATHY: AGGRAVATING FACTORS
Several features in this patient are associated with PVC cardiomyopathy. First, the PVC’s burden is >24%. This cut-off value best separated patients with PVC-induced cardiomyopathy from patients without PVC-mediated cardiomyopathy.3 Of note is that although based on ROC curves this cut-off value could be determined, not everyone with a PVC burden >24% had evidence of PVC-induced cardiomyopathy. About 25% of the patients with a higher PVC burden had normal left ventricular function. On the other hand, patients with a lower PVC burden were also at risk for PVC-induced cardiomyopathy, and the lowest PVC burden associated with PVC-induced cardiomyopathy was 10%.
By history, this patient’s PVCs were present for at least 10 years. Despite the fact that there is no documentation that the patient’s PVC burden was constant, data from Niwano et al suggest that a particular PVC burden often persists over several years.4 Multivariate analysis has recently demonstrated that a history of palpitations persisting more than 60 months was independently associated with PVC cardiomyopathy.5 In this study, the duration of palpitations was used as a surrogate for the amount of time a patient was exposed to PVCs.
Finally, this patient was asymptomatic, which appears to be another factor predisposing patients to PVC-induced cardiomyopathy.5 It is likely that asymptomatic patients seek medical attention later than symptomatic patients, thereby prolonging the exposure time to frequent PVCs.
PVC CARDIOMYOPATHY: NATURAL HISTORY
Not much data is available for the long-term natural history of patients with idiopathic PVCs, that is, in the absence of structural heart disease. In many prior reports where PVCs were associated with adverse outcome, the absence of structural heart disease was not well established.6 Niwano et al4 followed 239 patients without structural heart disease (confirmed by echocardiography and MRI) for at least 4 years. During follow-up, a decline in left ventricular function (>6%) was found in 13 patients. Most of these patients had very frequent PVCs that were defined as >20,000/24 hours in this study.
PVC CARDIOMYOPATHY: MECHANISM
The mechanism of PVC-induced cardiomyopathy is not known. Short-term animal research does not support fibrosis as a mechanism. This is supported by clinical studies confirming the absence of scar detected by MRI in patients with PVC-induced cardiomyopathy.7 A form of tachycardia-mediated cardiomyopathy is also unlikely, since the average heart rate in patients with PVC-induced cardiomyopathy is usually not different from patients with frequent PVCs without cardiomyopathy.8
PVC CARDIOMYOPATHY: THERAPY
PVC suppression by either medical therapy or ablation usually results in improvement and normalization of left ventricular function and dimensions.9,10 In the majority of patients, LV function normalizes within 4 months after an effective ablation, but this case illustrates that the process can take a longer period of time,11 possibly depending on the length of exposure to frequent PVCs.
PVCs: MAPPING AND ABLATION
Activation mapping is the preferred mapping modality over pace-mapping. This case illustrates that at the earliest endocardial mapping site no perfect match of the pace-map with the spontaneous PVC was demonstrated. In theory, pacing at the site of origin of a ventricular arrhythmia should result in a perfect replication of the targeted ventricular arrhythmia morphology, provided that the pacing cycle length is equal to the cycle length of the ventricular arrhythmia (for VT) or equal to the coupling interval in the setting of PVCs. Perfect pace-maps, however, are not always present, even when the ventricular arrhythmia can be eliminated within seconds of a radiofrequency energy application. A pace-map score of ≥10/12 leads when comparing the paced QRS morphology to the targeted ventricular arrhythmia QRS-morphology is often used to indicate a “matching pace-map.” With intramural foci, there is an early activation at the endocardial breakthrough site; however, the pace-map does not match the targeted morphology of the ventricular arrhythmia, similar to the case illustrated here. The PVC focus was successfully eliminated at the location of the earliest endocardial activation. The earliest site was on the interventricular septum, arguing for an intramural focus. Intramural septal foci can be effectively ablated from one side of the septum, but may require ablation from the other side as well.12 This was not necessary in this patient.
CASE PRESENTATION 2
A 19-year-old woman presented with syncope and rapid palpitations to the emergency department. She had undergone a failed VT ablation procedure 2 weeks ago and was treated with verapamil. She was transferred to our hospital for further treatment. Prior to the initial ablation, a 24-hour Holter monitor showed frequent PVCs with a PVC burden of 12% and frequent runs of repetitive, nonsustained VT (ns VT; 1100 runs). After the initial ablation procedure, during which an RVOT focus was targeted, her PVC burden was 30%, with only 69 runs of nsVT. The PVCs (Figure 18-4A) had a similar morphology when compared with the VT (Figure 18-4B). The patient was taken to the EP laboratory; with isoproterenol infusion she developed frequent PVCs and easily inducible, sustained, and nonsustained VT. The VT morphology was a right bundle branch block, inferior axis morphology. The mapping procedure was started within the coronary venous system that was mapped with a multipolar catheter documenting the earliest activation time of −25 ms within the distal great cardiac vein (Figure 18-5). Pacing from poles 9/10 produced a similar pace-map (Figure 18-6). Mapping of the aortic cusp using an open irrigated-tip catheter with an electroanatomic mapping system and with intracardiac ultrasound was performed subsequently. A site in the left cusp was identified where a sharp potential preceded the onset of the QRS complex by 35 ms. Radiofrequency energy was delivered. This, however, failed to eliminate the VT. The catheter was moved more cephalad, closer to the left main ostium, and a site with a prematurity of −37 ms was identified (Figure 18-7). Pacing at this site failed to reproduce the same morphology of the targeted VT (see Figure 18-7). The ostium of the left main coronary artery was identified by intracardiac ultrasound and was marked in the 3-D echocardiographic reconstruction of the aortic cusp and the left ventricle (Figure 18-8). The left main coronary artery was canalized with a diagnostic catheter and felt to be about 1 cm away from this site (Figure 18-9). Radiofrequency energy was delivered during VT, while repeated injections into the left main coronary artery were performed in order to ensure continued patency of the vessel (see Figure 18-9). The VT terminated during RF energy delivery and could no longer be induced subsequently. At this point the procedure was terminated. The patient had no recurrence of her VT or PVCs.
FIGURE 18-4 (A) Single lead ECG tracing from a Holter recording showing a trigeminal rhythm. (B) Same single lead tracing showing nonsustained VT. The single lead tracing of the PVC is very similar to the nonsustained VT.
FIGURE 18-5 Surface ECG tracings I, II, III, and V1 as well as recordings from a multipolar catheter that is deployed within the great cardiac vein. The earliest timing within the coronary venous system was an activation time of −25 ms.
FIGURE 18-6 (A) Twelve-lead ECG morphology of the targeted VT. (B) Pace-map from within the coronary venous system from the earliest site displayed in Figure 18-5.
FIGURE 18-7 (A) Twelve-lead ECG of the targeted VT and intracardiac tracings illustrating the earliest activation time recorded from the left aortic cusp. (B) Pacing from this location failed to reproduce the same morphology of the targeted VT. Pacing was performed with a high output (20 mA) in order to achieve capture.
FIGURE 18-8 Three-dimensional reconstruction of the left ventricular cavity by intracardiac echocardiography. The left ventricle is displayed from a right anterior oblique view. The left main ostium is marked (olive tag) as well as the aortic valve annulus (AVA) and the left ventricular apex. The distance of the site where radiofrequency energy was delivered to the left main ostium measured 12.6 mm.
FIGURE 18-9 Shown is a right anterior oblique view of the ablation catheter within the left aortic cusp. A diagnostic coronary catheter is placed in the left main coronary artery while radiofrequency energy is delivered.
PATHOPHYSIOLOGY AND MECHANISM
Triggered activity is the etiology of most outflow tract ventricular tachycardias. Most often, outflow tract tachycardias originate from the right ventricular outflow tract, but can also originate from the aortic cusps, the epicardium, or the pulmonary arteries.
DIAGNOSIS AND MAPPING
The 12-lead ECG is critical in identifying the site of origin of an outflow tract VT. An early transition in lead V3 and a broad R wave in lead V1 and V2 points toward the aortic cusps, the mitral annulus, or the basal left ventricular epicardium. A multipolar catheter within the great coronary vein (see Figures 18-6 and 18-8) demonstrated early activation in the epicardium. However, within the left aortic cusp, a site with even earlier timing was identified. Intracardiac echocardiography helped in identifying critical structures like the left main ostium, and in determining the approximate distance of the left main ostium to the target site within the cusp. The pace-map of the multipolar catheter (electrodes 9/10, the site of the earliest activation within the coronary venous system) that was placed in the great cardiac vein showed a better pace-map compared to the site where the VT was actually ablated, which had a substantially earlier activation time. Unfortunately, pace-mapping in the aortic cusps often requires a high output to capture myocardial tissue, resulting in a mismatch of the pace-map with the targeted ventricular arrhythmia. This was the case in this patient as well.
Delivery of radiofrequency energy was performed after identification of the left main coronary artery and confirmation that the target site was at a safe distance (ie, >7 mm) from the ostium of the left main coronary artery. Simultaneous injection of the left main coronary artery as radiofrequency energy was delivered was performed, since the earliest site of activation appeared closer to the left main coronary artery than expected (see Figure 18-9). A 3.5-mm irrigated-tip catheter was used for this purpose using a power of up to 30 watts.
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