Use of the Surface Electrocardiogram to Define the Nature of Challenging Arrhythmias.

Despite unprecedented advances in technology, the electrocardiogram (ECG) remains essential to the practice of modern electrophysiology. Since its emergence at the turn of the nineteenth century, the form of the ECG has changed little. What has changed is our ability to understand the complex mechanisms that underlie various arrhythmias. In this article, the authors review several important principles of ECG interpretation by providing illustrative tracings. The authors also highlight several important concepts that be can used in ECG analysis. There are several fundamental principles that should be considered in ECG interpretation.

Catheter ablation of haemodynamically unstable or non-sustained ventricular tachycardia.

BACKGROUND: Ventricular tachycardia (VT) may be haemodynamically unstable or non-sustained, interfering with detailed activation mapping. Non-contact mapping permits beat-by-beat analysis of VT, projected upon a 3-dimensional reconstructed geometry of the cardiac chamber. Objective - The aim of the present study is to determine the utility of non-contact endocardial mapping to guide ablation of haemodynamically unstable VT or non-sustained VT. METHODS AND RESULTS: Eighteen VTs in 17 patients were induced (cycle length 336 +/- 58 ms) and mapped. Three patients were mapped during premature ventricular complexes (PVCs) because sustained VT could not be induced. Analysis of the archived non-contact activation maps was performed to identify the exit point and/or the diastolic pathway of theVT reentry circuit. The endocardial exit points (10 +/- 16 ms before QRS) were defined in 17/18 VTs (94%). A diastolic pathway was identified in 5/6 ischaemic VTs. The earliest activation sites were identified in all 3 patients with PVCs. Radiofrequency current was applied around the exit point or to create a line of block across the diastolic pathway. Catheter ablation was performed in 17/18 VTs, including 3 patients mapped using only PVCs. Ablation was successful in 16/18 VTs (89%) and in 1 5/17 patients (82%). Catheter ablation was not performed in one patient (peri-hisian VT) and was unsuccessful in one patient (mapped during PVCs). CONCLUSIONS: Non-contact endocardial mapping is useful to guide radiofrequency catheter ablation of untolerated or non-sustained VTs.

Echo-driven V-V optimization determines clinical improvement in non responders to cardiac resynchronization treatment.

Echocardiography plays an integral role in the detection of mechanical dyssynchrony in patients with congestive heart failure and in predicting beneficial response to cardiac resynchronization treatment. In patients who derive sup-optimal benefit from biventricular pacing, optimization of atrioventricular delay post cardiac resynchronization treatment has been shown to improve cardiac output. Some recent reports suggest that sequential ventricular pacing may further improve cardiac output. The mechanism whereby sequential ventricular pacing improves cardiac output is likely improved inter and possibly intraventricular synchrony, however these speculations have not been confirmed. In this report we describe the beneficial effect of sequential V-V pacing on inter and intraventricular synchrony, cardiac output and mitral regurgitation severity as the mechanisms whereby sequential biventricular pacing improves cardiac output and functional class in 8 patients who had derived no benefit or had deteriorated after CRT. Online tissue Doppler imaging including tissue velocity imaging, tissue synchronization imaging and strain and strain rate imaging were used in addition to conventional pulsed wave and color Doppler during sequential biventricular pacemaker programming.

Vein of Marshall activity during sustained atrial fibrillation.

BACKGROUND: The human vein of Marshall (VOM) activation patterns during sustained (persistent or permanent) atrial fibrillation (AF) have not been studied in detail. METHODS: VOM was cannulated via coronary sinus in six patients (67.3 +/- 7.5 years old) having either persistent (N = 4) or permanent (N = 2) AF presenting for radiofrequency catheter ablation. RESULTS: At sinus rhythm in patients with persistent AF, there were frequent ectopic beats from the VOM as well as from left and right pulmonary veins (PVs). The ectopic activity originating from the VOM was highly fragmented. The P wave morphology associated with VOM ectopy was isoelectric in leads I and aVL, positive in leads II, III, aVF, and V2-V5, which is similar to the P wave morphology associated with left PV ectopic beats. During AF the activation cycle length at VOM was 140 +/- 31 msec, which was significantly shorter than that in other atrial sites (P < 0.05). Similarly, the dominant frequency at VOM (9.71 Hz +/- 1.52 Hz) was significantly higher than that at other atrial sites (P < 0.0001). In one patient, VOM ablation was associated with AF termination during radiofrequency energy application. CONCLUSIONS: Ectopic activity with complex local electrogram originating from VOM is commonly seen in patients with sustained AF. The P wave morphology associated with the ectopic beats from VOM and from the left PVs was similar. The rate of activation at VOM is significantly faster than other atrial and PV sites during AF. These findings show that rapid activation is present in the VOM during sustained AF in human patients.

Electrical connections between left superior pulmonary vein, left atrium, and ligament of Marshall: implications for mechanisms of atrial fibrillation.

The importance of the ligament of Marshall (LOM) to rapid activations within the left superior pulmonary vein (LSPV) during atrial fibrillation (AF) remains poorly understood. We aimed to characterize the importance of electrical coupling between the LSPV with the left atrium (LA) and the LOM in the generation of high-frequency activations within this PV. We performed high-density mapping of the LSPV-LA-LOM junction in eight dogs, using 1,344 electrodes with a 1-mm resolution before and after posterior ostial ablation to diminish PV-LA electrical connections. A LOM potential was recordable up to 6.5 mm (SD 2.2) into the LSPV in all dogs during sinus rhythm (SR) and LA pacing. Functional LOM-LSPV electrical connections bypassing the PV-LA junction were present in five of eight dogs. Direct LOM-LSPV connections contributed to 46.5% (SD 16.0) of LSPV activations during AF, resulting in a greater propensity to develop focal activations (P < 0.05) and a higher activation rate during AF of LSPVs with direct LOM connections compared with those without (P < 0.03). Posterior LSPV ostial ablation without damaging the anterior wall or LOM slowed residual LA-PV conduction (P < 0.001). This diminished PV-LA coupling prevented the reinduction of LSPV focal activations in all dogs. However, persistent LOM focal activations in two dogs continued to activate the LSPV rapidly [cycle length 151.8 ms (SD 4.8)] via direct LOM-LSPV connections. LOM-LSPV connection forms an accessory pathway that contributes to the electrical coupling between LSPV and LA during SR and AF. This pathway may contribute to rapid activations within the LSPV during AF.

[Noncontact endocardial mapping to guide ablation for hemodynamically unstable or nonsustained ventricular tachycardia].

OBJECTIVE: To determine the feasibility and assess the validity of noncontact endocardial mapping to guide ablation of hemodynamically unstable or nonsustained ventricular tachycardia (VT). METHODS: Noncontact mapping permitted individual-beat analysis of ventricular arrhythmias. Three-dimensional electroanatomical mapping allowed detailed reconstruction of a chamber geometry and activation sequence. Eighteen hemodynamically unstable or nonsustained VTs were induced (cycle length: 336 ms +/- 58 ms) in 17 patients and mapped by noncontact mapping using an EnSite 3000 system performed for the guidance of catheter ablation. RESULTS: Three patients were mapped during premature ventricular complexes (PVCs) because sustained VT could not be induced. Analysis of the archived noncontact activation maps was performed to identify the exit site and/or the diastolic pathway of the VT reentry circuit. The endocardial exit sites 10 ms +/- 16 ms before QRS were defined in 9 right ventricular outflow tract (RVOT) and 5 ischemic VTs. The diastolic pathway was identified in 5 ischemic VTs. The earliest endocardial diastolic activity preceded the QRS onset by 60.1 ms +/- 42.6 ms. The earliest activation sites were identify in 3 patients with nonsustained VTs or PVCs. Radiofrequency current was applied around the exit site or to create a line of block across the diastolic pathway. Catheter ablation was performed in 17/18 (94%) VTs and 15/17 (88%) VTs was successfully ablated. Two (67%) of the three patients with non-sustained VTs were mapped and successfully ablated during PVCs. Catheter ablation was not performed in 1 patient (peri-Hisian VT) and was unsuccessful in 2 patients. CONCLUSION: Noncontact endocardial mapping is able to be used to guide ablation of untolerated or nonsustained VTs.

Radiofrequency ablation of accessory pathways guided by the location of the ligament of Marshall.

INTRODUCTION: In humans, complex muscle connections are present near the junction between the coronary sinus (CS) and the ligament of Marshall. We hypothesize that these complex muscle connections participate in accessory pathway conduction. METHODS AND RESULTS: Electrophysiologic studies and radiofrequency ablation were performed in four patients with refractory AV reciprocating tachycardia. Case 1 was a 19-year-old male. Marshall bundle potentials were recorded by a catheter in the vein of Marshall. Radiofrequency energy application from that catheter resulted in successful ablation. Case 2 was a 43-year-old male who had undergone two unsuccessful radiofrequency ablation procedures of a left free-wall accessory pathway by conventional techniques. Coronary sinus electrography during tachycardia and ventricular pacing showed a long V-A interval. Radiofrequency energy application directed toward the ligament of Marshall eliminated the pathway conduction. Case 3 was a 17-year-old male who had undergone three unsuccessful ablation procedures. Radiofrequency energy application directed toward the stump of the vein of Marshall successfully eliminated the pathway conduction. Case 4 was a 20-year-old female who underwent one unsuccessful ablation procedure. Successful ablation was achieved in the left atrial free wall, approximately 1 cm above the AV annulus, at a location near the ligament of Marshall. CONCLUSION: We report four patients in whom successful accessory pathway ablation was achieved by targeting the ligament of Marshall. These findings suggest that the complex muscle connections among the coronary sinus, ligament of Marshall, and left atrium is important in accessory pathway conduction and maintenance of circus movement tachycardia in these patients.

Selective atrionodal input ablation for induction of proximal complete heart block with stable junctional escape rhythm in patients with uncontrolled atrial fibrillation.

BACKGROUND: The study tests the hypothesis that ablating all inputs to the atrioventricular (AV) node can result in complete heart block with stable junctional escape rhythm. METHODS AND RESULTS: We attempted atrionodal input ablation in 76 consecutive patients with uncontrolled atrial fibrillation. Fast and slow pathways were first ablated. If there was no AV block, additional energy applications were done between fast and slow pathway locations. The patients were followed for 42 +/- 11 months. Group I (n = 57) comprised patients with complete heart block and junctional escape rhythm (53 +/- 4 beats/min) at the end of the procedure. The escape rhythm remained stable throughout follow-up. Group II (n = 15) were patients who failed the stepwise atrionodal input ablation and required AV junctional ablation guided by His bundle potential to achieve complete heart block. Four patients showed a slow escape rhythm after ablation (33 +/- 4 beats/min). Others had no escape rhythm. All 15 pts remained pacemaker dependent. The total death rate of groups I and II was 18/57 (31.6%) vs 10/15 (66.7%), respectively (p < 0.02). These differences could not be explained by a difference of left ventricular ejection fraction (0.42 +/- 0.07 vs 0.41 +/- 0.04, respectively, p = NS). CONCLUSIONS: (1) In most patients, ablation of both fast and slow pathways did not result in complete heart block, indicating the presence of multiple atrionodal inputs. (2) Ablation of all atrionodal inputs may result in complete heart block with stable junctional escape rhythm. (3) As compared with AV junctional ablation, atrionodal input ablation was associated with a lower mortality rate on long-term follow up.

Simultaneous biatrial computerized mapping during permanent atrial fibrillation in patients with organic heart disease.

INTRODUCTION: Activation patterns during permanent atrial fibrillation (AF) in patients with organic heart diseases are unclear. METHODS AND RESULTS: We studied six patients with permanent AF and organic heart diseases undergoing surgery. The duration of AF averaged 4.9+/-7.6 years. Computerized epicardial mappings of the right atrial (RA) free wall and the left atrial (LA) posterior wall were simultaneously performed with 224 bipolar electrodes at 3-mm spatial resolution. In the RA, large wavefronts and conduction blocks were frequently observed. The lines of block correlated with the crista terminalis and large pectinate muscles. In contrast, the LA had rapid repetitive activities originated from corners of the electrode plaque, near the four pulmonary veins (PVs). On average, 2.8+/-1.2 sites of rapid repetitive activities were identified per patient. They activated continuously, intermittently, or alternately during AF. The mean activation cycle length in the RA (196+/-22 msec) was significantly longer than that in the LA (179+/-26 msec; P = 0.004). The maximum dominant frequency in the LA was higher than that in the RA (6.41+/-1.18 Hz vs 5.66+/-0.55 Hz; P = 0.049). The maximum dominant frequency was consistently located in areas with rapid repetitive activations near the PVs. CONCLUSION: During human permanent AF associated with organic heart diseases, the activation cycle length was shorter in the LA posterior wall than in the RA free wall. Rapid repetitive activities are consistently observed in the LA posterior wall, at or near the PVs.