Ventricular Tachycardia and Ventricular Fibrillation in Patients with Short P-R Intervals and Narrow QRS Complexes

Eleven patients with short P-R Intervals and narrow QRS complexes had ventricular tachycardia due to organic heart disease: mitral valve prolapse with mitral insufficiency (2 patients); alcoholic (?) cardiomyopathy (2 patients); and coronary artery disease (7 patients). Intracardiac studies showed short A-H intervals during sinus rhythm in all cases. The onset of ventricular fibrillation (which, to our knowledge, has not been observed in patients having short P-R and A-H intervals coexisting with narrow QRS complexes) was documented in 4 cases. Only 1 patient (with quinidine syncope) had been premedicated. In the 3 other patients the episodes of ventricular fibrillation appeared during bouts of atrial fibrillation with rapid ventricular rates which could have been an expression of the “enhanced A-V conduction” that had been manifested in sinus beats by short P-R and A-H intervals. In clinical settings and physiological conditions proven to be hemodynamicaliy unstable (such as transient ischemia or acute myocardial infarction) these rapid ventricular rates could have led to ventricular fibrillation; directly because of the R-on-T phenomenon, and/or indirectly due to decreased coronary perfusion. Ventricular tachycardia and ventricular fibrillation due to organic heart disease probably occur more often than suggested by the few reported cases in the literature. Its significance, however, has to be clarified by further prospective studies     

Atrial Pacing: Intracardiac Conduction Assessed by His Bundle Electrograms Acquired from the Permanent Atrial Electrode at Implantation

His bundle electrograms were recorded from conventional J-shaped atrial electrodes at implantation in twelve consecutive patients who had sinus node disorder. Five patients with impairment of atrioventricular conduction, received atrioventricuIar (DVI) pacemakers. His bundle recording by this method is simple and reliable, avoids the discomfort of the conventional technique, and represents a new application for the well established atrial "J" electrode.     

Noninvasive Recording of the His Bundle Electrogram: Value of Supplementary Verapamil

We obtained noninvasive recordings of the His bundle electrogram using the Marquette high resolution MAC unit in 65 patients and 5 normal subjects. Overlap of atrial activity prevented identification of a His potential in 25 subjects, in 23 of whom the PR interval was equal to or less than 160 ms. After intravenous verapamil (10 mg) the AH interval was lengthened, with an increase in the PR interval of 10-60 (mean 20) ms. A characteristic His bundle electrogram was recorded in 48 of the 70; in 8 there was persistent atrial activity and in 4 electrical interference could have obscured a His potential. In 10 patients the absence of a His complex despite a clear "window" of at least 70 ms between the end of atrial activity and the onset of ventricular depolarization suggested that its vector was outside the plane of the electrode arrangement, or that there was a prolonged H-V interval; the latter has been confirmed in 2 patients. Intracardiac His bundle recordings in 25 subjects who had characteristic surface electrical activity of the His bundle disclosed good correlation between invasive and noninvasive measurements of the H-V interval. This noninvasive technique using portable equipment, which permits serial evaluation of the His bundle electrogram, may facilitate prospective studies in patients with conduction disease.     

His Bundle Electrogram in Patients with Acute Myocardial Infarction

Thirty-seven patients with acute myocardial infarction complicated by atrioventricular or bundle branch block, or a combination of both, has His bundle electrogram studies performed during their stay in the coronary care unit. The acute mortality of the 14 patients with a complicating bundle branch was 50%. Pump failure was the main cause of death. Three patients in this group had a prolonged H-V interval and one patient had a split blundle of His. The presence or absence of a prolonged H-V interval did not affect mortality in this group of patients. The acute mortality of the 16 patients with an inferior wall myocardial infarction was 6%. The H-V interval was normal in all but one of these patients. The atrioventricular block was caused by a proximal block in all cases. The acute mortality of the seven patients with an anterior wall myocardial infarction was 29%. The H-V interval was prolonged in two of seven patients. Pump failure was the acute cause of the deaths. The presence or absence of a prolonged H-V interval did not affect mortality in this group of patients.     

Atrial and His Bundle Stimulation with an Accessory Nodo-Ventricular Connection

A 39-year-old man with a history of frequent paroxysmal tachycardias for 27 years was referred for electrophysiology study. His resting electrocardiogram showed left bundle branch block, which persisted during paroxysmal tachycardia. Electrophysiology study demonstrated the presence of a right-sided accessory nodo-ventricular connection.¹ The case is of particular importance as it illustrates the diagnostic value of QRS normalization with left atrial pacing and the therapeutic use of rapid His bundle pacing to terminate the tachycardia.     

His Bundle Ablation with the Laser Thermal Probe ("Hot Tip"): A Feasibility Study

Successful percutaneous ablation of the bundle of His requires accurate localization together with delivery of the minimum effective energy to avoid unwanted effects. The energy output from laser sources can be controlled very precisely but is not easily directed to the bundle of His using conventional fiber optics. The laser thermal probe ("hot tip") consists of an optical fiber and a terminal metal cap that is rapidly heated during energy delivery. When applied to cadaver hearts at energies of 100-150 joules (10 watts for 10-15 seconds) the 2.0-mm diameter peripheral artery probe was able to damage the bundle of His without extensive surrounding damage. The right ventricular free wall and interventricular septum were perforated during some applications at these energies leaving a tract with a diameter of less than 2.0 mm. The atrioventricular (AV) membranous septum, Foramen Ovale, right atrial appendage, and septal leaflet of the tricuspid valve were more resistant at these energy levels and perforations were always less than 1.0 mm in diameter. The probe was modified for use during electrophysiological studies and good quality unipolar electrograms were recorded from the metal cap confirming that the probe could be accurately positioned adjacent to the bundle of His. The laser thermal probe deserves further study as a "self directing" ablation tool.     

Idiopathic Ventricular Tachycardia Originating from the Left Ventricle Near the His Bundle

A 62‐year‐old man with idiopathic ventricular tachycardia (VT) exhibiting left bundle branch block and left inferior axis QRS morphology with a Qr in lead III underwent electrophysiological testing. Successful ablation was achieved in the left ventricle (LV) at a site with an excellent pace map, adjacent to the His bundle electrogram recording site. At that site, the sequence of the ventricular electrogram and late potential recorded during sinus rhythm reversed during spontaneous premature ventricular contractions with the same QRS morphology as the VT. This case shows that VT can arise from the LV ostium adjacent to the membranous septum. (PACE 2010; 33:e114–e118)     

Non-invasive Recording of His Bundle Activity in Patients with Wolff-Parkinson-White Syndrome

Ten patients with Wolff-Parkinson-White syndrome underwent external His bundle recording using an advanced signal-averaging technique. Surface ECG waveforms were recorded and digitized at 1.28 kHz (10 bit resolution) and then averaged with a CDC-6600 computer. A cross-correlation function, operating in the frequency domain (using the Fast Fourier Transform algorithm) was employed to extract fiducial synchronizing marks for the waveform alignment. Using this technique, reliable His bundle activity could be recorded in nine of ten patients. There was a good correlation between the HQ and HV intervals obtained during external and internal His bundle recordings, respectively, in seven patients who underwent both recordings. Administration of ajmaline enabled to obtain the His bundle activity using a digital filter with low frequency cut-off of 30 Hz as compared to the cut-off of 150 Hz which was necessary during control to reduce the electrical activity of the delta wave. We conclude that using a computerized cross-correlation signal-averaging technique enables the external His bundle recording in patients with WPW syndrome.     

Detection of Atrial Fibrillation During Sinus Tachycardia Induced by Exercise in Patients with Implantable Atrial Defibrillators

Accurate detection of atrial fibrillation (AF) is essential for appropriate operation of an implantable atrial defibrillator (IAD). However, during episodes of sinus tachycardia, distinction between AF and sinus rhythm (SR) using the quiet interval and baseline crossing analysis in the detection algorithm of the IAD may be difficult. The efficacy of this AF detection algorithm was tested in five patients implanted with an IAD (MFTRIX, Model 3000 or 3020, InControl Inc.) during treadmill exercise testing. The IADs were programmed to Monitor Mode with a wake up cycle of 1 minute for AF detection using the device nominal parameters or modified parameters, and to mark rhythms appropriate for shock delivery. A mean peak heart rate of 137 ± 26 beats/min was reached during maximum exercise, and one patient developed transient AF. Seventy-eight (75 in SR, 3 in AF) and 91 (89 in SR, 2 in AF) runs of AF detection were performed using the nominal and modified parameters, respectively. The IAD detected AF and SR accurately, except for one episode of false-positive AF detection during sinus tachycardia at the nominal settings, but inappropriate shocks were prevented by minimum RR interval criteria that limited discharge at high heart rate. These results indicate that the AF detection algorithm in the IAD may become more vulnerable to false-positive AF detection during sinus tachycardia, which were avoided by reprogramming the Quiet Interval and minimum RR interval criteria for AF detection. Exercise testing appeared useful to program optimal settings of the IAD in preparation for daily activities.     

The Value of Rate Regularity and Multiplicity Measures to Detect Ventricular Tachycardia in the Presence of Atrial Fibrillation or Flutter

The predominant cause of inappropriate therapy by implantable antitachycardia devices with pacing and nonpacing cardioverter defibrillators, is mistaking a fast ventricular response during atrial fibrillation or flutter with true ventricular tachycardia (VT). The distinction between these arrhythmias is an important consideration in addressing the problem of reducing false-positives in detection mechanisms for implantable devices. Dual chamber analysis that examines atrial and ventricular event ratios has been proposed as a solution to this problem, but would still fail in distinguishing paroxysmal VT requiring treatment from a fast but otherwise benign ventricular response during atrial fibrillation or flutter. In this study, two methods for discriminating these tachyarrhythmias were evaluated. Method 1 examined ventricular rate and rate regularity as a method for VT detection. Method 2 combined rate and regularity as well as an additional multiplicity criterion for recognition of atrial flutter with a fast ventricular response. In 20 patients. Method 1 had 100% sensitivity of VT detection and 80% specificity for detection of atrial fibrillation or flutter. Method 2 had 90% sensitivity and 90% specificity. These results suggest that use of these algorithms in future implantable devices would result in a decrease in false-positive device therapies.     

Atrioventricular Nodal Supraventricular Tachycardia with 2:1 Block above the Bundle of His

A patient with narrow complex supraventricular tachycardia underwent electrophysiological study at which time a tachycardia was initiated which had 2:1 AV conduction, with block occurring above the His bundle. The modes of tachycardia initiation, as well as the responses to atrial and ventricular premature depolarizations during tachycardia, made a diagnosis of atrioventricular nodal reentry as the tachycardia mechanism. The unusual finding of 2:1 supra-His block suggests the presence of tissue situated between the tachycardia circuit and His bundle, and effectively excludes the possibility of a His-atrial bypass tract as the retrograde limb of the tachycardia circuit.     

Intravenous Adenosine During Atrioventricular Reentrant Tachycardia: Induction of Atrial Fibrillation with Rapid Conduction Over an Accessory Pathway

Adenosine is considered to be a safe agent for termination of orthodromic atrioventricular reentrant tachycardia in patients with accessory pathways. A case with initially successful accessory pathway ablation and without preexcitation during sinus rhythm is presented, in which intravenous adenosine (6 mg) during orthodromic tachycardia was followed by atrial fibrillation and sudden onset of preexcitation with subsequent rapid ventricular response with moderate hemodynamic compromise.     

Clinical Utility of Intraatrial Pacemaker Stored Electrograms to Diagnose Atrial Fibrillation and Flutter

POLLAK, W.M., et al. : Clinical Utility of Intraatrial Pacemaker Stored Electrograms to Diagnose Atrial Fibrillation and Flutter. The purpose of this study was to determine if intraatrial electrograms (EGMs) are required to diagnose specific types of atrial tachyarrhythmias detected by pacemaker diagnostics. DDD pacemakers in 56 patients were programmed to store episodes of atrial tachyarrhythmias. Some episodes had a stored atrial EGM snapshot of the atrial tachyarrhythmia. The EGMs were analyzed to confirm whether the stored episodes were true atrial tachyarrhythmias or other pacemaker-sensed events. EGM confirmation of atrial tachyarrhythmias correlated with increasing duration and rate of episodes. In particular, using EGMs, 8 (18%) of 44 episodes < 10 seconds in duration confirmed atrial tachyarrhythmias compared to 16 (89%) of 18 episodes > 5 minutes in duration (  P < 0.001  ). Only 10 (18%) of 56 detected atrial arrhythmia episodes at rates < 250 complexes per minute were confirmed by the atrial EGM as true arrhythmias compared to 33 (57%) of 58 detected episodes at rates > 250/min (  P < 0.001  ) Twenty-nine (91%) of 32 EGM confirmed episodes of atrial fibrillation/flutter had an atrial rate > 250 complexes per minute and were a minimum of 10 seconds in duration. Fifteen (88%) of 17 episodes meeting the combined stored data criteria of > 250 complexes per minute and duration > 5 minutes were confirmed as atrial fibrillation or flutter by stored EGMs. Atrial EGMs identified that 71 (62%) of 114 stored high atrial rate (HAR) episodes were events other than true atrial tachyarrhythmias. Pacemaker diagnostic data with intraatrial EGMs can diagnose specific atrial tachyarrhythmias and identify other pacemaker-sensed events. Stored episodes > 250 complexes per minute and > 5 minutes in duration had a high correlation with atrial fibrillation and flutter.     

Role of the Atrial Rate as a Factor Modulating Ventricular Response during Atrial Fibrillation

Background: During atrial fibrillation (AF), RR interval histograms show different populations of predominant RR (pRR) intervals. These pRR intervals have been suggested to be multiples of the refractory period of the atrioventricular (AV) node or caused by the existence of a dual AV node physiology. In this study, the hypothesis that pRR intervals are related to the dominant atrial fibrillatory rate is tested. Methods: In this study, Holter electrocardiogram signals from 55 patients with persistent AF were analyzed. Number and position of pRR intervals were detected and compared with mean and standard deviation of the dominant atrial cycle length (DACL). In addition, effects of an enhancement of vagal activity and rate‐control treatments (β‐blockers and verapamil) were evaluated. Results: In all patients with more than one pRR interval and in 47% with one pRR interval, RR interval populations were statistically related with multiples of the DACL. During night activities and during β‐blockers treatment, mean ventricular rate was decreased (P < 0.01). This change was associated with a variation in the percentage of occurrences of each pRR (P < 0.01), whereas no statistical differences were present in the mean DACL or in the position of pRR intervals. A variation of the DACL due to verapamil was associated with a consistent modification in the position of the pRR intervals. Conclusion: The relation between pRR and multiples of the DACL during AF suggests that more probable RR intervals are caused by different conduction ratios of the atrial rate. (PACE 2010; 33:1510–1517)     

Radiofrequency Catheter Ablation and Modulation of Atrioventricular Conduction in Patients with Atrial Fibrillation

We attempted radiofrequency ablation of the AV junction with a sequential right- and left-sided approach in 78 patients affected by severely symptomatic, drug refractory atrial fibrillation. Stable third-degree A V block was obtained in 99% of cases and, after 3 months, persisted in 92% of cases. Single session, stepwise, radiofrequency modulation of the AV node was attempted in 13 patients with paroxysmal atrial fibrillation. During sinus rhythm, ablation of the slow and fast AV node pathways was performed in order to increase the nodal refractory period or to slow conduction. Clinically successful modulation of AV conduction was achieved in 15% of cases and persisted during a 3-month follow-up. In conclusion. AV junction ablation is a well-established means of treating atrial fibrillation, but implies the implant of a permanent pacemaker. AV node modulation avoids the pacemaker implant, but is efficacious only in a minority of patients. Thus, in patients affected by paroxysmal atrial fibrillation, AV modulation should be attempted first; if this is ineffective. AV ablation can be performed during the same session.     

Spatial Relationships between the Pulmonary Veins and Sites of Complex Fractionated Atrial Electrograms During Atrial Fibrillation

Background: Pulmonary vein (PV) isolation is used for the treatment of atrial fibrillation (AF). Complex fractionated atrial electrogram (CFAE) mapping has been introduced to guide AF ablation. However, the spatial relationship between PV and CFAE is not well defined.
Methods and Results: The study included 21 patients (mean age 57 ± 11 years, 17 men, 14 paroxysmal, two persistent, and five long-standing persistent AF) referred for PV isolation. Electrograms were sampled for 8 seconds at each site during stable AF (13 induced). High-frequency was defined as <80 ms of CFAE value. The distance between CFAE and the nearest PV ostium was measured. The PV ostia and antra were demarcated by fluoroscopy guidance and endocardial reconstruction. Among 82 PV mapped (left common four, superior 17, inferior 17; right superior 21, inferior 21, middle 2), 52.4% and 25.6% of high-frequency CFAE were located on the anterior and posterior walls, respectively, inside the PV or at the ostium. No high-frequency CFAE was observed in two out of 60 and one out of 20 PV anteriorly, versus seven out of 60 and 11 out of 20 PV (P < 0.001) posteriorly, in paroxysmal and persistent AF, respectively. In the PV with high-frequency CFAE, the mean shortest distances to the PV ostia in paroxysmal versus persistent AF were 2.7 ± 5.1 versus 7.4 ± 5.4 mm anteriorly (P < 0.01), and 6.5 ± 6.4 versus 9.4 ± 8.4 mm posteriorly (ns).
Conclusions: During PV isolation, extending the ablation lesions by up to 10 mm from the PV ostia might cover most high-frequency CFAE around the PV antra. High-frequency CFAE were more often located in the PV ostia in paroxysmal than in persistent AF.     

Using Intracardiac Catheter Recordings from the His and Proximal Coronary Sinus to Distinguish Isthmus Conduction Block During Catheter Ablation of Type I Atrial Flutter

Isthmus conduction block, demonstrated with the use of multipolar catheter recordings, is considered the preferred endpoint for ablation of type I atrial flutter. This study investigated the feasibility of using recordings from the His and coronary sinus (CS) to document isthmus conduction block. Isthmus conduction block was produced with linear radiofrequency (RF) ablation in 27 patients with type I atrial flutter. In 13 patients (group I), RF was delivered until bidirectional isthmus conduction block was demonstrated with multipolar Halo catheter recordings. In 14 patients (group II), RF was delivered during pacing from the lateral isthmus at 600 ms until a reversal in activation of the proximal CS and His occurred. At this point, data from the Halo recordings were reviewed to see if reversal correlated with conduction block; if not, further ablation was performed until block was demonstrated. The initial reversal in His and CS activation during RF energy delivery correlated with isthmus block in only 4 (28.6%) of 14 patients in group II. Additional RF delivery produced isthmus block in the other ten patients resulting in a further increase in the St-CS interval of 35 ± 20 ms. A His-CS interval of at least -40 ms signified isthmus block with a sensitivity and specificity of 48% and 100%, respectively. Reversal in His-CS activation during pacing from the lateral margin of the isthmus is not specific for the creation of isthmus block. While activation of the proximal CS bipole > 40 ms after activation of the His appears specific for isthmus block, the low sensitivity of this finding limits its clinical use.     

Incremental Changes in QRS Duration Predict Mortality in Patients with Atrial Fibrillation

Background: The purpose of this study was to evaluate serial changes in QRS duration in the 12-lead electrocardiogram (ECG) and their prognostic value in patients with atrial fibrillation (AF).
Methods: Retrospective evaluation of the 12-lead ECG was performed in 822 patients with AF. Inclusion criteria included AF in two sequential ECGs and an echocardiogram obtained within 7 days of the second ECG. The mean age of the 228 patients enrolled in the study was 71.2 ± 12.9 and 45.6% were females. Nearly half of the patients had hypertension (49.5%) and a history of heart failure (44.7%). The patients were followed for 21 ± 19 months, and the end point was all-cause mortality.
Results : Cox proportional hazards analysis demonstrated that the independent predictors of mortality in AF patients were age, renal insufficiency, a history of stroke, heart rate, incremental QRS prolongation (P = 0.0418), and the absence of warfarin use. Patients with QRS prolongation >15 ms had a worse prognosis than those with QRS prolongation ≤15 ms (P = 0.0019).
Conclusions: A progressive increase in QRS duration predicted a poor prognosis in patients with AF in our study. A prospective study is needed to substantiate the prognostic value of QRS prolongation in AF patients.