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.

Prediction of sudden cardiac death by fractal analysis of heart rate variability in elderly subjects

OBJECTIVES

The aim of this study was to test the hypothesis that abnormal scaling characteristics of heart rate (HR) predict sudden cardiac death in a random population of elderly subjects.

BACKGROUND

An abnormality in the short-term fractal scaling properties of HR has been observed to be related to a risk of life-threatening arrhythmias among patients with advanced heart diseases. The predictive power of altered short-term scaling properties of HR in general populations is unknown.

METHODS

A random sample of 325 subjects, age 65 years or older, who had a comprehensive risk profiling from clinical evaluation, laboratory tests and 24-h Holter recordings were followed up for 10 years. Heart rate dynamics, including conventional and fractal scaling measures of HR variability, were analyzed.

RESULTS

At 10 years of follow-up, 164 subjects had died. Seventy-one subjects had died of a cardiac cause, and 29 deaths were defined as sudden cardiac deaths. By univariate analysis, a reduced short-term fractal scaling exponent predicted the occurrence of cardiac death (relative risk [RR] 2.5, 95% confidence interval [CI], 1.9 to 3.2, p < 0.001) and provided even stronger prediction of sudden cardiac death (RR 4.1, 95% CI, 2.5 to 6.6, p < 0.001). After adjusting for other predictive variables in a multivariate analysis, reduced exponent value remained as an independent predictor of sudden cardiac death (RR 4.3, 95% CI, 2.0 to 9.2, p < 0.001).

CONCLUSIONS

Altered short-term fractal scaling properties of HR indicate an increased risk for cardiac mortality, particularly sudden cardiac death, in the random population of elderly subjects.

Fractal analysis and time- and frequency-domain measures of heart rate variability as predictors of mortality in patients with heart failure

Time-domain measures of heart rate (HR) variability provide prognostic information among patients with congestive heart failure (CHF). The prognostic power of spectral and fractal analytic methods of HR variability has not been studied in the patients with chronic CHF. The aim of this study was to assess whether traditional and fractal analytic methods of HR variability predict mortality among a population of patients with CHF. The standard deviation of RR intervals, HR variability index, frequency-domain indexes, and the short-term fractal scaling exponent of RR intervals were studied from 24-hour Holter recordings in 499 patients with CHF and left ventricular ejection fraction < or =35%. During a mean follow-up of 665 +/- 374 days, 210 deaths (42%) occurred in this population. Conventional and fractal HR variability indexes predicted mortality by univariate analysis. For example, a short-term fractal scaling exponent <0.90 had a risk ratio (RR) of 1.9 (95% confidence interval [CI] 1.4 to 2.5) and the SD of all RR intervals <80 ms had an RR of 1.7 (95% CI 1.2 to 2.1). After adjusting for age, functional class, medication, and left ventricular ejection fraction in the multivariate proportional-hazards analysis, the reduced short-term fractal exponent remained the independent predictor of mortality, RR 1.4 (95% CI 1.0 to 1.9; p <0.05). All HR variability indexes were more significant univariate predictors of mortality in functional class II than in class III or IV. Among patients with moderate heart failure, HR variability measurements provide prognostic information, but all HR variability indexes fail to provide independent prognostic information in patients with the most severe functional impairment.

Spontaneous paroxysmal atrioventricular block in patients with positive tilt tests and negative electrophysiologic studies

A subgroup of patients with neurocardiogenic syncope and negative electrophysiologic studies and adenosine tests (in 5 of 6 cases), who developed symptomatic paroxysmal atrioventricular block in the natural, ambulatory state, had positive tilt tests without advanced block. Lack of concordance between electrocardiographic changes may have reflected differential effects of the autonomic nervous system in the sinus and atrioventricular nodes, occurring in diverse circumstances and less likely because of the protocol used for tilt testing.

An innovative application of anatomic electromagnetic voltage mapping in a patient with Ebstein's anomaly undergoing permanent pacemaker implantation

A novel application of the Biosense CARTO System anatomic electromagnetic voltage mapping is presented, utilized as a guide for permanent pacemaker placement. The technique is illustrated in the successful implantation of an atrial lead in a patient with Ebstein's anomaly characterized by a severely dilated right atrium and extremely low-amplitude voltage signals, requiring a DDD pacemaker. Electromagnetic voltage mapping can be used in selected patients with structural heart disease to determine the optimal site for permanent pacemaker lead placement.

Decreased heart rate variability in appropriate sinus tachycardia and effects of rapid rate

This study revealed that conventional temporal and spectral indexes of heart rate variability were reduced in patients with sinus tachycardia due to various, easily detectable, causes. These findings were attributed to the fast rates, per se, regardless of the cause, without reflecting a particular shift in the degree of autonomic activity and tone.

Dynamic behavior and autonomic regulation of ectopic atrial pacemakers

BACKGROUND

Heart rate (HR) variability reflects the neural regulation of normal pacemaker tissue, but the autonomic nervous regulation of abnormal atrial foci originating outside the sinus node has not been well characterized. We compared the HR variability of tachycardias originating from the ectopic foci and the sinus node.

METHODS AND RESULTS

R-R-interval variability was analyzed from 24-hour Holter recordings in 12 patients with incessant ectopic atrial tachycardia (average HR 107+/-14 bpm), 12 subjects with sinus tachycardia (average HR 106+/-9 bpm), and 24 age- and sex-matched subjects with normal sinus rhythm (average HR 72+/-8 bpm). Time- and frequency-domain HR variability measures, along with approximate entropy, short- and long-term correlation properties of R-R intervals (exponents alpha(1) and alpha(2)), and power-law scaling (exponent beta), were analyzed. Time- and frequency-domain measures of HR variability did not differ between subjects with ectopic and sinus tachycardia. Fractal scaling exponents and approximate entropy were similar in sinus tachycardia and normal sinus rhythm, but the short-term scaling exponent alpha(1) was significantly lower in ectopic atrial tachycardia (0.71+/-0.16) than in sinus tachycardia (1.16+/-0.13; P<0.001) or normal sinus rhythm (1.19+/-0.11; P<0.001). Abrupt prolongations in R-R intervals due to exit blocks from the ectopic foci or instability in beat-to-beat R-R dynamics were the major reasons for altered short-term HR behavior during ectopic tachycardias.

CONCLUSIONS

HR variability obtained by time- and frequency-domain methods does not differ between ectopic and sinus tachycardias, which suggests that abnormal atrial foci are under similar long-term autonomic regulation as normal pacemaker tissue. Short-term R-R-interval dynamics are altered toward more random behavior in ectopic tachycardia, which may result from a specific autonomic disturbance or an intrinsic abnormality of ectopic atrial pacemakers.

Muscarinic receptor stimulation with edrophonium hydrochloride does not elevate ventricular fibrillation thresholds in humans

INTRODUCTION

Although decreased vagal tone, as measured by heart rate variability is a risk factor for ventricular fibrillation (VF) and sudden cardiac death, it is unknown whether increasing vagal tone has an antiarrhythmic effect. The purpose of this study was to determine whether edrophonium hydrochloride (HCI), a vagomimetic agent, increases VF threshold.

METHODS AND RESULTS

Twenty-eight consecutive patients with previously implanted defibrillators had two inductions of VF by monophasic direct-current shocks delivered at 10 to 30 msec after the T wave peak, escalating energies (0.4, 1, then 3 J) until VF was induced. If VF was not induced, this protocol was repeated at the T wave peak and then at 10 to 30 msec before the T wave until VF was induced. Patients were randomized to receive edrophonium HCl (12 to 18 mg) or no drug before repeating the protocol for the second VF induction. The mean sinus cycle length increased from 782 to 872 msec in the group receiving edrophonium HCI (P = 0.006 ). In the control group, the mean sinus cycle length remained unchanged (838 vs 858 msec). The mean energy to induce VF, coupling interval relative to the T wave, and the number of attempts to induce VF were not different between VF induction attempts 1 and 2, and they were not different between the group receiving edrophonium HCl and the control group.

CONCLUSION

In a sedated patient population with implantable defibrillators, edrophonium HCI infusion prolongs sinus cycle length but does not change inducibility of VF using T wave shocks.

Heart rate variability in inappropriate sinus tachycardia

Analysis of heart rate variability in patients with inappropriate sinus tachycardia showed a 24-hour decrease in all temporal and spectral indexes, even after attempted correction to a rate of 75 beats/min. This may have resulted from a global decrease in parasympathetic activity or from a rapid sinus rate produced by other ill-defined mechanisms.

Phenylephrine increases T wave shock energy required to induce ventricular fibrillation

INTRODUCTION

Previous reports in experimental models have suggested that ventricular fibrillation threshold (VFT) can be changed by manipulating cardiac neural tone using agents such as phenylephrine. The purpose of this study was to determine whether phenylephrine increased the energy required to induce VF in humans undergoing such induction using DC energy applied to the T wave.

METHODS AND RESULTS

In this prospective investigation, 18 consecutive patients with previously implanted cardioverter defibrillators had induction of VF by placing DC monophasic shocks into the T wave coupled 310 msec after the eighth paced ventricular complex at 400 msec. The T wave shock energy was titrated from 0.2 to 12 J until sustained VF or ventricular tachycardia was induced. Phenylephrine was infused either before the first or second VF induction in a randomized fashion to increase systolic blood pressure by more than 20 mmHg. The mean energy required to induce VF was 1.1 J at baseline and increased to 1.7 J during phenylephrine infusion (P = 0.036). The mean arterial pressure increased from 88 to 114 mmHg (P < 0.001), and the mean sinus cycle length increased from 850 to 1070 msec (P < 0.001). Ten of 13 (77%) patients with sinus cycle length prolongation had increased energy requirements to induce VF compared with only 1 of 5 patients (20%) without sinus cycle length prolongation (P < 0.05).

CONCLUSION

Phenylephrine increases VFT in humans presumably by reflex activation of the baroreceptors decreasing sympathetic and/or increasing parasympathetic cardiac efferent effects.

Defibrillation shocks over epicardial patches produce sympathetic neural dysfunction in man

INTRODUCTION

The purpose of this study was to determine the effect of direct current (DC) shocks on cardiac sympathetic innervation in humans using I-123-metaiodobenzylguanidine (MIBG) scintigraphy. Decreased efferent sympathetic neural function has been demonstrated following > 10-J DC shocks delivered through epicardial patch electrodes in dogs. To evaluate the effect of DC shocks on cardiac sympathetic innervation in humans, we performed MIBG scintigraphy in 11 patients (ages 46 to 75 years) prior to and after receiving shocks from an implantable cardioverter defibrillator (ICD).

METHODS AND RESULTS

This study was performed during an ICD generator change in 7 patients with epicardial patch electrodes and at the time of initial ICD implantation in 4 patients: 2 with epicardial patch electrodes, and 2 with a transvenous ICD system. All patients had spontaneous and inducible ventricular tachycardia. Prior to ICD implantation and remote from any cardioversions or shocks, baseline MIBG and thallium-201 scintigraphy were performed. Repeat MIBG scintigraphy was performed after delivery of ICD shocks and compared with the baseline scans to determine the effect of the shock on sympathetic neural function. The baseline scans revealed focal areas of reduced MIBG uptake in areas of thallium perfusion defects in all patients except the patient without structural heart disease whose scans were normal. Postshock, patients with epicardial patch electrodes who received at least one 24-J shock and had the postshock MIBG scan performed within 4 hours demonstrated no cardiac uptake of MIBG. Two patients with epicardial patch electrodes had no change in the postshock MIBG scans: 1 had a maximal shock of 20 J, and the other had the postshock scan delayed for 11 hours. The 2 patients with a transvenous lead system demonstrated no change in the postshock MIBG scan when compared with baseline.

CONCLUSIONS

This study demonstrates that following DC shocks delivered over epicardial patch electrodes, there is diffuse reduction in MIBG uptake that probably represents cardiac sympathetic neural dysfunction that appears to be transient. Sympathetic function does not appear to be affected by shocks delivered over a transvenous lead system.

Spontaneous echo contrast following delivery of a shock from a transvenous implantable cardioverter defibrillator

Spontaneous echo contrast has never been described in association with cardiac defibrillation. In this report, we present a patient who developed dense echo contrast as a result of a shock delivered from a transvenous defibrillator system.

Regional cardiac sympathetic denervation in patients with ventricular tachycardia in the absence of coronary artery disease

OBJECTIVES

The aim of this study was to determine whether patients with ventricular arrhythmias in the absence of coronary artery disease also have abnormalities in sympathetic innervation.

BACKGROUND

We have previously shown by cardiac sympathetic scintigraphy using iodine-123-metaiodobenzylguanidine (I-123-MIBG) that patients with ventricular tachycardia after myocardial infarction have regional cardiac sympathetic denervation. It is not known whether patients with ventricular tachycardia in the absence of coronary artery disease also have regional cardiac sympathetic denervation.

METHODS

We performed cardiac I-123-MIBG and thallium-201 single-photon emission computed tomographic (SPECT) scans at rest in 18 patients (mean age 47 +/- 18 years) with cardiomyopathy (n = 6), left ventricular hypertrophy (n = 1), valvular disease (n = 2) or a structurally normal heart (n = 9) who presented with monomorphic (n = 15) or polymorphic (n = 3) ventricular tachycardia. These scans were compared with scans in 12 control patients without ventricular tachycardia (mean age 30 +/- 17 years) who had cardiomyopathy (n = 3) or a structurally normal heart (n = 9). Cardiac sympathetic denervation was defined as myocardial areas having thallium uptake with reduced or absent I-123-MIBG uptake.

RESULTS

Twelve (67%) of 18 patients with ventricular tachycardia had regional cardiac sympathetic denervation compared with 1 (8%) of 12 patients who did not have ventricular tachycardia (p = 0.002). In the nine patients with a structurally normal heart and ventricular tachycardia, five (55%) patients had regional cardiac sympathetic denervation compared with zero of nine control patients with a structurally normal heart (p = 0.029). Five patients underwent right ventricular radiofrequency ablation for ventricular tachycardia, and sympathetic denervation was adjacent to the ablation site in one of these patients.

CONCLUSIONS

Patients with ventricular tachycardia in the absence of coronary artery disease have abnormal cardiac sympathetic innervation detectable by cardiac sympathetic scintigraphy. The role of regional cardiac sympathetic denervation in arrhythmogenesis remains to be determined.

Multiple monomorphic ventricular tachycardia configurations predict failure of antiarrhythmic drug therapy guided by electrophysiologic study

OBJECTIVES

The purpose of this study was to determine whether the induction at electrophysiologic study of sustained monomorphic ventricular tachycardias with multiple QRS complex configurations predicted failure of subsequent serial electrophysiologic study guided antiarrhythmic drug testing.

BACKGROUND

Ventricular tachycardias with multiple QRS complex configurations are associated with failure of surgical therapy for ventricular tachycardia. As such, the presence of multiple monomorphic QRS complex ventricular tachycardias during electrophysiologic testing may predict failure of subsequent medical therapy.

METHODS

Fifty-one consecutive patients with coronary artery disease had reproducible induction of monomorphic ventricular tachycardia during a baseline electrophysiologic study. Each patient then underwent a mean of 1.5 antiarrhythmic drug trials. An antiarrhythmic drug regimen that suppressed induction of ventricular tachycardia was identified in 13 (26%) of the 51 patients.

RESULTS

Patients with only one inducible monomorphic QRS complex ventricular tachycardia at baseline study were more likely to have an antiarrhythmic drug regimen identified that suppressed inducible ventricular tachycardia than were patients with multiple monomorphic QRS complex ventricular tachycardias (12[36%] of 33 patients vs. 1 [6%] of 18, p = 0.04). In seven patients with only one induced configuration of ventricular tachycardia, a second monomorphic ventricular tachycardia with a different QRS complex configuration occurred during attempts at pacing termination of the induced ventricular tachycardia. None of these seven patients then had successful drug suppression of inducible ventricular tachycardia. Thus, 12 (46%) of 26 patients with a single monomorphic QRS complex ventricular tachycardia observed at baseline study had successful serial drug testing compared with 1 (4%) of 25 patients with multiple QRS complex ventricular tachycardia configurations (p = 0.002).

CONCLUSIONS

The induction or observation of multiple monomorphic QRS complex ventricular tachycardias at baseline electrophysiologic study predicted failure of subsequent serial electrophysiologic study--guided antiarrhythmic drug therapy.

Radiofrequency ablation for atrioventricular node reentrant tachycardia: comparison between fast (anterior) and slow (posterior) pathway ablation

OBJECTIVES

We compared the electrophysiologic effects on atrioventricular (AV) node physiology of selective "fast" versus selective "slow" pathway radiofrequency ablation in 42 patients with drug-resistant AV node reentrant tachycardia who underwent 51 ablation attempts to prevent tachycardia recurrence while preserving AV conduction.

BACKGROUND

The recent introduction of radiofrequency ablation to treat AV node reentrant tachycardia allows the opportunity to study the effects of selective elimination of the different limbs involved in AV node reentrant tachycardia.

METHODS

Selective fast pathway ablation was attempted in 13 patients by delivering radiofrequency energy anteriorly across the tricuspid valve anulus. Selective slow pathway ablation was attempted in 29 patients by delivering radiofrequency energy posteriorly across the tricuspid valve anulus at sites where putative slow pathway potentials were recorded.

RESULTS

Selective fast pathway ablation eliminated AV node reentrant tachycardia without AV block in 6 (46%) of 13 patients after one ablation session and in an additional 3 patients (69% of total) after repeat ablation sessions. Slow pathway ablation eliminated AV node reentrant tachycardia without AV block in 26 (90%) of 29 patients after one radiofrequency ablation session and in an additional 2 patients (97% of total) after repeat ablation sessions. Selective fast pathway ablation increased the PR interval (140 to 220 ms, p = 0.0001) and AH interval (66 to 153 ms, p = 0.0001), whereas slow pathway ablation did not change these intervals. Fast pathway radiofrequency ablation caused retrograde block in 7 (64%) of 11 patients, whereas no patients undergoing slow pathway ablation developed selective retrograde block. Single AV node echo beats were commonly induced after slow but not fast pathway ablation (17 of 29 patients vs. 1 of 11 patients, respectively, p = 0.01) and did not predict recurrence of AV node reentrant tachycardia.

CONCLUSIONS

Successful selective radiofrequency ablation of fast or slow pathways in patients with AV node reentrant tachycardia resulted in different electrophysiologic properties after ablation. Slow pathway ablation produced more successful outcomes, with a decreased prevalence of recurrent AV node reentrant tachycardia or AV block.