A pilot study in hemodialysis of an electrophysiological tool to measure sudden cardiac death risk.

BACKGROUND: The hemodialysis procedure may play a role in the elevated risk of sudden cardiac death seen in hemodialysis patients. METHODS: Microvolt T wave alternans, a promising noninvasive electrophysiological test developed to measure sudden cardiac death risk, was used to test the hypotheses that high-risk hemodialysis patients commonly manifest cardiac electrophysiology that is associated with higher sudden death risk in nondialysis patients and that the hemodialysis procedure modifies cardiac electrophysiology in a manner predisposing to malignant ventricular arrhythmias. To test this hypothesis, microvolt T wave alternans tracings were done in 9 patients before and immediately after an early week hemodialysis session. RESULTS: 7 of 9 individuals had non-negative (i.e. higher risk) tracings either before or after hemodialysis. 2 of 4 subjects with tracings initially negative before hemodialysis became non-negative after hemodialysis. CONCLUSION: This pilot study provides the first objective preliminary evidence using microvolt T wave alternans that high-risk hemodialysis patients commonly exhibit abnormal cardiac repolarization and that hemodialysis treatments can acutely alter repolarization in a potentially harmful manner.

Excessive charge time delaying ventricular tachycardia therapy.

A 70-year-old man with a single-chamber implantable cardioverter defibrillator (ICD) placed for ventricular tachycardia presented with syncope. He was found to have ventricular flutter/fibrillation with capacitor charge time in excess of 1 minute before defibrillation. The excessive charge time was secondary to ICD capacitor malfunction. The generator was explanted and replaced, and the patient recovered uneventfully.

Limited response to cardiac arrest by police equipped with automated external defibrillators: lack of survival benefit in suburban and rural Indiana--the police as responder automated defibrillation evaluation (PARADE).

OBJECTIVE: To assess the out-of-hospital cardiac arrest (OHCA) survival advantage after providing police with automated external defibrillators (AEDs) in rural and suburban Indiana. METHODS: An observational evaluation was conducted in six Indiana counties (population: 464,741) before (retrospective) and after (prospective) training and equipping police with AEDs. The primary outcome evaluated was survival to hospital discharge for all cases of ventricular tachycardia/ventricular fibrillation (VT/VF) OHCA. Other factors evaluated include age, gender, race, arrest location, witnessed arrest, bystander cardiopulmonary resuscitation, response intervals, and survival to discharge for all OHCAs. Results are reported using chi-square, Student's t-test, and logistic regression. RESULTS: Police were equipped with 112 AEDs, increasing total defibrillator capability by 43.2%. During the study period, AED-equipped police responded prior to emergency medical services (EMS) in 26 of 388 cases (6.7%). The time intervals from 911 call-to-scene and 911 call-to-shock were shortened by 1.6 minutes (95% confidence interval [95% CI] = 0.0 to 3.1, p = 0.05) and 4.8 minutes (95% CI = 1.3 to 8.3, p = 0.008), respectively, with police response as compared with EMS response. Survival to hospital discharge for VT/VF OHCA was 15.0% (3/20) in cases in which police responded first and 10.0% (16/160) in cases in which EMS responded first (relative risk [RR] 0.63, 95% CI = 0.17 to 2.39, p = 0.45). Survival to hospital discharge for VT/VF OHCA did not improve from the prestudy period (16/204, 7.8%) to after police AED availability (19/180, 10.6%) (RR 0.72, 95% CI = 0.36 to 1.45, p = 0.38). CONCLUSIONS: Out-of-hospital cardiac arrest survival in suburban and rural Indiana did not improve after police were equipped with AEDs, likely related to poor police response.

A comparison of T-wave alternans, signal averaged electrocardiography and programmed ventricular stimulation for arrhythmia risk stratification.

OBJECTIVES: The goal of this study was to compare T-wave alternans (TWA), signal-averaged electrocardiography (SAECG) and programmed ventricular stimulation (EPS) for arrhythmia risk stratification in patients undergoing electrophysiology study. BACKGROUND: Accurate identification of patients at increased risk for sustained ventricular arrhythmias is critical to prevent sudden cardiac death. T-wave alternans is a heart rate dependent measure of repolarization that correlates with arrhythmia vulnerability in animal and human studies. Signal-averaged electrocardiography and EPS are more established tests used for risk stratification. METHODS: This was a prospective, multicenter trial of 313 patients in sinus rhythm who were undergoing electrophysiologic study. T-wave alternans, assessed with bicycle ergometry, and SAECG were measured before EPS. The primary end point was sudden cardiac death, sustained ventricular tachycardia, ventricular fibrillation or appropriate implantable defibrillator (ICD) therapy, and the secondary end point was any of these arrhythmias or all-cause mortality. RESULTS: Kaplan-Meier survival analysis of the primary end point showed that TWA predicted events with a relative risk of 10.9, EPS had a relative risk of 7.1 and SAECG had a relative risk of 4.5. The relative risks for the secondary end point were 13.9, 4.7 and 3.3, respectively (p < 0.05). Multivariate analysis of 11 clinical parameters identified only TWA and EPS as independent predictors of events. In the prespecified subgroup with known or suspected ventricular arrhythmias, TWA predicted primary end points with a relative risk of 6.1 and secondary end points with a relative risk of 8.0. CONCLUSIONS: T-wave alternans is a strong independent predictor of spontaneous ventricular arrhythmias or death. It performed as well as programmed stimulation and better than SAECG in risk stratifying patients for life-threatening arrhythmias.

Predictors of clinical outcome following percutaneous intervention for in-stent restenosis.

Percutaneous intervention for the first episode of in-stent restenosis was performed in 177 patients 5.4 +/- 0.3 months after native coronary stent implantation. Medical records were reviewed and patients contacted 13.3 +/- 1.2 months after in-stent intervention to ascertain the subsequent clinical course. The effects of demographic, procedural, and angiographic variables on clinical outcomes were determined. At 2 years, Kaplan-Meier estimated survival was 93 +/- 3% and freedom from death, myocardial infarction, and a third target artery revascularization (TAR) was 67 +/- 4%. The actuarial frequency of a third TAR was 26 +/- 4% at 1 year. Stratification of outcomes according to timing of in-stent intervention revealed an approximate twofold higher frequency of adverse events among patients with early (

Amiodarone reduces the prevalence of T wave alternans in a population with ventricular tachyarrhythmias.

INTRODUCTION: Testing for the presence of microvolt T wave alternans (TWA) is useful for arrhythmic risk stratification. Whether antiarrhythmic pharmacotherapy affects the presence of TWA is unknown. We tested whether patients with known ventricular tachyarrhythmias who were receiving amiodarone were less likely to manifest TWA as compared with those not receiving amiodarone. METHODS AND RESULTS: Forty-four patients with a history of ventricular tachyarrhythmias and an implantable cardioverter defibrillator (ICD) implanted at least 1 month earlier underwent TWA testing. In this group, 14 patients were receiving amiodarone and 30 were not. Indeterminate test results occurred in 13 patients without a significant difference in those receiving or not receiving amiodarone. In the 31 patients with determinate TWA testing, a positive test was less likely in those receiving amiodarone (1 of 9 [11%]) as compared with those not receiving amiodarone (14 of 22 [64%]; P = 0.04). During a follow-up period averaging 0.9 +/- 0.2 years, the presence of TWA (P = 0.04) and decreased left ventricular ejection fraction (P = 0.05) predicted appropriate ICD therapy for ventricular tachyarrhythmias. CONCLUSION: The prevalence of TWA was decreased in a chronic ventricular tachyarrhythmic population receiving amiodarone as compared with a population not receiving amiodarone.

Interactions between electronic article surveillance systems and implantable cardioverter-defibrillators.

BACKGROUND: In patients with implantable cardioverter-defibrillators (ICDs). inappropriate shocks have been reported with exposure to electronic article surveillance systems. The risk to patients with ICDs of walking through or lingering near surveillance systems requires further investigation. METHODS AND RESULTS: We evaluated the response in ICD function in 170 subjects during a 10- to 15-second midgate walk-through of and during extreme (2 minutes within 6 in of the gate) exposure to 3 common article surveillance systems. Complete testing was done in 169 subjects. During a 10- to 15-second (very slow) walk-through of the 3 surveillance systems, no interactions were observed that would negatively affect ICD function. During extreme exposure (169 subjects) and during extreme exposure and pacing via the ICD (126 subjects), interactions between the ICD and the article surveillance systems were observed in 19 subjects. In 7 subjects, this interaction was clinically relevant and would have likely (3 subjects) and possibly (4 subjects) resulted in ICD shocks. In 12 subjects, the interaction was minor. CONCLUSIONS: It is safe for a patient with an ICD to walk through electronic article surveillance systems. Lingering in a surveillance system may result in an inappropriate ICD shock.

Effects of multisite ventricular pacing on cardiac function in normal dogs and dogs with heart failure.

INTRODUCTION: We studied the effects on cardiac function of pacing two right and two left ventricular sites in normal and failing hearts with a normal QRS duration. METHODS AND RESULTS: Hemodynamic parameters were studied in isoflurane-anesthetized dogs with normal hearts and dogs with heart failure induced by rapid ventricular pacing. Unipolar intramyocardial electrodes were placed at the high right atrium and the apex (A) and base (B) of the left (L) and right (R) ventricles (V). Data were collected after pacing for 5 to 20 minutes. In normal dogs, without bundle branch block (BBB), pacing at either the apex or the base of the left ventricle increased cardiac output by approximately 10% compared with right ventricular apex (RVA) pacing with an AV delay of 0 msec. Positive dP/dt increased approximately 10% during four-site left and right ventricular apex and base (LRVAB) pacing compared with RVA pacing. In dogs with heart failure but without BBB, cardiac output increased by 8.5% (P < 0.01) during four-site ventricular pacing with AV delays of 0 and 60 msec compared with RVA pacing. Positive dp/dt increased by 23.5% (P < 0.001) with an AV delay of 0 msec and 9.6% (P < 0.001) with an AV delay of 60 msec during LRVAB pacing compared with RVA pacing. His-bundle pacing was associated with increased cardiac output compared with RVA pacing. CONCLUSIONS: We conclude that pacing simultaneously at two right and two left ventricular sites significantly improves cardiac function compared with single RVA pacing, with or without sequential AV synchrony, in dogs with rapid ventricular pacing-induced heart failure and no BBB.

Software error resulting in malfunction of an implantable cardioverter defibrillator.

Loss of ventricular output resulting from an unexpected software error in a dual chamber implantable cardioverter defibrillator (ICD) is reported. A 70-year-old man with a dual chamber ICD implanted for a history of cardiac arrest and infra-Hisian block presented with acute onset of dizziness. He was found to have loss of ventricular output due to an internal software problem. The problem was corrected by software reprogramming via the programmer. This malfunction exemplifies the potential ability to correct current-generation ICD software problems noninvasively, thus avoiding the need for replacement.

Antithrombin activity during the period of percutaneous coronary revascularization: relation to heparin use, thrombotic complications and restenosis.

OBJECTIVES: This study evaluated changes in antithrombin (AT) activity around the time of percutaneous transluminal coronary revascularization (PTCR) with unfractionated heparin anticoagulation and the effects these changes had on major thrombotic complications of PTCR. BACKGROUND: Heparin is used during PTCR to prevent thrombosis. However, heparin, a cofactor for AT, causes AT activity to fall. AT activity <70% is associated with thrombosis. There is a prothrombotic state after heparin discontinuation that has not been well explained. METHODS: Antithrombin activity was sampled at the start and end of PTCR and the next two mornings in 250 consecutive patients. We recorded occurrence of major thrombotic events, defined as 1) major thrombotic complications of PTCR; 2) major in-lab thrombus formation; or 3) subacute occlusion. Discriminant analysis was employed to evaluate the relationship of AT activity to these events. Change in AT activity and its relationship to heparin was evaluated. Evidence of restenosis at six months was obtained. RESULTS: There were 14 major thrombotic events. Antithrombin activity <70% was strongly (p = 0.006) associated with these events. The AT activity fell significantly through the morning after PTCR when 21% of patients had AT activity <70%; AT activity did not normalize until >20 h after heparin discontinuation. Pre-PTCR use of heparin led to lower AT activity in proportion to duration of heparin use. There was no relationship between AT activity and restenosis. CONCLUSIONS: Low AT activity may contribute to major thrombotic complications of PTCR. The way heparin is used before and after PTCR is important to development of low AT activity.

Radiofrequency catheter ablation for postinfarct ventricular tachycardia.

Catheter mapping and radiofrequency ablation of postinfarct sustained ventricular tachycardia (VT) remain one of the greatest challenges for the electrophysiologist. Although there were no major breakthroughs during the past year, several refinements and clarifications of existing mapping criteria were published. In addition, initial reports appeared describing new mapping systems and ablation technologies that may significantly impact the way ablation studies are performed as well as the way in which they affect success rates. Uncertainties remain as to how effective catheter ablation will be as a longterm cure for this type of VT. For the foreseeable future, catheter ablation in postinfarct VT will remain adjunctive rather than primary therapy.

Atrial macroreentry involving the myocardium of the coronary sinus: a unique mechanism for atypical flutter.

Atrial flutter involving either clockwise or counterclockwise rotation around the tricuspid annulus utilizing the subeustachian isthmus has been well described. However, macroreentrant atrial circuits in atypical atrial flutter in patients who have not undergone previous surgery or without atrial disease are not well defined. We describe a patient without structural heart disease who presented with an atrial macroreentrant rhythm. Entrainment mapping demonstrated a critical isthmus within the coronary sinus. Activation mapping demonstrated double potential throughout the length of the coronary sinus with disparate activation sequences. A circuit involving the myocardium of the coronary sinus, exiting in the lateral left atrium, down the interatrial septum, and reentering into the coronary sinus was identified. Successful ablation of the rhythm was accomplished by a circumferential radiofrequency application within the coronary sinus.

Advances in the treatment of arrhythmias: implantable cardioverter-defibrillators.

Implantable cardioverter-defibrillators are commonly used in patients who have life-threatening ventricular arrhythmias. With these implanted electronic devices, bradyarrhythmias and tachyarrhythmias can be recognized promptly and treated with electrical pacing, cardioversion or defibrillation. Implantable cardioverter-defibrillators have been shown to substantially reduce the incidence of sudden cardiac death in patients with known life-threatening ventricular arrhythmias. Their role in the primary prevention of sudden cardiac death in patients at high risk for ventricular arrhythmias is being evaluated. Technologic advances have allowed transvenous implantation of cardiac leads, obviating the need for open heart surgery and thereby lowering the risk of perioperative morbidity and mortality. Most electrical therapies are triggered appropriately to treat ventricular tachycardia/fibrillation. Inappropriate discharges may occur secondary to supraventricular causes of tachycardia, environmental interference from electromagnetic devices or malfunction of the cardioverter-defibrillator. All episodes of discharge merit investigation. With recurrent or frequent discharges, prompt evaluation and hospitalization are often necessary.

Comparison of the rate-dependent properties of the class III antiarrhythmic agents azimilide (NE-10064) and E-4031: considerations on the mechanism of reverse rate-dependent action potential prolongation.

INTRODUCTION: Reverse rate-dependence, a lessening in Class III antiarrhythmic agent action potential duration (APD) prolongation as heart rate is increased, has been proposed to be related to an incomplete deactivation of the slow component (IKs) of the delayed rectifier K+ current (IK). The rate-dependent properties of block of IK by azimilide were compared to E-4031, which selectively blocks the rapid component (IKr) of IK, in guinea pig ventricular muscle. METHODS AND RESULTS: Azimilide prolonged APD in isolated papillary muscles in a concentration-dependent manner and to a greater degree than E-4031. Both agents prolonged APD less at fast than slow rates, consistent with a similar reverse rate-dependent effect. Isolation of azimilide block of IKs by subtraction of APD during E-4031 plus azimilide from E-4031 alone revealed rate-independent prolongation of APD. In voltage clamp experiments on single ventricular myocytes, activation of IKs was similar following 30 seconds of conditioning pulses of physiological duration (125 to 200 msec) with either a fast (cycle length 250 msec) or slow (cycle length 2000 msec) rate. The block of IKs by azimilide 3 microM was greater after a fast conditioning pulse train. CONCLUSIONS: Selective block of IKs prolongs APD in a rate-independent manner. In voltage clamped myocytes, no evidence of a rate-dependent accumulation of IKs was observed. These findings support a mechanism of reverse rate-dependent APD prolongation by Class III antiarrhythmic agents that block IKr independent of IKs.

Internal mammary arteriography without selective cannulation using a new balloon occlusion catheter.

Internal mammary artery (IMA) angiography can be difficult and time-consuming. We evaluated a custom designed balloon-tipped catheter, a Berman catheter (Arrow International, Reading, PA) modified by creating an end-hole to allow passage of a wire through the central lumen, for imaging the IMA without selective cannulation. We compared ease of use, procedure time, and image quality of the new catheter with the standard selective catheter technique. Thirty-six patients with IMA grafts were randomly assigned to imaging with either the study catheter or a standard catheter. Image quality, graded from poor to excellent, time to catheter placement in the subclavian artery (TIME 1), time to initial IMA angiography (TIME 2), and the difference between these two (TIME 3) were recorded. TIME 3 defined the time required to find and seat the catheter at the IMA site. The image quality was good or excellent in all but one patient. This one patient, randomized to the standard catheter technique, had poor image quality with the selective catheter. However, exchange for the study catheter resulted in excellent image quality. There was no difference in TIME 1 (P = 0.57) or TIME 2 (P = 0.55) between the two techniques. There was a significant difference in TIME 3 (P = 0.05) favoring the study catheter. There were no complication using either technique and the total contrast volume used was not significantly different between the two techniques (P = 0.32). We conclude that a new catheter technique for imaging the IMA without selective cannulation is safe, fast, easy to use, and may offer particular advantage in patients whose internal mammary artery is difficult to access.

Use of implantable cardioverter-defibrillators in the congenital long QT syndrome.

We surveyed the use of implantable cardioverter-defibrillators in patients with congenital long QT syndrome. The implantable cardioverter-defibrillator was used primarily in high-risk persons and appeared safe and effective over a mean 31-month follow-up.