William J. Groh

Electrocardiographic Abnormalities and Sudden Death in Myotonic Dystrophy Type 1

BACKGROUND Sudden death can occur as a consequence of cardiac-conduction abnormalities in the neuromuscular disease myotonic dystrophy type 1. The determinants of the risk of sudden death remain imprecise. METHODS We assessed whether the electrocardiogram (ECG) was useful in predicting sudden death in 406 adult patients with genetically confirmed myotonic dystrophy type 1. A patient was characterized as having a severe abnormality if the ECG had at least one of the following features: rhythm other than sinus, PR interval of 240 msec or more, QRS duration of 120 msec or more, or second-degree or third-degree atrioventricular block. RESULTS Patients with severe abnormalities according to the entry ECG were older than patients without severe abnormalities, had more severe skeletal-muscle impairment, and were more likely to have heart failure, left ventricular systolic dysfunction, or atrial tachyarrhythmia. Such patients were more likely to receive a pacemaker or an implantable cardioverter-defibrillator during the follow-up period. During a mean follow-up period of 5.7 years, 81 patients died; there were 27 sudden deaths, 32 deaths from progressive neuromuscular respiratory failure, 5 nonsudden deaths from cardiac causes, and 17 deaths from other causes. Among the 17 patients who died suddenly in whom postcollapse rhythm was evaluated, a ventricular tachyarrhythmia was observed in 9. A severe ECG abnormality (relative risk, 3.30; 95% confidence interval [CI], 1.24 to 8.78) and a clinical diagnosis of atrial tachyarrhythmia (relative risk, 5.18; 95% CI, 2.28 to 11.77) were independent risk factors for sudden death. CONCLUSIONS Patients with adult myotonic dystrophy type 1 are at high risk for arrhythmias and sudden death. A severe abnormality on the ECG and a diagnosis of an atrial tachyarrhythmia predict sudden death. (ClinicalTrials.gov number, NCT00622453.)

Thoracic Spinal Cord Stimulation Reduces the Risk of Ischemic Ventricular Arrhythmias in a Postinfarction Heart Failure Canine Model

Background—Thoracic spinal cord stimulation (SCS) is a promising therapy in treating refractory angina. This study was designed to investigate SCS with regard to the risk of arrhythmias during myocardial ischemia and its cardiac electrophysiological effects. Methods and Results—We studied 22 dogs with healed anterior myocardial infarction (MI) and superimposed heart failure (HF) induced by rapid ventricular pacing. SCS was applied at the dorsal T1–T2 segments of the spinal cord (at 50 Hz, 0.2 ms) for 15 minutes. Transient (2-minute) myocardial ischemia was induced on 2 separate occasions (no SCS and SCS) to provoke ventricular arrhythmias (ventricular tachycardia/ventricular fibrillation; VT/VF). Ischemic episodes were separated by 90 minutes, and dogs were randomly assigned to receive SCS or no SCS before the first or second ischemic episode. SCS reduced the occurrence of VT/VF from 59% to 23% when SCS was applied during transient myocardial ischemia (odds ratio, 0.36; 95% confidence interval, 0.1626 to 0.5646; P=0.0009). SCS also decreased sinus rate by 7.5±14 bpm (P=0.048), increased the PR interval by 11.1±14.7 ms (P=0.009), and reduced systolic blood pressure by 9.8±13.6 mm Hg (P=0.02). Conclusions—Thoracic SCS appears to protect against ischemic VT/VF in a canine model of healed MI and HF. SCS reduced sinus rate and systolic blood pressure, changes consistent with the previously known antisympathetic effect of SCS, which may have contributed to the antiarrhythmic benefits.

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.

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

Macroreentry Involving the Coronary Sinus. 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.

The Public Access Defibrillation (PAD) trial: study design and rationale.

The PAD Trial is a prospective, multicenter, randomized clinical study testing whether volunteer, non-medical responders can improve survival from out-of-hospital cardiac arrest (OOH-CA) by using automated external defibrillators (AEDs). These lay volunteers, who have no traditional responsibility to respond to a medical emergency as part of their primary job description, will form part of a comprehensive, integrated community approach to the treatment of OOH-CA. The study is being conducted at 24 field centers in the United States and Canada. Approximately 1000 community units (e.g. apartment or office buildings, gated communities, sports facilities, senior centers, shopping malls, etc.) were randomized to treatment by trained laypersons who will provide either cardiopulmonary resuscitation (CPR) alone or CPR plus use of an AED, while awaiting arrival of the communitys emergency medical services responders. The primary endpoint is the number of OOH-CA victims who survive to hospital discharge. Secondary endpoints include neurological status, health-related quality of life (HRQL), cost, and cost-effectiveness. Data collection will last approximately 15 months and is expected to be completed in September 2003.

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.

Arrhythmias in the muscular dystrophies

The muscular dystrophies are a group of inherited diseases affecting skeletal muscle that also affect cardiac muscle. Cardiac involvement occurs as a degenerative process with fibrosis and fatty replacement of the myocardium. Electrophysiologists are asked to participate in the care of muscular dystrophy patients because of the risk of atrial arrhythmias, conduction disease, bradycardia, ventricular arrhythmias, and sudden death. Duchenne, Becker, and limb-girdle types 2C-2F and 2I are muscular dystrophies in which the development of a dilated cardiomyopathy is common. Arrhythmias and conduction disease occur after the development of the dilated cardiomyopathy. Patients are considered for pacemakers or implantable cardioverter-defibrillators on the basis of guidelines used for nonischemic cardiomyopathies. Myotonic types 1 and 2, Emery-Dreifuss, limb-girdle type 1B, and facioscapulohumeral muscular dystrophies present with conduction disease and associated arrhythmias and variably with a dilated cardiomyopathy. In myotonic type 1, Emery-Dreifuss, and limb-girdle type 1B muscular dystrophies, conduction abnormalities are frequent and often require pacing. Recent studies support the use of prophylactic implantable cardioverter-defibrillators rather than pacemakers. In all the muscular dystrophies, respiratory muscle involvement can impact quality and quantity of life and needs to be factored in when considering a prophylactic device.

Increased mortality with left ventricular systolic dysfunction and heart failure in adults with myotonic dystrophy type 1.

BACKGROUND Myotonic dystrophy type 1 (DM1) is a neurologic disorder with known cardiac involvement, including left ventricular systolic dysfunction (LVSD), heart failure (HF), atrioventricular and intraventricular conduction system disease, and sudden death. We studied the prevalence of these conditions and associated findings in a large population with DM1. METHODS History, physical examination, genetic testing, and electrocardiography were performed on 406 patients with DM1, and cardiac imaging was performed on 180 (44.3%) of these patients. RESULTS Left ventricular systolic dysfunction and clinical HF were found in 34 (18.9%) of 180 and in 23 (5.7%) of 406 of enrolled subjects, respectively, yielding an overall prevalence of LVSD/HF in 41 (10.1%) of 406. Increasing age, male sex, electrocardiographic conduction abnormalities, presence of atrial and ventricular arrhythmias, and implanted devices were all significantly associated with LVSD/HF, whereas cytosine-thiamine-guanine repeat length and neuromuscular severity score were not. The interval≥240 milliseconds (relative risk 4.1, 95% CI 1.7-9.6, P=.001) and QRS duration≥120 milliseconds (relative risk 4.2, 95% CI 2.0-8.5, P<.001) were significant predictors of LVSD/HF. The presence of LVSD/HF was also significantly associated with all-cause death (relative risk 3.9, 95% CI 2.3-6.4, P<.001) and cardiac death (relative risk 5.7, 95% CI 2.6-12.4, P<.001). CONCLUSIONS A significant prevalence of LVSD/HF exists in patients with DM1. The presence of LVSD/HF in DM1 is significantly associated with all-cause and cardiac death.

Survival and CTG repeat expansion in adults with myotonic dystrophy type 1.

An association is observed between the severity of myotonic dystrophy type 1 (DM1) and the genetic abnormality of cytosine–thymine–guanine (CTG) repeat expansion. It is unknown whether an association exists between survival and CTG repeat expansion.

A retrospective analysis of proceduralist-directed, nurse-administered propofol sedation for implantable cardioverter-defibrillator procedures

BACKGROUND There is controversy whether proceduralist-directed, nurse-administered propofol sedation (PDNAPS) is safe. OBJECTIVE To assess the frequency of adverse events when PDNAPS is used for implantable cardioverter-defibrillator (ICD)-related procedures and to determine the patient and procedural characteristics associated with adverse events. METHODS Consecutive ICD-related procedures using PDNAPS from May 2006 to July 2009 at a tertiary-care hospital were evaluated. Serious adverse events were defined as procedural death, unexpected transfer to an intensive care unit, respiratory failure requiring intubation/bag-mask ventilation, or hypotension requiring vasoconstrictor/inotrope support. Nonserious adverse events were defined as hypotension requiring fluid resuscitation or hypoxemia requiring augmented respiratory support with non-rebreather mask, oral airway, or jaw lift. RESULTS Of 582 patients (age 64 ± 14 years, 72.3% males) undergoing ICD-related procedures using PDNAPS, 58 (10.0%) patients had serious adverse events with no procedural death and 225 (38.7%) had nonserious adverse events. Longer procedure duration (relative risk [RR] = 2.1 per hour; 95% confidence interval [CI] = 1.6-2.8; P < .001) and biventricular implant (RR = 2.7; CI = 1.4-5.3; P = .003) were independent predictors of serious adverse events. A longer procedure duration (RR = 1.4 per hour; CI = 1.1-1.7; P = .001), heart failure class (RR = 1.4 per 1 class; CI = 1.1-1.7; P = .002), and use of propofol infusion (RR = 3.5; CI = 2.2-5.7; P < .001) were independent predictors of nonserious adverse events. CONCLUSION PDNAPS for shorter ICD procedures including single- and dual-chamber implants, generator changes, and defibrillation threshold testing have acceptable rates of serious adverse events and manageable nonserious adverse events and should be considered for further study. Biventricular implants and other complex procedures should be done with an anesthesiologist.