Alexandru B. Chicos

Use of an electrocardiographic screening tool to determine candidacy for a subcutaneous implantable cardioverter-defibrillator

BACKGROUND An electrocardiographic (ECG) screening test has been developed to identify patients being considered for a totally subcutaneous implantable cardioverter-defibrillator (S-ICD) at risk for T-wave oversensing. OBJECTIVE The purpose of this study was to determine the proportion of potential S-ICD recipients who fail the ECG screening test and to identify predictors of failure. METHODS Patients who already have an ICD but are not receiving antibradycardia pacing are representative of patients who might be considered for an S-ICD. One hundred such outpatients were enrolled in the study. Surface rhythm strips were recorded along the sensing vectors of the S-ICD system and the screening template applied. Clinical and standard ECG characteristics of patients who failed the test were compared to those who passed. RESULTS Patients had the following characteristics: 72% male, age 57 ± 16 years, body mass index 29 ± 6 kg/m(2), left ventricular ejection fraction 43% ± 17%, QRS duration 109 ± 23 ms, QTc interval 447 ± 39 ms, 44% had coronary disease, and 55% had heart failure. Among the 100 patients, 8% failed the screening test. There were no differences in patient clinical characteristics and most standard ECG measurements. However, patients with T-wave inversions in standard ECG leads I, II, and aVF had a 45% chance of failing. CONCLUSION Eight percent of potential S-ICD patients were not eligible for the S-ICD after failing the screening test designed to identify patients susceptible to T-wave oversensing. Patients with T-wave inversions in leads I, II, and aVF on a standard ECG were 23 times more likely to fail. More work is needed in S-ICD sensing algorithms to increase patient eligibility for the S-ICD.

Persistent sympathoexcitation long after submaximal exercise in subjects with and without coronary artery disease

There is an increased risk of cardiac events after exercise, which may, in part, be mediated by the sympathoexcitation that accompanies exercise. The duration and extent of this sympathoexcitation following moderate exercise is unknown, particularly in those with coronary artery disease (CAD). Twenty control subjects (mean age, 51 years) and 89 subjects with CAD (mean age, 58 years) underwent two 16-min bicycle exercise sessions followed by 30-45 min of recovery. Session 1 was performed under physiological conditions to peak workloads of 50-100 W. In session 2, parasympathetic blockade with atropine (0.04 mg/kg) was achieved at end exercise at the same workload as session 1. RR interval was continually recorded, and plasma catecholamines were measured at rest and selected times during exercise and recovery. Parasympathetic effect, measured as the difference in RR interval with and without atropine, did not differ between controls and CAD subjects in recovery. At 30 and 45 min of recovery, RR intervals were 12% and 9%, respectively, shorter than at rest. At 30 and 45 min of recovery, plasma norepinephrine levels were 15% and 12%, respectively, higher than at rest. A brief period of moderate exercise is associated with a prolonged period of sympathoexcitation extending >45 min into recovery and is quantitatively similar among control subjects and subjects with CAD, with or without left ventricular dysfunction. Parasympathetic reactivation occurs early after exercise and is also surprisingly quantitatively similar in controls and subjects with CAD. The role of these autonomic changes in precipitating cardiac events requires further evaluation.

QT-RR hysteresis is caused by differential autonomic states during exercise and recovery

QT-RR hysteresis is characterized by longer QT intervals at a given RR interval while heart rates are increasing during exercise and shorter QT intervals at the same RR interval while heart rates are decreasing during recovery. It has been attributed to a lagging QT response to different directional changes in RR interval during exercise and recovery. Twenty control subjects (8 males, age 51 ± 6 yr), 16 subjects with type 2 diabetes (12 males, age 56 ± 8 yr), 71 subjects with coronary artery disease (CAD) and preserved left ventricular ejection fraction (LVEF) (≥50%) (51 males, age 59 ± 12 yr), and 17 CAD subjects with depressed LVEF (<50%) (13 males, age 57 ± 10 yr) underwent two 16-min exercise tests followed by recovery. In session 2, parasympathetic blockade with atropine (0.04 mg/kg) was achieved at end exercise. QT-RR hysteresis was quantified as: 1) the area bounded by the QT-RR relationships for exercise and recovery in the range of the minimum RR interval at peak exercise to the minimum RR interval + 100 ms and 2) the difference in QT interval duration between exercise and recovery at the minimum RR interval achieved during peak exercise plus 50 ms (ΔQT). The effect of parasympathetic blockade was assessed by substituting the QT-RR relationship after parasympathetic blockade. QT-RR hysteresis was positive in all groups at baseline and reversed by parasympathetic blockade (P < 0.01). We conclude that QT-RR hysteresis is not caused by different directional changes in RR interval during exercise and recovery. Instead, it is predominantly mediated by differential autonomic nervous system effects as the heart rate increases during exercise vs. as it decreases during recovery.

Recovery of heart rate variability and ventricular repolarization indices following exercise

Background: There is a heightened risk of sudden cardiac death related to exercise and the postexercise recovery period, but the precise mechanism is unknown. We have demonstrated that sympathoexcitation persists for ≥45 minutes after exercise in normals and subjects with coronary artery disease (CAD). The purpose of this study is to determine whether this persistent sympathoexcitation is associated with persistent heart rate variability (HRV) and ventricular repolarization changes in the postexercise recovery period.

Bronchial effects of cryoballoon ablation for atrial fibrillation

BACKGROUND Damage to extracardiac structures, including the esophagus and phrenic nerve, is a known complication of cryoballoon ablation (CBA) during pulmonary vein (PV) isolation for atrial fibrillation (AF). Other adjacent structures, including the pulmonary bronchi and lung parenchyma, may be affected during CBA at the PV ostia. OBJECTIVE The purpose of this study was to prospectively study the bronchial effects of CBA in humans undergoing CBA for PV isolation. METHODS Ten patients undergoing CBA for AF under general anesthesia were enrolled in an institutional review board-approved prospective observational study. Real-time bronchoscopy was performed during cryoablation of PVs adjacent to pulmonary bronchi to monitor for thermal injury. Patients were followed for the development of respiratory complaints postprocedure. RESULTS In 7 of 10 patients (70%) and in 13 of 22 freezes (59%), ice formation was visualized in the left mainstem bronchus during CBA in the left upper PV. Ice formation was not seen in the right mainstem bronchus during right upper PV CBA. The average time to ice formation was 89 seconds. There was no significant difference (P = -.45) in average minimum balloon temperature during freezes with ice formation (-48.5°C) and freezes without ice formation (-46.3°C). No patients went on to develop respiratory complications. CONCLUSION Unrecognized ice formation occurs frequently in the left mainstem bronchus during CBA for AF. This information helps explain the source of cough and hemoptysis in some patients who undergo CBA. The long-term consequences of this novel finding and the implications for procedural safety are unknown.

Detection of cardiovascular autonomic neuropathy using exercise testing in patients with type 2 diabetes mellitus

AIMS This study investigated autonomic nervous system function in subjects with diabetes during exercise and recovery. METHODS Eighteen type 2 diabetics (age 55±2 years) and twenty healthy controls (age 51±1 years) underwent two 16-min bicycle submaximal ECG stress tests followed by 45 min of recovery. During session #2, atropine (0.04 mg/kg) was administered at peak exercise, and the final two minutes of exercise and entire recovery occurred under parasympathetic blockade. Plasma catecholamines were measured throughout. Parasympathetic effect was defined as the difference between a measured parameter at baseline and after parasympathetic blockade. RESULTS The parasympathetic effect on the RR interval was blunted (P=.004) in diabetic subjects during recovery. Parasympathetic effect on QT-RR slope during early recovery was diminished in the diabetes group (diabetes 0.13±0.02, control 0.21±0.02, P=.03). Subjects with diabetes had a lower heart rate recovery at 1 min (diabetes 18.5±1.9 bpm, control 27.6±1.5 bpm, P<.001). CONCLUSIONS In subjects with well-controlled type 2 diabetes, even with minimal evidence of CAN using current methodology, altered cardiac autonomic balance is present and can be detected through an exercise-based assessment for CAN. The early post-exercise recovery period in diabetes was characterized by enhanced sympathoexcitation, diminished parasympathetic reactivation and delay in heart rate recovery.

Parasympathetic effects on cardiac electrophysiology during exercise and recovery in patients with left ventricular dysfunction

Depressed parasympathetic activity has been proposed to be associated with an increased risk of sudden death. Parasympathetic effects (PE) on cardiac electrophysiology during exercise and recovery have not been studied in patients with left ventricular dysfunction. We performed noninvasive electrophysiological studies (NI-EPS) and characterized the electrophysiological properties of the sinus node, atrioventricular (AV) node, and ventricle in subjects with depressed left ventricular ejection fraction and dual-chamber defibrillators. NI-EPS were performed during rest, exercise, and recovery at baseline and after parasympathetic blockade with atropine to assess PE (the difference between parameter values in the 2 conditions). Ten subjects (9 men: age, 60 +/- 9 yr; and left ventricular ejection fraction, 29 +/- 8%) completed the study. All NI-EPS parameters decreased during exercise and trended toward rest values during recovery. PE at rest, during exercise, and during recovery, respectively, were on sinus cycle length, 320 +/- 71 (P = 0.0001), 105 +/- 60 (P = 0.0003), and 155 +/- 82 ms (P = 0.0002); on AV block cycle length, 137 +/- 136 (P = 0.09), 37 +/- 19 (P = 0.002), and 61 +/- 39 ms (P = 0.006); on AV interval, 58 +/- 32 (P = 0.035), 22 +/- 13 (P = 0.002), and 36 +/- 20 ms (P = 0.001); on ventricular effective refractory period, 15.8 +/- 11.3 (P = 0.02), 4.7 +/- 15.2 (P = 0.38), and 6.8 +/- 15.5 ms (P = 0.20); and on QT interval, 13 +/- 12 (P = 0.13), 3 +/- 17 (P = 0.6), and 20 +/- 23 (P = 0.04). In conclusion, we describe for the first time the changes in cardiac electrophysiology and PE during rest, exercise, and recovery in subjects with left ventricular dysfunction. PEs are preserved in these patients. Thus the role of autonomic changes in the pathophysiology of sudden death requires further exploration.

Moderate Sedation Reduces Lab Time Compared to General Anesthesia during Cryoballoon Ablation for AF Without Compromising Safety or Long-Term Efficacy.

Cryoballoon ablation (CBA) for paroxysmal atrial fibrillation (pAF) can be performed under general anesthesia (GA) or moderate sedation (MS). Our objective was to compare the effectiveness, safety, procedure duration, and time spent in the electrophysiology (EP) laboratory for CBA performed under GA and MS.

Arrhythmia in Acute Heart Failure

The ubiquity of arrhythmias, both atrial and ventricular, in chronic heart failure (HF) is well established, and their significance and treatment have been studied quite extensively. The prevalence, significance, and treatment of arrhythmias in acutely decompensated heart failure have been less studied.

Using floating atrial electrodes to combat the rising tide of inappropriate defibrillator therapies.

Despite various implantable defibrillator algorithms and strategies used to improve discrimination between potentially life-threatening ventricular arrhythmias (ventricular tachycardia/ventricular fibrillation [VT/VF]) and more benign supraventricular tachycardias (SVTs), this remains a problem. In addition to significant discomfort and impairment of quality of life, there is some suggestion that shocks may increase mortality.1 Recording atrial intracardiac electrograms during arrhythmic episodes would be expected to improve our ability to discriminate tachycardias and thus reduce the number of inappropriate shocks. It may also lead to the diagnosis of otherwise unsuspected atrial arrhyhmias that may require specific therapy, such as anticoagulation therapy for patients with atrial flutter or atrial fibrillation (AF). Article see p 56 The evidence available so far, however, does not clearly demonstrate that atrial electrograms reduce inappropriate shocks.2–7 Although some studies performed in patients with a dual-chamber device have shown a reduction in inappropriate detection, inappropriate shocks also were avoided in the single-chamber detection arm by using anti tachycardia pacing.2 In addition, placement of an atrial lead is associated with a risk of lead dislodgement (≈4.5%) and increased procedural and fluoroscopy times compared to a single-chamber defibrillator. Thus, there currently is no strong evidence to support the addition of an atrial lead for the sole purpose of SVT discrimination and reducing implantable cardioverter-defibrillator (ICD) shocks.8 Using a single-pass VDD defibrillator lead holds the promise of offering atrial electrograms without the additional risks and procedural time related to implantation of a separate atrial lead. Similar lead designs with integrated atrial electrodes have been used in VDD pacemakers.9 In a study published by Sticherling et al in this issue of Circulation: Arrythmia and Electrophysiology , the ADRIA (Study to Verify Proper Detection of Supraventricular Tachyarrhythmia With Single-Lead Dual-Chamber Implantable Cardioverter-Defibrillators) study, the authors investigated the use …