Karthik Ramaswamy

Use of Automated External Defibrillators by a U.S. Airline

BACKGROUND Passengers who have ventricular fibrillation aboard commercial aircraft rarely survive, owing to the delay in obtaining emergency care and defibrillation. METHODS In 1997, a major U.S. airline began equipping its aircraft with automated external defibrillators. Flight attendants were trained in the use of the defibrillator and applied the device when passengers had a lack of consciousness, pulse, or respiration. The automated external defibrillator was also used as a monitor for other medical emergencies, generally at the direction of a passenger who was a physician. The electrocardiogram that was obtained during each use of the device was analyzed by two arrhythmia specialists for appropriateness of use. We analyzed data on all 200 instances in which the defibrillators were used between June 1, 1997, and July 15, 1999. RESULTS Automated external defibrillators were used for 200 patients (191 on the aircraft and 9 in the terminal), including 99 with documented loss of consciousness. Electrocardiographic data were available for 185 patients. The administration of shock was advised in all 14 patients who had electrocardiographically documented ventricular fibrillation, and no shock was advised in the remaining patients (sensitivity and specificity of the defibrillator in identifying ventricular fibrillation, 100 percent). The first shock successfully defibrillated the heart in 13 patients (defibrillation was withheld in 1 case at the familys request). The rate of survival to discharge from the hospital after shock with the automated external defibrillator was 40 percent. A total of 36 patients either died or were resuscitated after cardiac arrest. No complications arose from use of the automated external defibrillator as a monitor in conscious passengers. CONCLUSIONS The use of the automated external defibrillator aboard commercial aircraft is effective, with an excellent rate of survival to discharge from the hospital after conversion of ventricular fibrillation. There are not likely to be complications when the device is used as a monitor in the absence of ventricular fibrillation.

Initial energy for elective external cardioversion of persistent atrial fibrillation

We conducted a prospective randomized study to determine the safety and efficacy rate of 3 commonly used energy levels (100, 200, and 360 J) for elective direct-current cardioversion of persistent atrial fibrillation. When compared with 100 and 200 J, the initial success rate with 360 J was significantly higher (14%, 39%, and 95%, respectively), and patients randomized to 360 J ultimately required less total energy and a lower number of shocks.

Biventricular pacing decreases the inducibility of ventricular tachycardia in patients with ischemic cardiomyopathy

Biventricular pacing (BV) has been studied extensively in patients with left ventricular dysfunction. Preliminary studies have shown improvement in hemodynamics and exercise tolerance in this patient population. However, the electrophysiologic effects of BV pacing remain poorly understood. The purpose of this study was to assess the effect of BV pacing on the inducibility of sustained monomorphic ventricular tachycardia (VT) in patients with coronary artery disease. We hypothesized that acute BV pacing reduces the inducibility of sustained monomorphic VT in patients with ischemic cardiomyopathy.

Effects of resynchronization therapy on sympathetic activity in patients with depressed ejection fraction and intraventricular conduction delay due to ischemic or idiopathic dilated cardiomyopathy

This study assesses the effect of biventricular pacing on sympathetic nerve activity (SNA) in patients with depressed ejection fraction and intraventricular conduction delay (IVCD). Biventricular pacing has been shown to result in hemodynamic improvement in patients with depressed ejection fraction and IVCD. The effect of biventricular pacing on SNA, however, remains unclear. A total of 15 men with a mean ejection fraction of 25 +/- 4% were enrolled. Arterial pressure, central venous pressure and SNA were recorded during 3 minutes of right atrial (RA) pacing and RA-biventricular pacing. Pacing was performed at a rate 5 to 10 beats faster than sinus rhythm, with an atrioventricular interval equal to 100 ms during RA-biventricular pacing. RA-biventricular pacing resulted in greater arterial pressures (p <0.05) than RA pacing (146 +/- 15/83 +/- 11 vs 141 +/- 15/80 +/- 10 mm Hg). There were no differences in central venous pressures between the 2 pacing modes (p = 0.76). SNA was significantly less during RA-biventricular pacing (727 +/- 242 U) than during RA pacing (833 +/- 332 U) (p <0.02). Furthermore, there was a positive correlation between baseline QRS duration and the decrease in SNA noted with RA-biventricular pacing (r = 0.58, p = 0.03). Biventricular pacing results in improved hemodynamics and a decrease in SNA compared with intrinsic conduction in patients with left ventricular dysfunction and IVCD. If the current findings are also present with chronic biventricular pacing, then this form of therapy may have a positive impact on mortality.

Increased sympathetic activity after atrioventricular junction ablation in patients with chronic atrial fibrillation.

OBJECTIVES The aim of this study was to determine the changes in sympathetic nerve activity (SNA) after atrioventricular junction (AVJ) ablation in patients with chronic atrial fibrillation (AF). BACKGROUND Polymorphic ventricular tachycardia (PMVT) has been reported after AVJ ablation in patients paced at a rate of < or =70 beats/min. We hypothesized that AVJ ablation results in sympathetic neural changes that favor the occurrence of PMVT and that pacing at 90 beats/min attenuates these changes. METHODS Sympathetic nerve activity, 90% monophasic cardiac action potential duration (APD90), right ventricular effective refractory period (ERP) and blood pressure measurements were obtained in 10 patients undergoing AVJ ablation. Sympathetic nerve activity was analyzed at baseline and during and after successful AVJ ablation for at least 10 min. Data were also collected after ablation at pacing rates of 60 and 90 beats/min. The APD90 and ERP were measured before and after AV block during pacing at 120 beats/min. RESULTS Sympathetic nerve activity increased to 134 +/- 16% of the pre-ablation baseline value (p < 0.01) after successful AVJ ablation plus pacing at 60 beats/min and decreased to 74 +/- 8% of baseline (p < 0.05) with subsequent pacing at 90 beats/min. Both APD90 and ERP increased significantly. CONCLUSIONS 1) Ablation of the AVJ followed by pacing at 60 beats/min is associated with an increase in SNA. 2) Pacing at 90 beats/min decreases SNA to or below the pre-ablation baseline value. 3) Cardiac APD and ERP increase after AVJ ablation. The increase in SNA, along with the prolongation in APD, may play a role in the pathogenesis of ventricular arrhythmias that occur after AVJ ablation.

Ischemia, metabolic disturbances, and arrhythmogenesis: mechanisms and management.

The development of ventricular arrhythmias is often a consequence of the interaction between structural abnormalities of the heart and transient disturbances in the electrophysiologic milieu. The critically ill patient is particularly susceptible to arrhythmias given the metabolic, ischemic, and neurohormonal stressors present in the intensive care unit. The significance of ventricular arrhythmias in the acute care setting is related to the presence of reversible causes and the extent of underlying heart disease. Long-term management of these patients is guided by an assessment of the risk for recurrent arrhythmias and the degree of left ventricular systolic dysfunction. In the absence of a reversible cause, symptomatic sustained arrhythmias are usually treated with an implantable cardioverter-defibrillator, a therapy that improves survival in this patient population. In many cases, however, proper long-term management of patients with ventricular arrhythmias is less clear, and the approach must be guided by a thorough understanding of the pathophysiology and the fundamental mechanisms of arrhythmogenesis.

Selective parasympathetic denervation following posteroseptal ablation for either atrioventricular nodal reentrant tachycardia or accessory pathways

Baroreflex gain and coronary sinus norepinephrine and epinephrine levels were measured before and immediately after radiofrequency ablation in the posteroseptal region in 9 patients with atrioventricular nodal reentrant tachycardia or posteroseptal accessory pathways. Arterial baroreflex gain was significantly reduced after radiofrequency ablation (p = 0.046), whereas coronary sinus epinephrine and norepinephrine levels did not change significantly compared with preablation levels.