Effect of Ventricular Shock Strength on Cardiac Hemodynamics

Ventricular Defibrillation and Cardiac Function . Introduction: The effect of implantable defibrillator shocks on cardiac hemodynamics is poorly understood. The purpose of this study was to test the hypothesis that ventricular defibrillator shocks adversely effect cardiac hemodynamics. Methods and Results: The cardiac index was determined by calculating the mitral valve inflow with transesophogeal Doppler during nonthoracotomy defibrillator implantation in 17 patients. The cardiac index was determined before, and immediately, 1 minute, 2 minutes, and 4 minutes after shocks were delivered during defibrillation energy requirement testing with 27- to 34-, 15-, 10-, 5-, 3-, or 1-J shocks. The cardiac Index was also measured at the same time points after 27- to 34-, and 1-J shocks delivered during the baseline rhythm. The cardiac index decreased from 2.30 ± 0.40 L/min per m² before a 27- to 34-J shock during defibrillation energy requirement testing to 2.14 ± 0.45 L/min per m² immediately afterwards (P= 0.001). This effect persisted for >4 minutes. An adverse hemodynamic effect of similar magnitude occurred after 15 J (P= 0.003) and 10-J shocks (P= 0.01), but dissipated after 4 minutes and within 2 minutes, respectively. There was a significant correlation between shock strength and the percent change in cardiac index (r = 0.3, P= 0.03). The cardiac index decreased 14% after a 27- to 34-J shock during the baseline rhythm (P < 0.0001). This effect persisted for <4 minutes. A 1- J shock during the baseline rhythm did not effect the cardiac index. Conclusion: Defibrillator shocks >9 J delivered during the baseline rhythm or during defibrillation energy requirement testing result in a 10% to 15% reduction in cardiac index, whereas smaller energy shocks do not affect cardiac hemodynamics. The duration and extent of the adverse effect are proportional to the shock strength. Shock strength, and not ventricular fibrillation, appears to be most responsible for This effect. Therefore, the detrimental hemodynamic effects of high-energy shocks may be avoided when low-energy defibrillation is used.     

Safety of Temporary and Permanent Suspension of Antiplatelet Therapy After Drug Eluting Stent Implantation in Contemporary “Real‐world” Practice

Objectives: To define the incidence of stent thrombosis (ST) and/or AMI (ST/AMI) associated with temporary or permanent suspension of dual antiplatelet therapy (DAPT) after coronary drug‐eluting stent (DES) implantation in “real‐world” patients, and additional factors influencing these events. Background: Adherence to DAPT is critical for avoiding ST following DES implantation. However, the outcomes of patients undergoing antiplatelet therapy withdrawal following DES implantation remain to be clearly described. Methods: Patients receiving DES from 05/01/2003 to 05/01/2008 were identified from a single‐center registry. Complete follow‐up data were available for 5,681 patients (67% male, age 66 ± 11 years, duration 1,108 ±446 days) who were included in this analysis. Results: Uninterrupted DAPT was maintained in 4,070/5,681 (71.6%) patients, with an annual ST/AMI rate of 0.43%. Antiplatelet therapy was commonly ceased for gastrointestinal‐related issues, dental procedures or noncardiac/nongastrointestinal surgery. Temporary DAPT suspension occurred in 593/5,681 (10.4%) patients for 17.6 ± 74.1 days, with 6/593 (1.0%) experiencing ST/AMI during this period. Of patients permanently ceasing aspirin (n = 187, mean 338 ± 411 days poststenting), clopidogrel (n = 713, mean 614 ± 375 days) or both agents (n = 118, mean 459 ± 408 days), ST/AMI was uncommon with an annual rate of 0.1–0.2%. Overall, independent predictors of ST/AMI were unstable initial presentation, uninterrupted DAPT and lower left ventricular ejection fraction. Factors predicting uninterrupted DAPT included diabetes, unstable presentation, prior MI, left main coronary PCI, and multivessel coronary disease. Conclusions: In real‐world practice, rates of ST/AMI following DES implantation are low, but not insignificant, following aspirin and/or clopidogrel cessation. Use of uninterrupted DAPT appears more common in high‐risk patients. (J Interven Cardiol 2012;25:482–492)     

Paradoxical Change in Atrial Fibrillation Dominant Frequencies with Baroreflex‐Mediated Parasympathetic Stimulation with Phenylephrine Infusion

Baroreflex Response and AF Dominant Frequency . Introduction: Parasympathetic stimulation is known to promote atrial fibrillation (AF) through shortening of atrial refractory periods. We hypothesized that baroreflex‐mediated parasympathetic stimulation via phenylephrine (PE) infusion would increase AF rate as measured by dominant frequency (DF). Methods and Results: The protocol was performed in 27 patients (24 M, 59 ± 1 years old) prior to AF ablation. For 10 patients in AF, PE was infused until systolic blood pressure increased ≥30 mmHg. Electrograms were recorded in the left atrium before and after PE. DFs of each recording were calculated offline. Atrial effective refractory periods (ERPs) were measured before and after PE in 11 patients who were in sinus rhythm during the procedure. DFs were also measured in 6 patients in AF before and after complete parasympathetic blockade with atropine (0.04 mg/kg). PE resulted in increased RR intervals during sinus rhythm (1,170 ± 77 to 1,282 ± 85 ms, P = 0.03) and AF (743 ± 32 to 826 ± 30 ms, P = 0.03), consistent with parasympathetic effect on the sinus and AV nodes, respectively. DFs were decreased by PE in the left atrium (6.2 ± 0.2 to 6.0 ± 0.2 Hz, P = 0.004). Correspondingly, atrial ERPs significantly increased from 218 ± 13 to 232 ± 11 ms (P = 0.04). Atropine resulted in a decreasing trend in DF in the left atrium (5.9 ± 0.1 to 5.8 ± 0.1 Hz, P = 0.07). Conclusions: Despite baroreflex‐mediated parasympathetic effect, PE produced a slowing of AF along with lengthening of ERP, while parasympathetic blockade also slowed DF. It is therefore likely that the direct and indirect adrenergic effects of PE on atrial electrophysiology are more prominent than its parasympathetic effects. (J Cardiovasc Electrophysiol, Vol. 23 pp. 1045‐1050, October 2012)     

Cross-Stimulation: The Unexpected Stimulation of the Unpaced Chamber

The ability to stimulate one chamber through a lead or output circuit to the opposite cardiac chamber is termed cross-stimulation. Three examples of this phenomenon are presented. The first involves the close proximity of the atrial lead to the ventricular myocardium with ventricular capture occurring at sufficiently high outputs; the second is due to the basic design of dual unipolar pacing systems which have output circuits that share a common anode; the third is a self-limited eccentricity of one device that occurs only during the first phase of magnet-induced asynchronous pacing. The mechanism and clinical significance of these observations are discussed.     

Diurnal Heart Rate Patterns in Inappropriate Sinus Tachycardia

Background: Inappropriate sinus tachycardia (IAST) is a supraventricular tachycardia originating from the sinus node. Proposed etiologies for this symptom complex include autonomic dysfunction, abnormal automaticity, or hypersensitivity of the sinus node. Methods: Patients with IAST were identified by symptomatic tachycardia, with P‐wave morphology consistent with origination from a sinus location. A matched set of control subjects was included. Hourly heart rate (HR) was measured as the average HR during each one hour period on an ambulatory 24‐hour Holter monitor. Patients were further divided into two subgroups based on average daily HR ≤ 80 and >80 bpm. Harmonic analysis was used to evaluate diurnal variation. Results: The mean HR was 86.0 ± 12.8 beats per minute (bpm) in the IAST group and 73.9 ± 8.6 bpm in the control group (P = 0.056). There was an increased overall heart rate for the IAST group, which appeared to be more prominent in the morning hours. In the IAST subgroup with average daily HR ≤ 80, hourly HR appears similar to controls for the period 8 pm–8 am. However, in the late AM, the IAST group had an increase in HR not seen in the control subjects. In the IAST subgroup with average HR > 80, there appeared to be a fixed difference in HR compared to the control group, without hourly change. Conclusions: Patients with IAST and elevated average daily HR exhibit normal diurnal variation around a higher mean HR. In contrast, patients with IAST and lower average daily HR had an exaggerated morning rise in HR. These diurnal patterns may be useful to classify the pathophysiology of IAST. (PACE 2010; 911–919)