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Competing Interests: Dr. Dandamudi reports advisory board and consulting roles with Abbott; advisory board, steering committee, and consulting roles with Medtronic; and an advisory board role with Biotronik. Mr. Clark is an employee of Abbott. The other authors report no conflicts of interest for the published content.

QT interval prolongation is associated with a risk of polymorphic ventricular tachycardia. QT interval shortens with increasing heart rate and correction for this effect is necessary for meaningful QT interval assessment. We aim to improve current methods of correcting the QT interval during atrial fibrillation (AF). Digitized Holter recordings were analyzed from patients with AF. Models of QT interval dependence on RR intervals were tested by sorting the beats into 20 bins based on corrected RR interval and assessing ST-T variability within the bins. Signal-averaging within bins was performed to determine QT/RR dependence. Data from 30 patients (29 men, 69.3±7.3 years) were evaluated. QT behavior in AF is well described by a linear function (slope ~0.19) of steady-state corrected RR interval. Corrected RR is calculated as a combination of an exponential weight function with time-constant of 2 minutes and a smaller "immediate response" component (weight ~ 0.18). This model performs significantly (p<0.0001) better than models based on instantaneous RR interval only including Bazett and Fridericia. It also outperforms models based on shorter time-constants and other previously proposed models. This model may improve detection of repolarization delay in AF. QT response to heart rate changes in AF is similar to previously published QT dynamics during atrial pacing and in sinus rhythm.

Cardiac implantable electronic device (CIED) has been increasingly used with expanding indications in patients with cardiac diseases. There is substantial evidence to suggest of their role in improving outcomes in patients with and without heart failure. Complications of the device implantation including infections are associated with increased morbidity and mortality and also substantial financial burden to the society. Several clinical characteristics have been recognized as risk factors for the occurrence of the infections. Considering that infections occur in the presence of multiple risk factors acting together, scoring systems have been developed in identifying patients at risk. Despite preventive measures, the rates of infections associated with CIEDs have increased over the last decade. Recent studies have documented the role of implantable antibiotic eluting pouches in reducing infections in patients undergoing CIED implantation. The present review will address the risk scoring systems studied and also address the role of antibiotic pouch and the recent patents in developing this technology.

Background: The Food and Drug Administration recently issued a class I recall of the St. Jude Medical Riata implantable cardioverter-defibrillator lead presumably because of increased risk of electric failure and mechanical separation via inside-out abrasion. We sought to examine the incidence and time dependence of inside-out abrasion in asymptomatic patients implanted with the Riata lead., Methods and Results: Asymptomatic patients implanted with the Riata lead at our institution were offered voluntary fluoroscopic screening in 3 views. Electric testing of the Riata lead with provocative isometric muscle contraction was performed at the time of fluoroscopic screening. Of the 245 patients undergoing fluoroscopic screening, 53 (21.6%) patients showed clear evidence of lead separation. Of these externalized leads, 0%, 13%, and 26% had a dwell time of <3 years, 3 to 5 years, and >5 years, respectively (P=0.037). Externalized leads had a significantly pronounced decrease in R-wave amplitude (-1.7±2.9 mV versus +0.35±2.5 mV; P<0.001), and more patients with externalized leads had ≥25% decrease in R-wave amplitude from baseline (28.0% versus 8.1%; P=0.018). One patient with externalization exhibited new noise on near-field electrogram., Conclusions: The Riata lead exhibits time-dependent high rates of cable externalization exceeding 20% at >5 years of dwell time. Externalized leads are associated with a more pronounced decrease in R-wave amplitude, which may be an early marker of future electric failure. The use of fluoroscopic and electric screening of asymptomatic patients with the Riata lead remains controversial in the management of patients affected by the recent Food and Drug Administration recall.

Aims: Discerning supraventricular tachycardia (SVT) mechanism during catheter ablation procedures can be difficult and time-consuming, which, when combined with diagnostic error, places patients at risk of unnecessary complications. Distinguishing atrial tachycardia (AT) from AV nodal re-entry tachycardia (AVNRT) may be particularly vexatious. Value-added techniques are thus always welcome, particularly if they are not time-consuming nor require complex intracardiac lead configurations. In this study, we assessed whether a new technique, simultaneous right atrial and right ventricular pacing (RA + RV) during ongoing SVT, met these criteria., Methods and Results: Using a simple intracardiac lead configuration (right atrial appendage, His bundle, right ventricular apex), the response to RA + RV delivered at 80-90% of the SVT cycle length, was examined in 80 patients referred for catheter ablation. In each patient, the actual tachycardia mechanism was adjudicated by standard electrophysiologic criteria ± successful catheter ablation. Mechanisms of SVT included, non-exclusively, AVNRT (24 patients), accessory pathway-mediated (orthodromic) re-entry (AVRT; 23 patients), AT (10 patients), and sinus tachycardia (ST induced with isoproterenol; 49 patients). Immediately after cessation of RA + RV pacing during persistent SVT, the first intracardiac electrogram observed was right atrial in all AT whereas it was His bundle in all AVNRT. The response during AVRT was mixed., Conclusions: In this preliminary evaluation, RA + RV pacing appears to add value to the existing armamentarium of electrophysiologic indices to discern SVT mechanism, in particular with respect to discriminating between AVNRT and AT.

Background: Clinical formulas for QT correction utilize instantaneous HR. We showed previously that longer-term HR affects QT duration. We extend these findings, identifying more accurate models of QT behavior., Method: Multiple models of QT dependence on HR were tested in 2 independent populations. Holter recordings were analyzed in population A (healthy volunteers, n = 14, 6 males, age 26.9 ± 12.3 yr). The hypotheses generated in population A were tested in an independent group population B, healthy volunteers, n = 15, 9 males, age 52.9 ± 15.6 yr). Linear models of QT interval dependence on a weighted average of RR intervals in the preceding 3 minutes were compared to models based on the immediately preceding RR interval (instantaneous HR)., Results: In population A, linear models based on RR intervals over the preceding minute performed better than the best nonlinear model based on the single RR interval immediately preceding the QT interval. Linear models including HR values preceding the QT interval by more than 60 s further improved model fit. This model hierarchy was confirmed in population B. Linear formula for QT correction based on exponential decay of HR effect with 60 s time constant outperformed Bazett and Fridericia formulas in both populations., Conclusions: QT duration in normal ambulatory subjects is affected by noninstantaneous HR, including HR history dating back more than 60 s. Exponential decay of this "memory effect" with time constant of 1 minute provides an accurate description of QT adaptation. This may be of clinical importance when HR is not steady., (©2011, Wiley Periodicals, Inc.)

Background: The prophylactic use of the implantable cardioverter-defibrillator (ICD) has been shown to decrease mortality in patients with depressed left ventricular ejection function (LVEF ≤ 35%). Whether this beneficial effect persists in the presence of chronic obstructive pulmonary disease (COPD) is not established., Methods: We examined the medical records of patients with LVEF ≤ 35% and COPD and analyzed the data for total mortality by ICD status. Each ICD patient was matched by age and LVEF with two to three controls. The Charlson comorbidity index and propensity score were used to correct for differences in comorbidities and biases between the study groups., Results: A total of 100 patients (30 with ICD and 70 controls) were included in this analysis. The overall cohort had a mean age of 65 ± 15 years with a predominance of white (79%) men (72%). Compared to controls, ICD patients had a wider QRS complex (150 ± 32 ms vs 110 ± 24 ms, P < 0.001) and were less likely to be on steroid therapy (10% vs 31%, P = 0.018) for COPD. At a mean follow-up of 3.1 ± 2.7 years, ICD patient had a lower total mortality (2-year survival of 88% in the ICD group vs 59% in the controls, P = 0.016). The lower death rate in the ICD group persisted after correcting for differences in the QRS interval and for discrepancies race and in the incidence of steroid use in a multivariate Cox regression model (odds ratio = 0.300, adjusted P = 0.016)., Conclusion: Patients with COPD extract survival benefit from the ICD and should therefore not be denied this life-saving therapy., (©2010, The Authors. Journal compilation ©2010 Wiley Periodicals, Inc.)

Background: Cardiac arrest (CA) concurrent with acute myocardial infarction (AMI) claims the life of many patients with coronary artery disease (CAD). In this study, we investigated the predictors of CA during AMI., Method: Patients admitted with CA concurrent with AMI (n = 31) were matched by age, gender, race, and left ventricular ejection fraction (LVEF) to patients with AMI but no CA (n = 70). All patients underwent coronary angiography. Binary logistic regression was used to identify independent predictors of CA during AMI., Results: A total of 101 patients (age = 61 +/- 13 years, men 76%, Caucasians 98%, LVEF 33 +/- 12%) admitted to the University of Pittsburgh Medical Center with AMI were included in this analysis. Patients with CA concurrent with the AMI were more likely to have proximal rather than distal coronary artery culprit lesions (odds ratio (OR) = 7.2, P = 0.019). Other predictors of CA in the context of AMI included negative family history of CAD (OR = 8.0, P = 0.026) and absence of sinus rhythm upon hospital admission (OR = 5.1, P = 0.030)., Conclusion: Proximity of culprit coronary lesion and presence of rhythm other than sinus rhythm at hospital admission are two strong predictors of CA in the context of AMI. The implication is that the mechanism of CA is primarily that of a large area of myocardial ischemia leading to lethal ventricular arrhythmia. Other predispositions such as genetic make-up cannot be ruled out.

Background: Most defibrillator (ICD) trials have excluded patients on hemodialysis (HD). It is therefore not known whether the ICD, when indicated, confers the same mortality benefit to HD and non-HD patients., Method: HD patients implanted with an ICD from July 2001 to June 2004 were matched by age, gender, left ventricular ejection fraction (LVEF), and class of heart failure to non-HD ICD recipients., Results: Forty-six (16 on HD) patients (age = 65 +/- 15 yrs, LVEF = 30 +/- 14%, 44% in class III-IV HF) were followed for a mean of 30 +/- 16 months (range, 4-61 months) after ICD implantation. During this period, 12/16 HD versus 9/30 non-HD patients died (P = 0.006). The two-year mortality rates were 54% and 29% in the HD and non-HD groups, respectively (P = 0.01). After correcting for age, gender, race, LVEF, class of HF, and ICD indication (primary vs. secondary prevention) in a Cox regression model, HD remained a significant predictor of the time to death (HR = 2.9, adjusted P = 0.023)., Conclusion: Despite having an ICD, HD patients have approximately a three-fold increase in total mortality and may therefore not extract the same survival benefits from the ICD as their non-HD counterparts. If duplicated in larger randomized trials, these results may demonstrate the futility of implanting defibrillators in HD patients.