Application of the 2015 ACC/AHA/HRS guidelines for risk stratification for sudden death in adult patients with asymptomatic pre-excitation.

The management of the asymptomatic pre-excited patient largely hinges on risk stratification and individual patient considerations and choice. A high threshold to treat patients may lead to a small overall risk of death while a low threshold clearly leads to increased invasive testing and ablation with associated cost and procedural risk. A firm recommendation to uniformly assess all by electrophysiology study or, alternatively, reassure all is inappropriate and unjustified by data as reflected in the recent guideline recommendations. The use of noninvasive and invasive parameters to identify the potentially at-risk individual with surveillance for symptoms in those comfortable with this approach or ablation for those choosing this alternative for individual reasons remains the cornerstone of best practice.

Risk of arrhythmia and sudden death in patients with asymptomatic preexcitation: a meta-analysis.

BACKGROUND: The incidence of sudden cardiac death (SCD) and the management of this risk in patients with asymptomatic preexcitation remain controversial. The purpose of this meta-analysis was to define the incidence of SCD and supraventricular tachycardia in patients with asymptomatic Wolff-Parkinson-White ECG pattern. METHODS AND RESULTS: We performed a systematic search of prospective, retrospective, randomized, or cohort English-language studies in EMBASE and Medline through February 2011. Studies reporting asymptomatic patients with preexcitation who did not undergo ablation were included. Twenty studies involving 1869 patients met our inclusion criteria. Participants were primarily male with a mean age ranging from 7 to 43 years. Ten SCDs were reported involving 11 722 person-years of follow-up. Seven studies originated from Italy and reported 9 SCDs. The risk of SCD is estimated at 1.25 per 1000 person-years (95% confidence interval [CI], 0.57-2.19). A total of 156 supraventricular tachycardias were reported involving 9884 person-years from 18 studies. The risk of supraventricular tachycardia was 16 (95% CI, 10-24) events per 1000 person-years of follow-up. Children had numerically higher SCD (1.93 [95% CI, 0.57-4.1] versus 0.86 [95% CI, 0.28-1.75]; P=0.07) and supraventricular tachycardia (20 [95% CI, 12-31] versus 14 [95% CI, 6-25]; P=0.38) event rates compared with adults. CONCLUSION: The low incidence of SCD and low risk of supraventricular tachycardia argue against routine invasive management in most asymptomatic patients with the Wolff-Parkinson-White ECG pattern.

Further evidence for the "muscle bundle" hypothesis of cavotricuspid isthmus conduction: physiological proof, with clinical implications for ablation.

INTRODUCTION: It has been suggested that the cavotricuspid isthmus (CTI) is composed of discrete muscle bundles with preferred paths of conduction. An ablation technique targeting high-voltage local electrograms (maximum voltage guided or MVG technique) has been described with the aim of preferentially targeting the muscle bundles. We hypothesized that the MVG technique could provide isthmus block even if the high voltage targets were clearly separated on different ablation lines. In contrast, conduction over a continuous sheet of muscle would require a single continuous ablation line. METHODS: Twenty-two consecutive patients (mean age 65 ± 11.7, 5 females) underwent ablation using the MVG technique on 2 noncontiguous lines in the CTI. Ablation lesions were first applied at the septal aspect of the CTI, targeting only the ventricular (anterior) aspect of the annulus. A line distinctly lateral and noncontiguous to the first was then chosen to target high voltage potentials on the atrial (posterior) aspect of the CTI. RESULTS: Complete CTI block was achieved in all study patients without complication. A mean of 7.8 ± 3.7 ablation lesions were required. Mean ablation time was 401.0 ± 414.5 seconds. CONCLUSION: Two nonoverlapping incomplete lines of ablation in the CTI consistently lead to bidirectional conduction block. This further supports the hypothesis that conduction over the CTI occurs over discrete muscle bundles. These bundles can be targeted individually for ablation without the need to ablate a continuous line over the CTI.

End-recovery QTc: a useful metric for assessing genetic variants of unknown significance in long-QT syndrome.

INTRODUCTION: Genetic variants represent benign single-nucleotide polymorphisms, disease causing mutations or variants of unknown significance (VUS). Resting, exercise, and recovery QTc intervals have been utilized to detect long-QT syndrome (LQTS) mutations. We sought to provide clinical data that may assist in classifying the presented VUS as disease causing/benign and to determine whether resting and/or end-recovery QT parameters can evaluate the significance of VUS. METHODS AND RESULTS: Twenty-six patients with a VUS in genes associated with LQTS (15 females, age 38 ± 16 years) and 26 age and gender matched controls (age 37 ± 20 years) were included. There were 10 VUS (5 KCNQ1, 4 KCNH2, 1 KCNE1) in 12 families. All but 1 VUS was associated with sudden cardiac death (SCD), aborted SCD or Torsade de pointes. A Schwartz score of ≥3.5 was observed in at least 1 family member with each VUS. Resting QTc was marginally longer in VUS patients compared with controls (458 ± 48 vs 437 ± 25, P = 0.052). A prolonged resting QTc (>470 ms males, >480 ms females) identified 6 VUS carriers and 1 control. VUS carriers had a substantially longer end-recovery QTc (502 ± 68 vs 427 ± 17, P < 0.01) with an end-recovery QTc > 445 ms in 20/26 VUS patients compared to 2/26 controls (P < 0.01). The area under the receiver operating characteristic curve for resting QTc was 0.68 (95% CI, 0.53-0.83, P = 0.03) compared to the end-recovery QTc of 0.88 (95% CI, 0.76-0.99, P < 0.0001). CONCLUSION: Variants in the current study appear to be disease causing. The end-recovery QTc is a useful metric when interpreting LQT VUS.

Long-term performance of submammary defibrillator system.

AIMS: There are various implantation techniques that have been used to minimize the cosmetic effect of implantable cardioverter defibrillator (ICD) implantation, including submammary implantation. There are limited data on submammary ICD implantation and no data on long-term follow-up. We report the long-term performance of submammary ICD systems implanted in young females. METHODS AND RESULTS: We gathered data from August 1994 to September 2009 on all submammary ICD implantations undertaken at two institutes in Melbourne, Australia. Twenty submammary ICDs were implanted. Mean age at implantation was 21 +/- 10 years. Fifteen single chamber (VR) and five dual chamber (DR) systems were implanted. Twenty-five per cent were implanted for primary prophylaxis. Implantable cardioverter defibrillator implantation was predominantly for non-cardiomyopathy indications. Mean follow-up duration was 60 +/- 46 months. There were no deaths during follow-up. There were two early lead dislodgements and three late lead revisions. No extractions were performed. Five patients had appropriate and five patients had inappropriate ICD therapy. Mean duration to first appropriate therapy was 58 +/- 40 months. Stable sensing and high voltage (HV) lead performance were demonstrated (mean lowest effective defibrillation at implant vs. follow-up: 13 +/- 6 vs. 14 +/- 4 J, P = 0.8; R-wave amplitude: 9 +/- 3 vs. 8 +/- 2 mV, P = 0.6; HV lead impedance: 52 +/- 6 vs. 44 +/- 9 ohm, P = 0.1). A clinically insignificant rise in ventricular pacing threshold (0.6 +/- 0.2 V at implant vs. 1.6 +/- 0.6 V at follow-up, P < 0.001) and a decrease in pacing impedance (621 +/- 223 vs. 471 +/- 89 ohm, P = 0.02) were noted. CONCLUSION: Submammary ICD implantation in young females is feasible and safe. Long-term follow-up data reveal stable sensing and HV lead performance.

Left ventricular ejection fraction and absence of ACE inhibitor/angiotensin II receptor blocker predicts appropriate defibrillator therapy in the primary prevention population.

INTRODUCTION: Implantable cardioverter defibrillators (ICD) significantly reduce mortality in patients with left ventricular (LV) dysfunction. However, little is known of the predictors of appropriate device activation in the primary prevention population. The aim of the present study was to determine predictors of appropriate device therapy in patients receiving ICDs for primary prevention. METHODS & RESULTS: One hundred twenty-six patients with a left ventricular ejection fraction (LVEF) of < 35% and no prior documented ventricular arrhythmias underwent ICD implantation. The ICD implanted was single chamber in 60 (48%), dual chamber in 10 (8%), and biventricular in 56 (44%) patients and programmed with a single ventricular fibrillation (VF) zone at >180 beats per minute. Mean age was 58 +/- 13 years and mean LVEF was 23 +/- 7%. Fifty-two percent had ischemic cardiomyopathy and 66% were New York Heart Association heart failure class II/III. During a mean follow-up period of 589 +/- 353 days, 17 (13%) patients received appropriate device therapy and three (4%) received inappropriate shocks. Appropriate ICD therapy was associated with reduced LVEF (mean 19.9% vs 23.7%, P = 0.02) and the patients were less likely to have received angiotensin-converting enzyme inhibitor (ACEI) or angiotensin II receptor blockers (AIIRB) (65% vs 90%, P = 0.04). Multivariate analysis revealed lack of ACEI/AIIRB (odds ratio [OR]= 0.06, 95% confidence interval [CI]= 0.01-0.37, P = <0.01) and lower LVEF (OR = 0.88, 95% CI 0.79-0.98, P = 0.02) predicted appropriate device activation. There was no difference in transplant-free survival between the appropriate therapy and no/inappropriate therapy groups, LVEF <20% and LVEF >20% group, and lack of ACEI/AIIRB and ACEI/AIIRB group. CONCLUSION: Appropriate device activation occurred in 13% of patients in a primary prevention population. LVEF and absence of ACEI/AIIRB predicted appropriate ICD therapy.

Pharmacologic management of tachycardia.

BACKGROUND: Cardiac arrhythmias may present with palpitations, chest pain, shortness of breath, dizziness and syncope. Diagnosis may be complicated by an inability to document the arrhythmia particularly when symptoms are infrequent and short lived. OBJECTIVE: This article aims to provide an overview of the pharmacological management of supraventricular tachycardia including atrial flutter and haemodynamically stable ventricular tachycardia. Management of atrial fibrillation is discussed in a companion article in this issue. DISCUSSION: Antiarrhythmic medications are effective in reducing symptoms, however, side effects are frequent. Fortunately nonpharmacological strategies such as catheter ablation have evolved which offer long term cure in the majority of patients. However, despite technological advances, pharmacotherapy retains an important place in the therapeutic approach to cardiac arrhythmias in many patients. It is important to remember that pharmacological management should also address any underlying cardiac disease process.