Monthly Archives: September 2016

Ventricular Tachycardia – Classification

Ventricular Tachycardia – Classification

Ventricular tachycardia is a common arrhythmia. The manifestations include mild symptoms of palpitation to sudden death. In next few blog posts, we will try to understand the basics of ventricular tachycardia/fibrillation and we will discuss management of these arrhythmias.


Ventricular arrhythmias are defined as arrhythmias that originate below the bifurcation of His bundle, in the specialized conduction system, the ventricular muscle, or in combination of both tissues.


Ventricular Tachycardia ECG

(Image created by Karthik Sheka, M.D. [CC BY-SA 2.5 (], via Wikimedia Commons)

There are different classifications of ventricular arrhythmias, according to their duration, morphology of QRS complexes, and clinical characteristics.

Classification According to Duration

(1) Premature ventricular complexes (PVC): isolated complexes originating from the His-Purkinje system or ventricular myocardium.
(2) VT: 3 or more consecutive QRS complexes at a rate greater than 100 beats per minute.
(3) Nonsustained VT: VT that terminates spontaneously within 30 seconds.
(4) Sustained VT: continuous VT lasting for ≥30 seconds or that requires an intervention for termination (such as cardioversion).

Classification According to Morphology of QRS Complexes

(1) Monomorphic VT: VT that has a similar QRS configuration from beat to beat. Some variability in QRS morphology at initiation is not uncommon.
(2) Multiple monomorphic VT: more than one morphologically distinct monomorphic VT, occurring as different episodes or induced at different times.
(3) Polymorphic VT: VT that has a continuously changing QRS configuration indicating a changing ventricular activation sequence.
(4) Pleomorphic VT: VT that has more than one morphologically distinct QRS complex occurring during the same episode of VT, but the QRS is not continuously changing.
(5) Ventricular flutter: rapid VT that has a sinusoidal QRS configuration that prevents identification of the QRS morphology.
(6) VF: ventricular tachyarrhythmia that has a totally chaotic

Classification According to Clinical Characteristics

(1) Clinical VT: VT that has occurred spontaneously based on analysis of 12-lead ECG QRS morphology and rate.
(2) Hemodynamically unstable VT: VT that causes hemodynamic compromise requiring prompt termination.
(3) Incessant VT: continuous sustained VT that recurs immediately despite repeated spontaneous or therapeutic termination.
(4) Repetitive monomorphic VT: continuously repeating episodes of self-terminating nonsustained VT.
(5) VT storm: 3 or more separate episodes of sustained VT within 24 hours, each requiring termination by an intervention.
(6) Unmappable VT: VT that does not allow interrogation of multiple sites to define the activation sequence or perform entrainment mapping. It may be due to hemodynamic
intolerance that necessitates immediate VT termination, spontaneous, or pacing-induced transition to other morphologies of VT, or repeated termination during mapping.

In the next post, we will discuss clinical features and ECG features.


Primary prevention ICD in Nonischemic cardiomyopathy

There is a recent online first article in NEJM  ( Defibrillator Implantation in Patients with Nonischemic Systolic Heart Failure – DANISH Study). The study is summarized below:


The benefit of an implantable cardioverter–defibrillator (ICD) in patients with symptomatic systolic heart failure caused by coronary artery disease has been well documented. However, the evidence for a benefit of prophylactic ICDs in patients with systolic heart failure that is not due to coronary artery disease has been based primarily on subgroup analyses. The management of heart failure has improved since the landmark ICD trials, and many patients now receive cardiac resynchronization therapy (CRT).


In a randomized, controlled trial, 556 patients with symptomatic systolic heart failure (left ventricular ejection fraction, ≤35%) not caused by coronary artery disease were assigned to receive an ICD, and 560 patients were assigned to receive usual clinical care (control group). In both groups, 58% of the patients received CRT. The primary outcome of the trial was death from any cause. The secondary outcomes were sudden cardiac death and cardiovascular death.


After a median follow-up period of 67.6 months, the primary outcome had occurred in 120 patients (21.6%) in the ICD group and in 131 patients (23.4%) in the control group (hazard ratio, 0.87; 95% confidence interval [CI], 0.68 to 1.12; P=0.28). Sudden cardiac death occurred in 24 patients (4.3%) in the ICD group and in 46 patients (8.2%) in the control group (hazard ratio, 0.50; 95% CI, 0.31 to 0.82; P=0.005). Device infection occurred in 27 patients (4.9%) in the ICD group and in 20 patients (3.6%) in the control group (P=0.29).


In this trial, prophylactic ICD implantation in patients with symptomatic systolic heart failure not caused by coronary artery disease was not associated with a significantly lower long-term rate of death from any cause than was usual clinical care.

This is the summary of the study. This study proves the point that primary prevention ICD doesn’t reduce the all cause mortality. But there are few points to consider in this very well designed study:

  1. SCD was the cause of death in 24 out of 120 (20%) total deaths in the ICD group. SCD was the cause of death in 46 out of 131 (35%) total deaths in the non-ICD (usual care group). So that means majority of mortality even in the non-ICD usual care group are due to non arrhythmic causes.
  2. The number of non-arrhythmic mortality in the ICD group is 96 out of total of 120 (80%) and in the non-ICD group is 65%.
  3. The question still remains that – How is a device (i.e. ICD) which prevents arrhythmic deaths, is expected to reduce the All Cause Mortality (the primary end point of this study) when the majority of deaths are due to non-arrhythmic causes.
  4. When considering the sudden cardiac deaths, ICD definitely reduced the mortality [Sudden cardiac death occurred in 24 patients (4.3%) in the ICD group and in 46 patients (8.2%) in the control group (hazard ratio, 0.50; 95% CI, 0.31 to 0.82; P=0.005)].

This study is a landmark study. It shows that the present indications for primary prevention ICD in non-ischemic cardiomyopathy are likely  include patients who may not after all benefit from a primary prevention ICD. It further shows that ICD is effective in preventing SCD in non-ischemic cardiomyopathy.

So to conclude this important study shows that we need to find markers of SCD in non-ischemic cardiomyopathy so that ICD implantation can be more effectively done in patients who are at high risk of SCD.

(Disclaimer: The views expressed are entirely personal of the author of this blog and are aimed towards an educational discussion on the study. These opinions are not meant for application in medical practice and are for the purpose of discussion only)

Keywords: Electrophysiology, Cardiomyopathy, Implantable cardioverter defibrillator, Sudden cardiac death